Comparison of Specimen Geometries for Measuring Through-Thickness Tensile Mechanical Properties of Fibre-Reinforced Polymer Composites

Abstract

Engineering design of fibre-reinforced polymer (FRP) composite components requires reliable methods for measuring out-of-plane mechanical properties in the through-thickness (T-T) material direction. Within this work, existing indirect and direct test methods and geometries for measuring T-T tensile properties have been evaluated through experimental testing and finite element analysis (FEA). Experimental testing showed variations, particularly in failure properties, for both indirect (failure strengths from 10–94 MPa) and direct (failure strengths from 48–62 MPa) geometries. Results were shown to be in good agreement with FEA, which also confirmed stress concentration factors. A linear relationship between the magnitude of stress concentration factors and experimentally determined T-T tensile failure strengths was observed for all but one of the direct geometries evaluated. Improved knowledge of stress concentration factors from this work should help instil confidence for industry to use T-T tensile properties determined from these methods.

Through‐thickness tensile characterization and analysis of fiber‐reinforced polymer composites using digital image correlation and finite element modeling

“…These concentrations have been reported in other spool specimen geometries using FRPC materials. 13,14 Nonhomogeneous strain distribution arises from the complex stress state in the specimen 15 and the complexity of the material structure at mesoscopic scale. 19 To further evaluate the uniformity of ε z by FEA and DIC, strain data were extracted at the left edge of the specimen (see dotted line in the inset of Figure 5).…”

“…11 However, there is yet no consensus in the international literature on the most suitable method for TT characterization of FRPCs. The ASTM D7291 procedure exhibits issues including failure out of the gage section, 12,13 misalignment, 14 and stress concentrations caused by the adhesive/end-tab interface. 15 Several alternatives to the ASTM D7291 procedure have been proposed for measuring TT mechanical properties of FRPC.…”

“…15 Several alternatives to the ASTM D7291 procedure have been proposed for measuring TT mechanical properties of FRPC. Pemberton et al published an extensive overview 13 of the available indirect and direct methods for measuring TT tensile strength and elastic properties. Indirect methods employ flexural or compressive loading to induce TT tensile stresses in the material.…”

“…12 On the other hand, direct methods typically use waisted specimens subjected to tensile loading through metal endloading bars attached to the specimen ends. 13 The extracted properties include elastic modulus, Poisson's ratios, and strength. However, direct-loading methods require specialized machining and time-consuming preparation, as well as strain measurement instrumentation to ensure proper alignment.…”

“…However, direct-loading methods require specialized machining and time-consuming preparation, as well as strain measurement instrumentation to ensure proper alignment. 13 Strain gages are undoubtedly the preferred method for local measurements of strain. However, strain gages are localized, highly dependent on the measuring position and on the length of the gage.…”