Cyclic Shear Loading Research Articles

Fatigue Life of Sn3.0Ag0.5Cu Solder Alloy Under Combined Cyclic Shear and Constant Tensile/Compressive Loads

Abstract Solder joints in electronic assemblies experience damage due to cyclic thermomechanical loading that eventually leads to fatigue fracture and electrical failure. While solder joints in smaller, die-sized area-array packages largely experience shear fatigue due to thermal expansion mismatch between the component and the substrate, larger area-array packages experience a combination of cyclic shear and axial tensile/compressive loads due to flexure of the substrate. Additionally, on larger processor packages, the attachment of heatsinks further exacerbates the imposed axial loads, as does package warpage. With the increase in size of packages due to 2.5D heterogeneous integration, the above additional axial loads can be significant. Thus, there exists a critical need to understand the impact on fatigue life of solder joints with superposed compressive/tensile loads on the cyclic shear loads. In this paper, we describe a carefully constructed multi-axial microprecision mechanical tester as well as fatigue test results on Sn3.0Ag0.5Cu (SAC305) solder joints subjected to controlled cyclic shear and constant compressive/tensile loads. The tester design allows one to apply cyclic shear loads up to 200 N while maintaining a constant axial load of up to 38 N in tension or compression. The tester is capable of maintaining the axial load to within a tolerance of ±0.5 N during the entirety of fatigue experiment. Carefully constructed test specimens of Sn3.0Ag0.5Cu solder joints were isothermally fatigued under systematically increased compressive and tensile loads imposed on the test specimen subject to repeated loading (R = 0) under lap-shear. In general, the imposition of the superposed compressive load increases the fatigue life of the solder joint compared to application of pure cyclic shear, while the imposition of the superposed tensile load decreases the fatigue life. At larger compressive loads, friction between fractured surfaces is responsible for significant energy dissipation during the cyclic load–unload cycles.

Fatigue evolution characteristic and self-healing behaviour of asphalt binders

ABSTRACT The self-healing ability of asphalt material has a significant effect on improving fatigue life of asphalt pavement. The objective of this paper was to investigate the stage characteristics of fatigue damage of asphalt binder and its associated self-healing behaviours. Firstly, the rheological behaviour and fracture surface morphology were discussed to investigate the fatigue evolution characteristics of asphalt binders. Secondly, an effective method for interpreting the self-healing capability of asphalt binder at different fatigue stages was proposed by conducting fatigue-healing-refatigue tests and Fourier transform infrared spectroscopy analysis. Finally, the effect of temperature on the self-healing properties of different aging asphalt binders at different fatigue damage stages was explored. The results show that the stage characteristics of fatigue damage of asphalt binders could be distinguished effectively by correlating complex shear modulus with ratio of dissipation energy change under load time history. The fatigue cracking morphologies of asphalt binders under cyclic shear loading are susceptible to the aging degree of asphalt binder. An index associated with initial dissipative energy and number of cycles could effectively evaluate the self-healing properties of different aging asphalt binders. After the occurrence of macrocracks, the mechanical properties of asphalt binder cannot be completely restored by increasing the temperature.

In-plane seismic behaviour of retrofitted masonry walls subjected to subsidence-induced damage

