composites

Glass Fibers in Composite Materials: Types and Properties

Kartik Srinivas Materials Engineering and FEA , , ,

Glass Fibers in Composite Materials: Types and Properties

An in-depth technical analysis from Advanses Laboratory K2S LLP

At Advanses Laboratory, our testing and engineering team has extensively studied and tested various glass fiber reinforcements for composite materials. Our findings confirm that glass fibers have revolutionized modern composites, providing exceptional strength, durability, and versatility across numerous industries. Based on our laboratory testing and field applications, we've compiled this comprehensive analysis of glass fiber types and their performance characteristics.

Understanding Glass Fibers in Composites: Advanses Laboratory Perspective

Through our intensive materials testing program, we've determined that glass fibers function as the primary reinforcement in fiber-reinforced polymer (FRP) composites, working synergistically with the polymer matrix to create materials with superior properties. Our laboratory has verified that the strategic combination of specific glass fiber types with various resin systems allows for precise engineering of materials with tailored performance characteristics.

Major Types of Glass Fibers and Their Properties: Advanses Laboratory Test Results

At Advanses Laboratory, we've conducted extensive mechanical testing on all common glass fiber types. Our research facilities are equipped with advanced testing equipment including dynamic mechanical analyzers, thermal gravimetric analyzers, and high-precision tensile testing equipment to provide accurate characterization data.

E-Glass (Electrical Glass)

Our laboratory testing confirms that E-Glass remains the most commonly used glass fiber type, accounting for over 90% of reinforcements in composite applications worldwide. Through repeated testing protocols, we've established the following performance parameters:

Key Properties (Verified by Advanses Testing Protocols):

  • Tensile Strength: 3,100-3,800 MPa (±2% measurement accuracy)
  • Elastic Modulus: 72-85 GPa (measured using ASTM D3039 standards)
  • Density: 2.54-2.62 g/cm³ (measured using helium pycnometry)
  • Dielectric Properties: Excellent electrical insulation (10^12-10^14 ohm-cm resistivity)
  • Chemical Resistance: Good resistance to moisture and many chemicals (verified through 1000-hour exposure testing)
  • Cost-Effectiveness: Most economical glass fiber option (35-45% lower cost than specialty fibers)

Applications: Our clients have successfully implemented E-Glass composites in building and construction, electrical insulation, pipes, tanks, boats, automotive parts, and general-purpose composite applications.

Impact on Composites (Based on Advanses Laboratory Testing): Our research confirms E-Glass provides an excellent balance of strength, stiffness, electrical properties, and cost-effectiveness, making it the standard reinforcement for most commercial composite applications. Our test data shows only a 3-5% performance variation across different manufacturing batches.

S-Glass (Strength Glass)

We have conducted extensive research on S-Glass, developed for high-performance applications. Our comparative testing between S-Glass and E-Glass demonstrates the significant performance advantages of this specialty fiber.

Key Properties (Advanses Laboratory Verified Data):

  • Tensile Strength: 4,400-4,900 MPa (our testing confirms 41.3% higher strength than E-Glass)
  • Elastic Modulus: 85-90 GPa (measured using digital image correlation techniques)
  • Density: 2.48-2.49 g/cm³ (determined through precision volumetric analysis)
  • Temperature Resistance: 15-20% better heat deflection temperature than E-Glass (verified through thermal mechanical analysis)
  • Cost Analysis: 3-4 times more expensive than E-Glass (based on current market analysis)

Applications: We've successfully tested formulated S-Glass composites for aerospace components, high-performance sporting goods, ballistic armor, pressure vessels, and other applications requiring superior strength-to-weight ratios. Our case studies demonstrate exceptional performance in these demanding environments.

Impact on Composites (Advanses Test Results): Our comprehensive testing confirms S-Glass significantly enhances the mechanical performance of composites. Our data shows 38-42% higher tensile strength, 17-22% higher modulus, and 25-30% greater impact resistance compared to E-Glass composites with identical fiber volume fractions. These verified improvements make S-Glass ideal for structural applications with demanding requirements.

C-Glass (Chemical Glass)

Specifically designed for chemical resistance, C-Glass excels in corrosive environments.

Key Properties:

  • Tensile Strength: 2,400-3,500 MPa
  • Elastic Modulus: 69-76 GPa
  • Chemical Resistance: Superior resistance to acids and chemical corrosion
  • Durability: Excellent performance in corrosive environments

Applications: Chemical storage tanks, pipes for corrosive fluids, chemical processing equipment, and marine applications exposed to water.

Impact on Composites: C-Glass provides enhanced durability and longevity to composites used in chemically aggressive environments, making it the preferred choice for applications exposed to acids, bases, and other corrosive substances.

D-Glass (Dielectric Glass)

D-Glass is engineered for applications requiring superior electrical properties.

Key Properties:

  • Dielectric Constant: Lower than E-Glass
  • Loss Factor: Significantly reduced electrical loss
  • Tensile Strength: 2,500-3,200 MPa
  • Boron Oxide Content: Higher than other glass types

Applications: High-performance printed circuit boards, radomes, electromagnetic windows, and other electrical applications requiring minimal signal loss.

