Failure Analysis under Combined Loading — Lesson 2

This lesson covers the hygro-thermo-mechanical analysis of laminate, which is the study of what happens when a laminate is subjected to mechanical, thermal, and hygroscopic load simultaneously. The lesson explains how to calculate the first ply failure load of a laminate under a thermal gradient of 50 degrees Celsius. It also discusses the concept of residual stresses and strains induced in different lamina of a laminate due to temperature changes. The lesson further explains how to determine the first ply failure load when the laminate is subjected to normal load and temperature gradient. The lesson uses a glass/epoxy laminate with a stacking sequence of 0, 45, 90 symmetric as an example to illustrate the concepts.

Video Highlights

01:00 - Discussion on the effect of thermal load on laminate
04:27 - Calculation of reduced stiffness matrix
09:49 - Determination of mid surface strains and curvatures
12:44 - Calculation of strains in all layers
20:22 - Probable failure modes
24:02 - Calculation of strength ratios for all plies
29:52 - Equivalent thermal load and moments
34:22 - Calculate the residual stresses

Key Takeaways

- The hygro-thermo-mechanical analysis of laminate involves understanding the behavior of laminate under simultaneous mechanical, thermal, and hygroscopic load.
- The first ply failure load of a laminate can be calculated using the reduced stiffness matrix and the mid surface strains and curvatures.
- The residual stresses and strains induced in different lamina of a laminate due to temperature changes can significantly affect the first ply failure load.
- The strength ratios for all plies can be calculated to determine the mode of failure for each ply.
- The first ply failure load under a thermal gradient can be determined by considering the residual thermal stresses and strains.