Single Shear Tests Research Articles

Yield Parameters for Iron Powder Compaction on Different Particle Size

Shear failure yield line in Drucker-Prager yield surface for iron powder on different particle size and amount of interparticle lubricant has been estimated. Critical stress state and uniaxial failure stress state have been determined by a single shear test and uniaxial failure test for a green compact. Compaction cap parameter has been estimated by the lateral force measurement test by instrumented die compaction system. By those estimations, materials input parameters for the Drucker-Prager Cap (DPC) model have been determined successfully, and differences in particle size and amount of lubricant can be recognized. Finite element method (FEM) analysis of simple closed-die compaction has been conducted. As a result, the materials input parameters for the DPC model on different powder properties have been successfully identified as the FEM analysis fairly predicts compaction pressure and density distribution on uniaxial compaction.

Comparative Shear Tests of Bolt Rods Under Static and Dynamic Loading

Abstract This article presents the methodology and results of single shear tests of bolt rods under dynamic impact loading generated by means of a drop hammer. Comparative analysis was also performed for bolt rod load capacity, stress and shear work under static and dynamic (impact) loading. The developed method of single shear testing of bolt rods under impact loading makes it possible to obtain repeatable test results concerning maximum bolt rod shearing force, shear stress and shear work values. Comparative shear tests of four types of bolt rods under static and impact loading showed that the APB-type bolt rods made of AP770 steel, which was characterised by having the highest strength, exhibited the greatest shear work. AM22-type bolt rods exhibited a very similar work value. Though the AM22-type bolt rods made of A500sh steel demonstrated lower strength than the APB-type bolts, as well as a smaller diameter and cross section, they dissipated the impact energy better thanks to their higher plasticity. This could indicate the direction of optimisation for bolt rods in order to increase their impact strength. Mathematical relationships were also formulated for selected tests, describing the real single shear courses F d =f(t) of bolts under impact loading. The obtained relationships could be applied in the load assessment process of bolt rods intended for use under roof caving, tremor and rock burst conditions.

Experimental study on the dynamic bond behavior between CFRP and concrete under different slip rates

In this paper, a series of single-shear tests were carried out to investigate the bond behavior between carbon FRP (CFRP) and concrete under quasi-static and dynamic loadings. The local bond stress-slip relationship and the ultimate bond strength between CFRP and concrete with different compressive strengths under different slip rates between 1.2 × 10−5 m/s and 9 m/s were derived and compared. Test results showed that the ultimate bond strength, maximum bond stress and slip at maximum bond stress increase with the increase of slip rate, while the effective bond length is not sensitive to the slip rate. Based on the testing data, several empirical formulas were proposed to predict the ultimate bond strength, maximum bond stress and slip at maximum bond stress under different slip rates. A local bond stress-slip model, which incorporates the effect of the slip rate, was also established.

Finite element modelling of dynamic bonding behaviours between fibre reinforced polymer sheet and concrete

In this study, dynamic debonding behaviour between fibre-reinforced polymer (FRP) and concrete is numerically investigated by using finite element code LS-DYNA. A three-dimensional (3D) finite element (FE) model is built and a bond-slip model is incorporated into the simulation of interfacial bond between FRP and concrete. To validate the accuracy of the numerical model, experimental results from 42 dynamic single shear tests on FRP-concrete joints are employed. The debonding load and shear slip responses, FRP strain distributions, and interfacial bond-slip responses are compared between the numerical and experimental results. It is found that the numerical model is capable of predicting the debonding behaviours under various loading rates. In addition, an analytical dynamic bond strength model is proposed to predict the ultimate debonding strain and debonding load by incorporating the dynamic increase factor and strain rate. In addition, a semi-empirical model is proposed to predict the ultimate debonding strain and debonding load by incorporating the dynamic increase factor and strain rate. The semi-empirical model is validated against the numerical results and 119 experimental tests with a good correlation.

Experimental Study on Stress Corrosion Index Governing Time-Dependent Degradation of Rock Strength

Rock fractures in geological conditions are caused not only by applied stress, but also by stress corrosion. Stress corrosion is an environmentally activated chemical process, associated with the fluid-assisted crack growth. Crack growth due to stress corrosion is related to the time-dependent behaviours of rocks and is a crucial factor in determining the stability of underground structures over the long period of time. In this study, constant stress-rate tests including Brazilian tension and three-point flexural tests for the tensile strength, short-beam compression and single-shear tests for the in-plane shear strength, and a torsion test of rectangular section specimens and a circumferentially notched cylindrical specimen test for the out-of-plane shear strength were conducted at a different loading rate from 0.01 to 10 MPa/s using Coconino sandstone. The results show that the rock strength was proportional to the 1/(n+1)th power of the loading rate, where the parameter n indicates the stress corrosion index. The stress corrosion index (n) ranged from 34 to 38, with an average value of 36. The stress corrosion indices (n) were similar, irrespective of the loading configuration and specimen geometry. The stress corrosion index (n) can, therefore, be regarded as a material constant of rocks.

