An Assessment of ASTM E1922 for Measuring the Translaminar Fracture Toughness of Laminated Polymer Matrix Composite Materials

Abstract

The main objective of this work is to predict the exact value of the fracture toughness (KQ) of fiber-reinforced polymer (FRP). The drawback of the American Society for Testing Materials (ASTM) E1922 specimen is the lack of intact fibers behind the crack-tip as in the real case, i.e., through-thickness cracked (TTC) specimen. The novelty of this research is to overcome this deficiency by suggesting unprecedented cracked specimens, i.e., matrix cracked (MC) specimens. This MC exists in the matrix (epoxy) without cutting the glass fibers behind the crack-tip in the unidirectional laminated composite. Two different cracked specimen geometries according to ASTM E1922 and ASTM D3039 were tested. 3-D FEA was adopted to predict the damage failure and geometry correction factor of cracked specimens. The results of the TTC ASTM E1922 specimen showed that the crack initiated perpendicular to the fiber direction up to 1 mm. Failure then occurred due to crack propagation parallel to the fiber direction, i.e., notch insensitivity. As expected, the KQ of the MC ASTM D3039 specimen is higher than that of the TTC ASTM D3039 specimen. The KQ of the MC specimen with two layers is about 1.3 times that of the MC specimen with one layer.

Mixed-mode fracture toughness of high strength FRC: a realistic experimental approach

“…Likewise, the current trend of K eff in MC specimens is compatible with the trend of K IC in mode I, which was found by Ali et al [39] experimentally and El-Sagheer et al [34] numerically. Like the present study, they found that the MC specimens with short fiber produced higher fracture toughness.…”

“…Unfortunately, such previous work was not only a waste of time and effort but also led the scientific research compass in this field in the wrong direction for solving such problems. The first attempt in the right direction for predicting the fracture toughness of fibrous composite materials was made by Salam and colleagues [34,[36][37][38][39]. Sallam and co-workers [36,39] successfully correlated the mode I fracture toughness of FRC using MC specimens, i.e., correlating a vectorial problem with a crack path independent of the initial crack length by scalar parameters such as Griffith's energy release rate..…”

“…At the same time, the TTC specimen is not applicable for fibrous composite materials due to the absence of fiber bridging between the surfaces of the precrack. Therefore, for long fiber-reinforced polymers (FRP) laminates, El-Sagheer et al [34] performed a matrix crack (MC) in FRP laminate like a real crack pattern to overcome this drawback in the standard test method for the fracture toughness estimation of FRP laminates (ASTM E1922) [35]. Their main objective was to avoid the lack of intact fibers behind the crack tip and find its intrinsic fracture toughness (K IC ).…”

Mechanical and Tribological Behavior of Functionally Graded Unidirectional Glass Fiber-Reinforced Epoxy Composites

“…The elastic constants and Hashin’s damage model strength data of the different layers, according to their V f %, are shown in Table 4 and Table 5 , respectively, extracted analytically as was described in refs. [ 31 , 43 ]. CZM was used to simulate the adhesive layers.…”

“… E / E nn = K 1 = ( E × α )/ t G 1 / E ss = K 2 = ( G 12 × α )/ t G 2 / E tt = K 3 = ( G 13 × α )/ t where E is the epoxy’s modulus of elasticity, G is the Shear modulus of epoxy, α is a constant = 50, and t = cohesive layer thickness. For more details, refer to Sec-1 : Mechanical properties of glass fiber-epoxy lamina; Sec-2 : Hashin Model Constants; Sec-3 : Hashin Damage Criteria; Computer Code : Computer Code.inp (see Supplementary Materials ) [ 31 , 40 , 43 , 45 ].…”