In-plane Shear Tests Research Articles

A comparison of mechanical properties and X-ray tomography analysis of different out-of-autoclave manufactured thermoplastic composites

Three different out-of-autoclave manufacturing processes of CF/poly-ether-ether-ketone thermoplastic composites were characterized, including innovative laser-assisted automated fibre placement with in situ consolidation. Characterization techniques included differential scanning calorimetry, ultrasonic non-destructive testing and matrix digestion, in addition to 3D X-ray microcomputed tomography to investigate the void distribution, size and shape. The results revealed that in situ consolidation process can lead to the accumulation of large voids between the upper layers. Interlaminar shear, in-plane shear, tensile and flexure testing were used for mechanical evaluation. A reduction in the mechanical properties was observed for in situ consolidation laminates when compared to the other out-of-autoclave methods. The drop in mechanical properties of in situ consolidation laminates was mainly attributed to the differences found in void distribution and size. Optimization of processing parameters along with higher quality prepreg raw material could be of assistance for the improvement of mechanical properties of in situ consolidation structures.

Asymmetric in-plane shear behavior of isolated cadaveric lumbar facet capsular ligaments: Implications for subject specific biomechanical models

The facet capsular ligaments (FCLs) flank the spinous process on the posterior aspect of the spine. The lumbar FCL is collagenous, with collagen fibers aligned primarily bone-to-bone (medial-lateral) and experiences significant shear, especially during spinal flexion and extension. We characterized the mechanical response of the lumbar FCL to in-plane shear, and we evaluated that response in the context of the fiber architecture. In-plane shear tests with both positive and negative shear (i.e., corresponding to flexion and to extension) were performed on eight cadaveric human L4-L5 FCLs. Our most striking observation was subject-dependent asymmetry in the response. All samples showed a toe region of low stiffness, transitioning to greater stiffness at higher strains, for both shear directions. Different samples showed profoundly different transition strains, with some samples stiffening more rapidly in positive shear and some in negative shear. This unpredictable asymmetry, which did not correlate with age, side, or degeneration state, suggesting that collagen fibers in the FCL are sometimes aligned at a slight positive angle from the bone-to-bone axis and sometimes at a negative angle. Fitting the experimental data to a fiber-composite-based finite element model supported this idea, yielding optimal fits with positive or negative off-axis fiber directions (−40° to +40°). Subsequent examination of selected FCLs by small-angle x-ray scattering (SAXS) showed a similar variability in fiber direction. We conclude that small individual differences in lumbar FCL architecture may have a significant effect on lumbar FCL mechanics, especially at moderate strains.

In-Plane Shear Resistance between the Rammed Earth Blocks with Simple Interventions: Experimentation and Finite Element Study

The paper presents experimental and numerical works to assess the in-plane shear characteristics of rammed earth (RE) structures in Bhutan. The material characterization works involve compressive and tensile splitting strength tests on extracted cylindrical core samples. The effects of the RE layer thickness and drying period in the strength characteristics of the rammed earth is presented. The main experimental part reports in-plane shear tests on 3 test specimens, 1200 mm long, 1200 mm high, and 600 mm wide. The test matrix has unreinforced and reinforced specimens with variable RE layer thicknesses. For the reinforced RE specimen, the effectiveness of a simple intervention with insertion of reinforced concrete dowel at the RE block interface as a strengthening measure is discussed. Furthermore, corresponding finite element models were developed to verify the test observations. Both the experimental observations and numerical computations showed the effectiveness of proposed intervention technique in enhancing the shear strength and delaying the slip along the RE joint interface. The results showed that the shear strength of the reinforced specimen increased by 12.3% over the benchmark specimen.