Evaluation of mechanical properties of nanoparticles using a constant-volume shear tester

Nanoparticles have advantageous small-size and surface effects that impart them with unique mechanical properties. To evaluate these properties, a constant-volume shear tester that can precisely measure stresses on the shear plane was used. Six samples, namely, hydrophilic and hydrophobic silica, alumina, and titania nanoparticles, were prepared for the shear tests. For each sample, a single shear test provided the void fraction, stress relaxation ratio, stress transmission ratio, powder yield locus, consolidation yield locus, critical state line, shear cohesion, and flow function. All the tests were conducted under ambient conditions using powder beds, in which the void fractions were in the range of 0.89–0.96. A series of analyses demonstrated that the hydrophilic nanoparticles have lower flowability than the hydrophobic nanoparticles, indicating that moisture on the surface increases the cohesion and inhibits the flow.

Bond stress and behavior of interface between untreated aluminum alloy surface and concrete

This paper explores the viability of using aluminum alloy (AA) plates as an externally bonded reinforcement (EBR) material that could overcome some of the shortcomings of the prevailing steel and FRP materials and provides new advantages. A total of 32 prisms with different concrete strengths have been prepared as single shear test specimens with AA plates bonded to the prisms at different lengths using epoxy adhesive. Single shear tests were conducted on the prism specimens until failure. Load-extension and load-strain values were recorded. Bond stress and bond slip values were calculated. Test results have shown that plain untreated AA surface is susceptible to premature debonding; however treating the AA surface, by roughening it, increases its bond strength and ultimate load capacity considerably. Generally, the ultimate load and maximum bond stress increased with the increase of the bonded length and concrete strength, on the average, for the AA roughened surface compared to the AA plain untreated surface, by up to 457%, 327%, respectively. It is also observed that the modes of failure were influenced by the changes in the bonded length, concrete strength and AA surface treatment.

Bonding Performance of Fiber-Reinforced Polymer-to-Concrete Joints under the Effect of Corrosion Cracking

Externally bonded (EB) carbon fiber-reinforced polymers (CFRPs) have been progressively considered for application in concrete structures. However, the corrosion of reinforcing steel bars (rebars) in reinforced concrete (RC), which is more common in coastal environments than in inland environments, can degrade structural performance. The bonding performance of FRP-to-concrete joints can be further deteriorated by the degradation of the interfacial bonding behavior between the rebar (or rebars) and concrete cross-sectional area reduction at the steel bar plane induced by rust expansion. In this study, the effect of rebar corrosion on the FRP bonding performance of RC components was experimentally investigated for the first time. Single shear tests assisted by a 3D optical displacement measurement system were used to obtain the full-field distribution of specimen displacements. The test results show that, although the corrosion level and diameter of the steel bar slightly affected the bonding strength of FRP-to-concrete, the corrosion crack width increased as the steel bar corrosion level increased, which affected the failure mode. Hence, as the corrosion level of the steel bars increased, the likelihood of concrete cover separation increased. Finally, a modified strength design model accounting for the rebar corrosion level was proposed in this paper.

Experimental and numerical investigation of debonding process of the FRP plate-concrete interface

Single shear tests performed to study the debonding between the concrete and the FRP plate of 2 mm thickness are presented. Specimens with five different bond lengths have been tested. In order to investigate the debonding mechanism and measure the complete strain distribution, digital image correlation (DIC) method was applied. The shear stress and slip distribution curves were calculated from the strain distribution functions fitted from measured strain data. Based on the features of the shear stress transfer zone under different load levels, the whole loading process has been divided into four stages: (1) elastic stage; (2) cracking stage; (3) debonding stage; (4) failure stage. According to the relationship between the relative bearing capacity and bond length, a concept of efficient bond length was suggested. A bi-linear bond stress-slip model was calibrated by the constitutive parameters of the experimental shear stress-slip curves. Based on the bi-linear bond stress-slip relationship, a numerical model of FRP plate-concrete interface was built using the bonded-particle model (BPM) and the debonding process was numerically analyzed. The numerical results present good agreement with the experimental results in the load-slip response and the shear stress distribution along the bond length. The comparison between the experimental and the numerical results shows that BPM can effectively simulate the debonding process of the FRP plate-concrete interface.

