Investigation Of Failure Mechanisms Research Articles

Experimental and theoretical investigation of failure mechanism in Al2O3/SiC composite under plane shock waves

The investigation of fracture and fragmentation is essential for evaluating the protection performance and structural design of ceramic armour. This paper focused on the dynamic failure and fracture mechanisms of the fine-grained Al2O3/SiC composite subjected to plane shock waves. The macroscopic shock response characteristic was determined through a series of plane impact tests, which included the Hugoniot curves of the composite. The results indicated that the fracture mechanism is significantly influenced by specific stress characteristics. The transgranular fracture in large grains and intergranular fracture in small grains exhibit obvious local plastic deformation characteristics. Moreover, the presence of second-phase SiC particles markedly influences both crack propagation and the microfracture mode of the composite. Lastly, a statistical analysis of the ceramic fragments was conducted after the soft recovery of specimens in impact experiments, and analytical models were developed and modified to predict the distribution of fragments under plane shock loading.

Failure mechanism and landslide fragility of reinforced concrete buildings considering uncertain flow properties

ABSTRACT This study examines the failure mechanism and landslide fragility of regular and irregular reinforced concrete (RC) buildings under flow-type landslides. Efficient intensity measures to evaluate landslide fragility of regular flat land buildings and irregular buildings, having step-back and split foundation configurations, are proposed. Further, a methodology is proposed to consider the uncertain flow properties in the investigation of failure mechanisms and landslide fragility. Uncertainty in landslide properties is considered based on some database of past landslide events and laboratory experiments conducted on the soil samples collected from four landslide-active sites in the Mandi district in Himachal Pradesh, India. Overturning moment (hv) is found to be the efficient as well as most proficient intensity measure (IM), among several other IMs for landslide fragility assessment of regular and irregular RC buildings. Further, it is concluded that the landslide performance of RC buildings is directly related to the seismic design level of the building. Moreover, the buildings with step-back configuration are found to be more vulnerable than their split foundation counterparts. Furthermore, structural deficiency of the short columns, typically observed in the considered building configurations, under landslide loading is highlighted and design recommendations are presented for improvements.

Investigation of failure mechanisms in dual-phase steels through cohesive zone modeling and crystal plasticity frameworks

Dual-phase (DP) steels are characterized by their good formability and interesting material properties, which primarily originate from their unique composition, combining the ductile ferrite phase with the hard martensite phase. At the microscale, DP steels exhibit various fracture mechanisms that need to be investigated through proper plasticity and failure models. These mechanisms include interface decohesion between ferrite–martensite and ferrite–ferrite phases, as well as martensite cracking, depending on the steel’s microstructure. In this study, crystal plasticity and cohesive zone frameworks are employed together with a ductile failure model in 3D polycrystalline Representative Volume Element simulations to address the multiscale characteristics of the fracture mechanisms in DP steels. The analysis requires an extensive parameter identification procedure, which is presented in detail. The obtained results demonstrate the framework’s capability to effectively identify the primary failure mechanisms correlated with crucial microstructural features, including crystallographic orientation, morphology, volume fraction, and stress triaxiality. Findings indicate that an increase in the connectivity of the martensitic phase induces a shift from ferrite–ferrite decohesion to ferrite–martensite decohesion and martensite cracking. Similarly, as the volume fraction of martensite increases, decohesions become constrained, making martensite cracking the main failure mode. The numerical observations regarding triaxiality highlight that as stress triaxiality increases, the predominant failure mechanism is changed from martensite cracking and ferrite–martensite decohesion to ferrite–ferrite decohesion.

Analysis of Failure Mechanism and Reliability Enhancement of Silicon Strain Gauge-Based Pressure Sensor for Automotive Applications

Hydrogen fuel cell vehicles have gained more attention as future automobiles due to their environmental benefits and extended driving ranges. Concurrently, the global hydrogen sensor market is also experiencing substantial growth. These sensors are integrated into vehicles to detect hydrogen leakage and concentration, thereby ensuring the safety of hydrogen fuel cell vehicles. In particular, hydrogen pressure sensors, commonly installed on the manifold and regulator of vehicles, can measure hydrogen pressure and diagnose safety concerns caused by hydrogen leakage in advance. In this paper, we identify the vulnerable points of hydrogen pressure sensors when exposed to vehicle driving environments, investigate failure mechanisms, and provide process optimization techniques. Specifically, our reliability modeling verifies that the components of a printed circuit board (PCB) exposed to humid environments undergo corrosion due to ion migration, leading to the generation of extrinsic series or parallel resistances, which in turn cause fluctuations of output voltage. Through structural and elemental analysis, we pinpoint process-related factors that make components vulnerable to humidity, thereby suggesting recommendations for enhancing the manufacturing process. Based on this analysis in the development stage, we can proactively address and improve reliability and further safety-related issues for future automobiles, thus preventing real field issues.

