Shear Stress Failure Research Articles

Stabilization of Gob-Side Entry with an Artificial Side for Sustaining Mining Work

A concrete artificial side (AS) is introduced to stabilize a gob-side entry (GSE). To evaluate the stability of the AS, a uniaxial compression failure experiment was conducted with large and small-scale specimens. The distribution characteristics of the shear stress were obtained from a numerical simulation. Based on the failure characteristics and the variation of the shear stress, a failure criterion was determined and implemented in the strengthening method for the artificial side. In an experimental test, the distribution pattern of the maximum shear stress showed an X shape, which contributed to the failure shape of the specimen. The shear stress distribution and failure shape are induced by a combination of two sets of shear stresses, which implies that failure of the AS follows the twin shear strength theory. The use of anchor bolts, bolts, and anchor bars enhances the shear strength of the artificial side. When this side is stable, the components can constrain the lateral deformation as well as improve the internal friction angle and cohesion. When the AS is damaged, the components prevent the sliding of broken blocks along the shear failure plane and improve the residual strength of the artificial side. When reinforced with an anchor bar, the AS is still stable even after mining operations for three years.

Interfacial strengthening and self-healing effect in graphene-copper nanolayered composites under shear deformation

The mechanism of interfacial strengthening and self-healing effect in graphene-copper nanolayered (GCuNL) composites under shear deformation is investigated at a theory and quantitative level. It is found that the interfacial constraining effect between graphene and copper layer highly improves the shear strength and toughness of GCuNL composites. The interlayer distance between graphene monolayers and the crystal stacking orientation of copper layers plays an important role in the shear yield strength of composites. The shear toughness of composites is jointly determined by the crystal orientation of copper layer and the chirality of graphene. The shear failure strain of zigzag-based composites is remarkably higher than that of armchair-based composites, while the shear failure stress of (100)-stacking composites is larger than that of (111)-stacking composites due to rotation of slip bands. Furthermore, we find a remarkable self-healing effect in GCuNL composites by interfacial trapping dislocations. The self-healing ability is determined by the interlayer distance between graphene monolayer. Synthesizing both the strengthening and self-healing effect, the optimum distance between graphene monolayers is ranging from 5 to 15 nm.

Investigation of the effects of connectors to enhance bond strength of externally bonded steel plates and CFRP laminates with concrete

Steel plates and carbon-fiber-reinforced polymer (CFRP) laminates or plates bonded to concrete substrates have been widely used for concrete strengthening. However, this technique cause plate debonding, which makes the strengthening system inefficient. The main objective of this study is to enhance the bond strength of externally bonded steel plates and CFRP laminates to the concrete surface by proposing new embedded adhesive and steel connectors. The effects of these new embedded connectors were investigated through the tests on 36 prism specimens. Parameters such as interfacial shear stress, fracture energy and the maximum strains in plates were also determined in this study and compared with the maximum value of debonding stresses using a relevant failure criterion by means of pullout test. The study indicates that the interfacial bond strength between the externally bonded plates and concrete can be increased remarkably by using these connectors. The investigation verifies that steel connectors increase the shear bond strength by 48% compared to 38% for the adhesive connectors. Thus, steel connectors are more effective than adhesive connectors in increasing shear bond strength. Results also show that the use of double connectors significantly increases interfacial shear stress and decrease debonding failure. Finally, a new proposed formula is modified to predict the maximum bond strength of steel plates and CFRP laminates adhesively glued to concrete in the presence of the embedded connectors.

Effect of structure and residual stresses of diamond coated cemented carbide tools on the film adhesion and developed wear mechanisms in milling

Abstract This article deals with the wear mechanisms of variously adherent nano-composite or multi-layer diamond coated tools in milling. The adhesion and residual stresses of these films on cemented-carbide inserts were characterized via inclined impact tests at diverse temperatures. The obtained results were evaluated through FEM-supported mathematical methods for estimating the maximum film residual stress and the shear failure stress (SFLS) of the coating–substrate interface. The coated inserts were used in milling AA7075 T6. The developed wear mechanisms were elucidated considering the film structure, the defined temperature-dependent SFLS and the FEM-determined stress and temperature distribution in the tool wedge region during cutting.