Experimental research on the wet bonding properties between RFRP and concrete

In this work, an improved wet bonding method was developed for strengthening of fiber-reinforced polymer. A self-made roughened carbon fiber–reinforced polymer sheet (hereinafter referred to as RFRP sheet) was externally attached to the surface layer of a nano-kaolin-modified concrete test piece to form an RFRP–concrete wet-bonded test piece. Then, the pull-off bond test and the single shear test were performed on 32 and 30 test pieces, respectively. The performance of the wet bonding interface of RFRP–concrete in the normal and tangential directions was investigated by changing the length of glass fiber cellosilk in RFRP bonding resin, the diameter of RFRP porous pelelith rock, and the ratio of nano-kaolin. In addition, by comparing the scanning electron microscopy images of untreated fiber-reinforced polymer sheet and the concrete block without nano-kaolin, the mechanism of the adhesion enhancement of the RFRP–concrete interface was explained. The results show that the differentiation between fiber-reinforced polymer–concrete wet bonding failure and RFRP–concrete wet bonding failure was mainly based on the large-scale concrete with peeled off concrete surface. RFRP effectively enhanced the wet adhesion performance of the interface with concrete in both normal and tangential directions. The interface bonding ability increased by 900% and 42%, respectively, compared with the control test pieces. The diameter of pelelith rock was found to be the most important factor affecting the shear wet bonding performance of the RFRP–concrete interface. The second important factor was the ratio of nano-kaolin. The optimum conditions for the best tangential anti-peeling ability of the RFRP–concrete structure were found to be the addition of 5-mm-diameter pelelith stone, 3% nano-kaolin, and glass cellosilk of 89 mm length. When the RFRP and the concrete were wet-bonded, the uncured cement mortar effectively filled the holes of the original pelelith rock and acted as a mechanical lock, thereby increasing the bonding stress.

Bond properties between carbon fibre-reinforced polymer plate and fire-damaged concrete

In this research, a single-shear test was conducted to investigate the bond properties between carbon fibre-reinforced polymer (CFRP) plates and fire-damaged concrete prisms. The investigation focused on the effects of fire exposure condition and the presence of internal steel reinforcements on the effective bond length, failure mode, bond strength (maximum joint load) and interfacial fracture energy. After being air-cooled, the concrete prisms were adhesively bonded with CFRP strips of different lengths, and then quasi-static tested at the ambient condition. The pull-off test results showed that the tensile strength of concrete substrate decreased after being exposed to elevated temperatures. Such deterioration of concrete substrate caused an increase in the effective bond length. It also decreased the bond strength and interfacial fracture energy. The steel reinforcements in concrete structures are beneficial as they minimize the effect of fire exposure on bond strength and effective bond length. An application of the fracture mechanics-based model for strength prediction of bond between fire-damaged concrete and the CFRP plate is proposed. A linear relationship between interfacial fracture energy and pull-off tensile strength of concrete could be assumed for the unreinforced concrete.

Influence of multiple anchor arrangement in the behaviour of FRP-to-concrete anchored joints

The effectiveness of fibre-reinforced polymers (FRP) external reinforcements is limited by premature delamination from concrete. In recent years, various anchoring systems were developed for FRP sheets. Among these, FRP anchors stand out for their effectiveness. When the unit strength of a connector is insufficient, multiple anchors may be employed. This paper presents an experimental campaign consisting of single shear tests on CFRP anchored narrow (100 mm width) and wide (200 mm width) sheets in concrete substrates. One anchor was installed in narrow sheets for comparison with wide sheets. Wide sheets were tested with one anchor and with two anchors transversally distributed to evaluate the influence of multiple anchors. Results from both literature and tests show that an optimal arrangement of one anchor in narrow FRP sheets or two transversally distributed anchors in wide sheets can be equivalent, which allows the anchored joints to develop more than twice the bond strength.

