The effect of a non-circular drawing sequence on delamination characteristics of pearlitic steel wire

In this study, a non-circular drawing (NCD) sequence was applied to investigate the effect of deformation behavior, microstructure and texture evolution on delamination characteristics of pearlitic steel wire under torsional deformation mode. The multi-pass NCD sequence was numerically and experimentally applied up to the 12th pass in comparison with conventional wire drawing (WD). For investigation of the deformation characteristics of the drawn wires, three-dimensional finite element and flownet analyses were carried out. These simulation results indicated that the NCD could impose relatively homogeneous plastic deformation on the wire compared to the WD. From the scanning electron microscopy and X-ray diffraction results, globular cementite and cylindrical texture component, which might increase likeliness of delamination fracture, were rarely observed in the NCD drawn wire. In the torsion test, the delamination fracture was observed in the WD drawn wire for the 10th pass while it did not occur for the 12th pass NCD. In addition, the ultimate tensile strength (UTS) of 2300 MPa grade wire was manufactured by the NCD and the UTS value was 257 MPa higher than the one of the WD. Therefore, it was demonstrated that the multi-pass NCD could impose relatively homogeneous plastic deformation on the wire, resulting in high-torsional ductility with better strength compared to the WD.     

Role of plasticity on interface crack initiation from a free edge and propagation in a nano-component

In order to elucidate the role of plasticity on interface crack initiation from a free edge and crack propagation in a nano-component, delamination experiments were conducted by a proposed nano-cantilever bend method using a specimen consisting of ductile Cu and brittle Si and by a modified four-point bend method. The stress fields along the Cu/Si interface at the critical loads of crack initiation and crack propagation were analyzed by the finite element method. The results reveal that intensified elastic stresses in the vicinity of the interface edge and the crack tip are very different, although the Cu/Si interface is identical in both experiments. The plasticity of Cu was then estimated on the basis of the nano-cantilever deflection measured by in situ transmission electron microscopy. The plasticity affects the stress fields; the normal stress near the interface edge is intensified while that near the crack tip is much reduced. Both the elasto-plastic stresses are close to each other in the region of about 10 nm. This suggests that the local interface fracture, namely, the crack initiation at the interface edge and the crack propagation along the interface, is governed by elasto-plastic normal stress on the order of 10 nm.     

New peel stopper concept for sandwich structures

The paper addresses the damage tolerance of sandwich structures, where the prevention and limitation of delamination failure are highly important design issues. Due to the layered composition of sandwich structures, face–core interface delamination is a commonly observed failure mode, often referred to as peeling failure. Peeling between the sandwich face sheets and the core material drastically diminishes the structural integrity of the structure. This paper presents a new peel stopper concept for sandwich structures. Its purpose is to effectively stop the development of debonding/delamination by rerouting the delamination, and to confine it to a predefined zone in the sandwich structure. The suggested design was experimentally tested for different material compositions of sandwich beams subjected to three-point bending loading. For all the tested sandwich configurations the suggested peel stopper was able to stop face–core delamination and to limit the delamination damage to restricted zones.     

Delamination in elastic shear deformable circular layers

This work extends the analytical solution of an interface crack in straight layered structures to circular layered structures. A small segment at the vicinity of an interface crack tip in a circular laminated beam is analyzed by a novel shear deformable bi-layered circular beam theory. Two concentrated forces are found existing at the crack tip due to the requirement of the equilibrium condition. Closed-form solution of the total energy release rate of the interface crack is obtained as the half of the product of the concentrated forces and the corresponding displacement gradient discontinuities at the crack tip. Closed-form expressions of the mode I and II components of the energy release rate are also obtained by global and local methods. Numerical verifications are conducted by analyzing the interlaminar delamination of a circular beam with an edged crack and comparing with the baseline results obtained through finite element analysis. Excellent agreements between the present method and finite element analysis on the predictions of total energy release rate and mode partition verify the accuracy and efficiency of the present solution.     

