Kinds Of Failure Modes Research Articles

Influence of a Dominant Fault on the Deformation and Failure Mode of Anti-dip Layered Rock Slopes

Toppling is a kind of failure mode that commonly exists in anti-dip rock slopes. Toppling deformation has a great influence on the stability of rock slopes, which often leads to geological disasters such as sliding and collapse of anti-dip slopes. However, a large number of faults and other structural planes will be produced in many rock slopes due to the action of geological structure movement. In the investigation, it is found that there are not only toppling deformation, but also faults and other geological structures in the toppling deformation rock slope. Previous studies have calculated the depth of toppling deformation, which is considered from the development characteristics of toppling deformation itself. In this paper, based on the field investigation of the anti-dip rock slope with bedding faults, the relationship between the depth of toppling deformation and the location of faults is analyzed by three-dimensional discrete element method. When the dominant structural plane and toppling fracture surface exist at the same time, the main factors affecting the failure of the reverse dip rock slope can be obtained by determining the different depths of the two planes. The final failure depth and failure mode of the toppling deformation in an anti-dip rock slope with a dominant structural plane can be preliminarily determined.

Data-driven model for predicting intermediate crack induced debonding of FRP-strengthened RC beams in flexure

There are a kinds of failure modes in flexurally strengthened RC beams using externally bonding FRP sheets. To evaluate the flexural strength of FRP-strengthened RC beam, the failure mode of the strengthened beam must be determined first. Intermediate crack (IC) induced debonding is the main failure mode in flexurally FRP-strengthened RC beams. In this study, a Back-Propagation Neural Network (BPNN) model is proposed to predict the intermediate crack (IC) induced debonding of FRP-strengthened RC beams. A database of 101 beams from different researchers are used to train and test the BPNN model. This model established in this study has eight inputs, including concrete strength, shear span ratio, tensile reinforcement ratio, the yield strength of reinforcement, stirrup reinforcement ratio, FRP stiffness, the ratio of sheet width to beam width, and the ratio of anchorage length to shear span, the output is FRP strain at the initial debonding, that is, the ultimate debonding strain of FRP reinforcements. The importance and sensitivity of the parameters are studied by the BPNN model and collected data. Based on the parametric study and Levenberg-Marquardt algorithm for nonlinear fitting, a design model is established for the prevention of IC debonding failure. The BPNN model and design model established in this study can accurately predicted the IC debonding of FRP-strengthened RC beams.

Stress-Strain Relationships of Fiber Reinforced Phosphogypsum under Uniaxial Compression

To investigate the stress-strain relationship of fiber reinforced phosphogypsum (PG) under uniaxial compression, a total of twenty-seven PG prism specimens were fabricated and tested. The influences of the content of admixture, content of fiber, and water-solid ratio on the stress-strain curve of the specimens were investigated. Three kinds of failure modes were summarized by observing the experimental phenomena; they were called “compaction failure,” “tension failure,” and “mixed stress failure,” respectively. Through in-depth analysis of the test data, it was found that decreasing the water-solid ratio can lead to increasing the peak stress and secant modulus of specimens; increasing the fiber content can lead to improving the mechanical property of PG mixture specimens. However, adjusting the contents of the cement and quicklime has no significant effect on the mechanical property of specimens. In addition, according to the test data and the characteristics of stress-strain curves, the stress-strain curve of PG specimens was divided into four parts, and a mathematical model was developed to predict the stress-strain curve of PG specimens. The validations of the model showed that the curves calculated by the proposed model were well in agreement with the test data of this study and previous studies.

Local buckling behaviour and capacities of Cold-Formed Steel Double-I-Box stub and short column sections