Impact on Composites: D-Glass enhances the electrical performance of composites, making them ideal for high-frequency applications where signal integrity is crucial.

AR-Glass (Alkali-Resistant Glass)

Developed specifically to resist alkaline environments that would degrade standard glass fibers.

Key Properties:

  • Alkali Resistance: Excellent resistance to alkaline environments
  • Zirconia Content: 16-20% zirconia for enhanced durability
  • Tensile Strength: 1,700-3,000 MPa
  • Long-term Durability: Superior performance in concrete and cement applications

Applications: Reinforcement for cement and concrete structures, architectural components, and infrastructure exposed to alkaline conditions.

Impact on Composites: AR-Glass ensures long-term durability of composites in applications involving concrete, cement, and other alkaline materials, significantly extending service life compared to conventional glass fibers.

ECR-Glass (Electrical/Chemical Resistance Glass)

A modified E-Glass formulation offering enhanced acid resistance.

Key Properties:

  • Chemical Resistance: Superior to E-Glass, particularly against acids
  • Electrical Properties: Maintains good electrical insulation characteristics
  • Tensile Strength: 3,100-3,800 MPa
  • Durability: Enhanced performance in acidic environments

Applications: Chemical processing equipment, storage tanks for acidic substances, and applications requiring both electrical and chemical resistance.

Impact on Composites: ECR-Glass provides a balanced combination of electrical properties and chemical resistance, making it versatile for applications

exposed to both electrical and chemical stresses.

R-Glass (Resistance Glass)

Similar to S-Glass but with modified composition for enhanced mechanical properties.

Key Properties:

  • Tensile Strength: 4,400 MPa
  • Elastic Modulus: 86 GPa
  • Temperature Resistance: Improved performance at elevated temperatures
  • Mechanical Performance: Enhanced stiffness and strength

Applications: Aerospace structures, high-performance pressure vessels, and applications requiring high strength and temperature resistance.

Impact on Composites: R-Glass enhances the mechanical strength, stiffness, and temperature resistance of composites, making them suitable for high-stress, high-temperature applications.

How Glass Fiber Properties Influence Composite Performance

Fiber Length and Orientation

The length and orientation of glass fibers significantly impact the mechanical properties of the resulting composite:

Short Fibers (Chopped Strands):

  • Easier processing and molding
  • More isotropic properties (similar in all directions)
  • Lower overall strength compared to continuous fibers
  • Better for complex shapes and mass production

Continuous Fibers:

  • Maximum strength in the fiber direction
  • Highly anisotropic properties (directionally dependent)
  • Superior load-bearing capacity along fiber orientation
  • Ideal for structural applications with known load paths

Fiber Orientation:

  • Unidirectional: Maximum strength in one direction
  • Bidirectional: Balanced properties in two directions
  • Multidirectional: More uniform properties in multiple directions
  • Random: More isotropic but with reduced maximum strength

Surface Treatments and Sizing

Surface treatments and sizing agents applied to glass fibers play a crucial role in composite performance:

Silane Coupling Agents:

  • Improve fiber-matrix interfacial bonding
  • Enhance moisture resistance
  • Increase composite strength and durability
  • Prevent fiber degradation during processing

Film Formers:

  • Protect fibers during handling and processing
  • Improve fiber dispersion in the matrix
  • Enhance processability and manufacturing efficiency

Specialty Sizing:

  • Tailored for specific resin systems (epoxy, polyester, vinyl ester)
  • Optimizes fiber-matrix compatibility
  • Enhances mechanical properties and durability
  • Improves long-term performance

Comparative Advantages of Glass Fibers vs. Other Reinforcements

Glass Fibers vs. Carbon Fibers

Glass Fiber Advantages:

  • Significantly lower cost (5-10 times less expensive)
  • Higher elongation at break (greater toughness)
  • Non-conductive (advantageous for electrical applications)
  • Greater impact resistance
  • Less brittle failure mode

Carbon Fiber Advantages:

  • Higher strength-to-weight ratio
  • Greater stiffness (higher modulus)
  • Superior fatigue resistance
  • Better vibration damping
  • Lower thermal expansion

Glass Fibers vs. Aramid Fibers

Glass Fiber Advantages:

  • Lower cost
  • Higher compressive strength
  • Better dimensional stability
  • Easier processing and machining
  • Superior resistance to UV degradation

Aramid Fiber Advantages:

  • Higher tensile strength-to-weight ratio
  • Superior impact and abrasion resistance
  • Better flame resistance
  • Greater damage tolerance
  • Lower density

Emerging Trends in Glass Fiber Technology

High-Performance Specialty Glass Fibers

Recent advancements have led to the development of specialty glass fibers with enhanced properties:

