While mechanical testing as per different ASTM and ISO standards provides invaluable data for the design and analysis of composite structures, there are several challenges associated with testing these heterogeneous and anisotropic materials:
1. Material Variability: Composite materials exhibit inherent variability due to factors such as fibre misalignment, voids, and resin-rich or resin-starved regions. This variability can lead to significant scatter in the mechanical properties, making it challenging to establish reliable design allowables.
Dynamic UTM with Temperature Controlled Chamber
2. Specimen Preparation: Preparing high-quality composite test specimens is crucial for obtaining accurate and repeatable results. Factors like specimen geometry, machining-induced defects, and fibre waviness can influence the test results, necessitating strict adherence to specimen preparation procedures.
3. Gripping and End-Effects: In tensile and compressive testing, the gripping of composite specimens can introduce stress concentrations, premature failures, and spurious results if not addressed properly. Special gripping techniques, such as adhesive bonding or tabbing, are often required to minimize gripping-related issues.
Composite Material Testing
4. Failure Modes: Composite materials can exhibit complex failure modes, including fibre breakage, matrix cracking, delamination, and their interactions. Interpreting and correlating these failure modes with the measured properties can be challenging, especially under multi-axial loading conditions.
5. Size Effects: The mechanical properties of composite materials can be influenced by the specimen size and geometry, making it difficult to extrapolate coupon-level test results to full-scale structural components or assemblies.
6. Environmental Factors: The influence of environmental factors, such as temperature, moisture, and chemical exposure, on the mechanical properties of composites can be significant. Accurately simulating and accounting for these effects during testing is crucial for predicting real-world performance.
7. Specialized Equipment:Mechanical testing of composite materials often requires specialized equipment, such as environmental chambers, high-temperature furnaces, and advanced instrumentation for strain measurement and damage monitoring, which can be costly and complex to operate.
8. Data Interpretation and Analysis: The analysis and interpretation of mechanical test data for composite materials can be intricate, involving advanced analytical techniques, failure criteria, and micromechanical models, necessitating expertise in composite material behaviour and failure mechanisms.
9. Anisotropy: Unlike metals, composites often have different properties in different directions, making testing more complex. Addressing these challenges requires a combination of rigorous testing procedures, advanced instrumentation, statistical analysis techniques, and a deep understanding of composite material behavior. Collaboration between material suppliers, testing laboratories, and design engineers is essential to overcome these challenges and ensure the reliable and safe implementation of composite materials in aerospace applications.
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The testing requirements for composite materials used in drone applications may differ slightly from those used in manned aircraft, as the safety considerations and regulatory framework can vary. However, many of the fundamental testing principles remain similar. Here are some common composite material testing requirements for drone applications:
Material Testing and Characterization for Different Applications
Material characterization: Basic material properties such as tensile, compressive, shear, and flexural strengths, as well as physical properties like density and fiber volume fraction, need to be determined through standardized testing methods.
Impact resistance: Composite materials used in drone structures should be tested for their resistance to low-velocity impacts, as drones may be subject to collisions with obstacles or debris during flight.
Fatigue testing: Cyclic loading tests are often performed to evaluate the fatigue life and damage propagation characteristics of composite materials under simulated flight conditions.
Environmental resistance: Tests for moisture absorption, thermal aging, and resistance to chemicals or fluids that may be encountered during operation or storage are typically required.
Vibration and acoustic testing: Composite materials may need to be tested for their response to vibrations and acoustic loads experienced during drone flight.
Repair and maintainability: Evaluation of repair techniques and the effects of repairs on the mechanical properties of composite materials may be necessary, particularly for larger or more critical drone components.
Qualification testing: Full-scale or component-level testing may be required to qualify the composite materials and structures for their intended use in drone applications, considering factors such as design loads, operational environments, and safety margins.
It’s important to note that the specific testing requirements may vary depending on the type of drone, its intended use (commercial, military, recreational), and the applicable regulations or standards set by governing bodies or industry organizations. Additionally, composite material suppliers and drone manufacturers may have their own internal testing protocols and acceptance criteria based on their design requirements and risk assessments.
