Papers by Keyword: Interfacial Fracture

Abstract: In this study, electro nickel coating was applied and its effect on the interfacial stability and cracking behaviors were investigated in the multi-layered Ni-plated-Cu/Al/Ni-plated-Cu clad composite. Ni plating with 5μm thickness on the Cu sheet before cladding does not form a continuous layer between Cu and Al because of its low ductility. Ni layer covers the part of the Cu/Al interface. In the interface region without Ni layer, CuAl₂, CuAl and Cu₉Al₄ were found to be formed after annealing whereas Al₃Ni₂ and Al₃Ni were found to be formed in the interface region with Ni layer. After bending, interface crack developed initially in the interface region with plated Ni layer. On the other hand, the interface region with no Ni layer, no interface cracks were found to formed, suggesting that the bonding between Al and Ni is not strong enough. After interface crack formation, cracks developed in the Al layer, which may lead to the fatal fracture.

Abstract: No one wants a material to fail. If it does happen then we have to know what the causes are and then what is the intensity at which it fails. To do this, we to do many experimental tests. The laboratory data for the laminated composites fractures normally exhibit scatter. This implies an element of uncertainty or vagueness in the results. Fuzzy logic is a natural means of expressing vague categories of information through fuzzy sets and offers means of performing logical operations. In this paper are considered some aspects regarding laminated composites fractures using fuzzy logic methods. The fuzzy logic treatment of the case considered in this work clearly show some risk of failures at lower parameter levels than might be expected using a deterministic treatment in which the vagueness of knowledge is masked and which might not be safeguard against by using a factor of safety value.

Abstract: This paper deals with an identification methodology of the interfacial fracture parameters to predict the lifetime of a metallic brazed joint. The methodology is based on an experimental-numerical study whereby the optimal parameters are obtained. The experimental data, using the scanning electron microscope analysis, allowed approving that failure of the assembly based AuGe solder seems first to appear near the interfaces. These results were confirmed by micrographs analysis of the solder/insert and solder/substrate interfaces. Then, using shear test results and parametric identification coupled with a finite elements model (FEM) simulation, the damage constitutive law of the interfacial fracture based on a bilinear cohesive zone model are identified. The agreement between the numerical results and the experimental data shows the applicability of the cohesive zone model to fatigue crack growth analysis and life estimation of brazed joints.

Abstract: The mechanical properties and microstructure of layered Cu/Al/Cu composites was investigated after annealing at various temperatures. The nature of intermetallic compounds in roll-bonded Cu/Al/Cu clad metals after heat treatment was investigated using SEM, XRD and EBSD.in the temperature range 200~500 ^oC. In the roll-bonded 3-ply Cu/Al/Cu clad metal, no visible interfacial reaction compound and defects were observed at the interfaces. The reaction layer was observed grow rapidly at the Cu/Al interface after annealing at and above 400 ^oC, which deteriorated the ductility of clad metals. Intermetallic reaction layers of Cu/Al/Cu clad materials annealed at 500 ^oC for 3, 5, 10hours was found to consist of three layers, CuAl2, CuAl and Cu9Al4. EBSD analyses revealed that intermetallic layers are polycrystalline. The drastic decrease of stress and elongation in Cu/Al/Cu clad composite annealed at 500 ^oC can be linked to the interfacial cracks between Al and Cu layer.

Abstract: The microstructures and bending properties of STS439/Al1050/STS304 clad plates were investigated after annealing process at various temperatures. Interfacial layer was developed at the STS439/Al1050 and Al1050/ STS304 interfaces at 550^OC. The presence of Al3Fe2 at the STS/Al interface was confirmed by EDX. The initial bending hardenability and load under condition A (STS439 side in tension) was found to be greater than under condition B (STS304 side in tension). The higher hardenability and load under condition A can be explained by the greater strain hardenability of STS439 (bottom side) in tension. No interfatial cracks were observed across the interface in the as roll-bonded clad composite and annealed clad composites at 450^OC. After annealing at 550^OC, the load drops in the early part of load-displacement curves associated with the interface debonding was observed. As-rolled clad metal and that annealed at 450^OC exhibited the relative high load.

