Quasi-static Shear Tests Research Articles

Characterization of resistance welded hybrid sandwich sheets with additively manufactured core structure

Abstract Production of additively manufactured sandwich sheets is limited to small sizes. In the new introduced process route, additively manufactured core structures are joined with rolled face sheets by resistance welding, and the formability of the hybrid sandwich sheets is investigated. The necessity of developing the humps to improve the quality of resistance welding is initially investigated. Two different core structures, namely honeycomb and hollow sphere, are selected, and electrical-thermal coupled simulations with the ABAQUS software are performed to study the temperature distribution during resistance welding without and with hump. The strength of the joints for the fabricated sandwich sheets is verified by a quasi-static shear test. It is experimentally proven that the sandwich sheets without a hump in the core structure are not fully joined, and desired temperature localization is possible only by applying the hump. This is because the hump reduces the contact area, which leads to an increase in current density at the point where the resistance ratios are changed. This leads to higher temperatures in the intended joining zone. Different hump geometries for the core structure are designed, fabricated, and joined to the face sheets under different process parameters. The spot contact yields up to 50% higher shear strength than the linear or area contact. The free air bending results show that the double weld is essential for successful subsequent bending. It is also concluded that increasing the resistance welding time by more than 120 ms does not affect the joining strength of hybrid sheets.

Investigation on shear and fatigue performance of CFRP/aluminum alloy single-lap adhesive joint

The size parameter is quite significant for the performance of adhesive joint. In order to investigate the effect of size parameters on the mechanical property and failure behavior of CFRP/aluminum alloy single-lap adhesive joint, T300 CFRP laminate and AA5182 aluminum alloy sheet were bonded by Sika Power 497 structural adhesive under different size parameters. The quasi-static shear test and fatigue test were implemented, and the failure behavior and failure mechanism were analyzed. Results showed that the increase of aluminum alloy sheet thickness or bonding area length could effectively improve the bonding strength of adhesive joint, when the strength of the aluminum alloy sheet or the adhesive layer was insufficient. The shear failure modes of adhesive joint mainly included adhesive failure, base material failure and mixed failure. The fatigue failure modes of adhesive joint were mainly adhesive cohesion failure and adhesive adhesion failure. At low stress levels, the aluminum alloy sheet might fracture. In addition, this work can provide a scientific guidance for the engineering application of adhesive bonding technology.

Effect of rivet arrangement on fatigue performance of electromagnetic riveted joint with [formula omitted]10 mm diameter rivet

Electromagnetic riveting (EMR) can effectively form large-diameter rivets and produce high-quality joints. In this paper, the effect of rivet arrangement on fatigue performance of electromagnetic riveted joint was investigated. Quasi-static shear tests, fatigue tests, numerical simulation and microstructure observation were carried out. The results showed that the rivet arrangement had little effect on the shear performance and had a great impact on the fatigue performance of the EMR joint. Specifically, the difference between the average maximum shear load of the V-joints (60.49 kN) and the H-joints (60.41 kN) was small. The fatigue life of the H-joints was higher than that of the V-joints at high fatigue load levels (Fmax>30.225 kN), while the result was opposite at low fatigue load levels (Fmax<30.225 kN). Furthermore, the fatigue fracture analysis showed that there were two typical failure modes for the joints: (I) the rivet fracture, and (II) the sheet fractured on the manufactured head side. The V-joints mainly displayed the coexistence of failure mode I and mode II, while the H-joints displayed failure mode II at all fatigue load levels. At high fatigue load levels, the significant stress concentration in both rivets resulted in the rivet fracture of the V-joints within a relatively short time. Due to multiple extension directions and a smaller extension zone, the fatigue life of H-joints was lower than that of the V-joints at low fatigue load levels. Therefore, the fatigue performance of the component could be improved by choosing a different rivet arrangement.

