Podcast
Questions and Answers
Which of the following is NOT a common failure mode in composites?
Which of the following is NOT a common failure mode in composites?
- Thermal expansion (correct)
- Fiber failure
- Matrix cracking
- Delamination
Which failure mode can beneficially distribute loads across the composite?
Which failure mode can beneficially distribute loads across the composite?
- Fiber failure
- Micro-cracking (correct)
- Matrix cracking
- Delamination
Which of the following is a common failure mode in a single lamina of a composite?
Which of the following is a common failure mode in a single lamina of a composite?
- Transverse tensile stresses leading to interface fracture (correct)
- Fiber pull-out
- Thermal expansion
- Void formation
Which failure criteria considers multiple stress components for a more accurate prediction of failures in composites?
Which failure criteria considers multiple stress components for a more accurate prediction of failures in composites?
Which failure criteria performs well in both tension and compression for different composite systems?
Which failure criteria performs well in both tension and compression for different composite systems?
Which approach is used for predicting composite material failures with higher computational costs?
Which approach is used for predicting composite material failures with higher computational costs?
What is the purpose of using failure criteria like Hoffman and Sidewalk criteria in the preliminary design of composite structures?
What is the purpose of using failure criteria like Hoffman and Sidewalk criteria in the preliminary design of composite structures?
What is the primary difference between the matrix failure criterion of the 1987 model and other failure criteria?
What is the primary difference between the matrix failure criterion of the 1987 model and other failure criteria?
What is the main purpose of using a progressive failure analysis technique in the design of composite structures?
What is the main purpose of using a progressive failure analysis technique in the design of composite structures?
What is the role of fracture mechanics in the assessment of interlaminar failure criteria for composite materials?
What is the role of fracture mechanics in the assessment of interlaminar failure criteria for composite materials?
What is the importance of validating analysis techniques through testing for the design of composite structures?
What is the importance of validating analysis techniques through testing for the design of composite structures?
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Study Notes
- Failure modes in composites include fiber failure, matrix cracking, delamination, and micro-cracking.
- Fiber failure and matrix cracking can significantly impact structural performance, while micro-cracking can beneficially distribute loads across the composite.
- Failure modes of a single lamina include fiber kinking, transverse tensile stresses leading to interface fracture, and fiber buckling.
- Fiber buckling is a common failure mode in composites, leading to kinking and eventual ultimate failure.
- Different failure criteria exist for predicting composite material failures, with interactive and non-interactive criteria available.
- Failure criteria can be based on stress states, strain values, or micro-mechanics considerations.
- Testing and analysis are crucial for understanding and predicting composite material failures accurately.
- Macro and micro-mechanics-based approaches are used for predicting failures, with varying computational costs.
- Maximum stress and maximum strain theories are common non-interactive failure criteria used for predicting failures in composites.
- Interactive failure criteria like the Tsai-Hill criterion and Hoffman criteria consider multiple stress components for a more accurate prediction of failures in composites.- Hoffman criteria performs well in tension and compression, especially against different composite systems like glass epoxy, graphite epoxy, and boron epoxy.
- Sidewalk criterion is more complex, involving thinner index A+B > 1, with values of F as functions of shear strength, tension/compression strength in fiber/matrix direction, and in-plane shear strength.
- Failure criteria like Hoffman criteria and Sidewalk criterion are important for preliminary design to ensure conservatism.
- Fiber-matrix shear failure criterion involves shear stress components and is sensitive to the stress levels in compression or tension.
- Matrix failure criterion of 1987 model distinguishes between compression and tension failures, providing formulas based on empirical evidence.
- Puck's failure criterion incorporates strain and stress terms, with magnification factor M typically ranging between 1 and 1.3.
- Interlaminar failure criteria aim to predict delamination in composites, with testing methods like short beam shear test, Iosipescu testing, modified Arcan testing, etc.
- Fracture mechanics approach can be used to assess interlaminar failure criteria, involving fracture toughness testing for mode 1 and mode 2 fractures.
- Progressive failure analysis technique allows for localized damage progression in composites, enhancing the understanding of failure mechanisms but may lead to repair concerns.- Progressive fail analysis is crucial for predicting and protecting hardware from failure initiations in preliminary design.
- Balancing between using the most conservative criterion in analysis without being too penalizing is important to avoid weight penalties.
- Validating analysis techniques through testing is essential for optimizing design, reducing weight, and improving accuracy.
- Failure analysis of composite materials, especially sandwich structures, involves various failure modes and criteria like the Parks criteria.
- Predicting failure in composite materials is challenging, requiring extensive test validation and consideration of applicable failure criteria compared to test data.
- It is recommended to tap into the extensive literature on failure analysis of composites for a better understanding and learning experience.
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