In-Situ Confocal Microscopy to Analyze Volume Expansion of Solid State Microbatteries

The rise of embedded objects put great interests in miniaturized power supply solutions. Solid State Microbatteries (SSM) are the most promising, as they can safely store high energy and power density. SSM have the advantage of being all-solid (no liquid leakage and flammability), to have low self-discharge and good cyclability. Despite the strong interest in the field, the mechanisms of Li plating and stripping at the anode are not well observed and not yet fully understood [1]. The study of these phenomena would bring new insights to mechanical behavior during cycling and therefore may lead to optimization approaches at the cycle life level. In this purpose, we investigated the morphological change of SSM during the charge/discharge cycle. We looked at the influence of the cathode thickness and the packaging. Thick LiCoO2 layers were used for the study with thickness from 5 to 30 µm. Volume variations upon cycling were followed thanks to a Neox microscope 3D (Sensofar) and were correlated to charge/discharge capacity.Microbatteries are consisting of LiCoO2 (LCO) cathode and LiPON electrolyte. The anode-free configuration was adopted for integration compatibility. The anode is formed in-situ during the first charge operation. Wafers with different LCO thickness and back end level have been carried out. Confocal microscope was setup in Ar-filled glovebox to monitor the volume expansion during the charge and discharge operations. SSM cycling was operated through Biologic instruments. Figure 1 depicts a schematic representation of the SSM and the setup. Images were acquired during chrono-amperometric full charge at 4.2 V and galvanostatic full discharge at Idischarge = -3.5 µA within 3-4.2 V.Charge/discharge operations and corresponding in-situ thickness variations are presented in Figure 2 for the samples with different LCO thickness. The complete charge is achieved when current reaches a threshold of 0.5 µA. Charge capacity linearly increased with cathode thickness: Qcharge = 2.0 µA.h for the 5-µm-LCO and Qcharge = 9.6 µA.h for the 30-µm-LCO. Thickness variation increase follows the same evolution as capacity during charge and discharge. Regardless of the cathode thickness, same plating and stripping speed are observed during charge and discharge operation, respectively. According to the Qcharge and the volume variation, a theoretical lithium density at the anode side has been observed for all LCO thickness.Figure 3 depicts 2D images of 5-µm-LCO SSM at the onset of the charge. Pristine SSM presents a smooth surface (Fig. 3.a). Li plating is initiated with nucleated grains (Fig. 3.b). Then, grains grow and tend to coalesce with each other, forming a uniform and smooth Li layer (Fig. 3.c). Figure 4 reports 2D images of 30-µm-LCO SSM at different states of cycling. Bumps at the edge formed during the charge are due to SSM device architecture: electric field bends and the increased ion flux induces a more important Li accumulation on the edge. Otherwise, a uniform and fully dense Li metal deposition is realized in solid-state configuration under zero external pressure [2]. At the end of discharge, the battery thickness is higher than the pristine one (+ 3.7 µm). The Li plating non-reversibility phenomena after the first charge is due to low diffusion coefficient at low state-of-charge [3].Figure 5 shows the electrical behavior (Fig 5.a) and the volume expansion (Fig 5.b) of a SSM over 10 cycles. After the first cycle, cycling is performed at ≈100% coulombic efficiency, demonstrating high reversibility of the phenomena and so high cyclability of SSM [3].Finally, we followed the influence of the encapsulation layers on the volume variation. 2D images of the SSM reveals same volume variation for both samples. Those observations suggest that the encapsulation layers has no significant mechanical effect on the Li plating.In-situ confocal microscopy under Ar atmosphere has been proved efficient to study the volume expansion of SSM upon cycling and is a promising technique to investigate failure mechanisms of SSM.[1] J. Park et al., « In situ atomic force microscopy studies on lithium ( de ) intercalation-induced morphology changes in Li x CoO 2 micro-machined thin fi lm electrodes q », J. Power Sources, vol. 222, p. 417–425, 2013, doi: 10.1016/j.jpowsour.2012.09.017.[2] D. Cheng et al., « Freestanding LiPON: from Fundamental Study to Uniformly Dense Li Metal Deposition Under Zero External Pressure », arXiv.org, 8 août 2022. https://arxiv.org/abs/2208.04402v2.[3] J. Celè, S. Franger, Y. Lamy, et S. Oukassi, « Minimal Architecture Lithium Batteries: Toward High Energy Density Storage Solutions », Small Weinh. Bergstr. Ger., p. e2207657, janv. 2023, doi: 10.1002/smll.202207657. Figure 1

