Interfacial Delamination Cracking Research Articles

Deformation and crack growth in multilayered ceramic capacitor during thermal reflow process: numerical and experimental investigation

PurposeThis study aims to investigate the possible defects and their root causes in a soft-termination multilayered ceramic capacitor (MLCC) when subjected to a thermal reflow process.Design/methodology/approachSpecimens of the capacitor assembly were subjected to JEDEC level 1 preconditioning (85 °C/85%RH/168 h) with 5× reflow at 270°C peak temperature. Then, they were inspected using a 2 µm scanning electron microscope to investigate the evidence of defects. The reliability test was also numerically simulated and analyzed using the extended finite element method implemented in ABAQUS.FindingsExcellent agreements were observed between the SEM inspections and the simulation results. The findings showed evidence of discontinuities along the Cu and the Cu-epoxy layers and interfacial delamination crack at the Cu/Cu-epoxy interface. The possible root causes are thermal mismatch between the Cu and Cu-epoxy layers, moisture contamination and weak Cu/Cu-epoxy interface. The maximum crack length observed in the experimentally reflowed capacitor was measured as 75 µm, a 2.59% difference compared to the numerical prediction of 77.2 µm.Practical implicationsThis work's contribution is expected to reduce the additional manufacturing cost and lead time in investigating reliability issues in MLCCs.Originality/valueDespite the significant number of works on the reliability assessment of surface mount capacitors, work on crack growth in soft-termination MLCC is limited. Also, the combined experimental and numerical investigation of reflow-induced reliability issues in soft-termination MLCC is limited. These cited gaps are the novelties of this study.

PROPERTIES OF HIGH-CHROMIUM CAST IRON/LOW-CARBON STEEL BIMETAL FABRICATED BY HOT-ROLLING

A bimetal composite plate including a high-chromium cast iron (HCCI) and low-carbon steel (LCS) cladding was fabricated with hot-rolling bonding in the form of a sandwich structure. In this work, the microstructure and mechanical properties of the bimetal composite were analyzed. Experimental results showed that the brittle HCCI layer achieved good thermoplastic deformation under the action of carbon-steel cladding. After hot rolling, the two metals were well bonded due to mechanical and metallurgical bonding, showing an excellent joint. C atoms diffused uphill the interface. A decarburization area was formed near the LCS side and a fine pearlite diffusion band with a thickness of about 2–3 µm was formed on the bonding interface. The tensile strength of the bimetal composite was 249.5 MPa, and a cleavage fracture appeared on the HCCI side. Interfacial delamination cracks and tunnel cracks of the HCCI were observed in the bimetal composite during a bending test.

Heterogeneous magnesium matrix nanocomposites with high bending strength and fracture toughness

Heterogeneous Mg matrix nanocomposites (Hetero-Mg-NCs) with different sizes/morphologies of soft phase were fabricated by planetary ball milling and subsequent hot-pressing sintering. The Hetero-Mg-NCs were subjected to non-notched and notched bending tests to investigate their bending behaviors. The results showed that high bending strength was successfully attained in the Hetero-Mg-NCs, especially the one with large soft phase exhibited a simultaneous improvement of bending strength and fracture toughness by 50% and 57.7%, respectively, compared with those of pure Mg. The fractography measurements revealed that the Hetero-Mg-NCs failed by a mixed-mode fracture. The abundant interfacial delamination cracks and micro-dimples were found in the Hetero-Mg-NC with large soft phase, indicating the enhancement of fracture toughness. By examining the crack propagation path, it was revealed that the Hetero-Mg-NC with large soft phase showed a longer zigzagging path, owing to the more profound crack tunneling, deflection and bifurcation phenomena. The results demonstrated that Mg–NCs with heterogeneous structure can simultaneously attain high strength and fracture toughness under bending loading.

