Abstract
Evaluation of fracture energy of adhesive joints under mode-III and mixed-mode III/II is a key issue when failure analyses have to be performed. It is thus useful to determine fracture toughness under mode-III and characterization of crack front behavior of bonded joints under mixed-mode III/II loading conditions, which were the overall goal of this paper. For this purpose, edge crack torsion (ECT) and six-point bending plate (6PBP) tests were employed using steel/epoxy adhesive joint. The experimental tests were performed under displacement control and three types of configurations were tested to achieve different mixed-mode ratios. Test results showed considerable linearity before the maximum load point both under pure mode III and mixed-mode III/II; also, failure examination indicated that dominate failure under tearing mode was adhesive/adherend interface, which will be discussed in detail. The experimental tests were numerically simulated and virtual crack closure technique (VCCT) was employed to reproduce behavior of crack front propagation. Both experimental compliance method and finite element analysis proved applicable for the fracture mechanism of adhesive assemblies under mode-III and mixed-mode III/II.
Highlights
Structural bonding is a well-known assembly technique used in many industrial sectors which includes aerospace, automobiles, electrical, electronics, packaging, etc
For the sake of clarity and conciseness, the present analysis focused on three types of the configurations adopted for 6PBP tests, which corresponded to the limit mode mix ratios (Figure 2): i
The typical load–displacement response of the edge crack torsion (ECT) and 6PBP specimens is shown in Figure 5
Summary
Structural bonding is a well-known assembly technique used in many industrial sectors which includes aerospace, automobiles, electrical, electronics, packaging, etc. In the transportation industry and in the aerospace and automotive industries, this assembly technique is used to: Improve energy management capability and enable using advanced high strength steel, Enable down-gauged steel and multi-material construction, Reduce the number of spot-welds, and Improve acoustics by increasing stiffness of the structure body, durability by overcoming fatigue problems and longtime durability by an anticorrosion barrier. A particular issue with the integrity of adhesive joints is the presence of cracks and flaws in the as-manufactured adhesive bond-line. The presence of these defects, at least in some scales, seems inevitable and propagation of such cracks/flaws has the potential of affecting the service life of the adhesively bonded joints and even causing catastrophic failure of bonded structures in service. A better understanding of crack propagation behavior under realistic types of combined (in-out of plane shear stress components) service loading is an important aspect of evaluating the potential performance of adhesively bonded joints
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