Toward Interpreting Failure in Sintered-Silver Interconnection Systems†

Abstract The mechanical strength and subsequent reliability of a sintered-silver interconnection “system” is a function of numerous independent parameters, and that “system” is still undergoing process development. Most of those parameters (e.g., choice of plating) are arguably and unfortunately often taken for granted and are independent of the silver's cohesive strength. To explore such effects, shear strength testing and failure analyses were completed on a simple, mock sintered-silver interconnection system consisting of bonding two DBC ceramic substrates. Silver and gold platings were part of the test matrix, as were drying strategies, and the consideration of stencil-printing vs. screen-printing. Shear strength of sintered-silver interconnect systems was found to be insensitive to the choice of plating, drying practice, and printing method provided careful and consistent processing of the sintered-silver are practiced. Lastly, with the examined interconnection systems, it was observed that a maximum shear failure stress of ~ 60 MPa is achievable.

Effect of the interface fatigue strength of NCD coated hardmetal inserts on their cutting performance in milling

The interface fatigue strength of coated tools with nano-crystalline diamond (NCD) coatings affects their milling performance. Depending on the developed cutting loads and temperatures, the repetitive impacts on the tool deteriorate progressively the coating-substrate interface strength, thus influencing the effective NCD film adhesion. Aiming at a comprehensive investigation of this effect, NCD coated cemented carbide inserts with improved or insufficient adhesion were manufactured. Hereupon, a parameter characterizing the coatings' interface adhesion strength, the shear failure stress (SFLS) was estimated by inclined impact tests and FEM calculations at ambient and elevated temperatures. This metric is significantly affected, among others, by the compressive residual stresses developed in the NCD film during cooling after its deposition and the coating operational temperature. A correlation between the determined SFLS at the investigated adhesion levels and the FEM calculated maximum shear stress in the coating interface during milling AA 7075T6 contributed to the explanation of the wear evolution on the employed NCD coated tools. Prime novelty statementThe submitted paper aims at investigating the effect of the interface fatigue strength of NCD coated hardmetal inserts on their cutting performance in milling. The fatigue strength of the NCD coating-substrate interface is a dominant mechanical property for the NCD coated tool life. In the submitted work, NCD coated cemented carbide inserts with different adhesion qualities were manufactured. The interface fatigue strength at temperatures up to 400°C was quantified using a critical shear failure stress (SFLS). This was attained by conducting appropriate FEM supported evaluation of the inclined impact test results at ambient and elevated temperatures. A correlation between the determined SFLS at various adhesion levels and the FEM calculated maximum shear stress in the film interface during milling AA 7075T6 contributed to the explanation of the wear evolution on the employed NCD coated tools. This is a new and original contribution to the field of testing NCD coatings and their effective application in cutting. The submitted paper is not being considered for publication elsewhere.

Temperature-Dependent Fatigue Strength of Diamond Coating-Substrate Interface Quantified via the Shear Failure Stress

A dynamic 3D-finite element method (FEM) thermomechanical model is employed for quantifying the temperature-dependent fatigue strength of nanocrystalline diamond (NCD) coating-substrate interface. This model simulates dynamically the inclined impact test on NCD-coated cemented carbide inserts considering the temperature-dependent residual stresses in the NCD coating structure. A fatigue damage of the NCD coating-substrate interface develops after a certain number of repetitive impacts depending on the applied impact load and temperature. After the interface fatigue failure, the high compressive residual stresses of the NCD coating structure are released, and the detached coating hikes up at a certain maximum height (bulge formation). The critical impact forces for avoiding the fatigue failure of the NCD coating-substrate interface, and the subsequent film detachment after 106 impacts at various temperatures were determined by conducting inclined impact tests up to 400 °C. Considering the critical impact forces, using the mentioned FEM model, the related shear failure stresses in the NCD coating-substrate interface at various temperatures were predicted.

Scale dependence of shear strength for a coarse granular soil using a superimposition-nest type of direct shear apparatus

This study applies a modified superimposition-nest type of direct shear apparatus (DSA) to exploring the scale dependence of shear strength from the direct shear test (DST) of soil. The modified apparatus enables the variation of the diameter D and height H of specimens and can adjust the gap T between the upper and lower shear box halves. The DSTs in different combinations of T, D, and H were conducted under a constant vertical normal stress σ for a coarse granular soil. In each combination situation, five sets of tests were performed in parallel under the same σ value to validate the reproducibility and reliability of testing. The gap effect results show the influence of T on the failure shear stress τ f. The diameter and height effect results reveal the dependence of τ f on the D and H of specimen. The reasonable values of T, D, and H relative to the maximum particle diameter d max of the soil are evaluated for the coarse granular soil as well as the reasonable shear strength envelopes.

