Why are measured properties in flexural testing not considered true material properties?
Because a smaller volume of material is under maximum stress. The smaller volume means there’s a lower chance of critical flaws or defects being present, which can lead to higher measured strength.
Why do we get an ‘Onset effect’ In the beginning of the stress strain curve during flexural testing?
In the beginning of the test, if the material is uneven or imperfect, it adjusts to the supports or loading surface
Why is a 4-point bending test more accurate than a 3-point bending test?
- The stress distribution is more uniform along the length between the two inner supports.
- Zero shear at midspan
- Smaller contact stresses
In a composite, how does the ply orientation together with the loading orientation influence the failure mode?
- if outermost plies are oriented in the loading direction, compression failure is more likely
- if outermost plies are oriented transverse, tensile failure occurs first
What is usually the purpose of testing a short beam in a 3-point bending test?
The small span to thickness ratio promotes shear failure. It is a popular shear-related test method. A strength value indicative of matrix shear and fibre-matrix interface bond is obtained. Not a true material shear property
What are the valid failure modes for short beam strength testing?
Only interlaminar shear (NOT flexure failure)
What are the purpose of the different parts of a sandwich construction?
- Face sheets: Takes up the bending moment
- Core: Transfers shear, provides stability, distribute stresses, absorbs impact load and prevents face sheets from buckling
- adhesive bond: Fix coore and sheet together
What are the most common failure modes in a sandwich structure?
- Face sheet yielding
- Face sheet buckling
- Core shear failure
- Core crushing
- Face adhesive bond failure