The Directorate General of Civil Aviation (DGCA) in India has set specific requirements for the testing of composite materials used in the aviation industry. These requirements are aimed at ensuring the safety and reliability of aircraft components made from composite materials. Here are some key aspects of the DGCA’s composite material testing requirements:
Material characterization: The DGCA requires comprehensive material characterization tests to be performed on composite materials, including tests for mechanical properties (tensile, compressive, shear, and flexural strengths), physical properties (density, fiber volume fraction), and environmental resistance (moisture absorption, thermal aging). Damage tolerance testing: Composite materials must undergo damage tolerance testing to assess their ability to withstand and resist the propagation of defects, such as impact damage, delaminations, and fatigue cracks. These tests may include compression after impact (CAI), open-hole compression (OHC), and fatigue testing. Environmental testing: Composite materials must be tested for their performance under various environmental conditions, such as elevated temperatures, humidity, and exposure to chemicals and fluids commonly encountered in aviation applications. Fire resistance testing: Composite materials used in aircraft interiors must meet specific fire resistance requirements, including tests for smoke density, heat release rate, and flame propagation. Quality control and process control: The DGCA requires manufacturers to establish and maintain robust quality control and process control procedures for the fabrication of composite components. This includes the use of appropriate manufacturing techniques, inspection methods, and non-destructive testing (NDT) techniques. Certification and approval: Composite materials and components intended for use in aircraft must undergo a rigorous certification and approval process by the DGCA. This process involves the review of design data, test reports, and manufacturing procedures to ensure compliance with applicable airworthiness standards.
It’s important to note that the specific testing requirements may vary depending on the application and criticality of the composite component, as well as the type of composite material being used. Manufacturers and suppliers of composite materials and components for the aviation industry in India must comply with the DGCA’s regulations and guidelines to obtain the necessary approvals for their products.
Understanding Poisson’s Ratio Testing for Composite Materials per ASTM D3039
Poisson’s ratio testing is an important material property that measures the negative ratio of transverse to axial strain. In other words, it quantifies how much a material contracts in the transverse direction when stretched in the axial direction. Knowing the Poisson’s ratio is critical for analyzing the behavior of materials under different loading conditions.
For fiber-reinforced polymer composite materials, Poisson’s ratio testing is performed according to the ASTM D3039 standard titled “Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials.” This standard covers the determination of tensile properties of reinforced polymer composites under controlled conditions.
Testing Procedure The basic procedure for Poisson’s ratio testing as per ASTM D3039 involves the following steps:
Specimen Preparation: Flat test specimens are prepared from the composite laminate with specified dimensions and geometry. Common specimen types are straight-sided or dog-bone shaped.
Strain Measurement: Strain gauges or extensometers are attached to the specimen in both the axial (loading) and transverse directions to measure longitudinal and lateral strains simultaneously during loading.
Tensile Loading: The specimen is mounted in the tensile testing machine grips and loaded in uniaxial tension until failure occurs. The load and strain data are recorded continuously.
Calculations: From the recorded strain data, Poisson’s ratio is calculated as the negative ratio of lateral strain to axial strain within the elastic region of the stress-strain curve.
Poisson’s Ratio Testing of Composite Materials as per ASTM D3039
Importance of Poisson’s Ratio Accurately determining Poisson’s ratio is crucial for several reasons:
Stress Analysis: Poisson’s ratio influences the stress distribution and deformation behavior of composite structures under different loading conditions.
Failure Prediction: Knowledge of Poisson’s ratio aids in predicting failure modes, such as delamination or matrix cracking, in composite materials.
Finite Element Modeling: Poisson’s ratio is an essential input parameter for finite element analysis (FEA) simulations used in the design and analysis of composite components.
Material Characterization: Poisson’s ratio provides insights into the microstructure and anisotropic nature of fiber-reinforced composites.
Adherence to the ASTM D3039 standard ensures consistent and reliable testing procedures, enabling accurate determination of Poisson’s ratio for composite materials. This data is invaluable for engineers and researchers working on the design, analysis, and optimization of composite structures in various industries, including aerospace, automotive, and renewable energy.
