Cause Of Mechanical Failure Research Articles

3D mesoscale modelling of recycled aggregate concrete

Mesoscale modelling is a promising tool to analyse the phenomenological causes of mechanical failure of recycled aggregate concrete (RAC). Most mesoscale models of RAC are two-dimensional (2D) and 3D models are lacking. This prevents the full understanding of the behaviour of each mesoscopic phase. This paper presents a 3D model of RAC and analyses its mechanical behaviour based on mesoscale phenomena. The analyses concern three types of tests carried out in concrete specimens: uniaxial compressive, uniaxial tensile and splitting tensile strength tests. The mechanical response and fracture behaviour of each mesoscopic phase is analysed in relation to the response of RAC specimen. The comparisons between uniaxial behaviour of 3D and 2D modelling as well as between uniaxial and splitting tensile behaviour of RAC are presented. The main findings of the paper are: (1) the full curve of uniaxial stress-strain response from 3D modelling is comparable to that from 2D modelling for RAC (therefore, 2D models are validated for RAC modelling); (2) the overall behaviour of the concrete elements remains elastic regardless of the fracture development in the ITZ and attached mortar of recycled aggregates until damage propagates to the new mortar matrix; (3) a relationship between modelled uniaxial and splitting strength of RAC is established and validated.

Bayesian calibration of a non linear damage model of steel structures with random material property: Sensitivity analysis and reliability assessment

For steel structures exposed to environmental loading, Polycyclic fatigue is one of the main causes of mechanical failure. Since a linear damage accumulation does not take into account the loading history, the formulation of a nonlinear accumulation seems to be a particularly suitable approach for minimizing control and maintenance. A deterministic model that takes into account the loading history is therefore chosen and a strategy is proposed to introduce material randomness by Bayesian calibration of the model parameters from random SN-curves. This model is then applied to the case of a tee joint loaded in fatigue for three different loads with random material parameters. On this example, the linear accumulation of damage underestimates the probability of failure compared to the non linear accumulation.

Advances in Methodology for Fatigue Assessment of Composite Steel–Concrete Highway Bridges Based on the Vehicle–Bridge Dynamic Interaction and Pavement Deterioration Model

Fatigue cracking is one of the most prominent causes of mechanical failure limiting the service life of existing steel and composite steel–concrete bridges and is among the central concerns of structural and bridge engineers. In this context, the current work presents some recent advancements in an existing methodology for fatigue analysis developed by the authors throughout the years. The methodology is specifically devoted to the fatigue assessment of composite steel–concrete bridges employing the local hot-spot S-N approach and a coupled vehicle–pavement–bridge system considering progressive pavement deterioration with stochastically generated roughness profiles. Two different methodologies were used to solve the dynamic equilibrium equations: the modal superposition method to solve the bridge dynamic equations and a direct integration method to solve the vehicle dynamic equations. From a computational point of view, the present approach is more efficient and detailed than previous versions, as it allows a significant reduction in the analysis time and the use of complex bridge and vehicle finite element models. In this regard, a case study of a highway composite steel–concrete bridge spanning 40 m was selected in order to demonstrate the usefulness of the presented improved methodology by carrying out a fatigue analysis. The results of this investigation (displacements and stresses) are presented, aiming to verify the factors that directly influence the structural response and, consequently, the service life of steel–concrete composite highway bridges.

A review on application and optimization processes used for wear testing machine (pin on disc apparatus)

This paper explored the techniques that may be employed to perform a wear test utilising a pin on disc apparatus, of the wear testing machine. The apparatus comprises of a horizontal spinning disc with a calibrated dead weight pin kept on it. The goal of this work is to evaluate the investigations conducted by researchers on various materials. As wear is a leading cause of mechanical failure, the author(s) computed wear characteristics and then performed investigations on different pin on disc equipment. Wear optimization has been done by using analytical tools such as ANSYS and ABAQUS. This investigation yields favourable findings in terms of machine operation and durability.