Effect of manufacturing errors on load distribution in large diameter slewing bearings of fast breeder reactor rotatable plugs

Fuel and other subassemblies in fast breeder reactor are handled through a combination of small rotatable plug, large rotatable plug and transfer arm. Rotation of the plugs is facilitated through large slewing bearings. These bearings are subjected to heavy loads and moments. Manufacturing errors on the rolling elements and races influence the load sharing among the elements. As a result, higher load acting on a rolling element causes excessive local deformation and unacceptable indentation. The higher load can also cause excessive sub-surface shear stress and fatigue failure of rolling races. Too stringent tolerances demand sophisticated machines, whereas liberal tolerances mean compromise on the performance and life of the bearing. There are no established methods for design of slewing bearings that include the influence of manufacturing errors. Hence, an attempt has been made to find the influence of manufacturing errors on load distribution among the rolling elements using finite element method. It is observed that size error on the ball and waviness error (waviness spacing and height) on the raceway are the two influencing factors on load distribution. To study the influence of waviness error on the raceway, three sectors of bearing simulating waviness spacing of 10.8°, 18° and 36° with different waviness (peak-to-valley) height of 30 µm, 50 µm and 75 µm are analysed. It is observed that waviness height has larger influence on the load distribution among bearing balls when compared to waviness spacing.

Effects of pore water pressure dissipation on rate dependency of shear strength in localised failure of soils

SUMMARYThe paper presents analytical solutions for the evolution of excess pore pressures in the vicinity of a shear band in a rate‐dependent, strain‐softening permeable soil, with the aim to explore, both qualitatively and quantitatively, the potential variation of failure shear stress in the shear band. The solutions encompass both dissipation of a pre‐existing pore pressure regime within the main soil domain, and the effects of generation of additional pore pressure within the shear band itself. The simplified analytical solutions were checked by numerical inversion of exact solutions in Laplace transform space, confirming their high accuracy. The solutions show that it is possible for the failure shear stress to rise initially because of short‐term dissipation of the pre‐existing excess pore pressure at a faster rate than generation of new excess pore pressure within the shear band. This apparent strain hardening in a strain‐softening soil can be misleading in that it can temporarily slow down the sliding mass and create a false sense of stabilization of the slope. It can also result in additional temporary shear resistance for sliding foundations or pipelines on the seabed. Copyright © 2015 John Wiley & Sons, Ltd.

Experimental Adhesive Failure Criteria for Analysis of Aerospace Structures

In order to develop a correct methodology that can be applicable when a standard aerospace bonded joint is being sized, first it is necessary to characterize adhesives through testing campaigns. For this preliminary approach the interest was to create a simple and realistic procedure able to produce practical but usable results that could be used for standard bonded models calculations. On the present research the main objective was to find results that can be implemented on the daily basis, adjusted to the imperfections made when manufacturing bonded joints. On this study two different tests were performed: an experimental calculation of the adhesive's elasticity modulus, and obtaining shear, tensile and combined failure stresses using a classical Arcan type fixture. From the Arcan tests it was possible to create a failure line of the adhesive tested. For the elasticity modulus an experimental value was calculated and compared with results found on the literature. It was observed a greater dispersion of combined test values in comparison with the pure tests results but, based on the assumptions with which this study was conducted, an accurate and practical curve was drawn that can be used safely when modelling adhesively bonded joints with this kind of adhesive.

Influence of the glide path on various parameters of root canal prepared with WaveOne reciprocating file using cone beam computed tomography.

Nickel-titanium (NiTi) rotary instrumentation carries a risk of fracture, mainly as a result of flexural (fatigue fracture) and torsional (shear failure) stresses. This risk might be reduced by creating a glide path before NiTi rotary instrumentation. The aim of this study was to compare various root canal parameters with the new WaveOne single-file reciprocating system in mesial canals of mandibular molars with and without glide path using cone beam computed tomography (CBCT). One hundred mandibular molar teeth with canal curvature between 20° and 30° were divided into two groups of 50 teeth each. In Group 1, no glide path was created, whereas in Group 2, a glide path was created with PathFiles at working length (WL). In both groups, canals were shaped with WaveOne primary reciprocating files to the WL. Canals were scanned in a CBCT unit before and after instrumentation. Postinstrumentation changes in canal curvature, cross-sectional area, centric ability, residual dentin thickness, and the extent of canal transportation were calculated using image analysis software and subjected to statistical analysis. Data were analyzed using Student's t-test and Mann-Whitney U-test (P < 0.05). The mean difference of root canal curvature, cross-sectional area, centric ability, and residual dentin thickness increased, whereas it reduced significantly for canal transportation in Group 2. WaveOne NiTi files appeared to maintain the original canal anatomy and the presence of a glide path further improves their performance and was found to be beneficial for all the parameters tested in this study.