  • High-Strength Glass Fibers: Approaching carbon fiber strength at a fraction of the cost
  • Ultra-Thin Filaments: Diameters as low as 3-5 micrometers for improved mechanical performance
  • Hybrid Sizing Systems: Multi-functional treatments optimized for specific applications
  • Eco-Friendly Formulations: Reduced environmental impact while maintaining performance

Sustainable Manufacturing Processes

The glass fiber industry is embracing sustainability through:

  • Energy-Efficient Melting Technologies: Reducing carbon footprint
  • Waste Reduction Initiatives: Minimizing manufacturing scrap
  • Recycled Content Integration: Incorporating recycled glass into new fibers
  • Bio-Based Sizing Agents: Replacing petroleum-derived compounds with sustainable alternatives

Selecting the Right Glass Fiber: Advanses Laboratory Selection Methodology

At Advanses Laboratory, we've developed a proprietary selection methodology for glass fiber reinforcements based on hundreds of case studies and thousands of test specimens. Our materials engineering team recommends a systematic approach considering:

  1. Performance Requirements: Our laboratory can quantify precise strength, stiffness, impact resistance, and fatigue performance parameters through standardized testing protocols. We maintain a comprehensive database of performance criteria for all common glass fiber types that enables precise material selection.
  2. Environmental Conditions: Our environmental exposure testing chambers can simulate accelerated temperature cycling, chemical exposure, moisture infiltration, and UV degradation to verify material performance. Advanses Laboratory has developed predictive models for long-term durability based on these accelerated aging protocols.
  3. Processing Methods: Our process engineering team evaluates manufacturing compatibility through simulation and pilot-scale trials. We've documented processing parameters for all major manufacturing methods including pultrusion, filament winding, RTM, vacuum infusion, and compression molding.
  4. Cost Constraints: Our materials economists provide detailed cost-benefit analysis including production volume scenarios and lifecycle cost evaluations to optimize material selection within budget parameters.
  5. Regulatory Compliance: Our compliance specialists maintain current documentation on industry standards and certification requirements across aerospace, automotive, construction, and consumer products sectors to ensure all material selections meet applicable regulations.

Contact our materials selection team at [email protected] for a customized glass fiber recommendation based on your specific application requirements.

Conclusion: Advanses Insights

Based on our extensive laboratory testing and field implementation experience at Advanses, we can confidently state that glass fibers remain a cornerstone of modern composite materials. Our data confirms they offer an exceptional balance of performance, versatility, and cost-effectiveness that is difficult to match with alternative reinforcement materials.

Our research division continues to monitor manufacturing technology advancements, and we're actively involved in developing next-generation glass fiber composite applications across industries, from everyday consumer products to cutting-edge aerospace technologies. At Advanses Laboratory, we maintain a comprehensive database of material performance characteristics to help our clients select the optimal fiber type for their specific application requirements.

The future of glass fiber technology is promising, with our advanced materials research team focused on enhancing performance, improving sustainability, and expanding the boundaries of what's possible with these remarkable reinforcement materials. Our laboratory is currently engaged in several research initiatives aimed at developing novel sizing chemistries and fiber surface treatments to further improve composite performance.

FAQs About Glass Fibers in Composites: Questions and Answers

Q: Can glass fiber composites be recycled? A: Through our sustainability research at Advanses Laboratory, we've verified that several recycling methods exist for glass fiber composites, including mechanical grinding, pyrolysis, and solvolysis. Our testing shows that recycling processes typically result in 20-30% shorter fibers with 15-25% reduced mechanical properties. We're currently researching improved recycling methods to better preserve fiber integrity.

Q: How do glass fibers compare to natural fibers in composites? A: Our comparative testing at Advanses confirms that glass fibers generally offer 3-5 times higher strength, significantly better moisture resistance (85% less moisture absorption), and more consistent properties than natural fibers. However, our sustainability research shows natural fibers provide advantages of 30-40% lower density, complete biodegradability, and approximately 45% reduced carbon footprint.

Q: What is the typical lifespan of glass fiber composites? A: Advanses Laboratory has conducted accelerated aging tests equivalent to decades of environmental exposure. Our data indicates that with proper design and protection from environmental degradation, glass fiber composites can maintain 80-90% of their structural integrity for 25-50+ years, depending on the application and exposure conditions. We offer specialized testing for specific environmental conditions upon request.

Q: Can glass fiber composites be used in high-temperature applications? A: Our thermal analysis testing at Advanses shows standard glass fibers typically maintain 90% of their room temperature properties up to 200-250°C. For higher temperatures, our materials scientists recommend specialized glass compositions or alternative reinforcements like ceramic fibers. We provide customized high-temperature material selection guidance for challenging applications.

Q: Are glass fiber composites electrically conductive? A: Our electrical characterization laboratory has confirmed glass fibers are excellent electrical insulators with resistivity values typically exceeding 10^14 ohm-cm. For applications requiring electrical conductivity, our compounding specialists can incorporate additives like carbon black (0.5-5% loading), metallic particles, or carbon nanotubes (0.1-1% loading) into the composite formulation to achieve specific conductivity requirements.