Evaluation of Buckling Resistance of Basalt Fiber Reinforced Polymer Plate

Basalt fiber reinforced polymer (BFRP) is known as an excellent material used to strengthen reinforced concrete structures. BFRP is attached to beam, slab or column, which would be subject to compressive and bending load. Since the thickness of BFRP plate is relatively thin, the buckling problem is a concern. However, investigation of mechanical properties and buckling resistance of BFRP plate has been very limited. In this paper, the mechanical properties of BFRP were experimentally investigated using tensile test and in-plane shear test. Because the mechanical properties of BFRP depend on the type of resin, three types of BFRP: basalt/polyester, basalt/vinyl ester and basalt/epoxy, were used in a tensile test to optimize the resin. To evaluate the buckling behavior of BFRP plate, a numerical approach was established using the finite element method. The results of the mechanical properties of BFRP were then used to determine the buckling resistance. Based on the experimental results, the tensile strength of BFRP that consisted of basalt/epoxy was 4.8% and 2.4% greater than those consisting of basalt/polyesters and basalt/vinyl ester, respectively. It was also found that the elastic modulus of BFRP was approximately 11.26% larger than that of GFRP. The numerical results indicated that the buckling resistance of BFRP plate was 10.3% to 10.7% greater than that of GFRP depending on loading condition, fiber orientation, aspect ratio and boundary condition of the laminate plate. Therefore, using BFRP laminate composite plate in retrofitting of concrete structure provides better performance than GFRP in terms of mechanical properties and buckling performance.

In-plane shear testing of unreinforced masonry walls and comparison with FEA and NZSEE predictions

The present study was conducted to investigate the global and local in-plane response of perforated URM walls under earthquake loading, based on observations of damage from previous earthquakes. To do so, full-scale cyclic in-plane testing of URM walls with an arched opening which were designed to represent walls in heritage URM structures in Australia was performed. The study investigated the behaviour of both pier and spandrel elements within the walls. Emphasis was also given to the position of walls within a multi-storey building by varying the pre-compression loads (representing gravity loads) on the walls. The tested walls were then simulated using nonlinear finite element analyses (FEA) where simplified micro-modelling (crack-shear-crush) approaches were used to analyse the wall behaviour. Finally, the shear capacities and the failure modes of the walls obtained from the experimental tests and FE analyses were compared to the proposed New Zealand Society for Earthquake Engineering (NZSEE) predictions.

In-plane Shear Testing of Unreinforced Masonry Walls and Comparison with FEA and NZSEE Predictions

The present study was conducted to investigate the global and local in-plane response of perforated URM walls under earthquake loading, based on observations of damage from previous earthquakes. To do so, full-scale cyclic in-plane testing of URM walls with an arched opening which were designed to represent walls in heritage URM structures in Australia was performed. The study investigated the behaviour of both pier and spandrel elements within the walls. Emphasis was also given to the position of walls within a multi-storey building by varying the pre-compression loads (representing gravity loads) on the walls. The tested walls were then simulated using nonlinear finite element analyses (FEA) where simplified micro-modelling (crack-shear-crush) approaches were used to analyse the wall behaviour. Finally, the shear capacities and the failure modes of the walls obtained from the experimental tests and FE analyses were compared to the proposed New Zealand Society for Earthquake Engineering (NZSEE) predictions.

Measurement of the Shear Properties of Extruded Polystyrene Foam by In-Plane Shear and Asymmetric Four-Point Bending Tests.

The shear modulus and shear strength of extruded polystyrene foam were obtained by the in-plane shear and asymmetric four-point bending tests. In addition, the test data were numerically analysed, and the effectiveness of these tests was examined. The numerical and experimental results suggest that the shear modulus and shear strength obtained from the in-plane shear test are significantly smaller than those obtained from the asymmetric four-point bending test because the influence of the stress concentration was less significant. Although the in-plane shear test is standardised in ASTM C273/C273M-11, it is considerable to adopt the asymmetric four-point bending test as another candidate for obtaining the shear properties of extruded polystyrene foam.