Please contact us to get your materials tested for Poisson’s Ratio
Introduction: Advanced Scientific and Engineering Services (AdvanSES), a leading materials science and engineering company, offers advanced testing services to ensure the hyperelasticity of materials used in various applications. From medical devices to aerospace and automotive components, the ability to withstand large deformations without breaking is crucial for their performance and safety. In this blog post, we will delve into the world of hyperelastic material testing at Advanses and explore the techniques and equipment used to evaluate the elastic properties of materials.
Advanses’ Hyperelastic Material Testing Services:
Advanses offers a wide range of testing services to assess the hyperelasticity of materials, including:
Uniaxial Testing: This is the most common type of material testing, where the material is subjected to uniaxial loading in one direction. Advanses uses advanced testing equipment, such as Instron or Zwick, to measure the material’s elastic properties under different loadings.
Multiaxial Testing: This test evaluates the material’s behavior under multidirectional loading conditions, mimicking real-world applications where materials are subjected to multiple forces simultaneously. Advanses’ testing equipment can simulate a variety of loading conditions, including torsion, bending, and compression.
Cyclic Testing: Hyperelastic materials often experience cyclic loading and unloading, which can affect their mechanical properties. Advanses offers cyclic testing services to study the material’s behavior under these conditions and ensure its durability over time.
Dynamic Testing: This test simulates the rapid deformation of materials under dynamic loading conditions, such as those encountered in impact or vibration applications. Advanses’ advanced testing equipment can measure the material’s response to high-speed loading conditions.
Equipment and Techniques Used at Advanses:
Advanses utilizes state-of-the-art equipment and techniques to evaluate the hyperelasticity of materials. Their testing capabilities include:
Universal Testing Machines: These machines are capable of applying forces up to 500,000 Newtons and can simulate a wide range of loading conditions.
Biaxial Testing Machine: This machine is designed for biaxial testing of hyperelastic materials in the aerospace and automotive industries.
Low Velocity Dynamic Testing System: This system enables the measurement of material response at impact speeds, typically in the range of 10s of meters per second. It is useful for evaluating the hyperelasticity of materials under impact loading conditions.
Finite Element Analysis Software: Advanses uses advanced finite element analysis software to simulate the behavior of materials under different loading conditions. This allows them to evaluate the material’s elastic properties without conducting expensive and time-consuming physical tests.
Benefits of Hyperelastic Material Testing at Advanses: By investing in hyperelastic material testing services, companies can gain valuable insights into their materials’ behavior under different loading conditions. The benefits of working with Advanses include:
Improved Material Performance: By understanding the elastic properties of their materials, companies can optimize their design and manufacturing processes to improve performance and safety.
Reduced R&D Costs: Finite element analysis software can significantly reduce the number of physical tests required, saving time and resources in the development process.
Faster Time-to-Market: Advanses’ testing services help companies quickly identify any issues or concerns with their materials, allowing them to address these problems more efficiently and bring their products to market faster.
Enhanced Compliance: By ensuring that their materials meet the required hyperelasticity standards, companies can demonstrate compliance with industry regulations and safety guidelines, reducing the risk of costly recalls or legal action.
Conclusion: Advanses’ hyperelastic material testing services provide companies with valuable insights into their materials’ behavior under different loading conditions. By leveraging their advanced equipment and techniques, businesses can optimize their designs, reduce R&D costs, and ensure compliance with industry regulations. With the ever-increasing demand for innovative materials in various applications, investing in hyperelastic material testing is crucial for companies to stay ahead of the competition and deliver safe and effective products to their customers.
Errors and uncertainties in the application of FEA for Composite Materials can come from the following many sources,
1) Errors that come from the inherent assumptions in the FEA theory and
2) Errors and uncertainties that get built into the system when the physics we are seeking to model gets transferred to FEA models.
A common list of these kind of errors are as mentioned below;
> Errors and uncertainties from the solver. > Level of mesh refinement and the choice of element type. > Averaging and calculation of stresses and strains from the primary solution variables. > Approximations in the material properties of the model. > Approx. and uncertainties in the loading and boundary conditions of the model.