The province of Groningen in the Netherlands is experiencing the continuous impact of gas extraction in the form of induced seismicity. Due to the absence of naturally occurring seismicity in the region, the historic building stock of Groningen was constructed without empirical design features typically encountered in naturally seismic regions. Further, gas extraction, in combination with soft topsoil, is responsible for substantial amounts of ground subsidence. This subsidence may compromise the capacity of existing structures to bear seismic loading.Historic masonry structures, particularly those lacking traditional earthquake-resistant features, are vulnerable to seismic loads. Further, their substantial weight, in-plane stiffness, low tensile strength and brittleness renders them vulnerable to settlement-induced damage. Given the cultural significance of architectural heritage, the performance of historic buildings in the Damage Limitation (DL) state is a matter of importance. Additionally, due to the incorporation of both vernacular and monumental architectural heritage buildings in the urban setting, their performance in the Near Collapse (NC) state is as important as that of ordinary building structures. Therefore, methods and techniques for enhancing the behaviour of historic buildings in both States need to be devised and evaluated.This paper focuses on the application and assessment of a retrofitting technique commonly used for damage prevention and repair in unreinforced masonry structures in the Netherlands, namely bed joint reinforced repointing. The technique consists in the embedment of stainless-steel bars in continuous bed joints, as well as their dry placement across cracks in the masonry. The technique is applied on a masonry wall tested under quasi-static cyclic in-plane shear loading for the evaluation of its performance not only in the DL state for which it was conceived, but also in the NC states. The wall features artificially introduced cracks that simulate settlement-induced damage prior to the installation of the bars.A finite element meso-model is used for the simulation of the wall tests, featuring the artificial damage and reinforcement elements. The model is used in non-linear cyclic analyses for the simulation of the experiments.Through experimental testing and numerical modelling, the efficiency of the strengthening technique is evaluated in terms of resulting shifts in wall capacity, stiffness and failure mode. Further comments are provided concerning its applicability and structural compatibility.

Hysteresis Model for Soft Cohesive Soils under Combinations of Static and Cyclic Shear Loads

Abstract The application of large-amplitude cyclic shear loads on soft soils results in large strains after a certain number of cycles. These strains are highly dependent on static shear load and c...

Behaviour of headed studs subjected to cyclic shear in steel frames with reinforced concrete infill walls

Headed studs are often used to facilitate composite actions between steel and concrete structures. In steel building structures, reinforced concrete walls are commonly used to ensure composite action to stiffen steel frames as a lateral resistance system against horizontal loads, such as earthquakes or wind. Such walls need to be anchored to the steel frame by headed studs, and these must be able to withstand shear and tension forces, as well as the interaction between these two. To design such anchors in concrete walls, it is necessary to describe experimentally their behaviour under monotonic and cyclic shear forces given that edge conditions and reinforcing details influence stud stiffness and strength.As very few experimental studies have examined headed studs subjected to monotonic or cyclic shear with usual boundary effects in steel frames with reinforced infill walls, a new experimental test setup and test results are presented herein. Four tests on headed studs were carried out to describe the behaviour of headed studs under monotonic and cyclic shear loading, as well as to validate the new test setup.This research shows that the behaviour of studs installed in infill walls without group effects are conservatively predicted by EC-4 and Makino’s formula under monotonic shear loading. Furthermore, a reduction factor of 0.70 is recommended to design studs subjected to cyclic shear forces.

Calculating the Permanent Displacement of a Rock Slope Based on the Shear Characteristics of a Structural Plane Under Cyclic Loading

When a rock mass shears along a structural plane, the shear resistance of the structural plane is affected by the structural plane undulations and by the friction between the contact regions. During an earthquake, the seismic load (composed of the cyclic and dynamic loads) produces a dynamic deterioration of the mechanical properties of the structural plane, which is mainly reflected as follows: (1) under cyclic shear of the seismic load, the undulant angle αk decreases. (2) Under the dynamic load, the frictional coefficient of the structural surface is reduced. The dilatancy angle is generally used instead of the undulant angle. When calculating rock slope stability, the frictional angle is equivalent to the sum of the basic frictional angle and the undulant angle. In this study, the equations for calculating the dilatancy angle of a structural plane under cyclic shear loading are determined based on cyclic shear tests of a split structural plane. The basic frictional angle for calculating the cyclic shear is also determined, based on previous research. Furthermore, according to the dynamic model of a rock slope, a method to calculate the permanent displacement of the rock slope is proposed, considering the effect of structural plane deterioration. We found that the effect of structural plane deterioration under a seismic load directly affects the stability and permanent displacement of the rock slope. The feasibility and engineering practicalities of this method are also verified by comparing the proposed method with previously developed methods.

