Types Of Failure Mechanisms Research Articles

Characterisation of CoB–Co2B coatings by the scratch test

New results about the scratch practical adhesion-resistance of the CoB–Co2B/substrate system developed at the surface of CoCrMo (ASTM-F75) alloy were estimated. The boron diffusion on the surface of the cobalt alloy was conducted using the powder-pack boriding process at temperatures of 1223 and 1273 K with different exposure times for each temperature. The scratch tests over the surface of cobalt borided alloy were performed with a 200 micrometres Rockwell C diamond indenter considering a continuously increasing normal force for the entire set of experimental conditions of the boriding process. The worn tracks produced on the coating/substrate system were analysed by optical and scanning electron microscopy to estimate and identify the critical loads and failure mechanisms, respectively. The results indicated that the critical loads varied between 95 and 142 N as a function of the boride coating thicknesses with a development of various types of failure mechanisms over the surface of the coating/substrate system.

Capabilities of Continuous and Discontinuous Modelling of a Complex, Structurally Controlled Landslide

In order to assess the stability of a landslide, continuous or discontinuous models have been proposed. Here, we compare the two methods in their capability to provide a reliable hazard assessment. Both models have been applied to long term monitoring data obtained from a landslide located in Passo della Morte (Eastern Italian Alps). The availability of accurate data obtained in a long-term campaign is a pre-requisite to correctly understand the dynamics of the process and to implement a sound numerical model. First, a detailed geological investigation located the different soil layers and rock formations with their distribution along the slope, allowing the identification of the structural controls of the unstable rock mass. Then, landslide long term monitoring data provided information on the type of failure mechanism. Both the continuous and discontinuous numerical solutions describe the kinematics for the landslide and allow to delineate a hazard assessment for the investigated area. The continuous model is better in delineating the development of the deep slip surface while the discontinuous allows to recreate the toppling phenomenon.

Minimum bending radius of Al-Li alloy extrusions in stretch bending

In this investigation, the attention is focused on the minimum bending radii of 2196-T8511 and 2099-T83 Al-Li alloy extrusions. To predict the failure of Al-Li alloys, sheet and extrusion stretch bending tests are developed, carried out and simulated using finite element model. The theoretical minimum bending radius is introduced to derive a safe lower limit for the bending radius which can serve as a guideline for tool and product design. Stretch bending tests of Al-Li alloys are performed using the three-point bending test and displacement-controlled stretch bending test at room temperature. The finite element model incorporates three-dimensional solid elements and ductile damage modeling. The experimental results show that Al-Li alloy extrusions in stretch bending show three types of failures, occurring at the unbent region near the entrance of the jaws, at the region below the exit of the die and within the region in contact with the die, respectively. Comparison between predicted values and experimental results has been made, a consistent agreement being achieved, reflecting the reliability of the present model. The three types of failure mechanisms which compete with each other are tensile localization failure, die-corner failure and shear failure, respectively. Based on the analytical models, experiments and simulations, it appears that the three distinct failures need to be applied to predict the minimum bending radius and range of failures that can occur with 2196-T8511 and 2099-T83 Al-Li alloy extrusions in stretch bending.

An experimental and numerical study of the dynamic response of composites under impact at low temperatures

ABSTRACTAn analytical method was applied to investigate the effects of strain rate, low temperature, and impact direction on the energy absorption of composite specimens. The performance of an analytical model was found to be adequate for modeling composites before failure initiation. Results indicated that impact performance of composites is affected over the range of temperatures. Failure mechanism was changed from matrix cracking at room temperature to delamination and fiber breakage at low temperatures. Moreover, it was shown that about 70% of total energy absorbed by a specimen was used to destroy the composite under different types of failure mechanisms.

