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The following information was taken from the following handbook:
The purpose of this is to present further information on the importance of composites testing and the various ways we can go about it.
Keep in mind that the testing of composites is much different than the testing of isotropic materials and therefore we must enhance our knowledge on this subject matter so we can do things much, much more efficiently in the future.
Overview of Testing
Building-Block Approach
For the most part in composites testing, you should always follow what’s known as the building-block approach, it is a series of tests that build off of each other, starting off using coupons which are just small pieces of material (just like we’re planning on doing right now) and slowly building up to a full-scale component, below is the pyramid of this approach:
Figure 1: Building-Block Approach for composites testing
We will most likely only go up to elements if even that as we cannot afford to do testing on our full components.
The building block approach can be summarized with the following steps:
Test Program Planning
Testing standards
This handbook follow the practice of the ASTM D-30 comittee (the comittee in charge of advanced composites testing). Below is a table that may prove useful right now or in the future of which test methods may be used to test various things, notes a, b, and c are also shown below
Figure 2: Standard test methods from which MIL-HDBK-17 currently accepts data
Specimen Preparation
The following graphic is the process of specimen preparation for testing that we should follow in the future:
Figure 3: Step-by-step process of specimen prep (obtained from ASTM D5687)
Note that steps 3-8 may not be required for particular test types or specimens. An example of this is that not every test may have tabs bonded if the test done is a three-point bending test or an impact test.
Below is guidance given by the ASTM standard on the 8-step process shown above:
Along with all of this, we can add our own nondestructive examniation (NDE) or other processing checks to assure that each step of the specimen prep process has been performed well. These NDE’s are described in the ASTM document (we should check it out).
Below is an NDE that can confirm if the surface is flat or dimpled:
Figure 4: Measuring of laminate surfaces
The above is done by using two different types of measuring probes.