Influence of the earthquake and progressive collapse strain rate on the structural response of timber dowel type connections through finite element modelling

This paper aims at understanding the influence of the strain rate, as those experienced under earthquake and progressive collapse events (referred to as “medium” strain rates), on the structural response of metal dowel type timber connections through the development of a finite element model. Past studies on timber connections have been mainly performed under quasi-static loadings. However, as metal and timber show different degrees of sensitivity to increased strain rate, such connections may exhibit different dynamic failure modes and load-carrying capacities than quasi-statically. To understand this phenomenon, a finite element model for dowel type timber beam-to-column connections, having a T-section aluminium bracket, was developed in this study. The model was validated incrementally, against (1) quasi-static and dynamic embedment tests, (2) single bolted connection quasi-static shear tests and (3) complete dowel type connection quasi-static shear and bending tests. Material properties under medium strain rates were then applied to the static model to study the structural response of the studied connection during earthquake and progressive collapse events. It was found that the change in material properties only contributes to a slight increase in capacity (up to 6.5%) but insignificant variations in initial stiffness (less than 4.1%) for the studied connection. This indicates that the connection can be safely designed statically for earthquakes and progressive collapse events. The methodology proposed in this paper and the finite element model developed can be extended to other types of timber connections.

Experimental investigation on shear strength of laser powder bed fusion AlSi10Mg under quasi-static and dynamic loads

This study deals with additive manufacturing (AM) products. Employing AM technology, complex-shaped, and lightweight parts can be fabricated using the aluminum alloy, AlSi10Mg. Typically, AM of this alloy is performed by laser powder bed fusion (LPBF). The mechanical properties of LPBF products are crucial for many engineering applications. Therefore, there have been efforts to measure the dynamic and quasi-static properties of such products. However, both the dynamic and quasi-static shear behaviors of this alloy are yet to be investigated. The present study is focused on experimentally investigating the shear behavior of LPBF AlSi10Mg. ‏Quasi-static shear tests were performed according to the ASTM B565 protocol, whereas dynamic shear tests were conducted using a standard split Hopkinson pressure bar equipped with an innovative sample holder that generates pure shear in a sample. The results of the performed tests showed that as the shear load rate increased, the shear strength considerably increased. In addition, in the quasi-static regime, the shear strength was practically independent of the product build direction. In contrast, under the dynamic shear conditions, samples built horizontally failed at a shear strength approximately 10% lower than that of those manufactured vertically. To investigate the build orientation effect on the shear behavior, this study conducted extensive microstructural characterization along with fracture analysis. Crack nucleation and propagation were analyzed in view of the effects of the unique microstructural characteristics of the LPBF AlSi10Mg, including the morphologies of the melt pool boundaries. The results obtained in this study suggested that for engineering applications in which dynamic loads are expected, the build orientation of AlSi10Mg parts produced using LPBF technology must be considered.

Effects of concrete type, concrete surface conditions and wood species on interfacial properties of adhesively-bonded timber – Concrete composite joints

To optimize the bonding performance between prefabricated concrete and wood in adhesive-bonded timber-concrete composite (TCC) system, the authors conducted quasi-static shear tests on several types of TCC joints bonded with epoxy resin in this study. The experimental variables considered were (1) concrete surface conditions (i.e. sandblasted, sanded and non-treated), (2) concrete type (i.e. normal strength concrete (NSC), high strength concrete (HSC) and ultra-high-performance concrete (UHPC)), and (3) wood species (i.e. glulam GL24 made of spruce and beech wood). The test results showed that the surface treatment on NSC (sandblasted) and HSC (sanded) significantly increased the shear bond strength of the TCC joints and changed the predominant failure mode from tearing-off of mortar-facial covers into failures in concrete substrates. Upon the surface treatment, using HSC increased the shear bond strength compared with the TCC joints using NSC. The joints with UHPC predominantly failed in the adhesive/concrete interface, and adhesion between adhesive and concrete, due to that the low porosity of UHPC impeded the penetration of epoxy resin into the substrate. When being bonded with UHPC, compared with the GL24 made of spruce, the beech wood increased the shear bond strength, since the wood-failure percentage decreased in the joints using beech wood. Furthermore, bond-line areas of all types of joints were examined under an optical microscope, to reveal the morphology (i.e. profile of a glue line, glue-line thickness, and penetration of resin into substrates). It was found that epoxy used in this study with a high initial viscosity (i.e. 6000 mPa·s at 23 °C) is suitable to bond surface-treated concrete and engineered wood, from the perspectives of penetration into substrates, the thickness of glue lines, and workability during gluing processes.

Quasi-Static Shear Test of Hybrid Adhesive Bonds Based on Treated Cotton-Epoxy Resin Layer.