Effect of Different Modes of Lateral Boundary Constraints of the Direct Simple Shear (DSS) Device under Monotonic and Cyclic Shear Loading

Abstract The direct simple shear (DSS) device is commonly employed to characterize the shear behavior of soil while representing a plane strain condition. In DSS devices that use cylindrical specimens, the plane strain condition is mimicked by constraining the lateral boundaries of the specimen against radial deformations during consolidation and shear loading. The current test standard recommends using either wire-reinforced rubber membrane or unreinforced rubber membrane enclosed with stacked rigid rings as suitable modes of confinement to constrain the lateral boundaries of DSS test specimens. Only limited studies have been performed to assess the effects arising because of these different ways of lateral boundary constraints on the test results, particularly when DSS tests are conducted at relatively higher vertical effective confining stress (σ′v0) levels. An experimental program was undertaken to study the effect of lateral boundary constraint mode during constant-volume monotonic and cyclic DSS tests. The constant-volume tests were conducted on reconstituted cylindrical DSS specimens prepared from a natural silty soil under the following three modes of lateral boundary constraints: (a) steel wire–reinforced rubber membrane only (Mode 1); (b) steel wire–reinforced rubber membrane enclosed with a set of thin, low-friction stacked rigid rings (Mode 2); and (c) unreinforced rubber membrane enclosed with a set of thin, low-friction stacked rigid rings (Mode 3). The findings from these tests, conducted on specimens initially consolidated to σ′v0 level up to 900 kPa, indicate that there was no significant difference in the shear response derived from the three cases of lateral boundary constraints. This suggests that the commonly used approach of simply confining the DSS test specimen using steel wire–reinforced rubber membrane alone (i.e., Mode 1) would be effective and adequate for use in monotonic and cyclic direct simple shear testing, for σ′v0 ≤ 900 kPa.

Numerical modeling on strengthening mechanisms of the harmonic structured design on CP-Ti and Ti–6Al–4V

The present work investigates and compares the deformation mechanism of harmonic structured (HS) CP-Ti and Ti–6Al–4V alloy to that of homogeneous coarse-grained (CG) counterparts. A set of simple shear tests on homogeneous CG and HS specimens for CP-Ti and Ti–6Al–4V was conducted under monotonic and cyclic simple shear loading conditions. Efforts have been made to develop a numerical model which is aimed to investigate the microstructure-related mechanical behavior of the materials. Numerical and experimental results were confronted to confirm the validity of the proposed model. To better understand the strengthening mechanisms of the HS design, comparisons between HS CP-Ti and HS Ti–6Al–4V were conducted and discussed in terms of macroscopic stress-strain response and distribution of stress/strain fields. Furthermore, forecasting mechanical properties of HS CP-Ti and HS Ti–6Al–4V including various volume fractions of fine-grained (FG) regions were simulated by using the developed model. It was demonstrated that strengthening mechanisms of harmonic designed CP-Ti and Ti–6Al–4V structures are different. This result explains why the HS design induces superior strengthening effect on CP-Ti than on Ti–6Al–4V.

A micromechanical model for loading and unloading behavior of fiber reinforced plastics under cyclic loading

AbstractThe high fatigue resistance and low weight features make the unidirectional‐carbon fiber reinforced plastics (UD‐CFRP) attractive for cyclic loading applications. However, the complex damage mechanisms within the composite hinder the understanding of its fatigue response. An energy‐based fatigue model has been proposed for the fatigue behavior of epoxy polymers. However, this kind of approaches dependent on the accurate description of the material's behavior. Our work aims to build a representative volume element model (RVE) for the simulation of the cyclic shear loading behavior of UD‐CFRP, which could support the later extension of an energy‐based fatigue model. To precisely reproduce the micromechanical stress‐strain distribution within the matrix, a nonlinear viscoelastic model has been implemented and validated against experimental data. As a result, the simulated UD‐CFRP hysteresis, as well as the stiffness and strain energy density were accurately reproduced for two load ratios (R = 0.1 and R = − 1). Additionally, the cyclic strain accumulation observed in the UD‐CFRP can be accurately described by the proposed model.