Abstract: The interface cracking and fracture behaviors of as-roll-bonded and heat-treated 3-ply Cu/Al/Cu clad metal were investigated Interfacial intermetallic layer were observed to be formed at the Cu/Al interface upon annealing at and above 300°C. The presence of Cu9Al4, CuAl, Cu3Al2 and CuAl2 at the Cu/Al interface was confirmed by XRD. The intermetallic reaction layer has a detrimental effect on the bonding strength of the Cu/Al/Cu clad metal, inducing interface cracks. The length of the delaminated region increased with increasing heat treatment temperature. No strain incompatibility and cracks were observed across the interface in the as roll-bonded clad composite and, for annealed clad composites at 300°C, some appreciable strain incompatibiliy developed, starting to form interface microcracks. For annealed clad composites at 450°C, the interface crack opened wide up with strain because the separated Cu and Al plate deform, developing their independent necks and fracture independently.

Abstract: The effect of heat treatment on the bending deformability and fracture behavior of roll-bonded Cu/Al/Cu clad plates were investigated. As-rolled clad plate and that annealed at 200OC exhibited the initial high load maintained for a short period and then a rapid drop of the load. The rapid softening promotes the continued localized bending once bending occurs because the work hardening due to the localized bending is negligible, leading to the localized fracture. Cu/Al/Cu clad metal annealed at 300OC, up to 450OC, initial load for bending decreased remarkably due to recovery/recrystallization, but work hardening occurred for an extended period before gradual softening took place. The initial extensive work hardening in the localized bent region tends to distribute the bending deformation uniformly, leading to the rather uniform bending. For annealed clad plates at high temperatures, the periodic cracks perpendicular to the interface were observed in the intermetallic layer and the localized slip developed both in Cu and Al emanating from the open cracks in the intermetallic layer. The localized slip marking was more evident in Cu than in Al, reflecting the lower stacking fault energy in Cu.

Abstract: The mechanical performance and fracture of roll-bonded Cu/Al/Cu clad metal were investigated after heat treatment in the temperature range 200~500OC. In the roll-bonded 3-ply Cu/Al/Cu clad metal, no visible interfacial reaction compound and defects were observed at the interfaces, ensuring the well-bonded Cu/Al interface until the final moment of fracture in tension. The reaction layer was observed at the Cu/Al interface after annealing at and above 400OC, which deteriorated the ductility of clad metals. The thickness of the reaction layer increased with increasing heat treatment temperature. The periodic cracks were formed perpendicular to the tensile direction due to the strain mismatch between metal layers and the reaction compound layer in the clad heat treated at high temperatures at 500oC. The slip localization and delamination induced premature crack formation in Cu and Al layer, resulting in the decreased clad metal fracture strain, especially after heat treating at 500oC.

Abstract: The interface fracture process of most layered or bonded structures is commonly under the control of mixed mode cracking where the interface shear and normal fracture components exist simultaneously when the hybrid joints are bonded with different adherend materials. In this work, a simple and novel method is proposed to realize and characterize the pure mode I interface fracture for the hybrid joints with dissimilar substrates. The theoretical and experimental results indicate that the present method may be considered as a standard test method for the characterization of hybrid joints with dissimilar materials.

Abstract: This paper presents a numerical investigation of fracture behaviors of concrete-steel interface under wedge splitting. The consideration of heterogeneity for the materials is achieved by assigning the elements random strength and elastic modulus by assuming a Weibull’s distribution. The fracture pattern transits from the predominated adhesive layer fracture to the dominated concrete cracking as the interface cohesive strength changes from lower than concrete tensile strength to higher than that. Local cracks can also occur duo the heterogeneous assumption. The numerical results and have an agreement with the experimental results.