Study on the strength of diameter-reducing solder balls by shear and pull tests

Purpose The purpose of this paper is to study the variation of the mechanical strength and failure modes of solder balls with reducing diameters under conditions of multiple reflows. Design/methodology/approach The solder balls with diameters from 250 to 760 µm were mounted on the copper-clad laminate by 1-5 reflows. The strength of the solder balls was tested by the single ball shear test and pull test, respectively. The failure modes of tested samples were identified by combing morphologies of fracture surfaces and force-displacement curves. The stresses were revealed and the failure explanations were assisted by the finite element analysis for the shear test of single solder ball. Findings The average strength of a smaller solder ball (e.g. 250 µm in diameter) is higher than that of a larger one (e.g. 760 µm in diameter). The strength of smaller solder balls is more highly variable with multiple reflows than larger diameters balls, where the strength increased mostly with the number of reflows. According to load-displacement curves or fracture surface morphologies, the failure modes of solder ball in the shear and pull tests can be categorized into three kinds. Originality/value The strength of solder balls will not deteriorate when the diameter of solder ball is decreased with a reflow, but a smaller solder ball has a higher failure risk after multiple reflows. The failure modes for shear and pull tests can be identified quickly by the combination of force-displacement curves and the morphologies of fracture surfaces.

Large scale experimental study on bond behavior between polymer modified cement mortar layer and concrete

The effectiveness of concrete structures reinforced by the high strength steel wire mesh-polymer mortar depends on the bond-slip behavior of the interface between the polymer modified cement mortar layer (referred as mortar layer) and the concrete. The areas of the mortar layer tested in the previous studies are generally very small and the obtained conclusions are with limited applications. In this study, the experimental approach was used to analyze the slip behavior of the interface between the concrete block and a larger scale mortar layer. 30 concrete blocks retrofitted with mortar layers were fabricated and the single shear tests on these specimens were conducted. The applied shear loads, slip displacement between the concrete block and the mortar, as well as the strain of the mortar were monitored during tests. The experimental results exhibit the specimens have two representative failure types: debond with and without cracks. Then the bonding performance of the interface was systematically explored by analyzing the failure modes of the specimens and the mechanical property of the mortar. Meanwhile, the slip behavior of the interface influenced by the bond area, the thickness of the mortar layer, the mortar strength and the roughness of the interface were discussed. It was presented that the interface roughness treatment and increasing the mortar strength could significantly improve the behavior of the interface.

Evaluation of rolling shear modulus and strength of Japanese cedar cross-laminated timber (CLT) laminae

Cross-laminated timber (CLT) panels are fabricated with their layers stacked crosswise. Owing to the low shear modulus and strength in the rolling shear direction, the shear properties of cross-layers influence the overall deflection and shear capacities of CLT panels. The aim of the present study is to determine the rolling shear properties of Japanese cedar and investigate how annual ring patterns and lamina geometry influence shear properties. Using a test configuration similar to the standard shear test configuration prescribed in European Standards (EN 408), a single lamina shear test was conducted. To investigate the influence of thickness-to-width aspect ratio of the lamina on the rolling shear properties, samples with three different widths, including 62, 88, and 112 mm, with a constant thickness of 24 mm were tested. The geometrical features of the annual ring patterns of each test sample were measured. The mean rolling shear moduli were 72, 91, and 109 MPa, and the mean rolling shear strengths were 1.54, 1.83, and 2.02 MPa for the 62-, 88-, and 112-mm sample widths, respectively. Shear strength was highly correlated with shear modulus. The mean shear modulus and strength, in addition to the 5% quantile, increased with an increase in lamina width. Across all sample widths, rolling shear modulus and strength decreased with an increasing radial distance from the pith. Using the principle of continuum mechanics, the influence of the annual ring angle relative to the shear force direction was examined quantitatively using the finite element method. The results suggest that shear modulus and its variance are influenced greatly by the annual ring structure.

Innovative approach to strata reinforcement in coal mines with reference to evaluation cable bolts shear strength

There is an increasing need to determine accurately the strength properties of tendons for an effective ground control on mines and underground structures as well as on modelling simulations. The strength properties of cables, used as cable bolts, have been evaluated mainly by their ultimate tensile strength, as this kind of test can be carried out in the field as well as in the laboratory. Only recently, there has been a growing interest in cable bolt failures in shear because of the documented field failure evidence. Accordingly, this paper reports various methods of shear testing of rock bolts and cables using different shear testing rigs, some have been developed by the rock bolting research team at the University of Wollongong. A programme of shear testing of a variety of cable bolts marketed in Australia was undertaken, the results of which were reported and conclusions were drawn. It was concluded that plain cable bolts were de-bonded during shearing when compared to spiral cables under the same testing conditions. In addition, both the single shear and double shear testing methodologies will result in the same outcome if there is no de-bonding, and a proper confinement is applied.