Preparation, microstructure and mechanical properties of CP-Ti/AA6061-Al laminated composites by differential temperature rolling with induction heating

In this research, a new, innovative method of differential temperature rolling with induction heating was proposed to prepare CP-Ti/AA6061-Al laminated composites in an argon protective atmosphere. The homogeneous deformation of titanium and aluminium was obtained, and the effect of rolling reduction on the mechanical properties and microstructure of the laminated composites was investigated in detail. The results showed that the interfacial bonding strength gradually increased with the rolling reduction, which was attributed to the increased mechanical meshing area and the wider element diffusion layer, leading to the microstructure of shear surface changing from brittle fracture to ductile fracture. When the rolling reduction was 50.5%, the shear strength of the Ti/Al clad plates reached a peak value of 122 MPa, close to the shear strength of the aluminium matrix (131 MPa). Ti/Al composites could improve the ultimate tensile strength of a single aluminium sheet. After tensile failure, the interfacial delamination length decreased from 7.64 mm to 0.22 mm with the reduction ranging from 17.5% to 50.5%, indicating that the strong interface could effectively impede the expansion of the interfacial delamination cracks, resulting in the improved resistance to delamination of composites. In summary, through the unique form of assembly and heating, the Ti/Al laminated composites achieved satisfactory microstructure and mechanical properties.

Interfacial delamination crack profile estimation in polymer foam-cored sandwich composites

Parabolic profile of cracks is well known in fracture mechanics, which typically develops in metallic systems. The profile of Interfacial delamination cracks in polymer foam cored sandwich composite structure is being investigated in this work using a procedure of embedded fiber Bragg grating sensor array with wavelength division multiplexing. The observed arbitrary nature of the crack profile in the mode I dominated loading condition, raises questions on the parabolic crack profile as well as on the assumption of numerous variables for numerical simulations of crack propagation problems especially for polymer foam-cored sandwich materials.

Microstructure and mechanical properties of hot rolled stainless steel clad plate by heat treatment

Series of stainless steel clad plates were heat treated at the quenching temperatures ranging from 900 °C to 1150 °C for holding time of 6min and 60min, respectively. It was observed that the ferrite and pearlite phases in the hot-rolled carbon steel substrate changed into lath martensite and needle-like ferrite through quenching treatment. The carburized layer thickness was gradually decreased till disappeared, and the interfacial shear strength was firstly increased and then decreased with the increasing quenching temperature, which was attributed to the sufficient alloy element diffusion and matrix softening at the high quenching temperature. At the quenching time of 6min, the shear fracture zone transmitted from the interface into the decarburized layer with the increasing quenching temperature, and the severe interfacial delamination cracks all existed at the clad interface. However, the main shear cracks were all presented at the decarburized layer for the quenching time of 60min, and there were no interfacial delamination cracks in the tensile samples, revealing that strong interface can be obtained by prolonging quenching time. The tensile behavior and fracture characteristics showed the ductile-brittle transition with the increasing quenching temperature.

Effect of heat treatment on the mechanical properties of copper clad steel plates

The mechanical properties anisotropy and heat treatment behavior of copper clad steel plates were investigated in detail. It was shown that the maximum yield strength and ultimate strength of copper clad steel plates are obtained along the tensile angle of 45°, whereas the minimum value of tensile ultimate strength (320.0 MPa) can be obtained at the tensile angle of 90°. The fracture region contains fibrous zone in the middle and the edge shear slip. The tensile ultimate strength and fracture elongation are gradually decreased with the increase of annealing temperature, which is attributed to the grain coarsening and interfacial delamination at high temperature. High residual compression stress is relieved at the annealing temperature, leading to low interfacial bonding state. There are no interfacial delamination cracks presented at all the cup drawing testing samples, all the fracture angles of raw clad plate and clad plates with annealing temperatures of 600 °C and 700 °C are almost 90° due to the mechanical anisotropy. However, due to disappearance of mechanical anisotropy of clad plate with annealing temperature of 800 °C, the fracture angle is far away from 90°.

