Abstract

Abstract

Composites trend to failure in their defects, which are randomly distribuited. This causes that the tensile strength decreases when the volumen of material tested increases. This fenomenon is known as size effect or volume effect. Knowing the value of the Weibull parameters is key for modeling and the correct design of large components. In this work, one tensile test are proposed, named the fragmentation test to obtain the shape and scale Weibull parameters that are validated with the scaled test. Carbon/glass hybrid composites can exhibit pseudo-ductile response in the stress-strain curves by having a part with small slope or plateau. The specimen design promotes fragmentation or gradual fracture of carbon layer and suppresses unstable delamination at the plateau. The facture events have been identified by video and accoustic emission monitoring in 11 specimens. The data of fracture strain has been adjusted to the Weibull distribution following the proposed iterative process. The process has been validated using previous results of Finite Elements. The volumen effect has been validated with the results of series of tensile tests, with dimensions scaled by factors of 2,4 and 8 in each direction. Another important advantage of hybridization is the suppression of the stress concentration in the carbon layer, which makes simple end-tab free specimens feasible. The results of two tests have been compared, obtaining very close values.

Abstract

This study analyzes delamination in CFRP adhesive joints under mode II loading in both static and dynamic regimes. The ENF test was used to evaluate the effect of exposure to salt spray and a climatic chamber over various periods—one, two, four, and twelve weeks—as well as for unaged specimens.

Based on the experimental data, fatigue initiation curves (ΔG-N) and fatigue crack growth curves (G-da/dN) were constructed to analyze both degradation processes. In the fatigue initiation phase, the data were analyzed using a probabilistic model based on a Weibull distribution.

The most relevant findings of this study are as follows: regarding the fatigue limits obtained for the adhesive joint under mode II fracture, a decrease in load-bearing capacity was observed due to degradation processes—around 20% under static loading conditions for salt spray exposure, and 25% for hygrothermal degradation. As for the fatigue crack growth phase, the crack propagation rates were found to depend on the specific environmental degradation process to which the tested specimens were subjected.