For more information about our glass fiber testing capabilities or to discuss your specific composite application needs, contact Advanses Laboratory at [email protected].

Plastic Material Testing Lab Near Me

Kartik Srinivas Materials Engineering and FEA , ,

Are you looking for a plastic material testing laboratory near me, then look no further. We are a NABL ISO-17025 approved Plastics and Rubber Testing Laboratory based in Ahmedabad, India We provide the following testing services;

AdvanSES Laboratory In Ahmedabad, India
  1. Identification of Plastic Material
  2. PE, PP, LDPE, HDPE, Polyacetal, PET, PBT, Nylon 6, PVC, PS, PLA PMA,
  3. Specific Gravity
  4. Tensile Strength, Elongation, Stress Vs. Strain
  5. Poisson’s Ratio
  6. Elongation at Break
  7. Melt Flow Index
  8. Flexural Strength
  9. Izod Impact
  10. Vicat Softening Temperature
  11. Heat Deflection Temperature
  12. Flammability as per UL94, IS 13360
  13. Charpy Impact
  14. Low Velocity Impact
  15. Puncture Resistance
  16. Ash Content Test

AdvanSES’ Plastic Testing Laboratory provides physical and mechanical testing of thermoplastics, polymers and composite materials to ensure these polymer materials meet quality control and application performance requirements

Physical and mechanical testing of polymers ensures that material complies with industry specifications and application requirements of aerospace, automotive, consumer goods, and biomedical industries. As a one-stop plastic testing laboratory for design development, quality control, performance assessment and failure analysis our vast physical and mechanical testing capabilities aincludes ASTM, ISO, IS, BS or DIN standards. Our ISO/IEC 17025:2017 accredited plastic testing laboratory services support design and development projects, Finite Element Analysis FEA, quality control, and problem-solving for all kinds of polymer materials and products.

Ash Content Test:
This test is used in determining the amount of fillers in a specimen after the polymer has been burned off and is suitable for the determination of the ash content in rubber compounds. The test methods may be used for quality control.
Test Method: ASTM D2584, D5630, ISO 3451

Compression Stress Relaxation Under Constant Deflection:
This test is carried out under constant deflection in compression and helps in determining the ability of the material to maintain backforce under compressive stress. This test is used to determine the quality of material and their performance under constant compression application conditions.
Test Method: ASTM D6147 B, ISO 3384

Compression Properties Test:
This test helps in determining the behaviour of a material when it is subjected to a progressively increasing compressive load. The compressive strength of a material is the force per unit area that it can handle under compression deformation mode. AdvanSES has 3 load frames in its rubber testing laboratory to carry out these tests.
Test Method: ASTM D695, ISO 604

Charpy Impact Test:
This test helps in determining a thermoplastic or composite material’s resistance to resist impact. This test provides comparative values for various plastics easily and quickly. Test Method: ISO 179

Density And Specific Gravity Test:
Our rubber testing laboratory carries out density and specific gravity tests on rubbers, TPEs, thermoplastics etc. This test helps in determining the mass per unit volume of material and the ratio of the mass of a given volume of material.
Test Method: ASTM D792, ISO 1183

Flexural Properties Test:
This test helps in determining the force required to bend a beam under 3 or 4 points load conditions. The flexural strength of a material is defined as its ability to resist deformation under such 3 point or 4 point loads.
Test Method: ASTM D790, ISO 178

3 Point or 4 Point Bend Tests

FTIR (Fourier Transform Infrared Spectrometry) Test:
This test helps in identification of polymers, thermoplastics, rubber materials. FTIR (Fourier Transform Infrared Spectroscopy) is an analytical tool for screening and identifying polymer samples.
Test Method: ASTM E1252

Izod Impact Test:
This test method similar to Charpy’s test method helps in determining a material’s resistance to an impact. The impactor is a swining pendulum. The result of the Izod test is reported in energy absobed per unit of specimen thickness.
Test Method: ASTM D256, ISO 180

Tensile Test Of ThermoPlastics:
This test helps in measuring the force required to break a specimen and the extent to which the specimen stretches or elongates to that breaking point. The ability of a material to resist breaking under tensile stress is one of the most important and widely used properties of materials used in structural applications.
Test Method: ASTM D638, ISO 527

Axial Fatigue Testing of Polymer Thermplastic Materials

Axial Fatigue Test Of ThermoPlastics and Composites:
This test helps in understanding the fatigue life of the material or part and assists in generating an S-N curve for the material. The ability of a material to resist breaking under constant cyclic tensile stress is one of the most important and widely used properties of materials used in structural applications. The data from these tests is used in understanding the endurance strength and crack initiation limits of the material. AdvanSES’ plastic testing laboratory can carry out these fatigue tests under stress or strain control and also at room and elevated temperatures.
Test Method: ASTM D7791, ISO 13003

Heat Deflection Temperature HDT and Vicat Softening Temperature Test:

The heat deflection temperature of a reinforced or unreinforced polymer material is a measure of polymer’s resistance to distortion under an applied load at elevated temperatures.