The tensile behaviors and fracture characteristics of stainless steel clad plates with different interfacial status

The mechanical properties and fracture characteristics of stainless steel clad plates by vacuum hot rolling at different rolling temperature of 1100°C (S1), 1200°C (S2) and 1300°C (S3) are investigated in detail. The carburized layer thickness and grain size is gradually increased with the increasing rolling temperature. The sufficient alloy element diffusion, recovery and recrystallization at the bonding temperature of 1300°C lead to the highest interfacial shear strength and the lowest longitudinal tensile strength among the three clad plates. However, the tensile ductility is increased with the increasing rolling temperature, which is attributed to the increased interfacial bonding strength. The strong interface can effectively delay the formation of interfacial delamination crack and premature localized necking, resulting into a prolong uniform plastic deformation stage with a low stress triaxiality. In addition, there are many intergranular tunnel cracks with the length of 50–150µm presented in the carburized layer due to Cr23C6 carbides on the grain boundary, which can effectively toughen the stainless steel clad plates.

Bending behaviors and fracture characteristics of laminatedductile-tough composites under different modes

The bending load-deflection curves and fracture characteristics of a range of laminated Ti(TiBw/Ti) composites were investigated under five modes. The results show ductile-brittle transition with decreasing Ti layer thicknesses and increasing volume fractions of TiBw, which is attributed to the constrained plastic deformation mechanism accompanying with high stress traixiality and tensile stress. The laminated composites with weak interfaces display superior fracture toughness under notched crack arrested orientation, which is related to the delamination cracks and multiple tunnel cracks. Moreover, single tunnel crack propagation and periodic multiple tunnel cracks were observed in the laminated composites under mode IV, which depend on the thickness and ultimate strength ratio of ductile Ti layer and tough TiBw/Ti composite layer. There are many interfacial delamination cracks and multiple tunneling cracks presented under mode V, playing an effective role in toughening the laminated composites. In addition, with decreasing the Ti layer thickness, laminated composites reveal obvious size effect characterized by more tunnel cracks.

Interfacial delamination cracking shapes and stress states during wedge indentation in a soft-film-on-hard-substrate system—Computational simulation and experimental studies

Abstract

Behavior of RC Beams Retrofitted with CARDIFRC after Thermal Cycling

This study investigates the effect of thermal cycling on the performance of concrete beams retrofitted with CARDIFRC, a new class of high performance fiber-reinforced cement-based material that is compatible with concrete. Twenty four beams were subjected to 24 h thermal cycles between 25 and 90°C. One third of the beams were reinforced either in flexure only or in flexure and shear with conventional steel reinforcement and used as control specimens. The remaining sixteen beams were retrofitted with CARDIFRC strips to provide external flexural and/or shear strengthening. All beams were exposed to a varied number of 24 h thermal cycles ranging from 0 to 90 and were tested in four-point bending at room temperature. The tests indicated that the retrofitted members were stronger and stiffer than control beams, and more importantly, that their failure initiated in flexure without any signs of interfacial delamination cracking. The results of these tests are presented and compared to analytical predictions. The predictions show good correlation with the experimental results.

Determining the interfacial toughness of low- k films on Si substrate by wedge indentation: Further studies

This paper presents further studies to determine the interface toughness of low- k films (black diamond (BD) film) using wedge indentation experiments and analysis. In addition, the effects of film thickness on the delamination mode are studied and an analysis methodology is proposed. The curvature of the delamination crack front is measured and compared for the films with different thicknesses, and this information is used to determine the critical buckling stress and the delamination mode: i.e. with or without buckling. For a thinner film with a straight crack front, there is greater likelihood of buckling delamination, while for a thicker film with a curved crack front buckling is less likely. Combining these results with those from a previous study, it is shown that the wedge indentation test is capable of accurately measuring the interface toughness of low- k films, and a pop-in event in the load–penetration curve can be used as an early indication of interface crack initiation. It is also found that the resistances to the initiation and propagation of the interfacial cracks for the porous methylsilsesquioxane (MSQ) and non-porous BD films are significantly different; this could be due to the fact that in the porous MSQ film, molecular bridges might provide an additional mechanism to resist interfacial delamination cracks.

