Abrupt Failure Research Articles

Direct and reversal shear behaviors of three kinds of slip zone soil in the Northwest of China

To clarify the sliding mechanism of a landslide, the shear behavior characteristics of slip zone soil are always vital. In the Northwest of China, thousands of landslides generally develop in three main types of slip zone soil, i.e., Quaternary loess, weathered Mesozoic-Cenozoic mudstone, and weathered Mesozoic-Paleozoic phyllite. In the present study, the shear behavior characteristics of these three kinds of slip zone soil were investigated through direct shear tests and their implications for the sliding mechanisms of landslide were also discussed. It was found that, in general, an abrupt failure of loess landslide could be related to the strong strain-softening behavior of loess in the direct shear test, while the ductile shear behavior of weathered mudstone and phyllite coincided with the creep deformation of the corresponding landslides. The residual friction angle of slip zone soil varied with the soil type and its mineral composition, and the lowest residual friction angle about 11.5° could be found in weathered phyllite (SET) with graphite. Compared with the previous research, it is interesting to find that the residual friction angles of mudstone and phyllite in the present study accorded reasonably with the empirical correlations proposed by Wen et al. (2007) for weak rocks in the Three Gorges area, China.

Possibilities and safety of physiotherapy in patients with implanted cardiac devices

Widespread implantation of cardiac devices, i.e. cardiac pacemakers, cardioverter-defibrillators and cardiac resynchronisation devices improved patients survival. It has resulted in increase in number of ageing patients with cardiac devices who need physiotherapeutic treatment due to accompanied comorbidities. Hence the study of the interaction between functions of cardiac devices and physiotherapeutic treatment techniques is particularly relevant. The use and safety of physiotherapeutic treatment techniques producing electromagnetic field which in turn eventually cause harm of the cardiac devices are being discussed in present review article. The possible adverse effects of such interaction are abrupt failure to stimulate or triggering of shock therapy with consequent arrhythmic events including cardiac arrest. The technical characteristics particularly associated with electromagnetic interference are discussed here in detail. The attention is also payed to analysis of possible causes and effects of electromagnetic interference and safety measures as well.

Anatomical, Mechanical and Fractographic Characterization of Needle Punched Musa sapientum Cellulosic Fiber/UPE Composites

Abstract This study focuses on the evolution of a new biodegradable material sourced from agro-waste, and how it plays a vital role in replacing nonbiodegradable material. In the present work, new fibers were extracted from the pseudo stem of the Nendran variety of the banana plant. Initially, anatomical studies were carried out on raw fibers to investigate cellulosic and noncellulosic structures to prove its reinforcement potentiality. Later the cellulosic fibers were needle punched and reinforced with unsaturated polyester matrix (UPE) to fabricate a needle-punched banana fiber composite (NPBFC). Subsequently, 30 mm of chopped banana fiber and chopped glass fiber was reinforced randomly with the UPE to fabricate random banana fiber composites (RBFCs) and random glass fiber composites (RGFCs), respectively. Tensile, flexural, hardness, and impact tests were conducted on different fiber wt.% of NPBFC, RBFC, and RGFC to compute the mechanical properties. The results revealed superior mechanical properties at 40 wt.% fiber content. However, beyond 40 wt.% (i.e., 50 wt.%), abrupt failure due to inferior interfacial bonding between the composite constituents was noted. Furthermore, the increases in tensile, flexural, hardness, and impact strength of optimized NPBFC were 26.17, 24.73, 53.41, and 19.54 %, respectively, which are more supercilious than RBFC and comparable with RGFC. Moreover, the thermal stability of optimized NPBFC was evidenced up to 260°C. Finally, field emission scanning electron microscopy observation inferred that the interfacial bonding failure in NPBFC is less significant than the RBFC and RGFC. This study concludes that the synthesized NPBFC can be used for the application of lightweight structural components.

