Shear Specimens Research Articles

Interfacial properties of geopolymer mortar and concrete substrate: Effect of polyvinyl alcohol fiber and nano-SiO2 contents

Geopolymer mortar, which is a new type of green cementitious material, can be used as an alternative to traditional cement mortar in the repair and reinforcement of defective structures, and the addition of polyvinyl alcohol (PVA) fiber and nano-SiO2 (NS) can improve the interfacial properties of geopolymer mortar and concrete substrate. In this study, the influence of PVA fiber and NS on the shear characteristics of geopolymer mortar and concrete substrate was studied through a double-interfaced shear experiment. Based on the results of this experiment, surface-based cohesive contact was utilized to analyze the shear behavior of the PVA fiber and NS-reinforced geopolymer mortar and concrete substrate, and a shear toughness evaluation method was proposed to further evaluate the shear behavior. The results indicated that the optimal bond strength was achieved when the geopolymer mortar was mixed with 0.8% PVA fiber and 2.0% NS; compared with geopolymer mortar without PVA fiber and NS, the bond strength increased by 34.76% and 13.78% respectively. The numerical modeling results were consistent with the mechanical mechanism and damage mode of the experimental results, which indicated that surface-based cohesive contact could accurately describe the shear characteristics of a double-interfaced shear specimen. Using the proposed shear toughness evaluation method, it was found that when the PVA fiber content was 0.8%, feq, γp and Tp reached their respective maximum values with increment of 0.69, 0.61 and 1.66, respectively, indicating that the toughening effect of geopolymer mortar was optimal. The shear toughness of geopolymer mortar first rose and then declined with the increase of NS content. The PVA fiber and NS had a positive synergistic effect on the shear toughness of geopolymer mortar and concrete substrate.

Experimental study on deformation evolution and fracture behaviors of pure titanium at different stress triaxialities

In this study, the deformation and fracture behaviors of pure titanium sheet specimens under different stress triaxialities are experimentally investigated. Digital image correlation (DIC) technique is used to determine the strain maps on the surface of the specimens during the deformation and failure process. The experimental results show clearly that the strain localization occurs in different specimens which leads to the formation of the crack in the localized region (LR). The characteristics of the LR are quantitatively identified by the strain distribution along axial and transverse directions, the evolution of effective strain is successfully used to obtain the strains of diffuse necking, local necking and strain at fracture. The fracture features of the specimens with different stress triaxialities are studied by the analysis of fracture surface morphology. The nucleation and growth of micro-voids in pure titanium is significantly dependent on the applied stress conditions. The slip mechanism dominates the failure of shear specimens. For tensile loading conditions, the higher stress triaxiality accelerates the growth and coalescence of micro voids which induce the decrement of fracture strain.

Characteristic Tearing Energy and Fatigue Crack Propagation of Filled Natural Rubber.

Below the incipient characteristic tearing energy (T0), cracks will not grow in rubber under fatigue loading. Hence, determination of the characteristic tearing energy T0 is very important in the rubber industry. A rubber cutting experiment was conducted to determine the T0, using the cutting method proposed originally by Lake and Yeoh. Then, a fatigue crack propagation experiment on a edge-notched pure shear specimen under variable amplitude loading was studied. A method to obtain the crack propagation rate da/dN from the relationship of the crack propagation length (Δa) with the number of cycles (N) is proposed. Finally, the T0 obtained from the cutting method is compared with the value decided by the fatigue crack propagation experiment. The values of T0 obtained from the two different methods are a little different.