This research evaluates the mechanical properties of hybrid adhesive bonds with various 100% cotton fabrics in static and quasi-static conditions and the influence of alkali surface treatment (NaOH) of the cotton fabrics on the mechanical properties. Biological fibers in polymers are characterized by low wettability with the matrix, which decreases mechanical properties. Adhesive bonds usually operate in cyclic stress, which causes irreversible failure before maximal strength. In this paper, a quasi-static test was used to load the adhesive bonds in 5–50% (192–1951 N) and 5–70% (192–2732 N) intervals with 1000 cycles. The results of SEM analysis showed good wettability of alkali treated cotton fabric with NaOH solution in hybrid adhesive bonds. The static test proved the influence of reinforcing cotton fabrics on shear tensile strength against pure resin, i.e., sample Erik up to 19% on 14.90 ± 1.15 MPa and sample Tera up to 21% on 15.28 ± 1.05 MPa. The adhesive bonds with pure resin did not resist either quasi-static tests. Reinforcing cotton fabrics resisted both quasi-static tests, even shear tensile strength increases up to 10% on 16.34 ± 1.24 MPa for the fabric Erik. The results of strain difference of adhesive bonds with Tera and Erik confirmed that a lower value of the difference during cyclic loading positively influenced the ultimate shear tensile strength.

Strength and failure analysis of adhesive single-lap joints under shear loading: Effects of surface morphologies and overlap zone parameters

ABSTRACT The adhesive bonding process is widely used in the automobile industry because of sealing, insulation and good mechanical properties. In this study, the effects of surface treatments and joint parameters on shear strength and failure mode were investigated. Four different sandpaper treatments, overlap length and adhesive thickness were selected to carry out quasi-static shear test. The failure behaviour of aluminium alloy single-lap adhesive joints was analysed and a dimensionless parameters δ was introduced to quantitatively evaluate the effect of overlap length on joint strength. Results showed that the joint strength was enhanced by sandpaper grinding due to the change of surface roughness. The specimens with 90°/0° grinding direction using P360 sandpaper had the best performance rather than an excessively rough surface. The joint shear strength decreased with the increase of adhesive thickness but the effect of overlap length on joint strength was limited. The adhesive thickness had little impact on joint shear strength when the overlap length over 40 mm. In addition, the joint strength could be improved by increasing overlap length until δ below 0.95. However, with the decrease of δ, there was almost no effect on joint strength because of high peeling stress at the both ends of the long joints.

Suitable rolling resistance model for quasi-static shear tests of non-spherical particles via discrete element method

Rolling resistance is a main consideration in quasi-static shear test simulations of particles via the discrete element method. However, not all rolling resistance models can satisfy the required objectivity and rate independence. A suitable model for spherical particles has been selected from five models in our previous works. In the current study, this model is combined with four normal and tangential contact models to confirm its applicability. After confirmation, the model is generalized to simulate direct shear tests on non-spherical particles. The stress–strain and dilatancy curves are rate-independent, and the relative rolling velocity between particles is objective. Furthermore, objectivity and rate independence for arbitrarily shaped particles are unchanged when normal stresses, volume fractions, or normal and tangential contact models are changed. Simulation results are also consistent with other experiment findings. For comparison, results are calculated for two other rolling resistance models; the shear curve at a single speed is consistent with the experiment, which has three stages: elastoplastic increasing, yielding, and keeping. However, the stress–strain curves at different shear rates do not coincide, which means that the models conflict with the rate independence of quasi-static granular systems. The virtues and defects of the five rolling resistance models are discussed from the perspectives of objectivity and rate independence. These two properties provide criteria for determining the appropriateness of a model, which has been rarely discussed in former studies.

Fail-safe design and analysis for the guide vane of a hydro turbine

A design for the fail-safe mechanism of a guide vane in a Francis-type hydro turbine is proposed and analyzed. The mechanism that is based on a shear pin as a sacrificial component was designed to remain simple. Unlike the requirements of conventional designs, a shear pin must be able to withstand static and dynamic loads but must fail under a certain overload that could damage a guide vane. An accurate load determination and selection of the shear pin material were demonstrated. The static load for various opening angles of the guide vane were calculated using the computational fluid dynamics Fluent and finite element method Ansys programs. Furthermore, simulations for overload and dynamic load due to the waterhammer phenomenon were also conducted. The results of load calculations were used to select an appropriate shear pin material. Quasi-static shear tests were performed for two shear pins of aluminum alloy Al2024 subjected to different aging treatments (i.e. artificial and natural aging). The test results indicated that the Al2024 treated by natural aging is an appropriate material for a shear pin designed to function as a fail-safe mechanism for the guide vanes of a Francis-type hydro turbine.