Effects of interfacial conditions on shape optimization of cementless hip stem: an investigation based on a hybrid framework

The typical biomechanical failure mechanisms associated with cementless Total Hip Arthroplasty (THA) are initial micromotion, stress shielding and interface stresses. While the former is a short-term load-induced failure criterion affiliated with the post-surgery rehabilitation period, the other two mechanisms are relatively longer term phenomena. At immediate post-operative stage, biologic fixation through bone ingrowth is yet to occur and implant stability is determined by the initial micromotion. However, by the time the other failure mechanisms become prominent, sufficient bone ingrowth already prevails and consequently, the implant-bone interface characteristic changes. Therefore, any preclinical simulation aimed at designing femoral implants needs to account for this dual interfacial behaviour while dealing with these failure objectives. The present study implements a hybrid framework comprised of neural network (NN), genetic algorithm (GA) and finite element (FE) analysis for a multi-criteria 3-D shape optimization of cementless femoral implant by addressing the dual interfacial behaviour. Bonded interfacial condition was used to analyse the effects of stress shielding and interface stresses, whereas a set of contact models were used to develop an NN for faster prediction of the initial micromotion based on implant geometry. The final trade-off implant models were analysed and subsequently, compared with a generic design of femoral implant.

Low cycle fatigue response of bolted T-stub connections to HSS columns — Experimental study

Characterization of the low cycle fatigue response of the connection dominated by the hollow structural section (HSS) column in flexural bending and the bolt in tension are necessary to the design of its constitutional semi-rigid joints under earthquake scenarios. This paper presents the results of an experimental programme to evaluate the low cycle fatigue related characteristics of bolted connections to HSS columns. A summary of a total of 69 tension tests of T-stub connections is reported. The geometric parameters were varied as the bolt gauge width, the tube wall slenderness, the bolt size and the tube sidewall depth. Based on the experimental test results, the typical failure mechanisms, the hysteretic load-deformation relation and the response characteristics such as degradations of strength and energy dissipation capacity of the connections are examined. It is shown that the bolt gauge width and the tube wall slenderness have significant influences on the failure mode, the tensile capacity and stiffness which prompt two design parameters; namely, bolt gauge width to tube width ratio (β) and the tube wall thickness-to-half wall width ratio (Ψ0), in quantifying most influential geometric details of the connection. Moreover, the low cyclic fatigue life test results are compared with the codified S–N curves through a transformation of displacement range into effective stress range. It demonstrated a better contrast with test results by further allowing for the geometric parameters of β and Ψ0. Finally, the damage model analysis is employed to study the deterioration progress of the test connections through a comparison with typical damage indices available in the literature. The deficiencies of referred index are identified thereby promoting the proposal of a new model incorporating the stiffness and the energy dissipation in the representation of damage under constant amplitude loading condition. It is shown that the proposed model can give a reasonably well prediction of experimental evidences.

Concrete beams stiffened by polymer-based mortar layers: Experimental investigation and modeling

In the present work, the main results provided by an experimental investigation, assessing the mechanical performances of concrete elements stiffened by a single or more layers of different kinds of polymer-modified cementitious repair mortar, are presented. The study aims to investigate the failure mechanism occurring in the samples under bending loading. In particular, the experimental investigation allows checking if the collapse mechanism is driven by delamination occurring along the interface among the overlays or by cracks propagating from the tensile region to the compressive zone, as it occurs in a typical failure mechanism driven by flexure. Thirty-eight precast and pre-stressed concrete samples were realized and cured to simulate load-bearing concrete ceiling beams widely employed as floor systems for residential buildings. After curing, the samples were subjected to three-point loading bending tests in order to evaluate the mechanical response of the specimens in terms of load vs. mid-span transverse displacement. Through the experimental tests, the crack initiation and propagation during the bending loading have been investigated also. Simplified finite element (FE) simulations were performed to properly reproduce the actual response of ceiling beams under non-symmetric loading bending. It is shown that the proposed FE model can be straightforwardly used to predict the behavior of concrete beams stiffened by polymer-based repair mortar layers.