Strain ratio effects on microstructure discovery and low-cycle fatigue behavior of DP600 steel under cyclic shear path

The fatigue behaviors of dual-phase steels (DP600) under cyclic shear path are studied and the effects of strain ratio are analyzed. Based on twin bridge shear specimens, complete reverse strain-controlled fatigue tests are carried out on DP600 sheet (1.2 mm) under different strain ratios (R = −1, −0.5, 0, and 0.5) with strain amplitudes in the range 0.8–3.0%. DP600 exhibits cyclic softening with a relatively constant softening rate related to amplitude and strain ratio. Smaller loading amplitude and higher strain ratio are beneficial to improve the softening ability of the material. The γ-fiber-type (<111>//ND) texture components are well developed at higher strain ratios, which improve the fluidity of the dual-phase steel, thus making the microstructure deformation more uniform and reducing the risk of damage caused by deformation compatibility. The uniform deformation of the material improves the absorption of plastic strain energy. Therefore, higher strain ratios are beneficial to improve the fatigue life of dual-phase steel.

Study on shear performance of notched connections for glulam-concrete composite beams under fire

Shear connection guarantees that the timber beam and concrete slab of a composite beam interact effectively. Shear connection performance markedly affects the fire resistance of timber-concrete composite beams. Shear connection experiments under fire are uncommon in comparison to those conducted at ambient temperature, and there have been few previous investigations on the shear performance of notched connections under fire. Six specimens were sheared at ambient temperature and ten specimens were sheared at elevated temperature in this study to determine the shear behavior of notched connections exposed to ISO fire. The length of the notch connection and the duration of fire exposure are two factors that may influence the shear behavior of the connections. With the increase of fire time, the shear bearing capacity and slip modulus of notched connections decreased. As notch length increased from 150 mm to 250 mm, the failure modes of shear specimens under fire changed from shear failure of concrete in the notch to compression failure of timber near the notch. Experimental results and finite element thermal analysis results were used to establish an analytical model for the shear bearing capacity of notched connections for glulam-concrete beams under ISO fire exposure.

Effect of elevated temperature on interfacial shear transfer capacity of self-compacting concrete

Interfacial shear stress transfer may occur in structural elements across concrete or between concrete and steel. The fundamental contributing parameters which improve the shear capacities are aggregate grading, compressive strength of concrete, type and area of the interfacial zone, and interfacial reinforcement pattern. During the event of a fire, these parameters are severely affected and mainly depend on the exposure level of the temperature and its duration. In the present investigation, the effect of elevated temperature on the interfacial Shear Transfer Capacity (STC) of Self-Compacting Concrete (SCC) was evaluated using shear (push-off) specimens. SCC was developed using Fly Ash (FA) and Ground Granulated Blast Furnace Slag (GGBFS) as Supplementary Cementitious Material (SCM). The study emphasises the proper understanding of degradation in shear strength of SCC exposed to elevated temperatures. Expanded Perlite Aggregate (EPA) is utilised as a partial replacement for fine aggregate. Also, a thermal protective coating is developed with Cement Perlite Plaster (CPP) for improving the performance of SCC. The European Federation of National Associations Representing for Concrete (EFNARC) guidelines were followed to ensure the workability of the developed SCC mix. Specimens were exposed to 30, 60, 90, and 120 min of heating durations following the International Organization for Standardization 834 (ISO 834) fire rating curve and tested to examine residual compressive strength, mass loss, STC after the natural air cooling process. The SCC specimens with EPA content have exhibited higher residual compressive strength and STC. All the protected SCC specimens coated with the CPP mixture contributed to retaining the original shear capacity by resisting the temperature. An empirical relationship was proposed to predict the residual STC of SCC after exposure to elevated temperature.

Fracture resistance characteristics of mild steel under mixed mode I-II loading

The fracture resistance of elasto-plastic materials varies significantly depending on the mode mixities, i.e., the loading combinations. This paper aims to experimentally investigate the fracture resistance and behaviour of two grades of mild steel under various in-plane loading combinations. A loading fixture with high loading capacity and modified compact tension shear (CTS) specimen are designed to conduct fracture tests on elasto-plastic materials under various mode mixities. A digital image correlation (DIC) technique-based method is developed and verified to detect the fracture initiation. It is found in the paper that the sensitivity of the fracture resistance of steel to mode mixity is attributed to the strain hardening capacity and the impurities in chemical composition of the steel. It is also found that the plastic strain concentration, crack tip blunting and fracture mechanism lead to different fracture resistance of both types of steel under various mixed mode loading combinations. The contribution of the paper is that an additional method to determine the fracture initiation under non-mode I loading is developed. The test results show the necessity of considering the mode mixity effect under the mode II loading dominance in practical engineering applications.

