THE INVESTIGATION OF SHEAR RESPONSE OF EPOXY MATRIX UNDER UNIFORM COMPRESSION
Topic(s) : Special Sessions
Co-authors :
Bohao ZHANG (UNITED KINGDOM), Gustavo QUINO (UNITED KINGDOM), Paul ROBINSON , Richard S. TRASK (UNITED KINGDOM)Abstract :
Unidirectional carbon fibre/polymer matrix composites exhibit excellent mechanical properties and thus are widely used in structural applications. However, these materials show poor mechanical performance upon axial compression due to the material instability and internal defects leading to kink band formation [1]. Such instability could arise from within the polymer matrix, since the matrix between adjacent fibres will be subjected to a combined compression-shear loading until the onset of yielding [2]. It is therefore critical to understand the behaviour of the polymer matrix under combined stress conditions, for the development of material constitute model for the finite element modelling of carbon fibre composites [3]. In the previous work [4], the shear response of an epoxy matrix under compression-shear test has been investigated. However, a significant variation in compressive strain in the gauge section of the specimens was observed; believed to have arisen due to the nonuniformly stress state globally. Therefore, the aim of this study is to investigate the shear behaviour of epoxy matrix subjected to uniform compressive stress.
Gurit Prime 37 epoxy resin was used in this study [5]. Solid cylinders were prepared from this material by casting in silicone moulds, followed by post-curing according to the manufacturer’s recommendation. Hollow, cylindrical specimens of 0.5 mm nominal wall thickness were machined from the cylinders. The ends of these specimens were bonded with steel plates which contain a dimple hole to locally position a ball bearing. This assembly was then bonded to a stainless steel end-cap (see Fig. 1a), as the load introduction point. The purpose of the ball bearing was to allow self-alignment whilst also transferring the compression force uniformly to the specimen.
Compression-shear tests were conducted on a Instron Electropuls E10000 fitted with a 10 kN axial and 100 Nm torsional load cell. Fig. 1b shows the test setup. Compression force of 660 N (i.e. compression strain of 20 MPa), was applied to the Prime 37 specimens in 60 seconds without the application of any torsion loading. Once stabilized, the specimens were loaded in torsion at 0.1°/s (whilst under the compression force) until failure. Stereo digital image correlation (DIC) was used to measure the compressive and shear strain of the specimens.
Fig. 2 shows the compression strain-time and engineering shear stress-strain curves of a typical Prime 37 specimen tested in compression-shear tests. The compressive strain of the specimen upon axial loading was uniform across the gauge section (as indicated in the DIC images). Further investigations on the effect of the uniform compressive strain on the shear response of the material will be conducted and discussed.
This refined testing methodology assessing the shear behaviour of the Prime 37 epoxy resin, with the modified endcaps, under pure-shear and compression-shear loading will be presented and discussed.
Gurit Prime 37 epoxy resin was used in this study [5]. Solid cylinders were prepared from this material by casting in silicone moulds, followed by post-curing according to the manufacturer’s recommendation. Hollow, cylindrical specimens of 0.5 mm nominal wall thickness were machined from the cylinders. The ends of these specimens were bonded with steel plates which contain a dimple hole to locally position a ball bearing. This assembly was then bonded to a stainless steel end-cap (see Fig. 1a), as the load introduction point. The purpose of the ball bearing was to allow self-alignment whilst also transferring the compression force uniformly to the specimen.
Compression-shear tests were conducted on a Instron Electropuls E10000 fitted with a 10 kN axial and 100 Nm torsional load cell. Fig. 1b shows the test setup. Compression force of 660 N (i.e. compression strain of 20 MPa), was applied to the Prime 37 specimens in 60 seconds without the application of any torsion loading. Once stabilized, the specimens were loaded in torsion at 0.1°/s (whilst under the compression force) until failure. Stereo digital image correlation (DIC) was used to measure the compressive and shear strain of the specimens.
Fig. 2 shows the compression strain-time and engineering shear stress-strain curves of a typical Prime 37 specimen tested in compression-shear tests. The compressive strain of the specimen upon axial loading was uniform across the gauge section (as indicated in the DIC images). Further investigations on the effect of the uniform compressive strain on the shear response of the material will be conducted and discussed.
This refined testing methodology assessing the shear behaviour of the Prime 37 epoxy resin, with the modified endcaps, under pure-shear and compression-shear loading will be presented and discussed.