This paper presents an experimental and numerical investigation on the local buckling behaviour of a new built-up Cold-Formed Steel (CFS) homogeneous and hybrid Double-I-Box Column sections (DIBCs and HDIBCs) under axial compression. In total, 24 experimental tests are conducted, out of those 12 tests are on stub columns and the remaining 12 are on short columns. The parameters considered are hybrid ratio (Φh), section’s breadth to depth ratio (B/D) and column height (H). The columns considered in this study are having an overall slenderness (λ) less than 0.20, and the flange plate slenderness (λpf) less than 1.85. Test specimens failed in either of the following three failure modes: local buckling, yielding or by the interaction of both. In all the tested specimens, typical Bottom Zone Local Buckling (BZLB) similar to the shape of Elephant’s Foot is identified. The deformation shape is recognized by expansion (outward buckling) along the major axis and contraction (inward buckling) along the minor axis at the bottom 1/4th height of the columns in opposite faces, followed by the collapse. This kind of failure mode is a clear representation of Poisson’s ratio effect at the ends causing a restraint which then creates a local imperfection under load which leads to a localized failure at bottom zones in the stub and short columns of DIBCs and HDIBCs. BZLB phenomenon is enhanced because of the tubular cross-section geometry, boundary conditions plate element slenderness, overall slenderness of these built-up sections. The ultimate capacities of both the stub and short columns are governed by their strength limits and slenderness. Nonlinear Finite Element Analysis (FEA) is performed on experimental FE models using ABAQUS software and verified against the test results and validated with the actual structural behaviour. Further FEA is performed on 96 ideal parametric FE models considering different material properties and slenderness values. Effect of the intermediate longitudinal stiffener and the influence of edge constraints on axial strengths are also reported. The axial strengths obtained from the experimental tests and FE parametric studies are compared with the predicted results using the Effective Width Method (EWM) as suggested in the Eurocode specifications to access the feasibility of the current design rules, which is found to produce reasonable predictions albeit slightly conservative. It is found that for stub columns with λ<0.1, the experimental values are found to be 1.25 times higher than the predicted values. It is also observed that for columns having λ≥0.1<0.2 with λpf>1.2 there is a reduction in local buckling resistance of around 2.5% for each increase of λpf by 10%. Hence, it is concluded that the concentric axial compression capacities of DIBCs and HDIBCs subjected to local buckling can be computed as the arithmetic summation of effective strengths of individual channel sections calculated by using the EWM design equations, as recommended in this study. The attained results prove that these sections have a considerable local inelastic reserve strength as specified in North American standards.

Effects of the geometry and material properties on the mechanical strength and failure modes of water hydraulic artificial muscles

To develop high-strength water hydraulic artificial muscle (WHAM) and ensure its reliability, the failure mechanism and the main effect factors of WHAM’s strength were studied. WHAM’s failure modes consist of end fitting slipping out, fibre sleeve loosening, the end of rubber tube breaking, rubber tube coming out from fibre sleeve and fibre fracture. It can be preliminarily confirmed that the strength of WHAM is mainly related to fibre sleeve, rubber tube and end fitting structure. Therefore, effects of structure and material properties on WHAM’s strength and failure modes were analysed. The structure parameters contain the initial braid angle, the number of fibre bundles, the rubber tube wall thickness, the diameter of crimping rings, and the number of crimping rings. The fibre spacing was optimized according to the analysis of the ratio of fibre sleeve coverage area to rubber tube outer wall area. The number of end fitting’s barbs and the crimping rings were improved by strength test. Moreover, it can be confirmed that the initial braid angle, fibre sleeve material, rubber tube wall thickness and deformation of rubber tube have strong effects on WHAM’s strength. Aiming to obtain the level of significance for effect factors and an appropriate set of structure parameters, the orthogonal experiment with four factors and two levels was designed. The structure parameters of high-strength WHAM were obtained according to the orthogonal analysis, which can provide theoretical guidance for high-strength WHAM design. The tests results show that the improved structure can effectively avoid the failure modes of end fitting slipping out, fibre sleeve loosening, and rubber tube coming out from fibre sleeve. Finally, only two kinds of failure modes, the end of rubber tube breaking and fibre fracture, occurred. The reliability of WHAM can be improved by studying the WHAM’s strength and failure modes.

Fragmentation Characteristics of Rocks Under Indentation by a Single Polycrystalline Diamond Compact Cutter