Evaluation of shear force and fractography of friction stir spot welded joints of AA 6082-T6 alloy

This experimental work investigates the tensile behavior of friction stir spot welded joints from 3 mm thick aluminum alloy AA6082-T6 sheets. Taguchi L9 Orthogonal array was used for process parameters - Tool rotational speed (TRS), Dwell time (DT) and Shoulder diameter (SD) with consideration of three levels. Friction Stir Spot Welding (FSSW) was performed on vertical milling machine. Tensile shear test was conducted on Universal testing machine (UTM) to find out the tensile shear failure load (TSFL). The optimal combinations of parameters were at tool rotational speed of 2,000 rpm, dwell time of 15 seconds and tool shoulder diameter of 16 mm. Tool rotational speed had a substantial effect on tensile shear strength of FSSW joint. Scanning Electron Microscopy (SEM) tests revealed that the changes in microstructure in different zones of FSSW joint were observed. Tensile shear specimen was analyzed using SEM to observe the behavior of fracture surfaces. Significant ductility in the fracture surface was an evident in the fractography. In this article, attention is focused on the influence of joining parameters on the mechanical behavior of the friction stir spot weld under the tensile shear load condition. Keywords: Fractography; friction stir spot welding (FSSW); heat affected zone (HAZ); scanning electron microscopy (SEM); thermo-mechanically affected zone (TMAZ).

Effect of mechanical loading history on fatigue crack growth of non-crystallizing rubber

Rubbers possess unique mechanical properties that make them indispensable for technological products such as seals and tires, which are normally subjected to quasi-static loading conditions which superimposes cyclic loads; their failure is mainly related to fatigue. In this study the focus is on the effect on fatigue of parameters connected to the mechanical history. Fatigue crack growth of a non-crystallizing rubber was investigated using cyclically loaded pure shear specimens considering different loading conditions. In a first step, the geometry of the specimens, in terms of width to height ratios and notch length, was considered to avoid specimen-influences on the results. Subsequently, several tests were implemented using both force and displacement control with different loading histories. Finally, the effect on the fatigue crack growth of parameters such as waveform, frequency and load ratio was investigated. In general, no significant influence of load or displacement control was found. Among the loading parameters, waveform and load ratio seem not to have a marked effect on the fatigue behavior of the material. In contrast, decreasing values of frequency were found to increase the crack growth rate.

Fatigue crack growth under mixed-mode I + II and I + III in heat treated 42CrMo4 steel

The paper contains the results of an experimental investigation of fatigue crack development under mixed-mode I + II and I + III in heat-treated 42CrMo4 steel. Tests were performed on heat-treated compact tension shear specimens and rectangular cross-section specimens for mixed-mode I + III. Mixed-mode I + II tests were conducted for 30 and 60° loading angle, while the test for I + III mixed-mode was conducted for 30 and 45°. Additionally, the paper presents fracture analysis results of fatigue crack path development.

Experimental Evaluation on Mixed Mode I/II Stress Intensity Factors using CTS welded and non-welded specimen of Aluminum Alloy AA3003

In the present paper, experimental investigation on the fracture of aluminum alloy AA3003 are conducted on the Compact Tension Shear CTS specimen non-welded and CTS specimen welded by FSW process under mixed mode loading by using Arcan loading device based on Richard’s principle suitable for mixed mode. All loading in mixed mode starting from pure tension (mode I) up to pure shear (mode II) can be obtained and tested by varying the loading angles from 0° to 90°. The stress intensity factor for the Compact Tension Shear (CTS) specimen are determined three normalized lengths cracks 0.3, 0.5 and 0.7.The length of notches influence on the variation of stress intensity factor KI, KII. For CTS specimen with notches with a short length, the values of KII are greater than those obtained for notches with a long length.