Characterization of closed-die forged AZ31B under pure axial and pure shear loading

Extruded AZ31B was closed-die forged at a relatively low temperature of 250 °C. Quasi-static axial and shear tests in addition to cyclic pure axial and cyclic pure shear tests were performed to characterize the uniaxial response of the forged parts. To examine the effect of forging on the mechanical behavior of the material, quasi-static and fatigue response of the starting extruded AZ31B was also studied under axial loading. The forging process refined the grain structure and modified the crystallographic texture of the extruded AZ31B. The intensity of texture and the orientation of c-axis in the forged part were found to be controlled by the extent and the direction of plastic deformation, respectively. The modified microstructure resulted in insignificant effect on yield strength, slight decrease in ultimate strength, and enhanced failure strain of the forged AZ31B under axial loading. However, the forged AZ31B exhibited superior yield strength, similar ultimate strength, and lower failure strain under shear loading. The cyclic axial strength of the forging was similar to the starting extruded material under high strain amplitudes, but slightly superior under lower strain amplitudes, due to the development of a smaller tensile mean stress. The half-life hysteresis response for the forged material was asymmetric under large axial strain amplitudes, but it was symmetric under cyclic shear loading. This difference is originated from activation of twinning/ detwinning deformation under cyclic axial loading, while dislocation slip is the dominant deformation mechanism during cyclic shear loading. Fatigue fracture surface of forged AZ31B depicts that fatigue cracks were initiated from multiple locations under both cyclic axial and shear loadings.

Shear-Torque Fatigue Performance of Geogrid-Reinforced Asphalt Interlayers

Interlayer reinforcement systems represent a valid solution to improve performance and extend the service life of asphalt pavements, reducing maintenance costs. The main issue is that the presence of reinforcement may hinder the full transmission of stresses between asphalt layers, reducing the overall pavement bearing capacity. This study aimed at evaluating the mechanical behavior of geogrid-reinforced asphalt interlayers under cyclic shear loading. To this purpose, a trial section, characterized by three types of interface (reinforced with carbon fiber grid, reinforced with glass fiber grid and unreinforced), was built. Cores were taken from the trial section to carry out shear-torque fatigue tests. Static Leutner shear tests were also performed on cored specimens having the same interface configuration. From data gathered in the present study, shear-torque fatigue tests have proved to be a powerful tool for investigating reinforced specimens. Results clearly ranked the investigated materials, showing that the glass fiber grid has the lowest shear fatigue performance in comparison with the other two interfaces at 20 °C. However, the shear fatigue resistance of glass fiber grid increases significantly at 10 °C. Finally, an interesting correlation was found between cyclic and static shear test results that should be better investigated in future studies.

An experimental and numerical study on masonry triplets subjected to monotonic and cyclic shear loadings

This paper presents an experimental and numerical study on the mechanical behaviour of masonry triplets subjected to monotonic and cyclic shear loadings. Masonry triplets were constructed with fired bricks bonded together with three different in composition (i.e. cement-to-sand ratios) mortars. Shear tests on triplets show that cyclic loading significantly reduces the peak shear strength (typically around 18%) with respect to monotonic loads, regardless of the mortar composition. The shearing behaviour of the triplets obtained from the experiments were successfully reproduced using an innovative discrete element modelling strategy in which masonry units and mortar were represented by a series of irregular particles (i.e. through Voronoi-shaped particles) with a fictitious random microstructure. Numerical results highlight that cyclic shear strength reduction can be attributed to the progressive formation of cracks in the mortar layers along with the cyclic loading. These observations provide new insight into behaviour of structural masonry and lead to suggestions for improving assessment techniques for masonry structures subjected to combined actions of compression and shear.

