It is necessary to consider the influence of moisture damage on the interlaminar fracture toughness for composite structures that are used for outdoor applications. However, the studies on the progressive variation of the fracture toughness as a function of moisture content M (%) is rather limited. In this regard, this study focuses on the characterization of mode II delamination of carbon/epoxy composites conditioned at 70 °C/85% relative humidity (RH). End-notched flexure test is conducted for specimens aged at various moisture absorption levels. Experimental results reveal that mode II fracture toughness degrades with the moisture content, with a maximum of 23% decrement. A residual property model is used to predict the variation of the fracture toughness with the moisture content. Through numerical simulations, it is found that the approaches used to estimate the lamina and cohesive properties are suitable to obtain reliable simulation results. In addition, the damage initiation is noticed during the early loading stage; however, the complete damage is only observed when the numerical peak load is achieved. Results from the present research could serve as guidelines to predict the residual properties and simulate the mode II delamination behavior under moisture attack.

Accurately predicting frictional performance of lubrication systems requires mathematical predictive tools with reliable lubricant shear-related input parameters, which might not be easily accessible. Therefore, the study proposes a semi-empirical framework to predict accurately the friction performance of lubricant systems operating across a wide range of lubricant regimes. The semi-analytical framework integrates laboratory-scale experimental measurements from a pin-on-disk tribometer with a unified numerical iterative scheme. The numerical scheme couples the effect of hydrodynamic pressure generated from the lubricant and interacting asperity pressure, essential along the mixed lubrication regime. The lubricant viscosity-pressure coefficient is determined using a free-volume approach, requiring only the lubricant viscosity-temperature relation as the input. The simulated rough surface contact shows transition in lubricant regimes, from the boundary to the elastohydrodynamic lubrication regime with increasing sliding velocity. Through correlation with pin-on-disk frictional measurements, the slope of the limiting shear stress-pressure relation $\gamma$ and the pressure coefficient of boundary shear strength m for the studied engine lubricants are determined. Thus, the proposed approach presents an effective and robust semi-empirical framework to determine shear properties of fully-formulated engine lubricants. These parameters are essential for application in mathematical tools to predict more accurately the frictional performance of lubrication systems operating across a wide range of lubrication regimes.

This work proposed a methodology to obtain the lamina and interface properties using minimal experimental works. Studies were limited to mode II delamination behavior of three quasi-isotropic quasi-homogeneous woven glass/polyester composites. It was found that the fracture toughness of 0//0, 0//45, and 45//45 laminates calculated using experimental calibration method were 0.91 N/m, 0.94 N/m, and 0.51 N/m, respectively. In addition, fiber twisting and shear cusps were observed on the delaminated surfaces of 45°-ply. Subsequently, a methodology was proposed to obtain the lamina properties for the numerical simulation without performing any additional experiment. An approach to account for the shear nonlinearity of the composite laminate due to the existence of 0°-ply was also presented. Finally, it was proposed that for reliable numerical modeling using cohesive zone model, the following parameters were recommended: penalty stiffness = 3 × 10⁶ MPa/mm, interface shear strength = 65 MPa, mesh size = 0.5 mm, and viscosity parameter = 1 × 10⁻³.