In-situ TEM observation of shear induced microstructure evolution in Cu-Nb alloy

Phase boundaries in multiphase alloys govern defect interaction and chemical intermixing across different phases during plastic deformation. Dynamic interaction of defects with phase boundaries in multiphase alloys, especially for immiscible alloys, has generated more research interest in recent years. Here, we describe a novel approach for carrying out in-situ TEM shear deformation to directly observe interfacial microstructural evolution of a Cu-Nb alloy. A unique double shear specimen geometry is microfabricated by a focused ion beam technique to apply shear deformation upon push loading inside the TEM. From the real-time observation, we discover that the phase boundary with a zigzag morphology effectively blocks stacking faults nucleated in a Cu grain from slipping into a Nb grain. Meanwhile, the Cu phase bears the most plastic deformation through slip or twinning mechanisms. This work sheds light on understanding the shear deformation and the behavior of phase boundaries in multiphase alloys during shear deformation.

Transverse shear properties of fiber reinforced polymer bars with different reinforced phases

In this study, a total of 105 shear specimens of fiber reinforced polymer bars with different reinforced phases, including the glass fiber, the hybrid of carbon fiber with glass fiber, and the hybrid of steel wire with glass fiber, were prepared to systematically investigate their transverse shear properties. The surface configuration of specimens, the performance characteristics and distribution pattern of reinforced phase were mainly regarded as variables. The results showed the shear strengths of glass fiber reinforced polymer bar specimens increased from 247.9 MPa to 263.5 MPa as the rib depth changed from shallow ribs to deep ribs, and their ultimate strain decreased from 0.374 to 0.328 with the increase in rib spacing from 8 mm to 16 mm. The shear strengths of carbon/glass hybrid fiber reinforced polymer (C/G HFRP) bar specimens declined from 247.4 MPa to 226.3 MPa as the distribution pattern of carbon fiber changed from centralized distribution to dispersed distribution. The shear strength of C/G HFRP bars decreased from 256.5 MPa to 247.4 MPa as the ratio of glass fiber to carbon fiber ranged from 0:1 to 1:4, and increased from 138.7 MPa to 214.8 MPa for steel wire/glass HFRP bars as the volumetric fraction of steel wire replacing glass fiber increased from 0 to 33.3%. This indicated that the surface configuration of specimen, the distribution pattern of fiber, and the performance characteristics of reinforced phase have great effects on the ultimate strain and shear strength of FRP bars, respectively.

Harnessing shape optimization techniques to develop novel methods to determine shear properties in PMCs

Shape optimization techniques are utilized to develop an optimal shear specimen for polymer matrix composites (PMCs) in which shear stresses result from simple uniaxial extension. An expanding array of composite applications means certification and damage tolerance are critical design factors. This methodology improves the ease of characterization for classically challenging material properties, such as shear failure. Numerical simulations were conducted using IM7/977-3 unidirectional prepreg mechanical properties. Large shear strain concentrations in the region of interest led to predicted failure in the region of interest under conditions consistent with shear. The geometry generated by the shape optimization should continue to be explored due to its capability generating a geometry which can measure the shear modulus and shear strength of a laminate. The shape optimization method’s ability to tailor a sample geometry for a desired strain state and failure mode leads the authors to recommend exploration of additional optimized test geometries for other failure modes and materials, in addition to the experimental investigation of the geometry generated for shear.