Characterization of edge damage induced on REBCO superconducting tape by mechanical slitting

Rare-earth barium-copper-oxide (REBCO) superconductors are high-field superconductors fabricated in a tape geometry that can be utilized in magnet applications well in excess of 20 T. Due to the multilayer architecture of the tape, delamination is one cause of mechanical failure in REBCO tapes. During a mechanical slitting step in the manufacturing process, edge cracks can be introduced into the tape. These cracks are thought to be potential initiation sites for crack propagation in the tapes when subjected to stresses in the fabrication and operation of magnet systems. We sought to understand which layers were the mechanically weakest by locating the crack initiation layer and identifying the geometrical conditions of the slitter that promoted or suppressed crack formation. The described cracking was investigated by selectively etching and characterizing each layer with scanning electron microscopy, laser confocal microscopy, and digital image analysis. Our analysis showed that the average crack lengths in the REBCO, LaMnO3 (LMO) and Al2O3 layers were 34 μm, 28 μm, and 15 μm, respectively. The total number of cracks measured in 30 mm of wire length was between 3000 and 5700 depending on the layer and their crack densities were 102 cracks mm−1 for REBCO, 108 cracks mm−1 for LMO, and 183 cracks mm−1 for Al2O3. These results indicated that there are separate crack initiation mechanisms for the REBCO and the LMO layers, as detailed in the paper. With a better understanding of the crack growth behavior exhibited by REBCO tapes, the fabrication process can be improved to provide a more mechanically stable and cost-effective superconductor.

Investigation of ventriculoperitoneal shunt disconnection for hydrocephalus treatment.

This investigation is aimed at gaining a better understanding of the factors that lead to mechanical failure of shunts used for the treatment of hydrocephalus, including shunt catheter-valve disconnection and shunt catheter fracture. To determine the root cause of mechanical failure, the authors created a benchtop mechanical model to mimic mechanical stressors on a shunt system. To test shunt fracture, cyclical loading on the catheter-valve connection site was tested with the shunt catheter held perpendicular to the valve. Standard methods were used to secure the catheter and valves with Nurolon. These commercial systems were compared to integrated catheters and valves (manufactured as one unit). To test complete separation/disconnection of the shunt catheter and valve, a parallel displacement test was conducted using both Nurolon and silk sutures. Finally, the stiffness of the catheters was assessed. All mechanical investigations were conducted on shunts from two major shunt companies, assigned as either company A or company B. Cyclical loading experiments found that shunts from company B fractured after a mean of 4936 ± 1725 cycles (95% CI 2990-6890 cycles), while those of company A had not failed after 8000 cycles. The study of parallel displacement indicated complete disconnection of company B's shunt catheter-valve combination using Nurolon sutures after being stretched an average 32 ± 5.68 mm (95% CI 25.6-38.4 mm), whereas company A's did not separate using either silk or Nurolon sutures. During the stiffness experiments, the catheters of company B had statistically significantly higher stiffness of 13.23 ± 0.15 N compared to those of company A, with 6.16 ± 0.29 N (p < 0.001). Mechanical shunt failure from shunt catheter-valve disconnection or fracture is a significant cause of shunt failure. This study demonstrates, for the first time, a correlation between shunt catheters that are less mechanically stiff and those that are less likely to disconnect from the valve when outstretched and are also less likely to tear when held at an angle from the valve outlet. The authors propose an intervention to the standard of care wherein less stiff catheters are trialed to reduce disconnection.

Chemical bonding, thermodynamic stability and mechanical strength of Ni3Ti/α-Al2O3 interfaces by first-principles study

We performed a first-principles calculation to investigate the 85 different Ni3Ti/Al2O3 interfaces. The study shows that the formation of metal-oxygen interfaces and high symmetric interfacial stacking sequences is highly favored both by work of adhesion and interfacial energy. At high temperature and O-poor condition, the metal-metal interfaces show higher thermodynamic stability than metal-oxygen interfaces. The first principles tensile test predicts that the main cause of mechanical failure in Ni3Ti/Al2O3 interface is attributed to the breaking of the Ti-Ni bonds proximity to the interface in the bulk Ni3Ti phase.

