The master's thesis of researcher Israa Subaih, a student in the College of Engineering, Department of Mechanical Engineering, University of Basra, was discussed. The thesis was titled "Fracture Mechanism Analysis of Sandwich Structures with Different Core Shapes and Under Different Loading Conditions."

Sandwich structures are among the most common engineering constructions. They usually consist
of a core material bonded between two thin, high-strength face sheets using adhesives. The core
resists shear stresses, while the face sheets carry tensile and compressive loads as they are
positioned away from the neutral axis where stresses reach their maximum values. One of the
most widely used cores is the honeycomb structure, which is characterized by a uniform
hexagonal cellular configuration governed by several factors, including cell dimensions, material
composition, wall thickness, and overall density. Such structures are widely used in marine,
aerospace, and automotive industries.
The study of fracture development in sandwich structures is relatively complex due to their
geometric nature, which makes precise prediction of crack propagation paths challenging.
Therefore, the present study investigates the fracture behavior of sandwich structures with
different core geometries, while developing an equivalent model that facilitates the calculation of
the stress intensity factor by correlating it with that of an equivalent plate. This analysis was
performed under different loading conditions, including tension, shear, and compression, using
the extended finite element method (XFEM) within Abaqus software under specified boundary
conditions. The equivalent elastic modulus was determined both theoretically and experimentally
to establish the equivalent model.
The results revealed that the equivalent elastic modulus decreases with increasing cell side length
due to the reduction in structural stiffness. Furthermore, the modulus varied with the geometric
shape of the core, with values recorded as (156, 138, 105, 81) GPa for the circular core, (133,
116, 103, 72) GPa for the triangular core, and (169.5, 162, 155, 144) GPa for the hexagonal core.
Comparison between theoretical and experimental results showed that the error did not exceed
10% for all three core shapes.
Regarding fracture behavior, it was observed that the cell size significantly influences the stress
intensity factor. Increasing the cell length by (10, 20, 30) mm resulted in an increase in the stress
intensity factor by (12.22, 24.56, 34.91) MPa·mm^1/2 for a crack length of 1.5 mm. This trend
was observed under both tensile and shear loading, attributed to the reduction in stiffness with
increasing cell length.
The influence of wall thickness was also examined. Increasing the wall thickness by (3, 6, 9, 12)
mm led to a decrease in the stress intensity factor by (65.46, 28.7, 18.14, 5.58) MPa·mm^1/2,
respectively. Comparing the three core shapes, the highest stress intensity factor was obtained in
the circular core (23.36 MPa·mm^1/2), followed by the hexagonal (17.69 MPa·mm^1/2), and the
triangular core (10.24 MPa·mm^1/2)