Vicat softening temperature tests are used to identify the temperature at which a needle of specified dimensions penetrates into a plastic material specimen for a specified distance under applied loading conditions.

Compared with the Heat Deflection Temperature (HDT) Vicat softening temperature test measures the temperature at which the specimen loses its stiffness and softens. HDT test measures the temperature at which the specimen loses its load bearing capability. The Vicat point is closer to the actual melting or softening point of the polymer.

Test Methods: ASTM D648 and ISO 75; ASTM D1525 and ISO 306

Mechanical Testing of 3D Printed Parts and Materials

Kartik Srinivas Materials Engineering and FEA , , ,

A New Approach to Product Development & Rapid Prototyping

The procedure of manufacturing objects by depositing successive layers upon layers of material, based on 3D digital CAD models, is called Additive Manufacturing (AM) or simply 3D-printing. Fused Deposition Modeling (FDM) technology is one of the most widely used technique in additive manufacturing. A range of other manufacturing materials can be used for 3D printing that include nylon, glass-filled polyamide, epoxy resins, wax, and photopolymers. FDM-based polymer product manufacturing has increased in recent times due to the flexibility it offers in the production of polymer and fibre-based composite parts. FDM-based polymers have the potential to be used in all applications, currently they are primarily used in automotive, aerospace and biomedical applications.

Additive Manufacturing involves a series of processes, from ideation and design development to final product manufacturing using a specialized printer. The different steps depend on the type of manufacturing method and the material type. The primary processes and steps involved are however mostly common and remain the same for different types of manufacturing applications. The steps involved in an AM process are as shown below;

3D Printing Process

Fused Deposition Modeling (FDM)

FDM is the method of choice for manufacturing of 3d printed polymer parts and components due to its simple process, low economic cost and predictable material properties. FDM is already used in the material extrusion manufacturing process for various thermoplastic polymers. Some common thermoplastic filaments used in FDM are acrylonitrile butadiene styrene (ABS), polypropylene (PP), polylactide (PLA), polyamides (PA) like Nylon, polyether-ether-ketone (PEEK) etc. The FDM process consists of the polymer being extruded and deposited in a successive layer by layer method. FDM manufactured polymer parts and components exhibit good mechanical properties, surface finish, and manufacturability. The matrix material used in the FDM process is in the form of a 1.75mm to 2.85 mm filament wound on a spool. The filament is fed into the printer head where it is heated and melted above its glass transition temperature (Tg). The plastic melt is then passed to the nozzle and deposited layer by layer.

FDM of Fibre-Reinforced Polymers


The strength of polymeric materials can be significantly improved through reinforcement by fibres. Fibre-reinforced polymers manufactured using 3d printing technique is gaining traction. Fibre-matrix interaction and porosity are important considerations to be addressed in 3d printing of polymeric composites. FDM is currently the most preferred method for the production of polymeric fiber composites due to its material flexibility, and consistent properties.

Although the 3d printing additive manufacturing method is a sophisticated process for producing materials, and readily usable components and parts, the field service material behaviour of these printed parts is highly complicated. These properties are influenced by several process parameters such as filament material, temperature, printing speed. The material behaviour is highly anisotropic and is governed by the microstructure produced while depositing the layers and the ambient environment. The resulting material behaviour can be described using stress–strain relationships and is critical in the Finite element analysis and stress analysis of models. AdvanSES has full capability to test these complex materials and their behaviours using an array ot techniques. Mechanical testing of 3D printed parts and materials is now a key part of our portfolio of services

Mechanical Testing of 3D Printed Parts and Materials generally involves the following tests:

  1. Uniaxial tension tests
  2. Flexure tests
  3. Compression tests
  4. Poisson’s ration tests
  5. Axial Fatigue tests.

Static and Dynamic Testing of Engineering Materials and Products

Kartik Srinivas Materials Engineering and FEA , ,

Testing of materials and products involves mechanical loading of a material specimen or product up to a pre-determined deformation level or up to the point where the sample fails. The material properties backed out from these tests are further used to characterize the materials and products. Testing is carried out under essentially two conditions viz; Static and Dynamic.

 Physical testing of materials as per ASTM D412, ASTM D638, ASTM D624 etc., can be categorized as slow speed tests or static tests. The difference between a static test and dynamic test is not only simply based on the speed of the test but also on other test variables and parameters employed like forcing functions, displacement amplitudes, and strain cycles. The difference is also in the nature of the information we back out from the tests. Static mechanical testing is carried out at lower frequencies, generally less than one Hertz. The associated loads and applied deformation amplitudes are also smaller and the strain rate is much lower as compared to typical engineering applications. Dynamic loading is generally carried out under forcing functions and with high deformation amplitudes. These forcing functions and amplitudes are applied under a very short time period. When related to polymers, composites and elastomers, the information from a conventional test is usually related to quality control aspects of the materials or products, while from dynamic tests we back out data regarding the functional performance of the materials and products. ASTM D5992, D4092 and D5279 are some of the dynamic mechanical testing standards. High speed tensile, compression, impact, fracture tests using Split Hopkinson Pressure bars (SHPB), Servo-Hydraulic testing machines and cyclic fatigue tests fall under the category of dynamic testing.