Abstract Polycrystalline diamond compact (PDC) bit accounts for the most drilling footage in the development of deep and geothermal resources. The goal of this paper is to investigate the PDC cutter-rock interaction and reveal the rock fragmentation mechanism. A series of loading and unloading tests are conducted to obtain the curves of contact force versus penetration displacement. A single practical PDC cutter is fixed on the designed clamping devices that are mounted on the servo experiment system TAW-1000 in the tests. The craters morphology and quantified data were obtained by scanning the fragmented rock specimen using a three-dimensional morphology scanner. Finally, a numerical model is established to get the stress and deformation fields of the rock under a single PDC cutter. The results show that there are two kinds of failure modes, i.e., brittle failure and plastic failure, in the loading process. Marble is more prone to brittle fracture and has the lowest specific energy, followed by shale and granite. The brittle failure in marble mainly occurs behind the cutter while that happens ahead of the cutter for shale. Curves of contact force versus penetration displacement illustrate that a cutter with a back rake angle of 40 deg has a better penetration result than that with a back rake angle of 30 deg. Enhancing loading speed has a positive effect on brittle fragmentation. The distribution of von Mises stress indicates the initiation point and direction, which has a good agreement with the experiment. The research is of great significance for optimizing the PDC bit design and increasing the rate of penetration.

Influence of diameter thickness ratio of main tube on bearing capacity of steel tube tower joints

In order to study the influence of steel tube diameter thickness ratio on the bearing capacity of steel tube angle steel tower joint, the finite element model of tube plate joint was established, and the failure mode and bearing capacity of the joint under different steel tube diameter thickness ratios were studied, and the influence law of steel tube diameter thickness ratio on the bearing capacity of steel tube tower joint was obtained, and the relationship between steel tube diameter thickness ratio and steel tube tower joint bearing capacity was established through regression analysis in this paper. The results show that angel steel tube plate K-type joint has two kinds of failure mode, and in a certain range, the bearing capacity of the joints increases with the increase of the steel tube diameter thickness ratio, and decreases after reaching the maximum bearing capacity.

Impact damage resistance of Jute/Kevlar hybrid composite laminates subjected to varying heights: An experimental approach

This work shows the after effects of a trial examination concerning the low-velocity impact response of Jute/Kevlar fiber epoxy hybrid composite laminates. Trial tests were executed according to ASTM principles utilizing an instrumented falling weight impact testing machine. Impact tests were directed to portray the type and extent of the damages observed in laminate subjected to various impacting heights: 50 to 250 mm. The reaction of these laminates to drop-weight low velocity impact at energy levels ranging from 0.4 to 2.3 J was examined. At impact height of 250 mm, there is a calamitous failure of laminates. It was discovered that the laminates displayed two kinds of failure modes viz., crack initiation and perforation of the laminate.

Comparison and mechanism of electromigration reliability between Cu wire and Au wire bonding in molding state

Electromigration (EM) reliability and failure analysis of Cu wire and Au wire bonding processes on Al substrates after molding were investigated and compared systematically. According to the resistance as a function of EM time trend, there were four stages during the EM test for wire bonding that can tentatively be referred to as the fluctuating resistance stage, stable resistance stage, rapidly increasing resistance stage and quick failure stage of the sample. When the applied current was 1.8 A on a wire with a diameter of 20 μm (at a current density of 5.7 × 105 A/cm2), the lifetimes of the Cu wire and Au wire bonding processes were 1032 h and 119 h, respectively, according to Weibull analyses. Two kinds of failure modes were observed: wire fracture and first bond fracture. Almost 90% of the failed samples belonged to wire fracture category. After the EM test, the thickness of intermetallic compounds (IMCs) at the anode interface was similar to that at the cathode interface for both the Cu wire and Au wire bonding cases, which means that the normal polarity effect during electromigration did not occur here. However, the thickness of the IMCs at the Au/Al bonding interface was thicker than that at the Cu/Al interface for both the aged and EM samples. Voids and cracks were observed within the Au wire-bonding interface. It is suspected that the Cu wire bonding process had a slower thermal diffusion and smaller EM flux than those of the Au wire bonding process. Due to a decrease in vacancy flux within the Cu wire bonding region, the cracks were also suppressed, which greatly extended the lifetime of the Cu wire bonds.

Effects of pre-strain and annealing on the fatigue properties of complex phase steel CP800

This work was to experimentally explore the fatigue properties under the conditions of pre-strain and annealing for CP800. Meanwhile, the elongation of grains caused by pre-strain and the increase content of bainite and martensite caused by annealing were observed by using optical microscopy (OM) and scanning electron microscopy (SEM), respectively. An effective pre-strain range was found to increase the yield and tensile strengths by dislocation strengthening. Besides, the pre-strain presents a negative effect on fatigue life, while the fatigue life can be increased by annealing treatment. It is confirmed that the combined effect of the large pre-strain and annealing treatment leads to cyclic hardening fracture. Furthermore, two kinds of failure modes caused by surface defects and inclusions were revealed by using SEM. Eventually, the fatigue life can be well predicted with a model based on strain energy method.

