The Master's thesis of researcher Haider Mohammed Ali Abdul Zahra was discussed at the College of Engineering, University of Basrah, Department of Mechanical Engineering, under the supervision of Professor Dr. Amin Ahmed Nassar. The thesis was titled "Combined Model Crack Propagation Analysis in Adhesive Joint Using Experimental and Extended Finite Element Method (XFEM)

A recent scientific study has been conducted to analyze the crack propagation behavior in adhesive joints, which are considered one of the modern technologies used for joining materials. Adhesive joints are distinguished by their ability to reduce structural weight and distribute stresses more uniformly compared with conventional mechanical joints such as bolts and screws. This makes them highly important in aerospace, automotive, and renewable energy industries.

The study adopted an integrated methodology that combines experimental testing and numerical modeling using the Extended Finite Element Method (XFEM) and the Cohesive Zone Model (CZM) to analyze the fracture behavior of adhesive joints. Four types of epoxy adhesives were tested, and the effect of adhesive layer thickness was investigated using seven different thicknesses ranging from 0.15 to 2.00 mm.

The experimental work included three standard joint configurations according to ASTM specifications, namely Single Lap Joint (SLJ), Double Cantilever Beam (DCB), and End Notch Flexural (ENF). In addition, the experiments involved lap shear tests and fracture tests in mode I and mode II.

The results showed a clear variation in the performance of the adhesives. The ARALDITE-2015-1 adhesive recorded the highest maximum load of 11.26 kN, while ARALDITE AV138 achieved the highest fracture energy in mode I. In mode II, the LOCTITE EA 9497 adhesive demonstrated the best performance at a thickness of 1.30 mm. The findings also revealed a nonlinear relationship between adhesive thickness and fracture behavior, where smaller thicknesses performed better in mode I, while larger thicknesses showed better performance in mode II.

In the numerical modeling part, the XFEM and CZM models demonstrated a high capability in predicting the fracture behavior of adhesive joints, with strong agreement with the experimental results. The XFEM model achieved accuracy coefficients ranging from 0.837 to 0.983.

The study also presented several design recommendations for industrial applications, including the use of AV138 adhesive with a thickness of 0.15 mm for applications subjected to tensile loads, and LOCTITE EA 9497 with a thickness of 1.30 mm for applications dominated by shear loads. A thickness of 0.30 mm was suggested as a suitable option for conservative designs under mixed loading conditions.

The study highlights the importance of integrating experimental investigations with numerical modeling to better understand fracture behavior in adhesive joints, contributing to the development of more efficient engineering designs and reducing the need for costly experimental testing in industrial applications.