The Modified Maximum Shear Stress Failure Theory of Ductile Material

In this study, the maximum and smallest vertical principle stresses σ1 and σ3 as well as maximum shear stress τmax distributions, obtained from Mohr circle in each quadrant, are used to investigate the applicability of various ductile material failure theories. Based on the yield tensile stress σyt equals to yield compressive stress σyc (σyt=σyc=σy) and the known practical yield shear stress and yield stress ratio τy/σy=0.42~0.75 of ductile materials, we prove that the maximum vertical stress failure theory cannot be applied to the first quadrant (σ1&gt;σ3≧0) as well as the third quadrant (σ3&lt;σ1≦0) while τy/σy&lt; 0.5, and it does also not applicable to the second or fourth quadrant (σ1&gt;0 and σ3&lt;0). In this study, the modified maximum shear stress failure line can be fit all ductile material depending on τy/σy=0.42~0.75 in all quadrants, thus the more reasonable results can be obtained.

Numerical Modelling of Ultra-High Molecular Weight Polyethylene Composite under Impact Loading

Numerical models are investigated and refined for analysis of ultra-high molecular weight polyethylene (UHMW-PE) composite under ballistic and hypervelocity impact. An existing non-linear orthotropic continuum model implemented in a commercial hydrocode (ANSYS® AUTODYN®) was evaluated using a previously published material data set. It was found that the material through-thickness shear performance was artificially degraded as a result of coupling to the through-thickness tensile properties, significantly affecting the model accuracy for impact velocities in the ballistic regime. In order to correct for this, the composite laminate was discretized into sub-laminates joined by bonded contacts breakable through a combined tensile and shear stress failure criterion. The sub-laminate method allows the through-thickness tension and shear failure to be decoupled in the bulk material. This method was investigated and validated against experimental ballistic and hypervelocity impact tests. Simulations showed improvement in ballistic limit predications for thin targets under low velocity impact. Prediction of target deflection is also significantly improved compared to the baseline model in terms back face deformation. Under hypervelocity impact, good agreement with the experimental ballistic limit and residual velocities is still maintained, with a small variation between the new and baseline models. A third validation case was performed to investigate the model performance with thicker targets (50mm) for impact velocities between the two baseline studies. Accuracy for this condition is poor and remains a challenge for the numerical model.

Parameter Study of Tool-Laminate Interface through Simulation for Composite Manufacturing Using Autoclave Process

Modeling the spring-back requires tool-laminate interaction to be taken into account. In this study, an interface based on orthotropic linear behavior coupled with an out-of-plane shear stress failure was proposed to simulate the tool-laminate interaction. The results from this particular model captured the out-of-plane shear stress distribution. The model allows predicting the warpage displacement in function of interface properties; shear modulus and shear stress failure which leads to the construction of Chart Design. Additionally, the influence of the number of plies was studied as well and the evolution of the maximum warpage agreed with the literature.

Finite element analysis of stress and strain distributions in mortise and loose tenon furniture joints

We studied the effect of loose tenon dimensions on stress and strain distributions in T-shaped mortise and loose tenon (M&LT) furniture joints under uniaxial bending loads, and determined the effects of loose tenon length (30, 45, 60, and 90 mm) and loose tenon thickness (6 and 8 mm) on bending moment capacity of M&LT joints constructed with polyvinyl acetate (PVAc) adhesive. Stress and strain distributions in joint elements were then estimated for each joint using ANSYS finite element (FE) software. The bending moment capacity of joints increased significantly with thickness and length of the tenon. Based on the FE analysis results, under uniaxial bending, the highest shear stress values were obtained in the middle parts of the tenon, while the highest shear elastic strain values were estimated in glue lines between the tenon surfaces and walls of the mortise. Shear stress and shear elastic strain values in joint elements generally increased with tenon dimensions and corresponding bending moment capacities. There was consistency between predicted maximum shear stress values and failure modes of the joints.