Experimental and numerical study on mechanical and fracture behavior of rock-like specimens containing pre-existing holes flaws

Laboratory tests and numerical simulation are conducted to study mechanical behavior of rock containing two pre-existing holes in this paper. First of all, rock-like specimens containing two pre-existing holes were prepared to investigate mechanical and acoustic emission characteristics in the uniaxial compression. Different geometries were obtained by changing the angle of the center line of holes with respect to the direction of axial loading. Experimental results show that the stress-strain curves present obvious fluctuation, and evolution process of acoustic emission signal can be divided into four stages. There are three kinds of failure modes: only shear failure, mainly shear and auxiliary tensile failure, mainly tensile and auxiliary shear failure. Then, parallel bonded mode (PBM) based on the particle flow code in two dimensions (PFC2D) were established to study strength and failure modes in the biaxial compression. Finally, process of cracks initiation, propagation and coalescence, and fracture mechanism were further discussed. The most important conclusion reached is that the deformation and failure process of rock mass containing holes defects can be divided into two stages: rock bridge penetration and overall instability, which are sequential.

Dependent Competing Risks Modeling for Mechanical Systems Under Component and Performance Failure

This paper establishes a competing failure analysis model for complex mechanical system under component failure and performance failure considering degradation. Traditionally, mechanical system is composed by a number of components. Meanwhile, mechanical system has the ability to accomplish its specific performance. Therefore, mechanism may fail because of two kinds of failure modes, the component failure due to degradation (such as component wear) and the performance failure (system couldn't complete performance). The two failure modes compete with each other because as soon as one mode occurs the system just fails. The component will degrade with time as system operates as well as the system performance. In this paper, Brownian motion (BM) with nonlinear drift is used to model the degradation of components based on which component failure is analyzed. The function of performance measurement is built by surrogate and performance failure is analyzed by it at different working circulation. Farlie–Gumbel–Morgenstern (FGM) copula is introduced to describe the dependence. The system reliability is analyzed by FGM copula as well as competing failure probability for each failure mode. Finally, a numerical example and an engineering case study are used to illustrate the proposed model.

Low cycle fatigue and ratcheting failure behavior of AH32 steel under uniaxial cyclic loading

In this paper, the low cycle fatigue failure and ratcheting behavior, as well as their interaction of AH32 steel were experimentally investigated under uniaxial cyclic loading. The effects of mean stress, stress amplitude and stress ratio on the low cycle fatigue life and ratcheting strain were discussed. It was found that the ratcheting strain increased while the fatigue life decreased with the increase of mean stress and stress amplitude, and the increasing stress ratio would result in smaller ratcheting and larger fatigue life. Two kinds of failure modes, i.e. low cycle fatigue failure due to crack propagates and ratcheting failure due to large plastic strain will take place respectively. Based on the experimental results, considered the effect of ratcheting on fatigue life, a model with the maximum stress and ratcheting strain rate was proposed. Comparison with the experimental result showed that the new model provided a good prediction for AH32 steel.

Study on BEOL Failures in a Chip by Shear Tests of Copper Pillar Bumps

A chip with 40 nm technology node and beyond generally incorporates low-k/ultra-low-k (LK/ULK) dielectric materials and copper traces in the back end of line (BEOL) to improve its electrical performance. Owing to the fragile low-k/ultra-low-k materials, the BEOL becomes vulnerable to external loads. When a copper pillar bump (CPB) above the BEOL sustains a shear force due to thermal mismatch between the components, failures occur in the microstructures of BEOL, especially in low-k materials. We fabricated CPBs on the chips and investigated fractures in the BEOL by a shear test approach. The shear speed and shear height are varied to examine their effects. The tested samples were analyzed via focused ion beam (FIB) and scanning electron microscope (SEM) to reveal the microstructures degradation or breaks in the BEOL, and they are classified into three kinds of failure modes. Assisted by a finite element analysis (FEA), the failure mechanism was explained and associated with the failure modes. The studies showed that the shear speed has a little influence on the maximum shear stress, but the increase of shear height leads to more fractures in the low-k materials. It indicated that decreasing the height of CPBs is helpful for reducing destruction risk of the BEOL under the thermomechanical loads. Based on a parametric study for shearing test simulation of a single CPB, the modulus and thickness of polyimide (PI) were found a larger impact on the stresses in the low-k material layer, but the modulus of low-k materials has a smaller effect on the stress. Generally, the shear test of a CPB can help to evaluate the integrity of BEOL in a chip.