The long list of error sources and uncertainties in the procedure makes it desirable that a framework of rules and criteria are developed for the application of finite element method. Verification procedure includes checking the design, the software code and also investigate if the computational model accurately represents the physical system. Validation is more of a dynamic procedure and determines if the computational simulation agrees with the physical phenomenon, it examines the difference between the numerical simulation and the experimental results. Verification provides information whether the computational model is solved correctly and accurately, while validation provides evidence regarding the extent to which the mathematical model accurately correlates to experimental tests.
The blue, red and green colored areas in Figure highlight the iterative validation and verification activities in the process. The green highlighted region falls in the domain of the laboratory performing the experiments.
Comparing the issue of code verification and calculation verification of FEA for Composite Materials, the main point of difference is that calculation verification involves quantifying the discretization error in the simulation. Code verification is rather upstream in the process and is done by comparing numerical results with analytical solutions.
The validation procedure has to be developed by the analyst. The following validation guidelines were developed at Sandia National Labs [Oberkampf et al.] by experimentalists, these are applicable to all problems from computational mechanics.
#1: The validation experiment should be designed by the FEA group & experiment engineers. The experiments should be designed so that validation falls inside the application domain. #2: The designed experiment should involve the full physics of the system, including the loading and boundary conditions. #3: The solutions of the experiments and from the computational model should be totally independent of each other. #4: The experiments and the validation process should start from the system level solution to the component level. #5: Care should be taken that operator bias or process bias does not contaminate the solution or the validation process.
Finite Element Analysis (FEA) is a powerful tool used in engineering to simulate the behavior of structures and materials under different conditions. However, the accuracy of FEA results depends on the accuracy of the input parameters and assumptions made during the simulation. Strain gauging is a technique used to verify the accuracy of FEA results by measuring the actual strains in a structure and comparing them with the predicted strains from the FEA model.
What is Strain Gauging?
Strain gauging is a technique used to measure the strain in a material or structure. A strain gauge is a device that changes its electrical resistance when subjected to strain. The change in resistance is proportional to the strain, and this relationship is used to calculate the strain in the material. Strain gauges are attached to the surface of the material using a special adhesive, and the electrical resistance is measured.
There are several types of strain gauges used for different applications. Some of the common types include:
Linear Strain Gauges: These have one measuring grid and measure the strain in one direction. They are suitable when only one direction of strain needs to be investigated.
Quarter-Bridge, Half-Bridge, and Full-Bridge Configurations: These are determined by the number of active elements in the Wheatstone bridge and the type of strain being measured. Quarter-bridge, half-bridge, and full-bridge strain gauges are used to measure bending and axial strain, and they have different sensitivities and applications.
Rosette Strain Gauges: These include membrane rosette, tee rosette, rectangular rosette, and delta rosette. They are used to measure strain in multiple directions and are suitable for complex stress analysis.
Shear Strain Gauges, Column Strain Gauges, and 45°/90°-Rosette: These are used for specific applications where the strain needs to be measured in a particular direction or orientation.
Each type of strain gauge has its own characteristics, advantages, and applications. The selection of the appropriate strain gauge depends on the specific measurement task and the type of strain to be measured.
How is Strain Gauging Used for Verification of FEA?
Strain gauging is used to verify the accuracy of FEA results by measuring the actual strains in a structure and comparing them with the predicted strains from the FEA model. The process involves the following steps:
Design and fabricate the structure to be tested.
Install strain gauges at critical locations on the structure.
Apply a known load or deformation to the structure.
Measure the strains using the strain gauges.
Compare the measured strains with the predicted strains from the FEA model.
Adjust the FEA model parameters and assumptions to improve the accuracy of the predictions.
Benefits of Strain Gauging for Verification of FEA
Strain gauging is a valuable technique for verifying the accuracy of FEA results. Some of the benefits of strain gauging include:
Provides a quantitative measure of the accuracy of FEA results.
Helps identify errors in the FEA model parameters and assumptions.
Improves confidence in the FEA results and reduces the risk of failure in the actual structure.
Can be used to optimize the design of the structure by identifying areas of high stress or strain.