Compact forced simple shear specimen: Design improvement based on quasi-static experiments and finite element simulations

Determination of the large-strain shear response of materials is important for an improved understanding of shear driven failure mechanisms as well as constitutive modeling efforts. While many shear specimen designs have been proposed in the literature, few systematic studies have examined the effects of varying sample geometry on the homogeneity of the resultant stress state and strain path. Here we propose modifications to the compact forced simple shear specimen of Gray et al. (2016), and use both digital image correlation and finite element analysis to determine the effect of specimen geometry on simple shear deformation at quasi-static rates in high purity wrought tantalum. For the specimens considered here, where a notch is used to create the shear zone, it is found that a notch inclination angle of 45 degrees provides a substantial improvement in the deformation behavior compared to a horizontally oriented notch. A parametric study of notch inclination angle is conducted using FEA simulation.

Welding versus adhesive bonding strength investigation

This paper was intended to investigate the strength of adhesive and welded connections to be used in a dynamic message sign (DMS). The tensile strength and shear strength were studied for both of the adhesive and welded specimens. A number of tensile specimens and shear specimens with variations in width and temperature were tested until failure according to the ASTM D638 and ASTM D1002, respectively. The specimens with a range of width from 13 mm to 38 mm were conditioned with temperatures between −56.67 °C and 93.33 °C. The effects of temperature and width on each of the strengths were evaluated by analysing the testing data in a graphical and statistical manner. As expected, all the tests revealed that the welded specimens have significantly higher strength compared to the adhesive specimens in tensile and shear loadings. For the adhesive specimens, due to the increment of temperature, the highest increments were found to be 31.9% and 30.4%. In addition to the tests, Response Surface Metamodels (RSMs) and practical design equations were developed with regression analysis of the testing data, so as to predict tensile and shear stresses of both adhesive and welded specimens in an efficient way. 3D plots generated from the RSMs showed a higher effect of the temperature and width on the ultimate tensile and shear strength for both adhesive and welded specimens, and the practical design equations were founded to be more reliable for the overall tensile and shear stress prediction compared to the RSMs.

Effects of Different Orientation Angle, Size, Surface Roughness, and Heat Curing on Mechanical Behavior of 3D Printed Cement Mortar With/Without Glass Fiber in Powder-Based 3DP.

Powder-based (inkjet) three-dimensional printing (3DP) technology presents great promise in the construction industry. The capacity to build complex geometries is one of the most appealing features of the process without formwork. This article focuses on the vital aspect of using a modified powder (CP) instead of commercial powder (ZP 151). It also discusses the effects of the size of specimens and the curing process of 3DP specimens. This article presents not only the improved mechanical properties of the mortar that are revealed through a heat-curing procedure but also the properties of the reinforced mortar with chopped glass fibers. Experiments are conducted on cubic printed mortar specimens and cured in an oven at different temperature regimes. Tests show that 80°C is the optimum heat-curing temperature to attain the highest compressive and flexural strength of the specimens. The orientation angle has a significant effect on the mechanical behavior of printed specimens. Therefore, specimens are prepared by printing at different orientation angles to compare the mechanical properties of common construction materials. Powder-based 3DP has three planes (XY, XZ, and YZ) along which a load can be applied to the specimen. The mechanical strength in each direction across each plane is different, making it an anisotropic material. For CP specimens, the highest compressive strength was obtained using a 0° rotation in the printing orientation of the XY plane. For shear strength, a 45° orientation gave the optimum result, while for tensile and flexural strength, a 0° orientation provided the highest values. The optimum strength for ZP 151 specimens in compression, shear, tension, and bending was obtained by printing with orientation angles of 0°, 30°, 0°, and 0°, respectively. Finally, laser scanning of the printed specimens has been conducted so the surface roughness profiles for the 3DP specimens of ZP 151 and CP can be compared and presented.