Fatigue Strength of Diamond Coating-Substrate Interface Quantified by a Dynamic Simulation of the Inclined Impact Test

Fatigue damage of the nanocrystalline diamond coating (NCD) bonding to the cemented carbide substrate develops when repetitive impact loads are applied onto the film. Thus, the highly compressive residual stresses of a NCD film are released leading to its lifting from the substrate (bulge formation). The present paper deals with the analytical description of the progressive failure of the NCD coating-substrate interface under repetitive impacts. In this context, an advanced 3D-finite element analysis model was developed for the dynamic simulation of the inclined impact test, using the LS-DYNA software. This model considers the high thermal compressive residual stresses developed in the NCD coating structure during cooling from chemical vapour deposition process temperature to ambient one. The fatigue failure of the NCD coating-substrate interface is associated with a critical shear failure stress (SFLS). The determined SFLS represents the maximum operational stress permitted in the NCD film-substrate interface in order to avoid the coating detachment initiation. According to the results obtained, the successive impacts lead to a progressive weakening of the initial film-substrate interface strength depending upon the pretreatments prior to the NCD coating deposition.

Breezing Thoroughbred Hoof Accelerations on Dirt and Synthetic Surfaces

IntroductionRacetrack surface type has been shown to affect horse injury rates, limb kinematics, and ground reaction forces. Understanding hoof‐surface interactions may direct surface design to reduce the incidence of musculoskeletal injury. Hoof accelerations have been recorded at the trot on different surfaces. This study extends these analyses to racing gallop with quantified surface properties.MethodsLeft fore‐hoof accelerations (triaxial, ± 500 g, 1000 Hz) were collected during gallop (10–16 m/s, 5 Thoroughbred racehorses) on dirt and synthetic surfaces of known shear strengths (shear vane). Accelerometric vectors were filtered (5th order Butterworth, stance 85 Hz, swing 30 Hz). Peak accelerations and stance phase durations (limb preparation, hoof landing {heel‐strike and slide}, support, and grab) were compared using a mixed model analysis of covariance with surface, lead, stride frequency, and interaction fixed effects, and horse random effect.ResultsPeak dorsopalmar accelerations were 40% greater during landing on the synthetic surface (P = 0.06). Grab phase was 32% shorter on the synthetic surface (P = 0.02), with 34% less dorsopalmar impulse/mass (P&lt;0.01). Previously reported failure shear stress of the synthetic surface was 20% greater, compared to dirt (normal stress &gt;400 kN/m2, equivalent to trotting racehorse).ConclusionsDorsopalmar hoof accelerations were greater on the surface with greater shear strength (synthetic). The finding that accelerations were greater on the synthetic surface compared to dirt is in contrast to that of trotting horses on all‐weather waxed and crushed sand surfaces. This discrepancy may be due to differences in horse gait, but also large variability in surfaces. Consequently, it is important to quantify surface behaviors to understand the effect of surface design and maintenance on limb biomechanics and propensity for injury.Ethical Animal ResearchStudy protocols were approved by the University of California, Davis Institutional Animal Care and Use Committee and owner informed consent was obtained for all study horses. Sources of funding: Grayson Jockey Club Research Foundation Inc., Southern California Equine Foundation. Competing interests: none.

Experimental Investigation of the Performance of Alluvium Soil Reinforced With Jute Cloth

Abstract Soil reinforcement is a recent and special field of soil improvement. It covers a range of techniques, which consists of placing inclusions in soil. The most conferences devoted partly or totally the behavior of foundation on reinforced subgrade without regarding the basic characteristics of the reinforced soil. So, the paper presents an experimental investigation into the mechanical and compressibility properties of the reinforced silty clay samples by jute cloth at intermediate depth. The effects of the reinforcement on shear stress and shear failure were studied, also, the presence the reinforcement on behavior of consolidation process was distinctly described. The laboratory tests were supported by the finite element analysis to identify only the consolidation process and explained the effect of the reinforcement on the effective vertical stress and pore water pressure. The results indicted that the presence of such reinforcement has a considerable effect in increasing the shear strength of the reinforced samples and decreasing the compressibility especially decreasing the soil movement also, relief both the effective and pore water pressure.

Cutting Force Model for Heat Assisted Titanium Alloy Milling

Thermal energy sources have been applied for softening the difficult-to-machine material when it is combined with conventional machining processes. Cutting forces has been reduced during the process. To investigate the plastic deformation property of workpiece materials heated by thermal sources, and its influence to the cutting forces, the analytical model of orthogonal cutting is established. The impact of cutting speed and initial temperature of the shear banding to the cutting forces are taken account of, based on adiabatic shear banding model and Johnson-Cook material constitutive law. The shear banding average shear stress failure criteria has been proposed to decide the fracture between workpiece and chip. Simulation has been carried out and compared with experimental data of laser-heat assisted titanium alloy milling, showing good agreement.