An investigation of plastic behaviour in cold-rolled aluminium alloy AA2024-T3 using laser speckle imaging sensor

The mechanical anisotropy of aluminium alloy AA2024-T3 with strong cold-rolled crystallographic texture is investigated in this paper. A non-contact and non-destructive laser speckle imaging sensor is developed for surface strain measurement so that extensive mechanical tests can be readily performed without surface preparation on the specimens. Both Hill’s 48 and Yld2004-18p yield functions are accurately calibrated using the experimental results from uniaxial tensile, pure shear and plane-strain tensile tests. The constitutive models based on these yield functions were successfully implemented in a commercial finite element (FE) package Abaqus via user material subroutine UMAT. Simulations of single element tensile tests and pure shear tests were carried out to validate the accuracy of UMAT subroutine. The performance of these constitutive models was further evaluated with deep drawing experiments in which the predicted earing profiles were compared with those obtained from FE simulations. The results showed that the constitutive model based on Yld2004-18p yield function accurate representing the anisotropic behaviour of AA2024-T3. The predicted earing profiles coincide well with experimental measurements.

Bond strength measurement for additively manufactured Inconel 718- GRCop84 copper alloy bimetallic joints

To benefit from the fascinating properties of multi-material structures, the interfacial joint should exhibit good mechanical strength. Evaluating the shear strength of a bimetallic joint via conventional methods is usually complex, and in most cases produces unreliable data due to induced bending stress among others. In this work, a novel single-shear test device was designed and fabricated to measure shear strength of bimetallic joints. The device was first standardized by shearing standard materials, and the results were in good agreement with published data. Subsequently, the shear strength of Inconel 718/copper alloy (GRCop-84) bimetallic joint built via laser engineered net shaping (LENS™) was evaluated. Compression test on the bimetallic joint was carried out as well for more mechanical characterization. Both shear and compressive yield strengths of the bimetallic joints were compared with the base materials in addition to influence of thermal cycling on the joint strength. Inconel 718/GRCop-84 bimetallic-joint shear strength was 220 ± 18 MPa and 231 ± 27 MPa for as-printed sample and after thermal cycling, respectively. Likewise, the bimetallic yield strength after compression test was 232 ± 3 MPa and 337 ± 15 MPa. No cracking through or along the interface was observed even after thermal cycling, which indicates no thermal degradation at the bimetallic interfacial joint. Increase in compressive yield strength after thermal cycling could be attributed to precipitation of Cr2Nb particles in GRCop-84 matrix along with strengthening due to gamma phases in Inconel 718. Scanning electron microscopy (SEM) and backscatter electron imaging were used to examine the interfacial microstructures and failure modes. EDS was used as well to analyze the interface elemental composition. The development of the single-shear test device can provide an added opportunity to effectively evaluate mechanical behavior, reliability and performance of additively manufactured multi-material structures through bond strength analysis.

Estimation of Yield Surface on Iron Powder Compaction for Finite Element Analysis using Drucker-Prager Cap Model

Shear failure yield line in Drucker-Prager yield surface for conventional atomized iron powder has been estimated with critical stress state and uniaxial failure stress state by single shear test and uniaxial failure test for green compact. Lateral force measurement test was also conducted using newly devised instrumented die compaction system to identify compaction yield characteristics as Cap yield surface. By those estimations, materials input parameters for Drucker-Prager Cap model have been determined successfully. Finite element analysis of simple closed-die compaction has been conducted and good correspondence in variation of compaction pressure with densification has been recognized.

Joining and mechanical testing of oxide/oxide (Nextel ™610/alumina-zirconia) ceramic composites

Efficient joining materials and techniques are of critical importance for the integration of CMCs in high performance structures. Continuous oxide fiber Nextel™ 610/alumina-zirconia composites were successfully joined to themselves by using a novel glass-ceramic based on the SiO2-CaO-Al2O3-MgO-Y2O3-ZrO2 system.Crystallization kinetic of the novel glass-ceramic was studied using Matusita, Sakka and Ozawa equations. Single lap off-set shear tests and four-point bending tests were performed at room temperature and at 850 °C to investigate the mechanical strength of the joints. Thermal ageing was performed at 850 °C for 100 h in air to check the thermal stability of the joined components. The results showed that the joints were oxidation resistant and the joined interfaces were well bonded. Single lap off-set shear tests on joined samples resulted in delamination of the composites. The average flexural strengths of the joined samples were 71 MPa and 81 MPa, at room temperature and at 850 °C, respectively.