Mechanical complications of shunt for hydrocephalus

Introduction: Hydrocephalus is the pathology most frequently addressed and studied in pediatric neurosurgery. Over 15,000 new cases are diagnosed each year. Although it is the most com-mon procedure performed by pediatric neurosurgeons, the shunt implant for drainage of cerebrospinal fluid (CSF) also presents the highest rate of failure and replenishment. The last 50 years have been marked by important advances in quality of these implants. How-ever, little has changed regarding the prevalence of these failures. We will comment here the main mechanical failures of the shunt: disconnection, migration, fracture and scrap-ing of the catheter, hollow visceral perforation and distal catheter knot. Methods: Literature review about the main causes of mechanical failure in shunts Conclusion: Shunt dysfunction is still very common, despite technological advances in the treatment of hydrocephalus. Mechanical causes of shunt dysfunction correspond to about 30% of the reasons for changing or overhauling valves. Most of these occur due to surgical problems. Therefore, safe measures reduces these events their clinical features.

Fracture strength estimation of L3-L4 intervertebral disc using FEA

Mechanical stress and fracture analysis of the human lumbar intervertebral discs are important in assessing disorders related to lower back pain and ageing. Finite element modelling and simulation approaches assist in easier prediction of the disc behaviour under different load conditions. The causes of mechanical failure and morphological changes still remain partially speculative. The present study addresses the issue by developing a finite element model of an L3-L4 lumbar intervertebral disc subjected to different axial compressive loadings. The morphological deformations and stress concentration regions within the disc are analyzed and reported. A mathematical relation is established to estimate the breaking strength of an L3-L4 intervertebral disc, thus indicating the risk of disc failure based on the applied load.

A review on the effect of creep and microstructural change under elevated temperature of Ti6Al4V alloy for Turbine engine Application

Creep is the likelihood of a solid material to permanently respond to deformation primarily due to initial mechanical stresses.Creep could be severe failure condition in materials that are subjected toheat and structural load which often occur near the melting point for a long period of time as it is the case in turbine engine under operating conditions. Creep is howeverstrainaccumulated and time dependent. This paper presents a review on processes models of experimental activities on the creep behavior of Ti6Al4V alloy under different high temperature applications andapplied stresses. This review was conducted by considering the material characterizations that have been carried out on some Ti6Al4V alloys at various levels of high temperatures by previous researchers. This will also feature in a related on-going investigation from a research study currently being undertaken by the authors. It however describes the major causes of mechanical failure of engineering components or structure due to creep mechanism.

제주도 주변 해역에서 발생하는 해양 사고의 동향과 정책의 효율성

The objective of this paper is to aid in basic directions for the countermeasure against marine accidents by using the statistical data of Jeju Coast Guard from 1983 to 2012. Marine accidents of about 600~1,000 vessels was reported in all the waters around South Korea from 2000 to 2008. From 2009, these accidents increased rapidly and reached 1,600~2,000 vessels. Although marine accidents of longline fishing vessels did not show a big change prior to 1993, the number have increased steadily until 2007. This is considered a tendency that appears when longline vessels, using the Port of Sungsanpo as a base and operating in fishing grounds in the East China Sea, are converted to long-term fishing from short-term fishing for reasons such as cost reduction due to the sudden rise of oil prices and the performance improvement of the fishing vessels. The number of vessels in marine accidents decreased gradually from 1999 to 2002 and for nearly 7 years from 2002 to 2008, the annual average of marine accidents stayed at 97 vessels. This is seemed to be the result of a change in the policy of either the central or local government and largely associated with changes in the way of statistical processing. This tendency is resulted in lower number of the accidents due to careless navigation which can be viewed as a human error than the number of marine accidents due to poor maintenance as a cause of mechanical failure in the same period. The increase rate in the marine accidents of Jeju Island-based fishing vessels is greater than that of other area-based fishing vessels among the fishing vessels operating in coastal and near sea around Jeju Island each year.

Thermo-Mechanical Stress Analysis in Electronic Packaging with Continuous and Partial Bond Layer

Interfacial stress due to thermal mismatch in layered structure has been considered as one of the major causes of mechanical failure in electronic packaging. The mismatch due to the differences in coefficient of thermal expansion (CTE) of the materials in multi-layered structure may induce severe stress concentration to the electronic composites namely interfacial delamination and die cracking. Therefore, the studies and evaluation of interfacial stress in electronic packaging become significantly important for optimum design and failure prediction of the electronic devices. The thermal mismatch shear stress for bi-layered assembly can be analyzed by using the mathematical models based on beam theory. In this study, Finite Element Method (FEM) simulation was performed to an electronic package by using ANSYS. The shear stress growth behavior at the interface of the bonded section was studied with the considerations of continuous and partial bond layers in the interfaces. Based on the analysis, it can be observed that the partial bond layer with small center distances can be simplified as a continuous bond layer for bi-layered shearing stress model analysis.