Collapse simulation of reinforced concrete frame structures

Summary Study of collapse-resisting properties of structures has attracted widespread attention because of frequently occurring earthquakes and extreme events (e.g. blast) around the world. The developments in computational methods have enabled researchers to numerically simulate the collapse of structures under different kinds of loadings and provide reliable assessments of the collapse performance of structures. The dynamic nature of structural collapse requires a direct integration algorithm to solve the equations of motion of the numerical simulation model. A major concern in such simulations is the computational efficiency, which stems from the need to use a small time step size in both implicit algorithm and explicit algorithm. In this paper, modeling techniques to simulate typical failure mechanisms in reinforced concrete frame structures combined with the application of the recently developed explicit, unconditionally stable, parametrically dissipative KR-α integration method to investigate collapse simulation are presented. A fiber beam-column element is used to model the frame members, where the material nonlinearities, especially material softening, are simulated by a plastic damage model combined with a failure criterion. Numerical examples are presented to illustrate the proposed collapse simulation technique. The results indicate that the proposed technique provides an accurate result and has exceptional computational efficiency. Copyright © 2015 John Wiley & Sons, Ltd.

Failure of Chain Anchor Pins on a Fork Lift Truck

This paper documents investigation of the cause of failure of chain anchor pins on a fork lift truck, including recommendations to prevent reoccurrence. The pins failed from hydrogen embrittlement caused by atomic hydrogen being produced as corrosion occurred in the crevice region of the anchor pin. High strength materials such as that used for this pin are susceptible to this type of failure mechanism. To prevent this type of damage, the chains and anchor pins need to be on a regular maintenance, lubrication, and replacement program. The objective is to keep the equipment clean and lubricated to prevent corrosion and minimize wear, in accordance with advice given by BITA, the British Industrial Truck Association and other manufacturers of truck lifts.

Multi-axial brittle failure criterion using Weibull stress for open Kelvin cell foams

Foam structures have found an increasingly wide utilization in modern industry because of their porous geometric characteristic and favorable mechanical properties like lightness, high strength and so on. Elastic buckling, plastic yielding, brittle fracture and crushing are typical failure mechanisms of foam structures. The influences of foam geometry and morphology on the failure mechanisms are still not fully understand. In this paper the Kelvin cell model is used to simulate the foam structure and to study the influence of relative density and geometric properties on failure behavior. By extensive FEM analyses of representative volume elements under multi-axial loading with periodic boundary conditions the macroscopic failure limit surface is calculated in stress space. Locally at the microstructure the probabilistic Weibull model and the maximum principal stress criterion are used as failure criterion.

Tool Steels in Die-Casting Utilization and Increased Mold Life

In die-casting molds, heat-checking is the typical failure mechanism. Optimizing the parameters that decrease this failure venture should be considered when designing and heat treating steels. The quality of die steels and their treatment continue to improve. This research investigated properties of the traditional materials 1.2343 and 1.2344 and the new steels (Dievar and TOOLOX 44) when applied to the die-casting mold specimens, after different experimental cycles. Also microstructures of the mentioned materials were analyzed by scanning electron microscopy (SEM) test. Chrome-molybdenum-silicon-vanadium steels have good hardening ability in oil and in air. Therefore, the hot-work steels have considerable toughness and plastic attributes through both regular and higher temperatures. So, it is a good traditional die-casting material. However, another special die steel, such as Dievar, is a particularly developed steel grade; its exclusivity profile is exceptional due to its chemical composition and the use of the latest production techniques. Dievar has good heat-checking and gross-cracking resistance as a result of both high toughness and good hot strength. An additional material, a new prehardened tool steel known as TOOLOX 44, exhibits control of the failure described above by optimizing the parameters of impact toughness that could reduce the heat-checking failures. A variety of heat treatment parameters exist for various reasons because the heat treatment operation is performed by a variety of companies. This issue of the diversity in heat treatments is resolved by TOOLOX 44; this steel is quenched and tempered in delivered state.