Adenylate kinase AK2 isoform integral in embryo and adult heart homeostasis

Adenylate kinase2 (AK2) catalyzes trans-compartmental nucleotide exchange, but the functional implications of this mitochondrial intermembrane isoform is only partially understood. Here, transgenic AK2−/− null homozygosity was lethal early in embryo, indicating a mandatory role for intact AK2 in utero development. In the adult, conditional organ-specific ablation of AK2 precipitated abrupt heart failure with Krebs cycle and glycolytic metabolite buildup, suggesting a vital contribution to energy demanding cardiac performance. Depressed pump function recovered to pre-deletion levels overtime, suggestive of an adaptive response. Compensatory upregulation of phosphotransferase AK1, AK3, AK4 isozymes, creatine kinase isoforms, and hexokinase, along with remodeling of cell cycle/growth genes and mitochondrial ultrastructure supported organ rescue. Taken together, the requirement of AK2 in early embryonic stages, and the immediate collapse of heart performance in the AK2-deficient postnatal state underscore a primordial function of the AK2 isoform. Unsalvageable in embryo, loss of AK2 in the adult heart was recoverable, underscoring an AK2-integrated bioenergetics system with innate plasticity to maintain homeostasis on demand.

Improving the Mechanical Performance of Shell Precast Concrete Blocks for Coastal Protection Structures of Hydraulic Works

Although the use of concrete and reinforced concrete for construction has been widespread, more studies are needed on marine structures exposed directly to corrosive environments to prolong their service life. This paper proposes a new type of shell precast concrete block for coastal structures, studying a beam consisting of 15mm High-Performance Glass Fiber-Reinforced Concrete (HPGFRC) at the bottom and 45mm Traditional Concrete (TC) for the rest of the structure. Steel bar reinforcements were placed at the bottom with a concrete cover of 25mm to avoid abrupt failure. The strength classes of HPGFRC and TC were 60MPa and 30MPa respectively. A reference beam consisting of TC only was also prepared for comparison. The four-point flexural bending test results showed that the first cracking strength of the proposed beam was 20% higher, as HPGFRC performed better on tension than TC. Additionally, HPGFRC's maximum strength was 25% greater than TC's. Furthermore, HPGFRC possessed more durable characteristics such as waterproof grade, abrasion resistance, and shrinkage than TC, promising to protect the reinforcement from the aggressive marine environment and corrosion, prolonging the service life of the structure.

Fracture and failure behavior of additive manufactured Ti6Al4V lattice structures under compressive load

The additive manufacturing technology can be used to manufacture the complex lattice structures that are difficult to be fabricated by the traditional manufacturing technologies. In order to study the fracture and failure behavior of Ti6Al4V lattice structures manufactured by selective laser melting under compressive load, the cell topologies of face centered cubic with vertical struts (FCCZ) and body centered cubic with vertical struts (BCCZ) were chosen. The bulk material samples and four kinds of FCCZ and BCCZ lattice samples were designed and manufactured. The compression tests were performed and progressive failure modes were studied and compared. And stress–strain curves, the compressive strength, the effective elastic modulus, and the specific compressive strength were calculated and compared. It is shown that the compressive strength of FCCZ samples is about 30% higher than that of BCCZ samples. Both 30 mm and 50 mm FCCZ samples exhibit abrupt shear failure, while the local buckling of lattice cells is the major failure mode for both 30 mm and 50 mm high BCCZ samples. Finite element analysis was conducted to study progressive damage of the lattice samples, and the numerical results can explain the experimental findings.

A Buffalo on the Banks of the Mzimvubu: The Zulu Invasions of Mpondoland, 1824 and 1828