Treatment of additively manufactured AlSi10Mg surfaces for improved bonding with fiber reinforced composites for sandwich applications

The performance of low weight, high stiff multi-materials relies on the interfacial bond quality between the adherends. This study analyses the effect of surface roughness, organosilane treatment and coating with diamond like carbon on the adhesion strength between carbon fiber reinforced composites and an additively manufactured (AM) AlSi10Mg counterpart. Extending applications to sandwich structures, both, bulk and honeycomb structured counterparts were considered. Double-Lap Shear specimens were fabricated in a co-curing process, and further investigated regarding the bond efficiency. Results were compared to the state-of-the-art joints applying an adhesive film layer. It was observed that surface roughness is not pivotal when using such adhesive film. In contrast, higher surface roughness generally tends to promote adhesion strength by promoting mechanical interlocking and increasing the available bond area. Further coating with organosilanes and diamond like carbon increases the surface energy and reduces the contact angle thus improving surface wettability by the matrix resin. In consequence, an improvement of up to 30% in adhesion strength was observed in case of coating the metallic surface with diamond like carbon. Prior surface polishing of the additively manufactured parts does not significantly affect the bond quality and is therefore not recommended.

Shear yielding and failure of cold-reduced G450 sheet steel

This paper presents experimental observations of cold-reduced G450 sheet steel subjected to shear. A total of 28 shear specimens of 1.5 mm and 3.0 mm thicknesses were tested. Two different test geometries were used to examine the shear state. The Digitial Image Correlation (DIC) technique was utilised to obtain the full fields of displacement and strain during the test execution. Strain distribution and evolution are used for quantifying shear stress- shear strain evolution inside the shear band. In terms of stress consideration, 0.35% proof shear strain is proposed to determine a yield stress in shear. The experimental results show that the cold-reduced G450 sheet steel follows von Mises criterion at yield (0.577), but possesses a higher ratio for the ultimate shear strength to tensile strength. Although the steel shows lower yield stress in the longitudinal rolling direction than that in the transverse, it possesses higher ultimate strength and ductility.

Joint Strength of a Braze Sealant with Metallic Interconnect in Solid Oxide Fuel Cell

To meet the quick start-up characteristics of metal-supported solid oxide fuel cell (MS-SOFC), brazing seals have been used in many MS-SOFC systems. During the cyclic operation of SOFC, thermal stresses are unavoidably generated due to temperature gradient and mismatch of coefficient of thermal expansion (CTE) between components. Excessive thermal stresses may damage the structural integrity of an SOFC stack, which in turn reduces the efficiency and lifetime of the SOFC. Therefore, it is essential to study the mechanical properties of the joint between braze sealants and metallic interconnects at room temperature (RT) and operating temperatures for developing a reliable MS-SOFC stack. The aim of this study is to investigate the mechanical strength of a braze sealant/metallic interconnect joint in SOFC. The braze sealant used is a silver-based alloy which is developed at the Institute of Nuclear Energy Research (INER) for MS-SOFC. The metallic interconnect used is a commercial ferrite stainless steel (Crofer 22 H). Two types of sandwich-like joint specimens are made to determine the shear and tensile joint strength at RT and 750 °C. Experimental results indicate that a bonding time of 30 min produces better joint strength at RT than 20 and 40 min, and it is thus selected as the bonding time for the specimens used in the subsequent tests. For tensile loading mode, the joint strength at RT and 750 °C is of 30.63 ± 3.2 MPa and 13.43 ± 0.99 MPa, respectively. For shear loading mode, the joint strength at RT and 750 °C is of 40.02 ± 2.88 MPa and 10.06 ± 0.36 MPa, respectively. Fractography analysis reveals that regardless of testing temperature, fracture of the tensile specimens occurs at the interface between the braze sealant and the Cr2O3 oxide layer and occasionally within the Cr2O3 oxide layer. When the testing temperature of the shear specimens is increased from RT to 750 °C, the location of rupture changes from the interface between the braze sealant and Crofer 22 H to the interface between the braze sealant and the Cr2O3 oxide layer.