Reliability analysis of ultrasonic power transducers

Ultrasonic power transducers are commonly used in applications like cleaning, plastics welding or sonochemistry. Typically, the design of transducers for new applications is a tedious iterative process of design, prototype construction and tests. The transducers must fulfill the needs and restrictions of the specific application, as otherwise the transducer might be oversized or fail during operation. While reliability has been studied worldwide intensively in the case of piezoelectric multilayer actuators—driven by car industry which now uses such actuators in their fuel injection systems—nearly no literature is available for the reliability of ultrasonic power transducers. As well, manufacturers seldom present data about aging or lifetime of their components. To enhance the knowledge about typical failure mechanisms of ultrasonic power transducers under different load conditions, our contribution—as a first step—reports on a theoretical study on the reliability of common known ultrasonic transducers and gives some examples of typical failures and their influence on the characteristics of the transducer.

A Certain Type of Tracked Vehicle Transmission Cabinet Failure Analysis and Fatigue Life Evaluation

Transmission casing fatigue fracture is one of the most serious failure of the transmission system in the form of tracked vehicles. This article through the analysis of materials and structural stress analysis of a typical fracture failure mechanism of the tracked vehicle transmission cabinet. And in obtaining the stress on the basis of load spectrum its fatigue life was calculated. The results show that in the structure of the stress concentration and cabinet material number ZL101 cast aluminum defects such as inclusions, porosity are the main cause of fatigue crack initiation and propagation.

Discrete element study of viscous flow in magnetorheological fluids

Using discrete element simulations, we gain insight into the structure of a magnetorheological fluid (MRF) under shear. In simulations with flat walls, the particles arrange in chains, sheet-like structures, or columns along the magnetic field lines, depending on the strength of the applied external magnetic field. Corresponding to the structure formation, three different types of failure mechanisms can be identified. For the characterization of the different regimes, specific particle coordination numbers are introduced. The three structural regimes can be distinguished and described by means of these coordination numbers. To analyze the contact between the MRF particles and the walls of the shear cell, additional simulations with rough walls have been conducted. The resulting structure formation could be successfully classified by the introduced coordination numbers. Based on the analysis of the shear stress transmission both in the case of flat and rough walls, possibilities for shear stress enhancement for technological applications are discussed.

Loss-of-stability induced progressive collapse modes in 3D steel moment frames

This paper deals with the progressive collapse analysis of a tall steel frame following the removal of a corner column according to the alternate load path approach. Several analysis techniques are considered (eigenvalue, material nonlinearities, material and geometric nonlinearities), as well as 2D and 3D modelling of the structural system. It is determined that the collapse mechanism is a loss-of-stability-induced one that can be identified by combining a 3D structural model with an analysis involving both material and geometric nonlinearities. The progressive collapse analysis reveals that after the initial removal of a corner column, its two adjacent columns fail from elastic flexural-torsional buckling at a load lower than the design load. The failure of these two columns is immediately followed by the failure of the next two adjacent columns from elastic flexural–torsional buckling. After the failure of these five columns, the entire structure collapses without the occurrence of any significant plastification. The main contribution is the identification of buckling-induced collapse mechanisms in steel frames involving sequential buckling of multiple columns. This is a type of failure mechanism that has not received appropriate attention because it practically never occurs in properly designed structures without the accidental loss of a column.

Experimental study on the bending properties and failure mechanism of 3D integrated woven spacer composites at room and cryogenic temperature

Three-point bending tests at room and liquid nitrogen temperature (as low as −196°C) are conducted on the 3D integrated woven spacer composites with different core heights. Macrofracture morphology and SEM micrographs are examined to understand the deformation and failure mechanism. The results show that the bending properties at liquid nitrogen temperature are improved significantly than those at room temperature. Meanwhile, the bending properties both at room and liquid nitrogen temperature can be affected greatly by the core height. Moreover, the damage and failure patterns of composites vary with the core height and test temperature. At room temperature, three typical failure mechanism have been obtained for composites with different core heights. At liquid nitrogen temperature, the composites show gradual failure process which extends from the external layers of the compression face to the interior core layers. Furthermore, the brittle failure feature becomes more obvious and the interfacial adhesion capacity is enhanced significantly.