The conventional wisdom concerning Shaka’s invasions of Mpondoland in 1824 and 1828 tends to dismiss these as cattle raids. It likewise dismisses the alignment between the 1828 invasion and Shaka’s embassy to King George of Britain as nothing more than an unfortunate coincidence. Drawing in part on hitherto ignored isiXhosa-language sources, this article seeks to explain Shaka’s invasion of 1828, partly in terms of his long-contemplated revenge for the failed invasion of 1824, and partly as a means to subjugate every African kingdom between himself and the Cape Colony, so that there might be only two kings in the world: King George, the king of the whites, and himself, Shaka, the king of the blacks. Only the abrupt failure of his diplomatic initiatives can explain Shaka’s adverse reaction to the generally successful campaign of 1828 triggering, as it did, the near-insane and utterly disastrous northern campaign against Soshangane which directly provoked his assassination. Fully sensitive to the dangers of a ‘great man’ interpretation of history, the article attempts to differentiate, in Lefebvre’s terms, between the ‘temperament’ of Shaka and the ‘inner necessity’ driving the evolution of the Zulu state.

Bernoulli vacation model for MX/G/1 unreliable server retrial queue with bernoulli feedback, balking and optional service

The study of unreliable server retrial bulk queue with multiphase optional service is analyzed by incorporating the features of balking, Bernoulli vacation and Bernoulli feedback. On the occasion when the server is occupied with the service of the customers, an arriving customer finding the long queue, can join the retrial orbit and receives its service later on by making re-attempt. The system is reinforced with multi phase optional service along with essential service and joining customer can opt any one of optional services after getting essential service. Furthermore, the essential/optional service can be aborted due to abrupt failure of the server. There is an immediate support of multi phase repair facility to take care of the failed server, but sometimes repair may be put on hold by virtue of any unexpected cause. If the service is unsatisfactory, the customer can rejoin the queue as feedback customer. Bernoulli vacation is permitted to the server following the respective busy period. For evaluating the queue size distribution and other system performance metrics, supplementary variable technique (SVT) is used. The approximate solutions for the steady state probabilities and waiting time are suggested using maximum entropy principle (MEP). We perform a comparative study of the exact waiting time obtained by the supplementary variable technique and the approximate waiting time derived by using maximum entropy principle by taking the numerical illustration. Quasi Newton method is used to find optimal cost. To verify the outcomes of the model, numerical illustrations and senstivity analysis have been accomplished.

Ground Subsidence Hazards due to Crushing and Removing Large Isolated Boulder by Tunneling

AbstractTo date, cases of severe ground subsidence or abrupt cave-in failure of roadway without warning after crushing and removing boulders in the sand matrix by tunneling have been frequently rep...

Harmonizing mechanical responses of nanostructured CrN coatings via Ni additions

CrN coatings are often brittle and prone to abrupt failure. Incorporation of Ni is known to have significant effects on the chemical composition, microstructure and mechanical behaviour of chromium nitride coatings synthesised by PVD, and thus imparting toughness. In this study, a series of NiCrN coatings, with varying Ni concentrations, were deposited onto AISI M2 tool steel substrates through closed-field unbalanced magnetron sputtering ion plating (CFUMSIP). The phase compositions, microstructure, mechanical properties and deformation behaviour of the coatings were characterised by XRD, AFM, FIB, TEM/EDS and indentation testing. Residual stresses of these as-prepared coatings were measured by the XRD-sin2ψ method. A columnar structure was observed in all coatings, although grain refinement at higher NiCr target currents was noted. High hardness values of ~20 GPa were found in the coatings with the lower Ni (~5–14 at%) contents, associated with the effects of solid solution hardening, high compressive residual stress and grain refinement. Moreover, significant damage-tolerance, coupled with good hardness values (greater than ~12 GPa), was found in the NiCrN coatings deposited at INiCr ≥ 2 A. The presence of a metallic nickel-rich phase, together with nanoscale porosity, may contribute to stress dissipation and help maintain structural integrity.