Quasi Static Tests of Adhesive Bonds of Alloy AlCu4Mg

An application of an adhesive bonding technology is limited by cyclic loading of an adhesive bond. The aim of the experiment is to clarify a fatigue behaviour (low-cyclic tests of the fatigue) of four structural two-component epoxy adhesives applied to an alloy AlCu4Mg. The aim of the research was to evaluate a service life of the adhesive bond in terms of its fatigue stressing at the quasi static shear test. From that reason values of a passing loading for low-cyclic fatigue test were chosen for tested adhesives, i.e. 25 %, 50 % and 75 % from a reference value of a maximum force gained at the static test according to CSN EN 1465. The critical value at the low-cyclic fatigue test was determined from the experiment results for the adhesive bond as 75 %. Most of the adhesive bonds did not reach 100 cycles at this value.It is obvious from the results that the considerable change of the adhesive bond strength did not occur after 100 cycles at the passing loading corresponding to 25 % and 50 % of the average maximum strength of the adhesive bond. The average fall of the resultant adhesive bond strength was in the interval 3 % to 11 %.

Mechanical properties of graphite/aluminum metal matrix composite joints by friction stir spot welding

Graphite/aluminum metal matrix composite (MMC) joints are successfully fabricated by friction stir spot welding (FSSW). During lap-joining processes of aluminum alloy sheets by FSSW, graphite/water colloid is applied between the tool shoulder and the upper plate. The Raman spectrum of the FSSW joint confirms that graphite/aluminum MMC is successfully induced in the stir zone. Quasi-static shear tests and micro hardness measurements of the FSSW joint also show that the strength and toughness of the joint are significantly improved by inducing graphite/aluminum MMC in the stir zone. The results of the present study suggest that the mechanical properties of structural components joined by spot welds can be easily enhanced by adopting MMC joints by FSSW, instead of changing the material or increasing the number of joints.

A durability study of externally bonded FRP-concrete beams via full-field infrared thermography (IRT) and quasi-static shear test

Durability of 36nos. externally-bonded CFRP-concrete beams was studied by monitoring the intermediate cracking (IC) processes using infrared thermography (IRT) and quasi-static direct shear test. Specimens were exposed to three elevated water temperatures (25°C, 40°C and 60°C) for 5, 15 and 30weeks. In addition to the measurement of the properties at ultimate state, this work attempts to characterize the intermediate states of the intact, softened and ruptured part during the IC debonding process. The results show that the adhesive bond layers of the 40°C and 60°C specimens were ruptured and softened at a force level much lower than that for the 25°C and control specimens. This is explained by the exposure condition that the water temperature exceeded the heat distortion temperature of the adhesive layer, which accelerated the bond deterioration of the composites.

Fatigue of the bone/cement interface and loosening of total joint replacements

The failure of cemented total joint replacements is often attributed to loosening of the implant in response to fatigue of the interface between the bone and cement. In the present study loosening of model cemented joint replacement specimens was examined under cyclic loading and the fatigue strength of the bone/cement interface was characterized. In addition, the potential for improving the fatigue strength by introducing a surgical bone surface preparation was assessed by texturing the bone to achieve different degrees of cement interdigitation. All specimens were subjected to cyclic shear loads up to 10 million cycles and the extent of loosening at the bone/cement and prosthesis/cement interfaces was quantified using Digital Image Correlation (DIC). Results showed that the displacement history exhibited three distinct regions of response and that fatigue failure occurred as a result of loosening along the bone/cement interface. The apparent fatigue strength of the engineered bone/cement interfaces corresponding to 40 years of function ranged from 0.8 to 4.4 MPa; the fatigue strength increased with the surface roughness of bone and degree of cement interdigitation. Regardless of the bone surface topography the ratio of fatigue strength and ultimate shear strength of the interfaces was approximately 0.2. Results of the evaluation suggest that the fatigue strength of the bone/cement interface in cemented total joint replacements can be estimated from simple quasi-static shear tests.

Mechanical and Physical Properties of Grasses

ABSTRACT QUASI-STATIC shear tests on grasses were used to evaluate their shear strengths, resistances to penetration and shear energies. The dependence of these mechanical properties on crop properties (maturity, size and dry matter) and on shearing conditions (velocity and blade level) were elucidated. A comparison with literature data suggested that future studies should ex-press shear or cutting energies on a per unit dry cross-sectioned area basis so that the influence of internal pore space, moisture content and stem diameter may be diminished.