Conclusion
Strain gauging is a valuable technique for verifying the accuracy of FEA results. It provides a quantitative measure of the accuracy of the FEA model and helps identify errors in the model parameters and assumptions. By using strain gauging to verify FEA results, engineers can improve confidence in the design of structures and reduce the risk of failure.
References:
Helm JD, Sutton MA, McNeill SR. Deformations in wide, center-notched, thin panels, part II: finite element analysis and comparison to experimental measurements. Opt Eng 2003; 42(5): 1306–1320.
Hertelé S, de Waele W, Denys R, Verstraete M. Investigation of strain measurements in (curved) wide plate specimens using digital image correlation and finite element analysis. The Journal of Strain Analysis for Engineering Design. 2012;47(5):276-288.
Kartik Srinivas, Verifications and Validations in Finite Element Analysis, https://www.researchgate.net/publication/341727057_Verifications_and_Validations_in_Finite_Element_Analysis_FEA
The world of design engineering and materials testing is being reshaped by the advent of artificial intelligence (AI), particularly large language models (LLMs) like Google Bard or ChatGPT. These AI models are not just about generating text; they hold transformative potential for mechanical and materials engineers, especially in the drone and UAV industry.
AI in Design Engineering
LLMs can analyze, interpret, and even generate complex engineering documentation and instructions. This capability allows design and FEA engineers to automate repetitive tasks, freeing them to focus on innovative problem-solving.
These AI models use Natural Language Processing (NLP) techniques to understand codes, clauses, formulas, and standards. With proper fine-tuning, they can develop accurate relationships between engineering variables and requirements within their neural networks. This allows design engineers to create systems that can automatically perform calculations based on the relevant formulas and clauses required for drone design.
AI as a Design Assistant and FEA Engineer
AI can act as a design assistant, capable of making informed decisions and applying codified standards to repetitive types of work. This significantly enhances productivity and efficiency in design engineering workflows.
AI can rapidly generate numerous potential solutions given a problem statement or a design specification. This broadens the design space, uncovering innovative approaches.
AI can also automate many tedious engineering process tasks. For instance, creating CAD models for structure design and analysis can be time-consuming and require a high level of knowledge. However, design engineers can leverage LLMs to instantly generate a CAD model by inputting fundamental design parameters. The LLM can further refine the design based on additional feedback and input provided by the engineer, streamlining the iterative design process.
AI can also play a significant role in material testing. The vast amounts of data that LLMs are trained on means that they can identify patterns and relationships that are not immediately apparent to human designers. Through this unique capability, AI could suggest a material or configuration that increases efficiency or has superior performance compared to more conventional human-led designs.
By leveraging AI’s ability to uncover hidden insights within complex data sets, design engineers can explore novel design possibilities that push the boundaries of conventional engineering practices. This leads to innovative solutions that may have otherwise been overlooked.
Conclusion
The integration of AI into design engineering and materials testing holds significant potential. From automating tedious tasks to generating innovative solutions, AI can act as a powerful tool for design engineers. As we continue to fine-tune these models and explore their capabilities, we can expect to see even more transformative changes in the field of design engineering.
However, it’s important to remember that while AI can enhance and streamline many aspects of design engineering, it doesn’t replace the need for human oversight, intuition, and expertise. The goal is to create a collaborative environment where AI and humans work together, leveraging their respective strengths to drive innovation and efficiency.
So, whether you’re a mechanical materials engineer or a scientist looking to streamline your workflows or a company seeking to stay at the forefront of technological advancements, now is the time to explore the potential of AI and LLMs in your operations. The future of product engineering is here, and it’s powered by AI. At AdvanSES we have already started allocating resources to this emerging field.
Artificial Intelligence (AI) has found numerous applications in mechanical engineering and materials testing, revolutionizing the field with its ability to analyze vast amounts of data and reveal complex interrelationships. Here are some notable applications:
Machine Vision and Learning: AI, particularly machine vision and machine learning, can significantly improve the technical level of material testing¹. Machine vision inputs the characteristics of the inspected object into the computer, while machine learning enables the computer to better analyze these characteristics and make testing conclusions. This process is characterized by high accuracy and speed, and can be used in all aspects of material testing¹.
