Strength Failure Criteria — Part 1 — Lesson 1

This lesson covers the mechanics of fiber-reinforced polymer composite structures, focusing on the macromechanics of lamina. It delves into the stress-strain relationship of a lamina, the influence of direction-dependent stiffness on stress-strain behavior, and the difference between isotropic and orthotropic materials. The lesson also discusses the importance of understanding the behavior of lamina in the design of a laminate, and how the fiber angle impacts these properties. It further explores the concept of laminate performance under load, the strength of a laminate, and the strength of a lamina. The lesson concludes with an explanation of the strength failure theories under macromechanics, the concept of strength of a lamina, and the different types of failure theories.

Video Highlights

03:36 - Understanding the strength of a laminate and a lamina
06:50 - Discussion on different types of failure theories
10:28 - Discussion on strain based failure theory and its application to orthotropic materials
17:31 - Discussion on stresses in the principle material direction
34:18 - Discussion on Macro Mechanical failure theories
41:17 - Concept of non-interactive or independent theories and interactive theories in macroscopic failure theories
45:08 - Application of maximum stress failure criterion to determine the off-axis tensile and shear strength of a lamina

Key Takeaways

- The stress-strain relationship of a lamina is influenced by the direction-dependent stiffness of the lamina.
- The behavior of lamina plays a crucial role in the design of a laminate.
- The strength of a laminate is determined by the strength of the lamina comprising it.
- The strength failure theories under macromechanics do not consider the individual constituents of the lamina.
- The strength of a lamina is determined by the maximum stress or combination of stresses it can withstand before it fails.
- There are different types of failure theories, including maximum stress theory and maximum strain theory.