Pre-strained Composite Test Coupons for Accurate Strength Testing
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Solution Overview
Problem
Existing test methods for composite laminate materials often undervalue material capabilities and provide inconsistent results, especially under varying test conditions, and may not accurately determine ultimate strength and modulus due to issues like adhesive tab degradation and inconsistent bonding processes.
Innovation Solution
A composite test coupon with a cross-ply layup design, featuring first and second ply layers with fibers oriented in different directions, is pre-strained by applying a threshold tensile load below the failure load, inducing stress cracks in the matrix material of the second ply layers, allowing for accurate determination of strength and modulus without adhesive tabs, even under harsh environmental conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If adhesive tabs are used to secure test coupons, then the testing process is simplified, but adhesive degradation occurs under harsh environmental conditions leading to inaccurate results
Solution Approach 1:
The patent removes adhesive tabs from the testing system entirely. Instead of using adhesives to secure the coupon, the test apparatus directly grips the coupon edges through mechanical means, eliminating the adhesive degradation problem while maintaining ease of operation.
Solution Approach 2:
The patent introduces a specialized test apparatus with gripping mechanisms as an intermediary between the operator and the coupon. This apparatus provides secure holding without requiring adhesive tabs, thereby eliminating the harmful adhesive-material interaction under harsh environmental conditions.
2Ease of operation
If standard test methods are used, then testing is straightforward, but material capability is undervalued and results are inconsistent
Solution Approach 1:
The patent applies a preliminary action by pre-straining the composite coupon to a specific strain level (e.g., 0.2% or 0.4%) before the actual strength testing. This preliminary straining step prepares the material in a controlled manner that reveals its true mechanical properties, eliminating the need for complex adhesive bonding procedures while improving measurement precision.
Solution Approach 2:
The patent changes the testing parameters by implementing a two-stage loading process: first applying a predetermined strain level, then continuing to apply load to determine failure. This parameter change approach allows accurate determination of ultimate strength and modulus while maintaining operational simplicity through automated control.
3Ease of manufacture
If adhesive tabs are used for bonding, then the bonding process is simplified, but bonding consistency varies under different test conditions
Solution Approach 1:
The patent completely removes the adhesive bonding process from the system. The test apparatus directly secures the coupon edges mechanically, eliminating variable bonding conditions and ensuring consistent test results across different manufacturing and testing environments.
Solution Approach 2:
The coupon itself serves its own securing function through its geometric design and the test apparatus's gripping mechanisms. The coupon's own structure provides the necessary attachment points, eliminating the need for external adhesive bonding agents that introduce variability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enables more accurate and consistent testing of composite materials by reducing the need for adhesive tabs, improving the accuracy of strength and modulus calculations, and allowing testing across a range of conditions without adhesive degradation, thus enhancing the characterization of composite materials at the ply level.
Implementation Method 1
The pre-stressed matrix material includes stress induced cracks between the second fibers of each of the second ply layers
Data Source
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AI summary
A composite test coupon (200) includes a plurality of plies. The plurality of plies include first ply layers (208) and second ply layers (210). The first ply layers (208) have first fibers and a substantially uniform matrix material associated with the first fibers. The second ply layers (210) have second fibers and a pre-stressed matrix material associated with the second fibers. The first fibers are oriented in a first direction, and the second fibers are oriented in a second direction that is different from the first direction. The pre-stressed matrix material includes stress induced cracks between the second fibers of each of the second ply layers (210).