Textile Material Testing: AI techniques such as image analysis, back propagation, and neural networking can be specifically used as testing techniques in textile material testing. AI can automate processes in various circumstances.
Materials Modeling and Design: AI techniques such as machine learning and deep learning show great advantages and potential for predicting important mechanical properties of materials. They reveal how changes in certain principal parameters affect the overall behavior of engineering materials. This can significantly help to improve the design and optimize the properties of future advanced engineering materials.
Mechanical Engineering: AI, especially machine learning (ML) and deep learning (DL) algorithms, is becoming an important tool in the fields of materials and mechanical engineering. It can predict materials properties, design and development of new materials, and discover new mechanisms of material formation and degradation.
These Artificial Intelligence AI applications in mechanical engineering and materials testing not only enhance the efficiency and accuracy of the testing process but also open up new possibilities for material discovery and design. AdvanSES has decided to be on the forefront of this emerging technology and has invested resources into new developments.
Source: (1) Application of Artificial Intelligence in Material Testing – ResearchGate. https://www.researchgate.net/publication/361295451_Application_of_Artificial_Intelligence_in_Material_Testing/fulltext/637efc6d2f4bca7fd0883bd8/Application-of-Artificial-Intelligence-in-Material-Testing.pdf. (2) Artificial intelligence (AI) in textile industry operational …. https://www.emerald.com/insight/content/doi/10.1108/RJTA-04-2021-0046/full/html. (3) Artificial Intelligence in Materials Modeling and Design. https://link.springer.com/article/10.1007/s11831-020-09506-1. (4) Artificial intelligence and machine learning in design of mechanical …. https://pubs.rsc.org/en/content/articlelanding/2021/mh/d0mh01451f. (5) Evolution of artificial intelligence for application in contemporary …. https://link.springer.com/article/10.1557/s43579-023-00433-3.
Material Characterization Testing of Drones and UAV Materials at AdvanSES
Composite Material Testing for Drones and UAV Applications
Unmanned Aerial Vehicles (UAVs), commonly known as drones, have revolutionized numerous industries, from agriculture and real estate to cinematography and defense. One of the key factors contributing to the versatility and performance of these drones is the use of composite materials in their construction [1,2]. Composite material testing for drones and UAV applications is both difficult and challenging. The use of fiber-reinforced plastic composite materials challenges drone UAV engineers to design and manufacture products with high strength, stiffness and low cost. The demand for more maneuverable, payload effective UAVs is increasing, where composite materials are playing an essential role in the progress of these new high-performance UAV aircrafts with special composite material characteristics like light weight and high strength. These composite materials are distinguished by Young’s modulus as compared to different kinds of metals and aluminum alloys. Multi-rotor type UAVs represent an extremely complex system in terms of design and control. Octacopter, hexacopter and Quadcopter are typical of such multi-rotor designs. Such a type of aircraft is an inherently unstable system, which results from the fact that it cannot independently return to the point of balance (hover) if it loses the functionality of the control loops but will fall or begin to move uncontrollably in space. Furthermore, multirotor UAVs are nonlinear systems since rotor aerodynamic forces and moment characteristics are nonlinear functions with respect to angular velocities and these reasons make the materials used in the manufacturing to be of high quality, load capacity with an infinite fatigue life for the application designed for.
Why Composite Materials?
Composite Material Layered Construction
Composite materials, such as polymers reinforced with carbon fibers (CFRP) and fiberglass (GFRP), are widely used in the manufacturing of drone components, including the fuselage, wings, and landing gear[1].
Polymer composite materials are widely used in various industries, including the manufacturing of drone UAV components, due to their numerous advantages:
High Strength-to-Weight Ratio: Polymer composites, such as those reinforced with carbon or glass fibers, offer a high strength-to-weight ratio[4]. This property is crucial in applications like drone manufacturing, where reducing weight while maintaining strength can enhance performance[4].
Durability: Composites are known for their durability. They do not rust, have high dimensional stability, and can maintain their shape in various conditions. This makes them suitable for outdoor structures and components that are designed to last for a long time.