Application of interval type-2 fuzzy logic systems to gas turbine fault diagnosis

Several approaches have been employed for gas turbine Fault Detection and Identification (FDI), since a reliable FDI system with minimum false alarm rate can effectively reduce maintenance cost and downtime. This paper introduces the application of Interval Type-2 Fuzzy Logic Systems (IT2FLSs) to gas turbine fault diagnosis for the first time. The proposed FDI system is composed of a bank of IT2FLSs, trained for state detection and health assessment of an industrial gas turbine at various operating conditions. For this purpose, train and test data are generated by applying mechanical fault signatures to gas turbine’s mathematical model. Fuzzy Rule Base is then developed by means of Interval Type-2 Fuzzy C-Means (IT2FCM) clustering, and parameters of the IT2FLSs are optimized using a metaheuristic algorithm. Finally, the performance of the IT2FL based FDI system is compared to several classification techniques. It is concluded that as a compromise among the objectives of online applicability, accuracy, reliability against measurement uncertainty, incipient fault diagnosis, robustness against abrupt sensor failure and generalization capacity, the proposed method demonstrates a promising performance.

Design and optimization of Metallic Foam Shell protective device against flying ballast impact damage in railway axles

Ballast impacts can initiate surface defects that cause abrupt failure of the axle and derailment of the railway vehicle. According to the Federal Railroad Administration the axle and bearing failure costs around 89 million dollars and causes 46 derailments in the US per year (2005–2010). In this study, the authors have suggested a novel protective mechanism (Metallic Foam Shell – MFS) by using a lightweight sandwich panel. At the first step, a preliminary study is conducted, followed up by the numerical simulations to determine the applicable materials. At the next step, experimental tests were performed to assess the efficiency of the suggested device against flying ballast impacts. An extended non-destructive (NDT) evaluation has been performed in order to find the most suitable technique for damage detection of the proposed device when on-service. The studied cases were GFRP and Aluminium sandwich panels, having an aluminium foam core with different densities and thicknesses. The results showed that the MFS can absorb up to 90% of the initial impact energy and significantly decrease the chance of rebounding impact to the other components. Moreover, the results were also analysed in order to propose the most reliable NDT method for this specific application.

Monitoring of friction-related failures using diffusion maps of acoustic time series

Friction-related failures are a frequent cause of catastrophic damage in mechanical systems, resulting in significant repair expenses and/or production delays in industry worldwide. Scuffing is one of the most concerning friction-related failures mechanisms. It is characterized by an abrupt failure mechanism, which makes its prediction unresolved today. Therefore, any in situ and real-time monitoring system of such failures is of great demand and this contribution is supplement to and enrichment of existing studies on this topic. We propose a probabilistic analysis of acoustic signals synchronously recorded with the coefficient of friction during real-life experiments. They, simulate a specific industrial operating condition of a cam, cylinder pairs and gear teeth. The experimental conditions are a reciprocating movement of a stainless steel cylinder (counter-body) against a grey cast iron body. The counter-body was under a constant load and had a line contact with the body. The acoustic signals from one-directional strokes are selected and substituted by their wavelet spectrograms. Then, diffusion maps are computed over several spectrograms. Their corresponding Fourier spectra are used as features of the surface state and so of the upcoming failures. The real surface state and damage were identified from the dynamical behavior of the coefficient of friction. Based on our approach, it was found that the friction behavior can be divided into four confidence intervals, three for the steady-state regime and one for the scuffing regime. The transients between the confidence intervals allow estimating the proximity of scuffing and this is the major achievement of this work. The first transient took place between 5 min 40 s. – 47 min 30 s. prior to scuffing. The second one took place between 50 s. and 13 min 40 s. The proposed in situ and real-time monitoring system has significant industrial potential since it is built as a client – server architecture and requires minimum modifications of existing commercial industrial machines.