Numerical Investigation of Uplift Failure Mode and Capacity Estimation for Deep Helical Anchors in Sand

The uplift capacity of helical anchors is generally taken as the control condition for design in different applications, including transmission tower foundations and offshore structures. However, it is difficult to identify the failure surface for a deep helical anchor, which may result in an incorrect assessment of uplift capability. This research proposes a new unified method to estimate the uplift capacity of deep single-helix and multi-helix anchors based on the investigation of failure mechanisms. The deep failure mode was identified by FEM analysis using a modified Mohr–Coulomb model considering the strain softening of sand, along with the coupled Eulerian–Lagrangian technique. Thereby, a simplified rupture surface is proposed, and the equations estimating the uplift capacity are presented by the limit equilibrium method. Two important factors—the lateral earth pressure coefficient and the average internal friction angle included in the equations—are discussed and determined. The comparisons with centrifugal tests verify the reasonability of the proposed method.

In situ investigations of failure mechanisms of silica fibers from the venus flower basket (Euplectella Aspergillum).

The fibers of the deep-sea sponge Euplectella aspergillum exhibit exceptional mechanical properties due to their unique layered structure at a micrometer length scale. In the present study, we utilize a correlative approach comprising of in situ tensile testing inside a scanning electron microscope (SEM) and post-failure fractography to precisely understand mechanisms through which layered architecture of fibers fracture and improves damage tolerance in tensile loading condition. The real-time observation of fibers in the present study confirms for the first time that the failure starts from the surface of fibers and proceeds to the center through successive layers. The concentric layers surrounding the central core sacrifice themselves and protect the central core through various toughening mechanisms like crack deflection, crack arrest, interface debonding, and fiber pullout. STATEMENT OF SIGNIFICANCE: Biological materials often exhibit multiscale hierarchical structures that can be incorporated into the design of next generation of engineering materials. The fibers of deep-sea sponge E. aspergillum possess core-shell like layered architecture. Our in situ study reveals astounding strategies by which this architecture delays the fracture of the fiber. The core-shell architecture of these fibers behaves like fiber-reinforced ceramic matrix composite, where the outer shells act as a matrix and the central core acts as a fiber. The outer shells take the environmental brunt and scarify themselves to protect the central core. The precise understanding of damage evolution presented here will help to design architected materials for load-bearing applications.

A novel additive manufacturing compression overmolding process for hybrid metal polymer composite structures

Metal polymer composites combining low density, high strength composites with highly ductile and tough metals have gained traction over the last few decades as lightweight and high-performance materials for industrial applications. However, the mechanical properties are limited by the interfacial bonding strength between metals and polymers achieved through adhesives, welding, and surface treatment processes. In this paper, a novel manufacturing process combining additive manufacturing and compression molding to obtain hybrid metal polymer composites with enhanced mechanical properties is presented. Additive manufacturing enabled deposition of polymeric material with fibers in a predetermined pattern to form tailored charge or preform for compression molding. A grade 300 maraging steel triangular lattice is first fabricated using AddUp FormUp350 laser powder bed system and compression overmolded with additively manufactured long carbon fiber-reinforced polyamide-6,6 (40% wt. CF/PA66) preform. The fabricated hybrid metal polymer composites showed high stiffness and tensile strength. The stiffness and failure characteristics determined from the uniaxial tensile tests were correlated to a finite element model within 20% deviation. Fractographic analyses was performed using microscopy to investigate failure mechanisms of the hybrid structures.