Influence of interfacial delamination on channel cracking of elastic thin films

Channeling cracks in brittle thin films have been observed to be a key reliability issue for advanced interconnects and other integrated structures. Most theoretical studies to date have assumed no delamination at the interface, while experiments have observed channel cracks both with and without interfacial delamination. This paper analyzes the effect of interfacial delamination on the fracture condition of brittle thin films on elastic substrates. It is found that, depending on the elastic mismatch and interface toughness, a channel crack may grow with no delamination, with a stable delamination, or with unstable delamination. For a film on a relatively compliant substrate, a critical interface toughness is predicted, which separates stable and unstable delamination. For a film on a relatively stiff substrate, however, a channel crack grows with no delamination when the interface toughness is greater than a critical value, while stable delamination along with the channel crack is possible only in a small range of interface toughness for a specific elastic mismatch. An effective energy release rate for the steady-state growth of a channel crack is defined to account for the influence of interfacial delamination on both the fracture driving force and the resistance, which can be significantly higher than the energy release rate assuming no delamination.     

基于多层数据库访问技术的自定义报表的研究

主要描述了一个基于多层数据库访问技术的自定义报表的实现原理.并简要介绍了部分实现方案和处理流程,举例说明了部分技术要点.     

XFEM simulation of delamination in composite laminates

In this paper, the extended finite element method (XFEM) is extended to simulate delamination problems in composite laminates. A crack-leading model is proposed and implemented in the ABAQUS® to discriminate different delamination morphologies, i.e., the 0°/0° interface in unidirectional laminates and the 0°/90° interface in multidirectional laminates, which accounts for both interlaminar and intralaminar crack propagation. Three typical delamination problems were simulated and verified. The results of single delamination in unidirectional laminates under pure mode I, mode II, and mixed mode I/II correspond well with the analytical solutions. The results of multiple delaminations in unidirectional laminates are in good agreement with experimental data. Finally, using a recently proposed test that characterizes the interaction of delamination and matrix cracks in cross-ply laminates, the present numerical results of the delamination migration caused by the coupled failure mechanisms are consistent with experimental observations.     

Electrochemical studies of the inhibition of the cathodic delamination of organically coated galvanised steel by thin conversion films

Scanning Kelvin Probe (SKP) measurements of thin amorphous conversion film coated galvanised steel in combination with current density-potential curves and electrochemical impedance spectroscopy (EIS) were performed with the aim to improve the understanding of electrode potentials at the coating/metal interface and their influence on corrosive de-adhesion. The thin hybrid conversion films contained Zn-phosphates, titanates and also complexing organic compounds and led to an inhibition of the cathodic oxygen reduction and anodic zinc dissolution. In the polymer coated area the conversion film leads to a cathodic shift of the potential as measured by means of the SKP. This cathodic potential shift is explained by the substitution of the n-semiconducting Zn-oxide with an insulating inorganic layer. When the SKP detects the potential of freely corroding iron at a defect, where no protective coating layer is, the interfacial potential for the conversion film coated zinc layer is more negative than the defect potential. This leads to a diminished driving force for an oxygen reduction induced delamination process which is of relevance for the understanding of cut-edge corrosion.     

Delamination failures of Stellite hardfacing in power plants: a microstructural characterisation study

In recent years, several incidents of cracking and failures have been observed in Stellite (Stellite is a registered trademark of the Deloro-Stellite Corporation) hardfacing used in valves of modern high temperature combined cycle gas fired power plants. These hardfacing layers are applied as an overlay onto a steel substrate, such as CrMo steel (i.e. Grade 22, WC9) or creep strength enhanced ferritic steel (i.e. Grade 91, C12A). Cracking has been observed in valve components at the Stellite/steel interface and in the weld dilution zone formed between the steel and clad. Ultimately, disbonding or delamination of the weld hardfacing from the valve body occurs and has resulted in collateral damage to components in the plant (such as to the turbine) or valve failure. In this study, the microstructure formed near the Stellite/steel interface is investigated. Based on thermodynamic modelling, microstructure formed at these regions is hypothesised and a simple methodology is proposed to predict the occurrence of these failures.     

The effect of moisture on buckle delamination of thin inorganic layers on a polymer substrate

Moisture-induced buckle delamination of thin inorganic layers on a polymer substrate was studied. Moisture has been found to have a significant effect on the failure mode. Experimentally, an increase in the buckle width, height and the total buckle delamination length with time and humidity was observed. Moreover, a transition from straight to telephone-cord buckle pattern was taken place in a humid environment. Applying only a uniaxial compressive strain on the thin layers did not result in the transition from straight to telephone-cord. For a compliant substrate the transition from straight to telephone-cord buckle occurred at significantly higher ratio of residual strain over critical buckling strain than for a rigid substrate. A simple model for buckling was applied. Using the energy release rate, the interfacial toughness was investigated as a function of relative humidity.