Exact analysis of mode-III cohesive fracture in layered elastic composites

This paper examines the mechanics of mode-III defect initiation and quasi-static growth in a composite consisting of N layers separated by nonuniform nonlinear cohesive surfaces. The exact analysis is based on the elasticity solution to the problem of a single layer of finite width and thickness subjected to arbitrary, nonuniform but equilibrated shear tractions on top and bottom surfaces. The formulation leads to a system of integral equations governing rigid body layer translations and cohesive surface slip fields (tangential jump discontinuities across layer interfaces). Cohesive surfaces are modelled by traction-slip relations (exponential, modified exponential) characterized by a cohesive strength, a force length and possibly friction parameters. Symmetric center, edge and array defects are modeled by cohesive strength functions that vary with surface coordinate. Infinitesimal strain equilibrium solutions are sought by eigenfunction approximation of the solution of the governing integral equations. Solutions indicate that quasi-static defect initiation/propagation occur under increasing applied shear traction. For small values of force length, brittle behavior occurs corresponding to sharp crack growth. At larger values of force length, ductile response occurs similar to linear “spring” cohesive surfaces. Both behaviors ultimately cause abrupt failure of the surface. Results for the stiff, strong cohesive surface with a center defect under a small applied traction agree well with static crack solutions taken from the literature. Detailed results are obtained for (i) an array of symmetric collinear defects accounting for defect–defect interaction, (ii) a symmetric defect in a bilayer with nonuniform material properties/thicknesses, (iii) a center defect accounting for decohesion and friction.

Failure analysis and modernization of high-pressure hydraulic press for drilling tubes testing

This research paper represents the results of abrupt failure investigation in the structure of industrial plant for hydrostatic pressure testing of tubes. The significant damages of testing machine elements are observed after the moving tube impact when the opposite tube end cap has been suddenly released because of the screw-thread defect. The water pressure inside the tube at the time of the incident was only 20 MPa while the maximal pressure of 125 MPa is required by tubes tests specification. Therefore, based on admitted assumptions, the detailed analysis is conducted of static and dynamic forces acting on elements of structure to avoid full machine destruction in case of the next incidents under higher pressures. Conditions are determined of the sharp cap end penetration into thrust plate and possible damage of upper protection casing from the water jet and tube pieces impacts under conditions of the crack opening in the tested tube. The two options are proposed of plant modernization to reinforce structure for safety work under pressure from 70 MPa to 125 MPa depending on tube size and testing conditions. The developed improvements of machine structure allow simultaneously increasing the productivity of testing plant up to 14–20 tubes per hour depending on their sizes.

Catastrophic Failure: How and When? Insights From 4‐D In Situ X‐ray Microtomography

AbstractCatastrophic failure of brittle rocks is important in managing risk associated with system‐sized material failure. Such failure is caused by nucleation, growth, and coalescence of microcracks that spontaneously self‐organize along localized damage zones under compressive stress. Here we present X‐ray microtomography observations that elucidate the in situ micron‐scale processes, obtained from novel tri‐axial compression experiments conducted in a synchrotron. We examine the effect of microstructural heterogeneity in the starting material (Ailsa Craig microgranite; known for being virtually crack‐free) on crack network evolution and localization. To control for heterogeneity, we introduced a random nanoscale crack network into one sample by thermal stressing, leaving a second sample as‐received. By assessing the time‐dependent statistics of crack size and spatial distribution, we test the hypothesis that the degree of starting heterogeneity influences the order and predictability of the phase transition between intact and failed states. We show that this is indeed the case at the system‐scale. The initially more heterogeneous (heat‐treated) sample showed clear evidence for a second‐order transition: inverse power law acceleration in correlation length with a well‐defined singularity near failure and distinct changes in the scaling exponents. The more homogeneous (untreated) sample showed evidence for a first‐order transition: exponential increase in correlation length associated with distributed damage and unstable crack nucleation ahead of abrupt failure. In both cases, anisotropy in the initial porosity dictated the fault orientation, and system‐sized failure occurred when the correlation length approached the grain size. These results have significant implications for the predictability of catastrophic failure in different materials.

Effects of fabric architectures on mechanical and damage behaviors in carbon/epoxy woven composites under multiaxial stress states

The mechanical properties and damage evolutions of carbon/epoxy woven fabric composites with three different fabric architectures, including one plain weave and two twill weave patterns, are experimentally investigated under multiaxial stress states. In particular, the effects of weave patterns are investigated by monotonic and cyclic off-axis tension tests. Both elastic modulus and strength degrade remarkably with increasing off-axis loading angle, while Poisson's ratio is much higher than that measured from on-axis tests and increases with loading strain gradually. Different fabric architectures show limited effects on the modulus and strength under multiaxial stress states, and they are well predicted by transformation equation and Tsai-Wu failure criteria, respectively. However, significantly different failure behaviors are observed in three fabric composites, and microstructure observation shows that fabric architecture affects the stress concentration and the damage development. Smaller crimp ratio and compacted structure postpone the damage development but result in more abrupt failure under multiaxial stress states.