Reversing Gear Failure Analysis of Mini-Car Variator Base on ANSYS Software

This paper attempts to give a detailed model and contact emulation analysis of gear models based on the ANSYS software, the method of which is superior to stree analysis figuring out the causes of mechanical failure. stress nephogram of the emulation analysis indicates the fracture of gear base is mainly caused by inclined press load which results in stress concentrate. This paper offers very valuable reference to product optimization and gear improvement.

Demonstration of a stall detection system for induced draft fans

Because aerodynamic stall is a major potential cause of mechanical failure in axial fans, effective stall-warning techniques have had wide application for many years. The study assesses the application of stall-detection to a class of heavy-duty fans for induced draft service in coal-fired power plants. With a multi-MW installed power, this class of fans operates at constant rotational speed, utilising variable-pitch in motion blades to adjust fan duty point. This load modulation system, in the presence of blade erosion or fouling, could result in fans becoming prone to stall as a consequence of the reduced pressure capacity. This article reports on a novel methodology, first proposed for the early detection of stall in low-speed axial-flow fans for tunnel ventilation. With respect to the original concept, which was based on the analysis of hydrodynamic pressure as measured on the fan ducting, the investigation demonstrates the potential of processing far-field pressure signals in identifying stall pre-cursors, and in so doing, establishing the stall incipience. This acoustic stall-detection system is characterised in a laboratory environment exploring the fan operating envelope. Time-resolved pressure measurements are carried out with pre-polarised pressure transducers fitted into (a) the fan casing over the fan blades (near field) and (b) in the inlet plenum 1 diameter upstream of the fan rotor (far field). The evolution of the rotating stall for the fan under scrutiny is first presented. The rationale of the signal processing technique is given, together with a sensitivity study on its metrical parameters. Finally, the signal visualization technique is used to compare the patterns related to the presence of stall in the pressure signals recorded in the near- and the far field.

Constrained Cups Appear Incapable of Meeting the Demands of Revision THA

Failure rates of constrained cups for treating recurrent dislocation in revision THA range from 40% to 100%. Although constrained liners are intended to stabilize the hip by mechanically preventing dislocation, the resulting loss of range of motion may lead to impingement and, ultimately, implant failure. We therefore documented the mechanisms of failure of constrained acetabular cups in revision THA and determined the type and severity of damage (wear, fracture, and impingement) that occurs in situ. We retrieved 57 constrained components of four different designs at revision THA and examined for the presence of rim impingement, oxidation, cracks within the liner, backside wear, pitting, scratching, abrasion, burnishing, and the presence of embedded particles. Articular wear was calculated from the volume of the concave articular bearing surface, which was measured using the fluid displacement method. Failure of the locking ring was responsible for 51% of failures, whereas 28% of revisions were the result of acetabular cup loosening, 6% backside wear, and 22% infection. Impingement damage of the rim of the polyethylene liner was seen in all retrievals with moderate or severe damage in 54%. The average volumetric wear rate of the articular surface was 95 mm(3)/year. Failure of the locking liner ring and loosening of the acetabular cup are the primary causes of mechanical failure with constrained liners; polyethylene is an inadequate material for restricting motion of the hip to prevent instability. The durability of these devices is unlikely to improve unless the mechanical demands are modified through increased range of motion leading to less frequent rim impingement.

Stall Warning in a Low-Speed Axial Fan by Visualization of Sound Signals

This study describes the development of a novel stall-detection methodology for low-speed axial-flow fans. Because aerodynamic stall is a major potential cause of mechanical failure in axial fans, effective stall-detection techniques have had wide application for many years. However, aerodynamic stall does not always result in mechanical failure. A subsonic fan can sometimes operate at low speeds in an aerodynamically stalled condition without incurring mechanical failure. To differentiate between aerodynamic stall conditions that constitute a mechanical risk and those that do not, the stall-detection methodology in the present study utilizes a symmetrized dot pattern (SDP) technique that is capable of differentiating between stall conditions. This paper describes a stall-detections criterion based on a SDP visual waveform analysis and develops a stall-warning methodology based on that analysis. This study presents an analysis of measured acoustic and structural data across nine aerodynamic operating conditions represented in a 3×3 matrix. The matrix is a combination of (i) three speeds (full-, half-, and quarter-speed) and (ii) three operational states (stable operation, incipient stall, and rotating stall). The matrix of SDPs and structural data are used to differentiate critical stall conditions (those that will lead to mechanical failure of the fan) from noncritical ones (those that will not result in mechanical failure), thus providing a basis for an intelligent stall-warning methodology.