Investigation of failure mechanism of aluminum-scandium wire bond contact under active power cycle test

The failure mechanism of aluminum-scandium (Al-Sc) wire bond in comparison with pure Al wire bond under active power cycle (APC) test was investigated. To monitor the degradation of the bond quality, bond shear forces (shear force) were measured over the testing cycles at different level of temperature swing (ΔT). The results show that the Al-Sc wire bond was much more robust than the pure Al wire bond when the ΔT (Tmax) was mild. On the other hand, as the ΔT was increased, the shear force reduction in the Al-Sc wire bond became more and more remarkable. In the cross-sectional analysis of bond contact after the APC tests, a significant crack propagation was observed even for low ΔT conditions for the pure Al wire, and the crack progressed primarily on the wire side of the bond area. As for the Al-Sc wire, while the bond crack was efficiently suppressed for low ΔT conditions, a significant progress of crack was observed at high ΔT conditions, and the crack grew mainly through the Al pad side of the bond area. A detailed analysis at the bond interface after the APC test at high ΔT condition revealed three phenomena at the Al pad side of the bond area: grain coarsening, precipitation of Cu particles, and large void formation. As the material strength is compromised by these effects, the crack grew more easily through the Al pad side of the contact area, resulting in a rapid reduction of shear force at high ΔT. The bond failure mechanism obtained in this study will provide a valuable insight for the future development of high reliability power semiconductor device.

Testing Reliability of Electronic Components and Converters Is Vital for Systems [From the Editor

<fig orientation="portrait" position="float" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <graphic orientation="portrait" position="float" xlink:href="bindra-3221629.tif"/> </fig> In modern energy production, storage, transmission, distribution, and consumption, power electronics has been playing a crucial role. Because power converters are critical links in electrical energy systems, impacting system security, safety, energy efficiency, and cost, the reliability of power electronic components and converter systems has become very important in these applications. In short, the reliability of energy systems is completely dependent on the reliability of electronic components and power converters. Consequently, testing is now considered a vital reliability engineering tool to investigate failure mechanisms, identify weakest points, and demonstrate robustness margins in components and converters. However, reliability testing is not simple and requires time, right amount of data, state-of-the-art testing facilities, and understanding of uncertainties of failure mechanism.

Application-Oriented Reliability Testing of Power Electronic Components and Converters

Power electronics have been and will continue to be an enabling technology for energy production, storage, transmission, distribution, and consumption. Power electronic converters are usually the critical links in electrical energy systems, affecting system security, safety, energy efficiency, and cost-of-ownership. As a result, the reliability requirements for power electronic components and converter systems generally become more stringent, for example, in e-mobility, renewable energy generation, and power system applications. Testing is one of the vital reliability engineering tools to investigate failure mechanisms, identify weakest points, and demonstrate robustness margins. It contributes to reliability growth along the product development process and the likelihood of failure reduction in field operation. The required resources (i.e., testing time, sample size, and testing facility) and the relevance of the testing results to field operation are two crucial considerations in implementing a reliability test. This article introduces the emerging application-oriented testing concepts and facilities through several component-level and converter-level examples.

Micromechanical behavior of jointed rock masses under uniaxial compression loading: a numerical study based on the discrete element method

The discrete element method is used to study the deformation process and failure mechanism of rock masses under uniaxial compression when the initial joint frequency increases. In this study, a systematic analysis is carried out to investigate failure mechanisms in rock masses with special emphasis on macroscopic deformation processes and the micromechanical origin. The influences of joints on strength, deformability, stress–strain relationship, and failure mode are studied at the macroscopic level. The tensile and shear crack distribution, fragment characteristics, and energy dissipation are also analyzed to advance the understanding of the deformation process and failure mechanism of jointed rock masses. The microevolution of fabric and forces anisotropy during loading and contact force distribution provide insights into the effect of increasing initial joint frequency on the macroscopic deformation behavior of rocks. The results reveal that with the increasing initial joint frequency, the specimen exhibits brittle-ductile characteristics, and the failure mode changes from splitting to sliding along the joint surfaces. They also show how the deceleration in the growth of fabric and contact forces anisotropy develops and confirm that the increase in initial joints and corresponding microstructural changes can suppress the development of anisotropy, thereby significantly reducing the strength of rock samples.

Investigation of Failure Mechanisms of 1200 V Rated Trench SiC MOSFETs Under Repetitive Avalanche Stress

In this article, the repetitive avalanche ruggedness of silicon carbide metal–oxide–semiconductor field-effect transistors (MOSFETs) with asymmetric trench (AT) and double trench (DT) structure is investigated experimentally. The different failure mechanisms, i.e., thermal-induced fatigue or field oxide breakdown for AT-MOSFET and electric field induced gate oxide degradation or breakdown for DT-MOSFET, are verified by device decapsulation and TCAD simulation. Different from the transient failure in single-pulse avalanche test, the degradation and failure under repetitive avalanche stress are related to the accumulation of gate oxide traps or thermal stress. Under high energy ratio condition, DT-MOSFET fails with shorted gate-drain terminal after only 2k unclamped inductive switching (UIS) cycles. Microscopic failure analysis shows an obvious crack through the bottom gate oxide to N-drift layer, whereas the electrical parameters of AT-MOSFET remain stable during 12k UIS cycles until gate leakage current of 10 mA exceeds the failure threshold of devices. The thermal-induced field oxide breakdown is found upon polysilicon gate in AT-MOSFET. Under low energy ratio condition, over 5% reduction of threshold voltage and <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -state resistance is observed in DT-MOSFET due to hot holes injection in gate oxide. However, the threshold voltage of AT-MOSFET is almost constant and an approximately 10% increase of <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -state resistance caused by thermal fatigue is observed.