Design Flexibility: Composites open up new design options that might be hard to achieve with traditional materials. They allow for part consolidation, and their surface texture can be altered to mimic any finish.
Improved Production: With advancements in manufacturing processes, composites are now easier to produce. Digital Composite Manufacturing (DCM), for instance, has made it possible to fabricate composite parts without manual labor.
Material Stability and Insulation: Polymers used in composites offer high material stability against corrosion, good electrical and thermal insulation, and are easy to shape, making them ideal for economic mass production[4].
These advantages make polymer composites an excellent choice for various applications, including the construction of drone components. However, it’s important to note that the use of these materials also necessitates comprehensive testing to ensure safety, reliability, and durability.
Moreover, compared to traditional materials like aluminum, composites can reduce weight by 15-45%, increase corrosion, fatigue, and impact resistance, and reduce noise and vibrations[1].
Testing Composite Materials
Testing composite materials is a critical aspect of ensuring their performance and reliability in various applications, including drone components. Here are some of the common methods used for testing composite materials:
Mechanical Testing: This includes tensile (tension), flexural, impact, shear, and compression testing[1,2]. These tests help determine the material’s strength and deformation under different types of loads.
Physical Testing: This involves tests like water absorption, density, hardness. These tests provide insights into the material’s physical properties and how they might change in different environments.
Thermal Testing: Dynamic Mechanical Analysis (DMA), and Thermomechanical Analysis (TMA) are used to study the material’s thermal properties2.
Moisture Testing: This includes tests like water absorption and moisture conditioning. These tests are crucial for applications where the material might be exposed to moisture.
Analytical Testing: This includes tests like density of core materials, ignition loss, void content, content analysis, and Fourier Transform Infrared Spectroscopy (FTIR). These tests provide a deeper understanding of the material’s composition and structure.
These tests help manufacturers understand the properties of the composite materials that go into a finished product. Composite material testing for drones and UAV applications is both difficult and challenging. The data derived from these tests can be used to compare the composite materials against conventional materials. It’s important to note that the specific tests used can vary depending on the type of composite material and its intended application
Mechanical Testing & Performance Assessment
Uniaxial Tension Test (Directional) (ASTM D638, ISO 527):
The stress (ζ) in a uniaxial tension testis calculated from;
ζ = Load / Area of the material sample ……………………………………..(1)
The strain(ε) is calculated from; ε = δl (change in length) / l (Initial length) ……………..(2)
The slope of the initial linear portion of the curve (E) is the Young’s modulus and given by; E = (ζ2- ζ1) / (ε2- ε1) ……………………………………..(3)
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.
4 Point Bend Flexure Test
This arrangement helps when testing high stiffness materials like ceramics infused polymers, 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, specially for 3d printed materials. 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. 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 as per ASTM D695:
The compressive properties of 3d printed materials are important when the product performs under compressive 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.
Uniaxial Flatwise Compression Testing
The test procedures pertaining to compression call for test conditions where the deformation is applied under quasi-static conditions negating the mass and inertia effects.
Modified Compression Test as per Boeing BSS 7260:
Modified ASTM D695 and Boeing BSS 7260 is the testing specification that determines compressive strength and stiffness of polymer matrix composite materials using a loading compression test fixture. This test procedure introduces the compressive force into the specimen through end loading.
Modified Compression Test as per Boeing BSS 7260
Axial Fatigue Test as per ASTM D7791 & D3479:
ASTM D7791 describes the determination of dynamic fatigueproperties of plastics in uniaxial loading conditions. Rigid or semi-rigid plastic samples are loaded intension (Procedure A) and rigid plastic samples are loaded incompression (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 5hz or lower.The tests can be carried out under load/stress or displacement/strain control. The test method allows generation of stress or strain as a function of cycles, with the fatigue limit characterized by failure of the specimen or reaching 10E+07 cycles.The maximum and minimum stress or strain levels are defined throughan R ratio.
Axial Fatigue Test as per ASTM D7791
3 Point Bend Flexure Test (ASTM D790):
Three point bending testing is carried out to understand the bending stress, flexural stress and strain of composite and thermoplastic 3d printed 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 radii are provided so as to have a single point or line of contact with the specimen. 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.