Investigating fatigue failure of core motion mechanism for a small oil-free wobble-plate compressor

Abstract The study is driven by a recent experimental test for a small-size high-speed oil-free wobble-plate compressor, in which abrupt local fatigue failure of the wobble plate is encountered. To explore the causes, a fatigue prediction method is proposed, which involves the dynamic force calculation, stress prediction, and fatigue analysis. The dynamic forces is obtained by solving the coupled dynamic, thermodynamic and kinematic models. The dynamic stress with thermal effect is predicted, where the temperature field is calculated by solving the thermal conduction equation with the experimentally measured solid-surface temperature acting as boundary conditions, and the obtained temperature distribution is incorporated into the FEM (finite element method) prediction for thermal-dynamic stress. It is found that intensive friction heating causes the wobble plate significant local temperature rise and it is largely responsible for the structural failure. The Goodman mean stress correction method and wobble plate material S–N (Stress amplitude versus cycle Number) curves are incorporated to predict the fatigue life of wobble plate. The predicted fatigue life is comparable to the experimentally measured, which has verified the developed method. The wobble plates of 7075-T6 aluminum alloy and H62 brass alloy are compared, and the former produces a smaller dynamic stress for its smaller elasticity modulus and larger specific heat but a shorter fatigue life due to its S–N curve smaller stress amplitude.

Feature Selection for Improving Failure Detection in Hard Disk Drives Using a Genetic Algorithm and Significance Scores

Hard disk drives (HDD) are used for data storage in personal computing platforms as well as commercial datacenters. An abrupt failure of these devices may result in an irreversible loss of critical data. Most HDD use self-monitoring, analysis, and reporting technology (SMART), and record different performance parameters to assess their own health. However, not all SMART attributes are effective at detecting a failing HDD. In this paper, a two-tier approach is presented to select the most effective precursors for a failing HDD. In the first tier, a genetic algorithm (GA) is used to select a subset of SMART attributes that lead to easily distinguishable and well clustered feature vectors in the selected subset. The GA finds the optimal feature subset by evaluating only combinations of SMART attributes, while ignoring their individual fitness. A second tier is proposed to filter the features selected using the GA by evaluating each feature independently, using a significance score that measures the statistical contribution of a feature towards disk failures. The resultant subset of selected SMART attributes is used to train a generative classifier, the naïve Bayes classifier. The proposed method is tested on a SMART dataset from a commercial datacenter, and the results are compared with state-of-the-art methods, indicating that the proposed method has a better failure detection rate and a reasonable false alarm rate. It uses fewer SMART attributes, which reduces the required training time for the classifier and does not require tuning any parameters or thresholds.

Modeling ageing effects for multi-state systems with multiple components subject to competing and dependent failure processes

This paper explores how the ageing process affects the two dependent and competing failure processes in the context of multi-state systems with multiple components. Ageing process is assumed to result in the decline of the product's intrinsic capacity to resist the exposed stresses. The state residence time is explicitly modeled with the consideration of the potential transition gap (the total number of states that the state transition process needs to stride across) and the cumulative ageing probability which is a measure of the likelihood that the product strength degrades. The random shock is assumed to cause abrupt changes in the one-step transition probabilities. The damage size is jointly determined by the shock magnitude and the cumulative ageing probability. Reliability analysis is conducted based on the continuous-time semi-Markov chain. Reliability functions for the degradation, abrupt failure, and competing failure processes are obtained respectively. An illustrative example of a multi-state transformer with four multi-state components is studied to demonstrate how the proposed method can be applied to the engineering practice.