Experimental Investigation of Failure Mechanisms of Granites with Prefabricated Cracks Induced by Cyclic-Impact Disturbances

Engineering rock mass is normally subject to cyclic–dynamic disturbances from excavation, blasting, drilling, and earthquakes. Natural fractures in rock masses can be reactivated and propagated under dynamic and static loadings, which affects the stability of rock mass engineering. However, fractured rock mass failure induced by cyclic-impact disturbances is far from clear, especially considering varying angles between the rock mass and the direction of impact loadings. This work investigated rock deformation and failure characteristics through cyclic impact tests on granite samples with cracks of different angles. A Hopkinson bar was employed for uniaxial cyclic impact tests on granite samples with the crack inclination angles of 0–90°. The magnetic resonance imaging technique was used to determine rocks’ porosity after cyclic impacts. The stress–strain curves, porosity, strength, deformation modulus, failure modes, and energy density of samples were obtained and discussed. Results showed that the crack inclination angles significantly affected the damage evolution and crack morphology of rocks. Under the constant cyclic impact, the dynamic deformation modulus and dynamic strength of rock samples first increased and then decreased with the increase in crack inclination angle. The failures of granite samples for inclination angles of 0 and 90° were dominated by tensile cracking, while those for the inclination angles of 30–60° were dominated by shear cracking. The energy density per unit time gradually decreased with the increase in impact cycles. The results can provide references for the stability analysis and cyclic-impact-induced failure prediction of fractured rock masses.

Decomposition of micromotion at the head-neck interface in total hip arthroplasty during walking

Fretting corrosion as one of the leading causes for failure of modular hip prostheses has been associated with micromotion at head-neck taper junction. Decomposition of micromotion is helpful to promote the development of more realistic experiments investigating failure mechanisms of the head-neck junction in total hip arthroplasty. The aim of this study was to decompose the complex three-dimensional micromotion at the head-neck junction into multiple fundamental modes, including three translational and three rotational components. A three-dimensional finite element model composed of head-neck junction, liner and acetabular cup with a typical 12/14 taper size, as well as the taper mismatch of −4', was developed during walking. The analysis was divided into three procedures: a) the assembly simulation of the head and neck during surgery, b) verification with a simplified axisymmetric model, and c) three-dimensional modelling under normal walking. This study revealed that the main forms of micromotion contained circumferential, longitudinal micromotion and longitudinal rolling toggling, and were closely related to the state of motion. The maximum translational micromotion was predicted to be 10.9 μm during the walking gait, with the predominant modes of the circumferential translation of 9.6 μm, the longitudinal translation of 5.5 μm and the longitudinal rotation of 0.29° along the taper junction. These findings may provide design considerations for further experimental testing about fretting and facilitate the understanding of the fretting mechanisms in hip prostheses.

Analysis of interpenetrating metal ceramic composite structures using an enhanced random sequential absorption microstructure generation algorithm

In this paper, we present the analysis of an interpenetrating metal ceramic composite structure. We introduce a new generation algorithm for the modeling of interpenetrating composite microstructures with connected, spherical cavities embedded into an open-porous foam structure. The method uses a geometric ansatz and is designed to create structures of special topology, as the investigated metal ceramic composite structures consisting of a connected AlSi10Mg phase showing spherical shapes embedded into an Al2O3 preform. Based on the introduced enhanced random sequential absorption approach, the generated microstructures yield numerical insights into the material that are not accessible by experimental techniques. The generated microstructures are compared to structures reconstructed from experimental CT scan data considering microstructural features and mechanical behavior. We show that the proposed method is able to generate statistically equivalent microstructures by using only a small number of statistical descriptors. The numerical formulation is validated using compression tests including plastic yielding in the aluminum and damage progression in the ceramic phase. Both the composite material and the pure ceramic preform are considered in this analysis, and good agreement is found between reconstructed and generated microstructures. Furthermore, the observations reveal the importance of the local geometrical sphere arrangement with respect to the mechanical behavior. A validation with experimental results is presented and it is shown that the model predicts microstructural properties and gives meaningful insights into the structural and material interplay. Finally, we discuss the potential of the method for the investigation of failure mechanisms.