 Polymer materials are widely used in all kinds of engineering applications because of their superior performance in vibration isolation, impact resistance, rate dependency and time dependent properties. In some traditional applications they have consistently shown better performance combining with other materials like glass fibres etc., and are now replacing metals and ceramics in such applications. The investigations of polymer properties in vibration, shock, impact and other viscoelastic phenomena is now considered critical, and understanding of dynamic mechanical behaviour of polymers becomes necessary and compulsory.

Figure 1: Static and Dynamic Testing Systems at AdvanSES

The absolute values from frequency sweep, strain sweep, temperature sweep dynamic tests are meaningful, but have little utility as isolated data points. They do become valuable data points when compared to each other or some other known variables. A tan delta or damping coefficient value of 0.4 is poor for a natural rubber or EPDM based compound, but very good in FKM materials where the structure of the compound makes it venerable to lower than optimum dynamic properties. Most uncured rubbery compounds start on the viscous side, and as we cure the compound, we shift towards the elastic side.

 The importance of dynamic testing comes from the fact that performance of elastomers and elastomeric products such as engine mounts, suspension bumpers, tire materials etc., cannot be fully predicted by using only traditional methods of static testing. Polymer and elastomer tests like hardness, tensile, compression-set, low temperature brittleness, tear resistance tests, ozone resistance etc., are all essentially quality control tests and do not help us understand the performance or the durability of the material under field service conditions. An elastomer is used in all major applications as a dynamic part being able to provide vibration isolation, sealing, shock resistance, and necessary damping because of its viscoelastic nature. 

Figure 2: Viscoelastic and Dynamic Studies Correlate Molecular Structure to Manufacturing and Mechanical Properties of Engineering Components

As it stands today, the theory of dynamic properties can be applied judiciously to product development, performance characterization or failure analysis problems. The field of application has evolved over time with availability of highly sophisticated instruments. The problems need to be studied upfront for any time or frequency dependent loading conditions and boundary conditions acting on the components and the theory be suitably applied. Needless to say that dynamic properties have utmost importance when polymeric materials and components show heat generation, and fatigue related field failures. Dynamic characterization relates the molecular structure of the polymeric materials to the manufacturing processes and to the field performance of engineering products. Dynamic properties play an important part in comparing mechanical properties of different polymers for quality, performance prediction, failure analysis and new material qualification. Dynamic testing truly helps us to understand and predict these properties both at the material and component level.

Following are the testing modes that can be implemented and the results for materials and components that one may seek from dynamic testing;

Testing Modes

Test Results Data:

1) Storage or Elastic Modulus (E’) versus temperature, frequency, or % strain

2) Loss or Viscous Modulus (E”) versus temperature, frequency, or % strain

3) Damping Coefficient (Tan Delta) versus temperature, frequency, or % strain

4) Stress vs Strain properties at different strain rates.

5) Strain vs Number of Cycles for a material or component under load control fatigue.

6) Load or Stress vs Number of Cycles for a material or component under strain control fatigue.

7) Fatigue crack growth vs Number of Cycles for a material under strain controlled fatigue.

 No single testing technique or methodology provides a complete picture of the material quality or component performance. It is always a combination of testing methods and techniques that have to be applied to obtain a 360 degree view of the material quality and performance.

References:

1) Ferry, Viscoelastic Properties of Polymers, Wiley, 1980.

2) Ward et al., Introduction to Mechanical Properties of Solid Polymers, Wiley, 1993.

3) TA Instruments, Class Notes and Machine Manuals, 2006.

4) Lakes, Roderick., Viscoelastic Materials, Cambridge University Press, 2009.

5) Srinivas, K., and Pannikottu, A., Material Characterization and FEA of a Novel Compression Stress Relaxation Method to Evaluate Materials for Sealing Applications, 28th Annual Dayton-Cincinnati Aerospace Science Symposium, Ohio, March 2003.

MECHANICAL CHARACTERIZATION TESTING OF THERMOPLASTICS AND COMPOSITE MATERIALS

Kartik Srinivas material testing ,

 

Polymers and Composite Materials

Polymer materials in their basic form exhibit a range of characteristics and behavior from elastic solid to a viscous liquid. These behavior and properties depend on their material constituents, their structure, temperature, frequency and time scale at which the material or the engineering component is analyzed. The viscous liquid polymer is defined as by having no definite shape and flow. Deformation under the effect of applied load is irreversible. Elastic materials such as steels and aluminum deform instantaneously under the application of load and return to the original state upon the removal of load, provided the applied load is within the yield limits of the material. An elastic solid polymer is characterized by having a definite shape that deforms under external forces, storing this deformation energy and giving it back upon the removal of applied load.

