Analysis of peel and shear strains in cracked lap shear specimens subjected to fatigue loading using digital image correlation

Adhesive bonding presents many advantages, such as efficient manufacturing and improved structural performance [1]. However, in structures subjected to fatigue, cracks might initiate and propagate in joints, leading to in-service failure [2]. Most adhesively bonded joints are subjected to combination of peel and shear loads, so mixed I+II mode loading conditions are present [3]. In this work, Cracked Lap Shear specimens, which feature mixed I+II mode loading conditions, were tested under fatigue loading. During tests, crack growth was monitored using Visual Testing and Digital Image Correlation. With Digital Image Correlation, opening and sliding displacements in the bondline were extracted from the substrates’ displacement fields and compared against a Finite Element Model, revealing a highly strained process zone ahead of the crack tip. Results highlight the usefulness of DIC in capturing the deformation behaviour of adhesive joints under mixed mode loading conditions

Analysis of peel and shear strains in cracked lap shear specimens subjected to fatigue loading using digital image correlation

Adhesive bonding presents many advantages, such as efficient manufacturing and improved structural performance [1]. However, in structures subjected to fatigue, cracks might initiate and propagate in joints, leading to in-service failure [2]. Most adhesively bonded joints are subjected to combination of peel and shear loads, so mixed I+II mode loading conditions are present [3]. In this work, Cracked Lap Shear specimens, which feature mixed I+II mode loading conditions, were tested under fatigue loading. During tests, crack growth was monitored using Visual Testing and Digital Image Correlation. With Digital Image Correlation, opening and sliding displacements in the bondline were extracted from the substrates’ displacement fields and compared against a Finite Element Model, revealing a highly strained process zone ahead of the crack tip. Results highlight the usefulness of DIC in capturing the deformation behaviour of adhesive joints under mixed mode loading conditions

Static and Fatigue Performance of Carbon Fibre Sheet Moulding Compound Components

In the last decade, Carbon Fibre Sheet Moulding Compounds (CF-SMCs) have gained the interest of both industry and academia. Those materials combine the fast manufacturing process of short fibre composites with mechanical properties closer to those of continuous laminates. CF-SMCs can thus be used in structural parts of high-volume industries, like the automotive sector. However, the lack of knowledge on the mechanical performance of the material (especially under fatigue loading) and the lack of efficient modelling techniques are hindering the widespread adoption of CF-SMCs. This research aims to reduce these gaps: experimental campaigns and model development were thus performed almost in parallel; the tests identified material features to be reproduced by the developed model, but also to serve as validation case. During the work, a CF-SMC prototype, developed from an actual chassis part, was designed, manufactured and tested. This served as validation case for the model, but also helped to better understand the implications of manufacturing thick CF-SMC parts.status: publishe

Development of a user-defined Cohesive Element to model delamination behaviour in composites under fatigue loads

The present thesis aims at developing a cohesive element behaviour for predictive analysis involving delamination in composites under cyclic loading. The key feature of the proposed method is the implementation of a degradation law that slowly decrease the cohesive properties of the element itself with the number of elapsed cycles. In this way, damage can be accumulated, and a crack can grow, also when local stress is lower than the cohesive strength of the element, that is the typical situation of fatigue problems. The formulation is capable of an automatic identification of the initiation zone, and can reproduce propagation of a crack as well. Several algorithms are developed, starting from a simple one to finally obtain a satisfying degradation law. Simulations are performed under various mode-mixity conditions using Double Cantilever Beam, End Notched Flexure and Mixed Mode Bending tests, as well as a more complex laminated structure. Finally, simulations performed to compare the model with experimental data proved quite satisfying

Assessment of state of the art prediction methodology for mechanical properties of CF-SMC structures

status: publishe

Morphology-induced fatigue crack arresting in carbon fibre sheet moulding compounds

status: Published onlin

MULTISCALE MODELLING OF A THICK CARBON FIBRE SHEET MOULDING COMPOUND AUTOMOTIVE COMPONENT: FROM MANUFACTURING TO STRUCTURAL SIMULATION

status: publishe