Investigation of failure mechanism of cement-fiber-tailings matrix composites using digital image correlation and acoustic emission

In this study, the failure mechanisms of cement-fiber-tailings matrix composites (CFTMCs) in unconfined compression strength tests were investigated using the digital image correlation (DIC) and acoustic emission (AE) techniques. The results indicated that the addition of polyacrylonitrile fiber to the backfill could optimize the microstructure and thus improve the mechanical properties of the material. The fiber exerted a significant restraining effect on the expansion of internal fractures in the backfill. Using DIC, it was observed that the addition of fibers could eliminate the strain concentration regions in the material to a certain extent and reduce the transverse deformation of the main fracture. In addition, the AE characteristics of cement paste backfill (CPB) and CFTMC differed significantly; the AE cumulative count of CPB decreased significantly after the yield point, whereas that of CFTMC increased abruptly after the stress peak. Furthermore, the degree of fluctuation in the AE cumulative count of the samples increased with the decrease in the cement / tailings ratio, and the destruction area became more apparent as the tailings content inside the CPB decreased. These conclusions can serve as an important reference for stability research on goafs filled with CFTMC.

Ductile failure predictions using micromechanically-based computational models

Three different micromechanically-based computational models for fracture in porous ductile solids are compared and assessed. Model A is a unit cell model of a porous ductile solid comprising a uniform periodic distribution of voids subjected to normal macroscopic loading. Models B and C, on the other hand, are unit-cell type models that represent an imperfection band governed by a doubly periodic array of voids separating two non-porous outer blocks. The outer blocks have a finite size in Model B and are semi-infinite in Model C. The non-porous material surrounding the voids, and the material of the outer blocks in Model B and Model C, are considered as an elasto-plastic isotropic material. Numerical simulations are performed for a wide range of macroscopic stress states. For each model, various criteria for determining the onset of ductile failure are evaluated to demonstrate their impact on the failure predictions. The results show that the failure loci strongly depend on the computational model and failure criterion employed. Thus, these three models cannot be used interchangeably – neither to investigate failure mechanisms nor to develop or calibrate fracture models – and an unambiguous failure criterion must be chosen.

Failure mechanism of resistance spot-welded DP600 steel under high cycle fatigue

Dual phase (DP600) steel is one of the most predominately used advanced high strength steel in the vehicle manufacturing. Resistance spot welding is the most frequently used joining methods in automotive industry. The vehicle during its lifetime in service experiences fatigue loads because of rough roads, load excursions, harshness, and vibrations. The fatigue failure of the spot-welds mostly occurs at lesser than that of the static joint strength. This kind of failure is of serious concern as it will directly affect the overall crashworthiness of the vehicle. DP600 steel of thickness 1.4 mm were resistance spot-welded at a weld current of 8.5 kA, weld time of 225 ms, and electrode force of 3.8 kN in tensile-shear configuration. The microstructure and failure behaviour were examined by optical microscopy. The microhardness distribution in the welds was determined by microhardness tester. The tensile-shear tests and fatigue tests were carried on universal testing machine. The objective of present work is to investigate failure mechanisms of DP600 steel by high cycle fatigue tests. The major conclusions from the present work: The load carrying ability is 22 kN and energy absorbed is 36 J for the joint under tensile-shear loading. The fatigue crack initiation primarily occurs from heat affected zone (HAZ) or from the region close to fusion zone. In the next stage fatigue crack would propagate in through thickness and width direction to complete the final failure. The failure mechanism of spot-welds under fatigue loading is primarily governed by stress concentration at the interface of two conjugated sheets, stress intensity factor, and strength of the base metal.

ESD Stress Effect on Failure Mechanisms in GaN-on-Si Power Device

This paper reports investigation of failure mechanisms of GaN-on-Si power device under electrostatic discharge (ESD) stress using on-wafer transmission-line pulse (TLP) testing. Hot-hole injections under the gate and filament formation in the buffer layer are examined by monitoring the threshold voltage (Vth) and on-resistance (Ron) subjected to a floating gate or an off-state gate voltage. Distinct and continued degradation has been observed after the ESD stress is removed indicating a slow de-trapping process due to deep-level buffer traps. Finally, 2D device simulation is used to probe the physical insight into failure mechanisms.