Mixed-mode analysis of superimposed thermo-elastic effects in fiber-reinforced composites with embedded interface delaminations

This paper deals with the 3D finite element analysis of superimposed thermo-elastic effect on embedded interfacial delamination crack growth characteristics in fiber-reinforced laminated composites. Interlaminar fracture at the delamination front is found to be a mixed-mode phenomenon due to the anisotropy and heterogeneity of thermo-physical properties of composite materials. This leads to the requirement of finite element evaluation of energy release rates, based on the principles of linear elastic fracture mechanics. The strain energy release rate components along the delamination front due to a uniform temperature drop, during the manufacturing stages of composite laminates, to room temperature and subsequent mechanical loading is obtained by superimposing their respective effects based on the assumptions of linear elasticity. Numerical calculations are carried out for multi-layered cross-ply and angle-ply composite laminates and energy release rate plots demonstrate large asymmetries along the delamination front due to the interaction of residual stresses and superimposed transverse loading.

Experimental and Numerical Life Prediction of Thermally Cycled Thermal Barrier Coatings

This article addresses the predominant degradation modes and life prediction of a plasma-sprayed thermal barrier coating (TBC). The studied TBC system consists of an air-plasma-sprayed bond coat and an air-plasma-sprayed, yttria partially stabilized zirconia top layer on a conventional Hastelloy X substrate. Thermal shock tests of as-sprayed TBC and pre-oxidized TBC specimens were conducted under different burner flame conditions at Volvo Aero Corporation (Trollhattan, Sweden). Finite element models were used to simulate the thermal shock tests. Transient temperature distributions and thermal mismatch stresses in different layers of the coatings during thermal cycling were calculated. The roughness of the interface between the ceramic top coat and the bond coat was modeled through an ideally sinusoidal wavy surface. Bond coat oxidation was simulated through adding an aluminum oxide layer between the ceramic top coat and the bond coat. The calculated stresses indicated that interfacial delamination cracks, initiated in the ceramic top coat at the peak of the asperity of the interface, together with surface cracking, are the main reasons for coating failure. A phenomenological life prediction model for the coating was proposed. This model is accurate within a factor of 3.

Study for the endurance of radial truck tires with finite element modeling

The paper describes the intention of the authors to determine whether it is possible to predict the endurance of radial truck tires using finite element modeling. Two approaches are used. One is a stress analysis parameter approach. According to the approach, by studying the effect of tire structure parameters (for example, belt structure parameters, bead structure parameters, etc.) on stress analysis parameters in critical regions of radial truck tires, the screening of the tire structure parameters is carried out. As an example, the predictability of the relative belt edge endurance in a radial truck tire is undertaken. The other is a fracture mechanics approach. Emphasis is here placed on the non-symmetric propagation model of the interfacial delamination crack in complex composite material structures. The finite element modeling techniques used in the paper is also briefly introduced.

Indentation-induced buckling of organic coatings part I: theory and analysis

The impact-induced buckling and delamination of a thin coating was analysed for the purpose of predicting the amount of coating removed when a single particle was launched, at a given velocity, against a coated substrate. A novel post-buckling analysis is presented in which the coating is modelled as a clamped disk prevented from buckling at an arbitrarily set inner radius, due to the presence of the indenting particle. A method for calculating the arrest strain energy release rate and mode mix of interfacial delamination cracks, based on the coupling of the presented buckling analysis with an existing strain energy release rate analysis [1] is then presented. A method to estimate the critical interfacial shear stress at crack initiation is also outlined. An accompanying paper [2] compares experimental results with the results of this analysis, and shows how the results can be used in the context of blast cleaning.