Lecture 10 - Strength Flashcards
What are the 3 strength modes?
In axial tensile strength, transverse tensile strength or shear tensile strength
What 2 cases of failure do we have when we talk about Axial tensile strength?
εmuεfu
what value of f is most common for long-fiber composites?
f=0.3-0.7
What is the difference between compressive and tensile strength?
Just the sign. Compressive is negative.
Why is it hard to estimate the transverse tensile strength?
because the interfacial bonding strength, fibre distribution, presence of voids etc. are not readily known
Compared to a unreinforced matrix, what can you say about strength and strain to failure?
In a composite the strength and strain to failure are less than that of the unreinforced matrix.
what failure are longitudinal compressive strength susceptible to?
- fibre compressive failure
- various forms of fibre and material internal instability (microbuckling / microinstability)
- fibre debonding or matrix failure caused by shear stress
- microcracking (microcrazing) from existing voids
- buckling phenomena, fibre instability is sensitive to imperfections such as local curvature and misalignment
- When compressive load is applied to curved fibres, shear stress develops between the fibre and matrix which can result in debonding or matrix cracking
What happens to the matrix during kinking?
It is stabilizing the fibers
Which are the most common failure criterias for ply failure?
- Maximum stress criterion
- Maximum strain criterion
- Tsai-Hill criterion
Which failure criteria is the one with the biggest safety factor?
Tsai-Hill criterion
how do we chose failure criteria?
there is no single criterion which is universal for the general case of any fibrous composite material subject to a multiaxial stress system!
Which is the most common failure criteria?
Maximum Stress or Maximum Strain theory
What are the advantages with Tsai-Hill criterion?
- Interactive failure criteria
* it is more conservative