3 Point Bend Flexure Test
For most composite materials,the compressive strength islower than the tensile and thespecimen will fail at thecompression surface. This compressive failure isassociated with the localbuckling (micro buckling) ofindividual fibres.
Drop Weight low Velocity Impact Test (ASTM D7136, ISO 6603):
The importance of understanding the response of structural composites to impact events cannot be emphasized enough. Low velocity impact occurs at velocities below 10 m/s and is likely to cause some dents and visible damage on the surface due to matrix cracking and fibre breaking, as well as delamination of the material. In some materials, impact tests characterize the face sheet quality and if they are suitable for the application.
Drop Weight low Velocity Impact Test
Summary:
A variety of standardized mechanical tests on unreinforced and reinforced 3d printed materials including tension, compression, flexural,and fatigue have been discussed.
Mechanical properties of 3d printed polymers, fiber-reinforced polymeric composites immensely depend on thenature of the polymer filament, fiber, and the layer by layer interfacial bonding. Advanced engineering design and analysis applications like Finite Element Analysis use this mechanical test data to characterize the materials. These material properties can be used to develop material models for use in FEA softwares like Ansys, Abaqus, LS-Dyna, MSC-Marc etc.
Conclusion
The use of composite materials in drone manufacturing presents a promising avenue for enhancing UAV performance. However, it also necessitates comprehensive testing to ensure the safety, reliability, and durability of these drones. As the drone industry continues to grow and evolve, so too will the methods for testing and optimizing the use of composite materials in drone construction.
Keywords: UAV, composite materials, drone components, material testing, CFRP, GFRP, finite element analysis, bending test.
References:
M Sönmez, Ce Pelin, M Georgescu, G Pelin, Md Stelescu, M Nituica, G Stoian, Unmanned Aerial Vehicles – Classification, Types Of Composite Materials Used In Their Structure And Applications.
Camil, Lancea et al., Simulation, Fabrication and Testing of UAV Composite Landing Gear. MDPI Journal, https://doi.org/10.3390/app12178598
National Research Council, Airframe Materials and Structures, Enabling Science for Military Systems
Non-linear Hyperelastic Material Characterization Testing for FEA
The characterization of materials for Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD) is a specialized process that involves extensive laboratory testing. At AdvanSES, we have become industry leaders in this field, particularly with our focus on the characterization of polymer materials. Through a series of specific tests, we are able to determine the unique properties of each material, thus providing valuable data for FEA and CFD.
Pure Shear
Our testing process begins with a pure shear test. This involves applying uniaxial tension to a test specimen using either a parallel or tangential method. The response of the material to this stress provides a baseline understanding of its characteristics under tension.
Volumetric Compression
We then proceed to a volumetric compression test. This study involves placing a sample of the material under hydrostatic compression deformation. The way the material responds to this form of stress provides valuable data on its behavior under compression.
Uniaxial Compression
Uniaxial compression testing is another key component of our testing process. Here, we evaluate the response of the material when compression stress is applied along a single axis. This test gives us a clear picture of how the material behaves under a single axis of compression stress.
Uniaxial Tension
Uniaxial tension testing involves applying tensile stress to a specimen. The result of this test provides us with further insights into the behavior of the material under tension.
Biaxial Tension
A biaxial tension test involves placing tensile stress on a specimen in two simultaneous directions. This test is particularly useful in understanding the behavior of a material under multiple tensions.
Creep and Stress Relaxation
The final testing stage is the creep and stress relaxation test. This involves a uniaxial tensile test followed by the maintenance of the elongation on the specimen for a specified duration. By observing the material’s response over this period, we can gain valuable insights into the long-term behavior of the material under stress.
Our laboratory is located at Plot No. 49, Mother Industrial Park, Zak-Kadadara Road, Kadadara, Taluka: Dehgam, District: Gandhinagar, Gujarat 382305, India.
For more information about our services and how we can assist with your material characterization needs, give us a call at +91-9624447567 or send us an email at [email protected].