Generalized hyper-viscoelastic modeling and experimental characterization of unfilled and carbon black filled natural rubber for civil structural applications

Unfilled and carbon black filled natural rubber have attracted considerable attention and have been extensively used as a novel construction material in civil infrastructure applications because of their superior physical and mechanical properties. However, their mechanical behavior is highly nonlinear and further complicated by the significant sensitivity to the loading rate. In this paper, a generalized constitutive model was proposed to improve the description of rate-dependent mechanical behavior of unfilled and carbon black filled natural rubber. The proposed model consisted of a hyperelastic spring to characterize the equilibrium response and a Maxwell element to capture the rate dependency as well as link the overstress to the loading rate. Subsequently, the stress–strain response of both unfilled and filled natural rubber subjected to the cyclic shear loading with different strain rates was experimentally characterized, multi-step relaxation and cyclic shear tests were carried out to calibrate material parameters in the model. Afterwards, a nonlinear viscosity coefficient was derived to completely establish the proposed model and its three-dimensional function versus strain and strain rate was also obtained based on the experimental data. Finally, comparing numerical simulations with cyclic shear tests and real-time hybrid simulation tests, it was found that the simulated results were in good agreement with the test results, indicating the proposed model is capable to accurately describe the hyper-viscoelastic behavior of both unfilled and filled natural rubber under cyclic shear loading, which might become an appropriate choice to be used by researchers and engineers for civil structural applications.

Structural behaviour of composite panels made of profiled steel sheets and foam rubberised concrete under monotonic and cyclic shearing loads

Abstract This research investigates the effect of using lightweight foam rubberised concrete as an infill material for double-skinned profiled composite panels under pure shear load through experimental and analytical modelling. Three concrete mixes were used as infill materials in this study: one control foam concrete (FC), and two foam rubberised concrete (FRC) with rubber contents of 8.5% and 17% by total mix volume. The pure shear behaviours of the profiled concrete and profiled steel-concrete composite panels were investigated by testing nine small-scale square panels. Three profiled concrete panels and three profiled steel-concrete composite panels were tested under monotonic pure shear load. In addition, three profiled steel-concrete composite panels were tested under repeated cyclic pure shear load. The monotonic test results showed comparable ultimate loads for both FRC and FC panels. Moreover, the FRC panels experienced a higher number of cracks and higher ductility. The cyclic shearing behaviour of FRC composite panels with 8.5% and 17% rubber contents outperformed the FC panels through increased capacities of about 10.3% and 8%, respectively. The increase in ductility of FRC panels with 8.5% and 17% rubber contents over that of FC panels was about 19.5% and 2.4%, respectively. The cumulative energy dissipation for FRC panels also showed a distinct increase over that of FC panels.

Investigation of self-heating and life prediction in CFRP laminates under cyclic shear loading condition based on the infrared thermographic data

In this work, the shear fatigue behavior of a Carbon Fiber Reinforced Polymer (CFRP) composite has been studied by carrying out tensile test on the laminates [±45°]8. The amount of heat generation rate per unit of volume within CFRP laminate under various cyclic loading condition is investigated by combining experimentation and numerical simulation. The generated heat during fatigue testing is classified into two parts – induced by internal frictions and induced by irreversible changes in CFRP laminates (delamination, crack propagation, …). It is considered that most of the fatigue damage is related to the irreversible changes while internal frictions do not cause any damage. The investigation shows that the total amount of heat generation related to damage is nearly independent of loading stresses. Based on this phenomenon, a rapid methodology is proposed to predict the S-N curve in a short time by measuring the temperature evolution curves under cyclic loading and conducting one or two specimens until final fracture. The prediction area is mostly inside the 95% confidence intervals of the experimental data, which shows a good agreement with the traditional fatigue test.