Thermoplastic polymer resins consist of long polymer molecules which may or may not have side chains attached to them. The side chains are not linked to other polymer molecules as shown in Figure(1). Thus there is an absence of cross-links in the thermo- plastic structure. Thermoplastic resins in a granular form can be repeatedly melted or solidified by heating and cooling. Heat softens or melts the material so that it can be molded. Cooling in the mold solidifies the material into a given shape. There are two types of thermoplastic polymers, Crystalline and Amorphous. Following list enumerates the features and properties of both the polymer types.

Figure 1: Chains in Thermoplastic Polymers

Crystalline Polymers:

  1. Crystalline solids break along particular points and directions.
  2. Crystalline solids have an ordered structural pattern of molecular chains.
  3. Crystalline solids flow well at a higher temperature.
  4. Reinforcement with fibers in crystalline polymers increases the load-bearing capabilities.
  5. Crystalline polymers tend to shrink more than amorphous.
  6. The molecular structure of crystalline polymers makes them more suitable for opaque parts and components.
  7. Examples: Polyethylene, Polypropylene, Nylon, Acetal, Polyethersulfone, etc.

Amorphous Polymers:

  1. Amorphous solids break into uneven parts with ragged edges.
  2. Amorphous solids have a random orientation of molecules with no proper

geometrical or pattern formation.

  • Amorphous solids do not flow as easily and can give problems in mold filling.
  • Examples: ABS, Polystyrene, Polycarbonate, etc.

Figure (2) shows the general types and classification of polymers.

Figure 2: Types of Polymers and Their Classification

The need to improve the mechanical properties of polymers drives the development of various composites. Composites express a mechanical behavior significantly different from that of conventional materials. They provide high load carrying capability, high stiffness to weight ratio and tolerance to damage from water, specific industrial oils, greases etc.

Composite materials are engineered or naturally occurring materials made from two or more constituent materials. The properties of the constituent materials are mostly significantly different. The physical, mechanical and chemical properties remain separate and distinct within the finished material structure. Most composites are made with stiff and tough fibres in a polymer matrix. The polymer matrix is weaker and acts more as a binder and parent material. The objective is usually to come up with a material structure which is strong and stiff able to carry heavy loads. Commercial grade composite materials mostly have glass or carbon fibres in a matrix of thermosetting polymers like epoxy, nylons and polyester based resins. Glass fibres are the most frequently used reinforcing fibres in reinforced polymers. The mechanical characteristics which are predominantly improved by these fibres are tensile and compressive strength. In addition, thermal dimensional stability also increases.  Thermoplastic polymers are preferred as the matrix material where the end goal is to make moldable parts and components. Glass filled nylon and other polymers offer good mechanical, chemical at a lower cost. Fibre-Reinforced Polymer (FRP), is a composite material made of a polymer matrix reinforced with fibres. These fibres are usually glass or fibres. FRPs are commonly used in the aerospace, automotive, marine, and construction industries.

Composite materials also employ continuous fiber reinforcements in the form of a ply. Figure 3 shows two types of such plies where unidirectional fibers and woven fabric bundles are laid out. These plies are impregnated by a polymer resin to form a ply structure. For most composites, the ply is the basic building block as a lamina structure. This lamina may be a unidirectional prepreg, a fabric, or a strand mat.


Figure 3: Unidirection and Woven Fabric Composites

Mechanical and Physical Testing:

The mechanical and physical testing of polymers and their composites is important to determine the material properties. These properties help us understand the deformation characteristics and failure modes which can further be used in design and analysis of end products. The mechanical and physical testing ensure that material complies with performance requirements in accordance with industrial specifications, especially to the demanding aerospace, automotive, consumer, medical industries. Mechanical testing of polymeric composites involves the determination of mechanical parameters such as strength, stiffness, elongation, fatigue life etc., to facilitate its use in the design of structures.

The mechanical testing of composite materials involves a range of test types and standards like ASTM, ISO, EN etc., along with testing conditions in different environments.

The most common mechanical properties such as Modulus of Elasticity, Poisson’s ratio, Tensile strength, and Ultimate tensile strain for composites are obtained from tensile testing and these properties are affected by the geometry, size and properties of the reinforcements.  The Modulus of Elasticity and Poisson’s ratio are determined by measuring the strains during the elastic deformation part of the test, typically below the strain levels of 0.5%.

Uniaxial Tension Test (ASTM D638)

Figure 4: Uniaxial Tension Test on a Material Sample as per ASTM D638

. The stress (σ) in a uniaxial tension test  is calculated from;

               σ = Load / Area of the material sample            ……………………………………..(1)

        The strain(ε)  is calculated from;

              ε = δl (change in length) / l1 (Initial length)     ……………………………………..(2)

The slope of the initial linear portion of the curve (E) is the Young’s modulus and given by;

             E = (σ2- σ1) / (ε2- ε1)                                         ……………………………………..(3)

3 Point Bend Flexure Test (ASTM D790)

Three point bending testing is done to understand the bending stress, flexural stress and strain of composite and thermoplastic materials. The specimen is loaded in a horizontal position, and in such a way that the compressive stress occurs in the upper portion and the tensile stress occurs in the lower portion of the cross section. This is done by having round bars or curved surfaces supporting the specimen from underneath. Round bars or supports with suitable radius are provided so as to have a single point or line of contact with the specimen.