Bearing capacity of embedded channel-shaped steel connections at precast concrete beam end

Embedded channel-shaped steel (ECS) connection at precast concrete beam-end proposed in this paper is a kind of novel connection. To study the performance of ECS connection, experiments on 12 specimens were carried out. The embedded length of the ECS, the stirrup spacing, the cavity in the mid-span of the beam and the eccentricity of the ECS were taken into account. Two kinds of failure modes were observed: lever-out of ECS and crushing of the beam-end concrete. The experimental results indicate the following: (1) as the length of ECS increases, the bearing capacity of the ECS connection increases; (2) the stirrup densification could significantly improve the bearing and deformation capacity; (3) the mid-span cavity of the beam has limited influence on the bearing and deformation capacity of the connection; (4) the eccentricity of ECS could slightly reduce the bearing capacity owing to the additional torsion. Subsequently, finite element (FE) models were developed using ABAQUS and validated by the test results. The FE simulations show good agreement with the test results. Based on the verified FE models, a parametric study was conducted, considering different ECS properties including embedded length, section and eccentricity, various stirrup spacing at the beam-end, concrete grade and the distance between cavity and ECS. Finally, to prevent the lever-out of ECS, the optimum design of the ECS connection was proposed according to previous discussion.

Pressure–Impulse (P–I) Diagrams for Reinforced Concrete (RC) Structures: A Review

In recent years, many studies have been conducted by governmental and nongovernmental organizations across the world attempt to better understand the effect of blast loads on structures in order to better design against specific threats. Pressure–Impulse (P–I) diagram is an easiest method for describing a structure’s response to blast load. Therefore, this paper presents a comprehensive overview of P–I diagrams in RC structures under blast loads. The effects of different parameters on P–I diagram is performed. Three major methods to develop P–I diagram for various damage criterions are discussed in this research. Analytical methods are easy and simple to use but have limitations on the kinds of failure modes and unsuitable for complex geometries and irregular shape of pulse loads that they can capture. Experimental method is a good way to study the structure response to blast loads; however, it is require special and expensive instrumentation and also not possible in many cases due to the safety and environmental consideration. Despite numerical methods are capable of incorporating complex features of the material behaviour, geometry and boundary conditions. Hence, numerical method is suggested for developing P–I diagrams for new structural elements.

Experimental Investigation on the Mechanical Characteristics and Deformation Behaviour of Fractured Rock‐Like Material with One Single Fissure under the Conventional Triaxial Compression

An experimental study was carried out on a rock‐like material specimen containing a single fissure to investigate its mechanical characteristics and deformation behaviour under triaxial compression. The mechanical characteristics, such as peak strength and residual strength, are discussed. The confining pressure had a distinct effect on the ductility characteristics of the specimen. “A distinct stress drop” occurred in the early stage of the stress‐strain curve when the length fissure was relatively long. The I‐crack, II‐crack, and III‐crack are all observed under triaxial compression, and the III‐crack is commonly observed under triaxial compression. Confining pressure plays an essential role in affecting the failure mode of the specimen. There are three kinds of failure modes in the triaxial compression experiment on a rock‐like material specimen with one single fissure: tensile‐shear comprehensive failure, “X”‐shaped shear failure, and shear failure along the fissure plane. These results are important and fundamental to understand the fracture mechanism of rock engineering.

