Papers by Keyword: Interface Fracture

Abstract: A single cantilever beam test was performed on joints constituted from unidirectional carbon fiber composite flexible beam bonded to a rigid polyamide/aluminium block. The loading was following a constant separation rate rule, for which steady-state fracture energy can be obtained. In addition to the standard resistance curve we have investigated, using backface strain monitoring technique, fiber bridging effect on load distribution in the vicinity of the crack front. A big impact of the fiber bridging on the overall R-curve behaviour was confirmed with local non self-consistency of the crack propagation. The results are backed up analytically.

Abstract: Delamination in layered materials is analyzed in a fracture mechanical framework. The work deals with quasi-static propagation of crack fronts along planar interfaces between different isotropic, elastic layers. Special focus is here on local effects at the sides of the layers which are assumed to be stress free. The interface crack front meets the free sides of the specimen at an angle which depends on the elastic mismatch in the system. Finite element calculations allowing the shape of the crack front to be arbitrary are carried out for double cantilever beam type specimens. An iterative procedure is formulated which adjusts the shape of the crack front so that an interface fracture criterion is satisfied locally along the front. Apart from the overall shape of the crack front, the angle of intersection with the free sides is in particular determined numerically by this procedure. Comparisons with analytical formulations and experimental results are performed.

Abstract: Multilayered electronic components, typically of heterogeneous materials, delaminate under thermal and mechanical loading. A phenomenological model focused on modeling the shape of such interface cracks close to corners in layered interconnect structures for calculating the critical stress for steady-state propagation has been developed. The crack propagation is investigated by estimating the fracture mechanics parameters that include the strain energy release rate, crack front profiles and the three-dimensional mode-mixity along the crack front. The developed numerical approach for the calculation of fracture mechanical properties has been validated with three-dimensional models for varying crack front shapes. A custom quantitative approach was formulated based on the finite element method with iterative adjustment of the crack front to estimate the critical delamination stress as a function of the fracture criterion and corner angles.

Abstract: The interfacial fracture strength in polymer blends is investigated in this study. The constitutive relations of polymeric matrix and inclusions are both approximately described by linear viscoelastic models. It is assumed that the interfacial de-boding between inclusions and matrix is dominantly induced by the hydrostatic component of remote stress. Based on the assumption, the interfacial de-bonding of a viscoelastic inclusion embedded in an infinite polymeric matrix is analyzed. It is found that the size of inclusion will strongly affect the magnitude of critical stress, and the effect of Poisson’s ratio on the de-bonding is so small that can be ignored.

Abstract: Corner cracks under steady-state delamination were investigated. The fracture mechanics parameters that include the strain energy release rate and the three-dimensional mode-mixity along the interface crack front are estimated. A numerical approach was then applied for coupling the far field solutions based on the Finite Element Method to the near field (crack tip) solutions based on the J-integral methodology. A quantitative approach was formulated based on the finite element method with iterative adjustment of the crack front nodal coordinates to estimate the critical delamination stresses as a function of the fracture criterion and corner angles.

Abstract: In this paper, the local approach was used to analyze the geometry dependence of coating specimens for interface brittle fracture initiation, and a definition of the fracture process zone was proposed in the paper. The results showed that the interface fracture behavior of two types of specimens with notch had been predicted from the test results of pre-crack specimens based on the local approach for interface brittle fracture, and the predicted distribution of the critical load for the notched specimens gave a good agreement with the test results. It indicated that the local approach not only can be used to describe the interface fracture behavior, but also can be used in the integrity evaluation for interface between different materials.

Abstract: In this paper, the local approach based on the Weibull stress criterion was used to investigate the interfacial fracture behavior between LX88A coating and Q345 steel. LX88A coating was deposited by high velocity electric arc spraying technology (HVAS). The finite element method (FEM) was used to analyze the stress-strain fields of the coating specimen which consisted of three different specimen geometrics or modes of loading. It was found that the Weibull stress for all specimen geometries was almost identical under the same fracture probability when the interfacial fracture initiation occurred for different specimen geometries. It showed that the geometry dependence on the interface brittle fracture toughness data can be reduced through application of the local approach, and the local approach can be used to describe the interfacial fracture behavior.

Abstract: Structural model of plastic electronic package under temperature and humidity is constructed, and the coupling of the thermal and moisture impact on structure field is implemented. The impact of thermal expansion, hygro-swelling and vapor pressure increases with increasing initial defect, especially the impact of vapor pressure. At certain crack length, KI and KII induced by thermal expansion is proportional to temperature difference, and KI and KII induced by vapor is proportional to vapor pressure. The impacts of thermal expansion and hygro-swelling on ERR decrease during crack propagation, but the impact of vapor pressure increases significantly.

Abstract: This paper investigated the thermo-mechanical bending failure characteristic of air plasma-sprayed (APS) thermal barrier coating (TBC) system at 1000 oC by three-point bending test. A through-width surface pre-crack on the centre surface of the top ceramic coating (TC) in TBC sample was firstly designed and made by air plasma spraying technology. The fracture characteristic and spallation phenomena of the TBC were investigated under bending test in air at 1000 oC. The effects of constant displacement rate, span width of bending equipment and thermal aging time on the thermo-mechanical bending failure of the APS TBC system were slight at 1000 oC. Using SEM observations and EDX analysis, the interface cracks initiation, propagation and coalescence were discussed in detail. Furthermore, the fracture surface located within the TBC close to the TBC/TGO interface for all APS TBC samples under bending at 1000 oC.