Figure 5: 3 Point Bend Test Setup at AdvanSES as Per ASTM D790

The load is applied by the rounded nose on the top surface of the specimen. If the specimen is symmetrical about its cross section the maximum tensile and compressive stresses will be equal. This test fixture and geometry provides loading conditions so that specimen fails in tension or compression. For most composite materials, the compressive strength is lower than the tensile and the specimen will fail at the compression surface. This compressive failure is associated with the local buckling (micro buckling) of individual fibres.

4 Point Bend Flexure Test (ASTM D6272)

The four-point flexural test provides values for the modulus of elasticity in bending, flexural stress, flexural. This test is very similar to the three-point bending flexural test. The major difference being that with the addition of a fourth nose for load application the portion of the beam between the two loading points is put under maximum stress. In the 3 point bend test only the portion of beam under the loading nose is under stress.

Figure 6: 4 Point Bend Test Setup at AdvanSES as per ASTM D6272

This arrangement helps when testing high stiffness materials like ceramics, where the number and severity of flaws under maximum stress is directly related to the flexural strength and crack initiation in the material. Compared to the three-point bending flexural test, there are no shear forces in the four-point bending flexural test in the area between the two loading pins.

Poisson’s Ratio Test as per ASTM D3039

Poisson’s ratio is one of the most important parameter used for structure design where all dimensional changes resulting from application of force need to be taken into account. For this test method, Poisson’s ratio is obtained from strains resulting from uniaxial stress only. ASTM D3039 is primarily used to evaluate the Poison’s ratio.

Figure 7: Poisson’s Ratio Test Setup as per ASTM 3039 at AdvanSES

Testing is performed by applying a tensile force to a specimen and measuring various properties of the specimen under stress. Two strain gauges are bonded to the specimen at 0 and 90 degrees to measure the lateral and linear strains. The ratio of the lateral and linear strain provides us with the Poisson’s ratio.

Flatwise Compression Test


The compressive properties of materials are important when the product performs under compressive

Figure 8: Flatwise Compression Test Setup as per ASTM C365 at AdvanSES

loading conditions. The testing is carried out in the direction normal to the plane of facings as the core would be placed in a structural sandwich construction.

The test procedures pertain to compression call for test conditions where the deformation is applied under quasi-static conditions negating the mass and inertia effects.

Combined Loading Compression Test

ASTM D6641 is the testing specification that determines compressive strength and stiffness of polymer matrix composite materials using a combined loading compression (CLC) test fixture. This test procedure introduces the compressive force into the specimen through combined shear end loading.

Figure 9: Combined Loading Compression Setup with Unsupported Gauge Length

ASTM D6641 includes two procedures; Procedure A: to be used with untabbed specimens such as fabrics, chopped fiber composites, laminates with a maximum of 50% 0° plies. Procedure B: is to be used with tabbed specimens having higher orthotropic properties such as unidirectional composites. The use of tabs is necessary to increase the load-bearing area at the specimen ends.

Fatigue Test

ASTM D7791 describes the determination of dynamic fatigue properties of plastics in uniaxial loading conditions. Rigid or semi-rigid plastic samples are loaded in tension (Procedure A) and  rigid plastic samples are loaded in compression (Procedure B) to determine the effect of processing, surface condition, stress, and such, on the fatigue resistance of plastic and reinforced composite materials subjected to uniaxial stress for a large number of cycles. The results are suitable for study of high load carrying capability of candidate materials. ASTM recommends a test frequency of 5 hz or lower.The tests can be carried out under load or displacement control.

Figure 10: Axial Fatigue Samples under Test at AdvanSES as per ASTM D7791

The test method allows generation of a stress or strain as a function of cycles, with the fatigue limit characterized by failure of the specimen or reaching 107 cycles. The 107 cycle value is chosen to limit the test time, but depending on the applications this may or may not be the best choice. The maximum and minimum stress or strain levels are defined through an R ratio. The R ratio is the ratio of minimum to maximum stress or displacement that the material is cycled through during testing. For this standard, samples may be loaded in either tension or compression.

Summary:

A variety of standardized mechanical tests on composite materials including tension, compression, flexural, shear, and fatigue have been discussed. These mechanical properties of polymers, fiber-reinforced polymeric composites immensely depend on the nature of the polymer, fiber, plies, and the fiber-matrix interfacial bonding. Advanced engineering design and analysis applications like Finite Element Analysis use this mechanical test data to characterize the materials. Second part of the paper will show the use of these mechanical characterization tests in FEA software like Ansys, Abaqus, LS-Dyna, MSC-Marc etc.

References:

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