A case of cochlear implant with internal mechanical failure

Cochlear implantation has been performed since the 1970s and has been proven to be an effective treatment for profoundly deaf people. In some cases re-implantation has also been reported due to trauma causing implant damage, mechanical failure, extrusion, and wound infections, or device upgrade. We present a case of a 9-year-old boy with a cochlear implant in which mechanical failure occurred after a blow to his temporal region. The clinical presentation and radiographic imaging findings suggested that the cause of mechanical failure was internal failure. We performed cochlear re-implantation to the same ear and it worked well. The explanted device analysis by the manufacturer concluded that the device had failed due to a cracked hybrid integrated circuit.

Corrosion of stainless steel sternal wire after long-term implantation

A variety of metallic components have been used in medical devices where lifelong durability and physical strength are demanded. To investigate the in vivo changes of implanted metallic medical devices in humans, stainless steel sternal wires removed from patients were evaluated. Stainless steel (316L) sternal wires removed from four patients after 10, 13, 22, and 30 years of implantation were evaluated using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Macroscopically, the removed specimens maintained their metallic luster and color. Under SEM, small holes were observed sporadically at 10 years and they tended to connect in the drawing direction. The longer the implanted duration, the more numerous and deeper were the crevices observed. By EDS, sulfur, phosphorus, and calcium were identified in all areas at 10 years, in addition to the component elements of stainless steel, comprising iron, chromium, nickel, and manganese. Corrosion products observed at 30 years were identified as calcium phosphate. In conclusion, stainless steel sternal wires develop corroded pores that grow larger and deeper with time after implantation; however, the pores remain shallow even after decades of implantation and they may not be a cause of mechanical failure. An amount of metal ions equivalent to the corroded volume must have been released into the human body, but the effect of these metal ions on the body is not apparent.

Custom cross-pin fixation of 32 tumor endoprostheses stems.

The main cause of mechanical failure of primary and revision cemented tumor endoprosthetic stems is aseptic loosening. The placement of custom designed pins through the bone, the cement, and the stem can create a bone-cement-prosthesis composite that resists the rotatory stresses that lead to aseptic loosening. At risk situations include large primary reconstructions where the residual short metaphyseal articular segments lack sufficient length and cortical contact to provide lasting fixation, and revision prostheses that are to be recemented into straight diaphyseal segments that already have experienced aseptic loosening. Current modular tumor endoprosthetic systems have improved availability and allow for some intraoperative flexibility, but they do not provide solutions for these at risk scenarios. Additional customization is necessary. We report on the 16-year experience with 32 custom cross-pin stems at the University of California, Los Angeles (UCLA). Twenty of these patients have been followed up for more than 2 years. There were three mechanical failures, three patients were lost to followup, and five patients died of disease. There have been no cases of aseptic loosening in this series. Cross-pin fixation has been effective when used in carefully selected cases.

Drilling Damage of GFRP and Residual Mechanical Behavior—Part II: Static and Cyclic Bearing Loads

The damage generated during the drilling of Glass Fiber Reinforced Plastics (GFRP) laminates can be detrimental for the mechanical behavior of the material around the hole, especially when the hole surface is subjected to a bearing load. The present work is the second part of a study aiming to investigate the effect of drilling conditions on the residual mechanical behavior of GFRP laminates subjected to a bearing load. To address this aim, holes drilled in different conditions were tested with static and cyclic bearing loads. The results of these tests were characterized through quantitative parameters and through microscopic observations of hole sections. Results indicate that for the range of the experimental conditions investigated, the main cause of mechanical failure is the micro damage generated at the inner part of the hole surface, while delamination plays a minor role. Therefore, despite the general attention paid during drilling to reduce delamination, the optimal drilling conditions should avoid the onset of microcracks distributed in the inner part of the hole.