Equivalent alternative test method for compressive strain of composite
ASTM D6641/D6641M-16 is one of the more widely used standard test methods for the compression properties of resin matrix composites.Due to the traditional strain gauge method has the problem that different types of adhesives need to be selected in different use environments and the strain gauge paste is greatly affected by the paste process,the strain test in the high-temperature and wet environment is always a difficulty in the mechanical properties test,which hinders the evaluation of the compression properties of aviation composite in harsh environments.Based on the compression test device and resistance strain gauge method recommended by ASTM D6641/D6641M-16 standard for strain measurement,the compression test device and compression fixture were optimized and improved,and the four-column compression fixture was designed to solve the defect that the sample working section was not easy to observe when the original fixture was used for strain testing.Three different strain measurement methods,including strain gauge method(using hydraulic clamping mode),contact extensometer method and non-contact video extensometer method were compared and tested,and the equivalent substitution test was completed.The results show that the optimized compression fixture has better stability,the average dispersion coefficients of compressive strength and modulus are 4.85% and 1.42% in the test of 7 different grades of laminates,respectively.At the same time,the fixture can be compatible with the non-contact video extensometer for strain testing,reducing the link of strain gauge pasting,reducing the cost of mounting and effectively reducing the test process.When the length of the working section of the sample is less than 21 mm,the hydraulic clamp-ing mode can replace the compression clamp method of the modulus test,so that the contact extensometer method becomes another feasible way of the compression modulus test.
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