Weibull reliability plots to study the strain rate effect on interfacial strengths of carbon fiber reinforced epoxy composites

• Published in: Polymer composites Vol. 43; no. 11; pp. 7804 - 7816
• Main Authors: Seif, Charbel Y., Hage, Ilige S., Hamade, Ramsey F.
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.11.2022; Blackwell Publishing Ltd
• Subjects: Carbon fiber reinforced plastics; Carbon fiber reinforcement; Carbon-epoxy composites; CFRE; Failure; Fiber composites; Fiber orientation; Fiber reinforced polymers; flexural testing; inter‐laminar shear strength; intra‐laminar peel strength; Laminates; Peel strength; Reliability; Shear strength; Strain rate; Weibull modulus
• ISSN: 0272-8397; 1548-0569
• DOI: 10.1002/pc.26888

Two‐parameter Weibull reliability plots are utilized to determine the effects of strain rate on the interfacial strengths of unidirectional carbon fiber reinforced epoxy (CFRE) composites. Laminate specimens with two different fiber orientations are tested to failure under flexural loading. Type 1 laminates with fibers running parallel to specimen length (fiber orientation of 0° with respect to specimen span length) enable measuring inter‐laminar shear strength (ILSS) of the interface (between adjacent lamina) with locus of failure along beam mid ply. Seventy‐two type 1 laminates are tested at five levels of flexural strain rates: 1.89 * 10−5 to 9.37 * 10−2 s−1. Type 2 laminates with fibers running perpendicular to specimen length (fiber orientation of 90° with respect to specimen span length) enable measuring intra‐laminar (matrix/fiber) peel strength (ILPS) for tensile (mode I) strength of the matrix/fiber interface with locus of failure at beam bottom ply. Thirty‐six type 2 laminates are tested at three levels of flexural strain rates: 2.09 * 10−5 to 3.49 * 10−3 s−1. For each level of strain rate, Weibull plots are constructed. Stress values at failure probability (Pf) of 63.1% are assigned as strength values. The results show a slight decrease of the Weibull modulus, m, with increasing strain rates. The modulus decreases from 12.37 to 10.49 and from 11.11 to 9.68, for laminates type 1 and 2, respectively. For laminates type 1, ILSS increases with increasing strain rates rising 16.1% over the range of the tested strain rates. For laminates type 2, ILPS increases with increasing strain rates rising 38.1% over the range. Two‐parameter Weibull reliability plots are constructed to determine the sensitivity to applied strain rate of the interfacial strengths of unidirectional graphite carbon fiber reinforced epoxy (CFRE) composites. Experimental measurements were made at five different strain rates of the inter‐laminar shear strength (ILSS) of the interface between adjacent lamina. Also measured was the intra‐laminar (matrix/fiber) peel strength (ILPS) for the tensile (mode I) strength at three different strain rates. Both ILSS and ILPS were found to be sensitive to applied strain rate (at room temperature) with strengths values increasing with increasing rates.