Session: 06-04-01: Beam, Plate, and Shell Structures

Paper Number: 173610

Modeling of the Debonding and Core Fracture in Sandwich Panels by a Combined Phase Field/cohesive Surface Approach 

Sandwich structures are widely used in the field of aerospace, naval and civil constructions due to the high specific stiffness, strength, and energy absorption capabilities. Interfacial debonding between the faces and core is one of the most common failure modes of sandwich structures, which can result from manufacturing defects, impact, or fatigue loading.  During crack propagation, the crack may also deflect (kink) into the core. Interfacial debonds significantly undermine the load-bearing capacity of the sandwich structures and can lead to catastrophic failure.

Interfacial debonding is essentially a bi-material fracture problem. Modeling the crack on an interface as a sharp displacement discontinuity has been extensively studied in the past using different approaches, either analytically or numerically. Sharp crack approaches are particularly useful in situations when the crack path is known, such as debonding. Cohesive elements are widely used in such situations, bringing together the simplicity of implementation with the versatility of constitutive behaviors through different traction-separation laws (TSL). However, when the crack path is not a priori known, such as crack kink and core fracture, it is very difficult to insert the cohesive elements at the correct location. Adopting other existing sharp crack methods, such as extended or generalized finite element method (XFEM/GFEM), additional efforts are usually needed.

In addition, cracks can also be described in a smeared sense. Over the last two decades, the phase-field fracture method has received great attention. The phase-field approach utilizes a smeared representation of discontinuities. Owing to the variational energy minimization framework for the problem of crack evolution, the phase-field fracture model allows for the automatic determination of crack nucleation, propagation, branching, and merging without requiring any additional techniques. Thus, the phase-field showed great versatility in modeling bulk fractures. Efforts have also been made to extend the phase-field approach to model interfacial debonding by adopting a smeared interface representation. However, several challenges remain, including complications in determining the effective smeared interface material parameters, difficulty in distinguishing between interface and bulk crack, and the need for fine meshes even in regions where debonding is not likely to occur, etc. 

This work presents a hybrid model that combines both sharp and smeared crack representations. The interface debonding is modeled as a sharp crack using the cohesive elements, while the bulk fracture is captured through a phase field approach. By integrating cohesive finite elements with the phase-field method, the model leverages the strengths of both approaches. Various coupling techniques between the sharp and smeared cracks are explored and evaluated. Numerical simulations are conducted to assess the impact of these coupling strategies on crack propagation—whether delamination or kinking—as well as on the maximum load-bearing capacity of the structure. The results are compared and validated with numerical results and experimental results that are available in the literature. It is also shown that the Young modulus of the core has a major influence on the angle of crack kinking.

Presenting Author: Zhangxian Yuan Worcester Polytechnic Institute

Presenting Author Biography: Zhangxian Yuan is an Assistant Professor in the Aerospace Engineering Department at Worcester Polytechnic Institute. His research focuses on the broad areas of solid mechanics, advanced composite materials, and computational methods for high-performance computing, with particular interests in structural stability, fracture and failure, impact and blast response, etc.

Authors:

Denis Molchanov Worcester Polytechnic Institute
Zhangxian Yuan Worcester Polytechnic Institute