Effect of Velocity on the Impact Resistance of Woven Jute Fiber Reinforced Composites

is present project investigated the impact penetration response of woven jute fiber reinforced composites subjected to wide range of low impact velocities. Hand layout woven jute fibers are thermally compressed to ensure no internal defects formed in the composites. Six layers of woven jutes are stacked together using different fiber orientations [0/q/0]s. Low impact velocities are used ranging between 5 – 20 m/s. Force-time, force-displacement and energy-time curves are obtained automatically during the impact tests. The results are then discussed with considering the composite fragmentations and failure mechanisms. It is found that 00 composite orientations capable to absorb sufficiently impact energy for 5 m/s but not for velocity greater than 10 m/s. When fiber orientations used between 15 – 450, the composite impact resistance increased indicating two significant peak forces. These peak forces represent different type of failure mechanisms occurred during the striker progresses.

Experimental study on the compression properties and failure mechanism of 3D integrated woven spacer composites

The compressive experiments on the 3D integrated woven spacer composites with different core heights are performed in the flat and warp direction. Macro-fracture morphology and SEM micrographs have been examined to understand the deformation and failure mechanism. The results show that the core height is an important parameter to influence the compressive properties and failure mechanism. For flat compression, the compressive properties decrease with the core height and load–displacement curves exhibit elastic, plasticity plateau and densification stages. For high core height, yet more than one peak load appears. For warp compression, the compressive properties increase greatly with the core height and the curves only have obvious elastic stage. Meanwhile, the failure mechanism is significantly different under the flat and warp compression. For flat compression, core fiber bundles dominate the failure and three typical failure mechanisms have been obtained for different core heights. For warp compression, it is the face sheet rupture and dislocation between the top and bottom face sheets that dominate the failure of the composites.

A New Method to Assess the Seismic Vulnerability of Existing Wood Frame Buildings

This paper aims at applying a direct displacement-based method to assess the seismic vulnerability of existing multi-storey wooden buildings. This procedure is consistent with Priestley’s direct methodology firstly developed for reinforced concrete structures. The distinctive characteristic of the proposed method is that the system response is quantified through the use of displacements instead of equivalent elastic strengths, according to the traditional force-based approaches. Consequently, in comparison to common force-based procedures, this method cannot only be considered as a rational alternative but also as a new seismic philosophy to design or assess structures. A representative timber construction system commonly used in Italy was selected as case study. The construction system illustrated in this work was analysed in detail, with special attention given to the mechanical connections typically used. The typical failure mechanisms and the energy dissipation capacity of the structure or of its members were identified on the basis of the mechanical properties of structural parts and connections, as well as of their geometry. In the proposed direct displacement-based assessment approach, the seismic intensity that would cause the limit state to be exceeded can be calculated by means of simple formulas. Therefore, the capacity to demand ratio can be simply derived. The procedure could be used to gauge the likelihood of losses, by combining it with simple loss models to account for probabilistic aspects.

ESD characterization of multi-chip RGB LEDs

In this paper we present an extensive analysis of the failure mechanisms of RGB (multi-chip) LEDs submitted to ESD testing: the tests have been carried out on several commercially available LEDs of three different suppliers. In order to better understand the failure mechanisms, we have submitted LEDs to ESD tests under reverse and forward bias condition separately, by means of a Transmission Line Pulser (TLP).The experimental results indicate that: (i) red LEDs (based on AlInGaP) have an higher ESD robustness with respect to green and blue samples (based on InGaN), both under reverse and under forward bias test; (ii) TLP negative pulses with a current smaller than the failure threshold can induce a decrease of the leakage current in GaN-based LEDs, due to a partial annihilation of defective paths responsible for reverse conduction; (iii) typical failure mechanism of devices is represented by a catastrophic event, with short-circuiting of the junction. Moreover, some of the analyzed red LEDs had shown “soft” failure, with gradual increase of the leakage current and corresponding decrease of the optical power, even without a catastrophic damage.