Parametric Study on Mixed Torsional Behavior of U‐Shaped Thin‐Walled RC Girders

Nowadays, U‐shaped thin‐walled concrete girders have been widely applied in the urban construction of rail viaducts in China as well as worldwide. However, the mixed torsional behaviors of these structures are not well understood. In this paper, the mixed torsional behaviors of the U‐shaped thin‐walled RC girders are theoretically analyzed, and a method predicting failure modes and ultimate torques is proposed. Nonlinear FE models based on ABAQUS to simulate the mixed torsional behaviors are built and calibrated with the test results. Parametric studies considering three crucial parameters (boundary condition, span length‐section height ratio, and ratio of longitudinal bars to stirrups) are conducted based on both the above suggested calculating method and the FE modeling. The calculated and the simulated results agree well with each other and with the test results. It is found that the failure modes of the U‐shaped thin‐walled RC girders under torsion are influenced by all the three parameters. Three kinds of failure modes are observed: flexural failures dominated by warping moment, shear failures caused by warping torque and circulatory torque, and flexural‐shear failures in the cases where flexural failure and shear failure appear almost at the same time.

Numerical Analysis for the Progressive Failure of Binary-Medium Interface under Shearing

Binary-medium specimens were fabricated using the particle flow code, and the shear strength, dilatancy, and failure behavior of the binary-medium specimens with different bond strength ratios (0.25, 0.5, 0.75, and 1.0) under different normal stresses were studied. Numerical results show that the bond strength ratio and normal stresses considerably influence the shear strengths of binary-medium interface. Shear strength increases as the bond strength ratio and normal stress increase. The dilation of interfaces with high bond strength ratios is more evident than those of interfaces with lower bond strength ratios, and the curves for the high bond strength ratio exhibit remarkable fluctuations during the residual stage. At increased normal stress and bond strength ratio, the peak dilation angle shows decreasing and increasing trends successively. In this study, the specimens exhibited three kinds of failure modes. In mode II, the sawtooth experienced shear failure, but some tensile cracks appeared on the interface of the binary-medium. In mode III, no sawtooth was cut off, indicating tensile failure on the interface. At a low bond strength ratio, damage or failure is mostly concentrated in the upper part of the model. Failure parts gradually transfer to the lower part of the model when the bond strength ratio and normal stress increase. Furthermore, evident tensile cracks occur on the interface. When the bond strength ratio reaches 1.0, the failure mode of the specimen gradually transforms from sheared-off failure to chip-off failure. The number of microcracks in the specimens indicates that the lower the bond strength ratio, the more severe the damage on the specimens.

Interfacial reaction and failure mechanism of Cu/Ni/SnAg1.8/Cu flip chip Cu pillar bump under thermoelectric stresses

Micro-interconnection copper pillar bumps are being widely used in the packaging areas of memory chip and high performance computer due to their high density, good conductivity and low noise. Studying the interfacial behavior of copper pillar bump is of great significance for understanding its failure mechanism and microstructure evolution in order to improve the reliability of flip chip package. The thermoelectric stress test, in-situ monitor, infrared thermography test, and microstructure analysis method are employed to study the interfacial reaction, life distribution, failure mechanism and their effect factors of Cu/Ni/SnAg1.8/Cu flip chip copper pillar interconnects under 9 groups of thermoelectric stresses including 2104-3104 A/cm2 and 100-150℃. Under thermoelectric stresses, the interfacial reaction of Cu pillar can be divided into three stages:Cu6Sn5 growth and Sn solder exhaustion; the Cu6Sn5 phase transformation, exhaustion and the Cu3Sn phase growth; voids formation and crack propagation. The rate of Cu6Sn5 phase transforming into Cu3Sn phase is positively correlated with the current density. There are four kinds of failure modes including Cu pad consumption, solder complete consumption and transformation into Cu3Sn, Ni plating layer erosion and strip voids. An obvious polar effect is observed during the dissolution of Cu pads on the substrate side and the Ni layer on the Cu pillar side. When Cu pad is located at the cathode, the direction of electron flow is the same as that of the heat flow, and it can accelerate the consumption of Cu pad and the growth of Cu3Sn. When Ni layer serves as the cathode, the electron flow can enhance the consumption of Ni layer. Under 150℃ and 2.5104 A/cm2, the local Ni barrier layer is eroded after 2.5 h, which results in the transformation of Cu pillar on the Ni side into (Cux, Niy)6Sn5 and Cu3Sn alloy. The life of Cu pillar interconnection complies well to the 2-parameter Weibull distribution with a shape parameter of 7.78, which is a typical characteristic of cumulative wear-out failure. The results show that the intermitallic growth behavior and failure mechanism at Cu pillar interconnects are significantly accelerated and changed under thermoelectric stresses compared with the scenario under the single high temperature stress.