Post-liquefaction pore pressure dissipation in sand under cyclic stress triaxial testing

Soil liquefaction has conventionally been studied as a pure undrained condition subject to cyclic shearing in the laboratory. However, in the field, ground settlement and expulsion of pore water in the form of sand boils are frequently observed, which conventional triaxial and simple shear apparatus are unable to replicate. In this study, a novel insight of coupled pore pressure generation and dissipation in liquefiable clean sand is discussed with the use of a modified cyclic triaxial testing set-up. Stress-controlled cyclic triaxial tests with controlled pore water drainage far lower than the soil's permeability were carried out to investigate ‘near-perfect undrained’ conditions, which are more representative of field conditions. Comparison of results from three sets of stress-controlled cyclic triaxial testing were carried out: (a) conventional shearing under an undrained condition; (b) shearing under controlled drainage; and (c) undrained shearing until liquefaction, and thereafter continual shearing under controlled drainage. The critical cyclic shear stress ratio where excess pore pressure dissipation dominates excess pore pressure generation is identified from the coupled cyclic shear loading and pore water drainage tests. In addition, this study also noted a critical void ratio where the soil is no longer susceptible to liquefaction even under considerable shearing amplitudes. These findings may offer guidance on the tolerable cyclic shear stress and minimum degree of densification to avoid occurrence of soil liquefaction in the field.

Investigation of Fatigue Behavior of Steel and GFRP Double-Strap Joints under Varied Cyclic Loading at Given Temperatures

AbstractThis paper examines the fatigue behavior of steel/glass fiber reinforced polymer (GFRP) double-strap joints under a variation of cyclic shear loading at different given temperatures. Initia...

Shear Slip Instability Behavior of Rock Fractures under Prepeak Tiered Cyclic Shear Loading

In this paper, shear displacement properties of rock fractures were studied, and the energy evolution process was analyzed before sliding instability under complex shear loading paths. The artificial prefabrication method was used to simulate the natural rock fractures, which are difficult to obtain in the natural environment. The prepeak tiered cyclic loading tests under constant normal loading were performed on six rock specimens with fractures by rock direct shear apparatus (RDS‐200). To obtain the stress difference of adjacent cycles, the direct shear test was conducted on the other six rock specimens with fractures before the prepeak tiered cyclic shear loading test. The variation trend of residual shear displacement (RSD) and the similarity of loading and unloading curves before slip instability were obtained by analyses of prepeak tiered cyclic shear loading test data. Energy evolution laws of rock fractures were analyzed with the consideration of the hysteresis characteristics, according to the hysteresis effect of shear displacement behind shear stress. This paper provides guidance for the study on shear instability of rock fractures under complex loading paths.

Modeling cyclic shearing of sands in the semifluidized state

SummaryLiquefaction is associated with the loss of mean effective stress and increase of the pore water pressure in saturated granular materials due to their contractive tendency under cyclic shear loading. The loss of mean effective stress is linked to loss of grain contacts, bringing the granular material to a “semifluidized state” and leading to development and accumulation of large cyclic shear strains. Constitutive modeling of the cyclic stress‐strain response in earthquake‐induced liquefaction and post‐liquefaction is complex and yet very important for stress‐deformation and performance‐based analysis of sand deposits. A new state internal variable named strain liquefaction factor is introduced that evolves at low mean effective stresses, and its constitutive role is to reduce the plastic shear stiffness and dilatancy while maintaining the same plastic volumetric strain rate in the semifluidized state. This new constitutive ingredient is added to an existing critical state compatible, bounding surface plasticity reference model, that is well established for constitutive modeling of cyclic response of sands in the pre‐liquefaction state. The roles of the key components of the proposed formulation are examined in a series of sensitivity analyses. Their combined effects in improving the performance of the reference model are examined by simulating undrained cyclic simple shear tests on Ottawa sand, with focus on reproducing the increasing shear strain amplitude as well as its saturation in the post‐liquefaction response.

Response of High-Density Polyethylene Geomembrane–Sand Interfaces under Cyclic Shear Loading: Laboratory Investigation

AbstractGeomembranes are thin polymeric sheets used as barriers to liquid or gas intrusion in earth structures due to their low permeability. The mechanical behavior of geomembrane-soil interfaces ...