We want to get key properties from our carbon fiber from the front bulkhead, in order to decide whether or not it needs to be redone.

Taking scrap pieces from the panel, after trimming the panel itself to size, and destructively testing seems to be the way to go - any other way such as test pieces could lead to 15%+ deviations from the true panel properties. These tests could then be recreated in ANSYS to see the deviations.

Goal:

• Load test pieces, acquire values and compare to ANSYS

Tests:

• tensile test

• 3 point bend test

Bulkhead pre-cut dimensions (cm)

Open

CAD dimensions (cm)

Open

3-Point Bend Testing

Large research and formatting has been inspired by this previous test conducted:

F2020 - Bottom Panel Structural Evaluation - Mechanical - Confluence (atlassian.net)

Special Note:

We are allowed to deviate from the specimen size and test parameters as long as we make sure to record the test parameters, i.e. the variables within each property calculation.

Specimen Preparation

Source: https://www.instron.us/testing-solutions/by-test-type/flexure/the-definitive-guide-to-astm-d790

• ASTM D790 Standard: 3.2 mm x 12.7 mm x 125 mm

  • 0.125” x 0.5” x 5.0”

  • The width (12.7 mm) should be cut pretty accurate to size. The length (125 mm) could be greater than indicated because it will just hang off the end of the support spans

• Reason behind specimen size:

  • Sheet materials with a thickness between 3.2 and 1.6 mm will have a width of 12.7 mm and a support span defined as specimen thickness X 16

Carrying Out the Test

• You usually want to play a 0.01 strain rate per minute or 0.10 strain rate per minute so that you can see in full detailed curve of how the material slowly reacts as stress increases over time.

  • considering you have a 125 mm length, you are looking at a load rate of about 0.01 mm/min and you are aiming to allow the material to reach 0.05 strain (about 6 mm) or failure. That is a total of 600 minutes to reach 0.05 strain.

    • to be honest I don’t clearly remember how to calculate maximum depth of testing. Worth revisiting. -Tommy

    • Maximum 3 mm deflection should be enough to see the carbon fibre sample eventually reach failure. You will see in-person the stress curve and if it does not fail, then feel free to continue the experiment.

• From experience, and for practical purposes, you can start at 0.5 mm/min. The testing lab technician will also like you better for this.

  • If you are doing multiple tests, and you think the maximum stress will be easily captured, you can speed up to 1 mm/min.

Data Processing

Source: https://en.wikipedia.org/wiki/Three-point_flexural_test#Standards

Results

Table #1: List of variables recorded for experiment

Table #2: Dimensions of test specimens

Tensile Testing

Specimen Preparation

The Definitive Guide to ASTM D3039 - Instron

• The minimum length of the specimen is equal to the total gripping length + 2 x width + gauge length, but greater lengths are recommended in order to minimize bending stresses.

• Need to ask Mark about gripping length and tabbing options

  • tabbing is required to reduce the chance of material failure at the grips

  • Can ask Mark about a wedge grip that helps to reduce stress concentrations

  • Can bond steel tabs at the ends of specimen

Load Rate

The Definitive Guide to ASTM D3039 - Instron

• ASTM D3039 requires that the test should produce a failure within 1 to 10 minutes. The suggested test speeds are either a strain rate of 0.01 min-1 or a constant crosshead speed of 2 mm/min (0.05 in/min). The general practice is to conduct the test at a constant crosshead speed.