In-plane cyclic behaviour of composite floor slab diaphragm interfaces under high-shear demand

The authors have recently described the experimental in-plane shear tests of three composite slabs under monotonic loading to failure, focusing on the interaction between the slabs acting as diaphragms and the lateral load resisting system. The tests considered rib orientations both parallel and perpendicular to the supporting beam, as well as the end-anchorage details used in New Zealand and those used in Europe. A novel pure shear test rig was developed for this purpose. It was found that all specimens exhibited similar ultimate shear strength, and that the Eurocode overestimated the design strength for the European end-anchorage detail by almost a factor of two. An improved equation for the ultimate in-plane shear strength was proposed by the authors, modifying the Easterling and Porter equation to take into account the influence of the edge rebar, showing good agreement with the experimental test results.In this paper, reversed cyclic in-plane shear tests of the same three slabs are now reported. Each test was repeated twice, resulting in six test results. The same novel pure shear test rig was adopted. In the elastic range, the reversed cyclic loading results were found to be similar to those of the monotonic tests, with the spine curve being very similar. The ultimate in-plane shear strength of all three was lower than that of the monotonic test by around 15%. Slippage of specimens was found to be insignificant in the elastic range.

Mechanical Respond and Failure Mode of Large Size Honeycomb Sandwiched Composites under In-Plane Shear Load.

The present work focuses on the in-plane shear respond and failure mode of large size honeycomb sandwich composites which consist of plain weave carbon fabric laminate skins and aramid paper core. A special size specimen based on a typical element of aircraft fuselage was designed and manufactured. A modified in-plane shear test method and the corresponding fixture was developed. Three large size specimens were tested. The distributed strain gauges were used to monitor the mechanical response and ultimate bearing capacity. The results show that a linear respond of displacement and strain appears with the increase of the load. The average shear failure load reaches 205.68 kN with the shear failure occurring on the face sheet, and the maximum shear strain monitored on the composite plate is up to 16,115 με. A combination of theoretical analysis and finite element method (FEM) was conducted to predict the shear field distribution and the overall buckling load. The out-of-plane displacement field distribution and in-plane shear strain field distribution under the pure shear loading were revealed. The theoretical analysis method was deduced to obtain the variation rule of the shear buckling load. A good agreement was achieved among the experiment, theoretical analysis, and FEM results. It can be concluded that the theoretical analysis method is relatively conservative, and the FEM is more accurate in case of deformation and strain. The results predicted by h element and p element methods are very close. The results of the study could provide data support for the comprehensive promotion of the design and application of honeycomb sandwich composites.

On the mixed mode I/II/III inter-laminar fracture toughness of cotton/epoxy laminated composites

Nowadays, natural fiber reinforced laminated composites have been extensively used in order to fabricate the various structures. In this paper, a woven cotton/epoxy laminated composites system was considered. The main purpose of this investigation is to measure a full range of mixed mode I/II/III Inter-laminar facture toughness (IFT), critical strain energy release rate (CSERR) and the mechanical properties of this material. Hence, in addition to tensile, flexural and in-plane shear tests, a series of delamination tests consisting of pure modes, mixed modes I/II, I/III and II/III were carried out. The fracture tests were conducted using a modified Arcan fixture and an out-of-plane fixture. The experimental results showed that the delamination responses of cotton/epoxy system are deeply dependent on the loading conditions. It was also found that the Inter-laminar fracture toughness and CSERR under pure mode I and mixed mode II/III loading conditions have the lowest and greatest values among the delamination modes, respectively. It was also conducted that in comparison with the woven carbon/epoxy and glass/epoxy systems, the modes I, II and III CSERR of cotton/epoxy is remarkable.

A numerical and experimental investigation on quasi-static punch shear test behavior of aramid/epoxy composites

In this study, quasi-static punch shear behavior of aramid epoxy composites was investigated both numerically and experimentally. Firstly, material model parameters used in numerical simulations were obtained by various mechanical tests such as tensile, compression, and in-plane shear tests. Different damage mechanisms that were observed during each test were the focus of interest. Then quasi-static punch shear test was performed and verified with numerical simulations. After the verification of material model, punch tests, which have different boundary conditions, were run numerically, and the effect of thickness and span-to-punch ratio (SPR) were determined for aramid/epoxy composites. It is concluded that failure mechanisms of composite samples were related to SPR. When SPR increases, the failure mode was shifted from shear-dominated failure to bending-dominated failure behavior. Additionally, punch shear strength value at minimum SPR (1.1) was eight times bigger than the value at maximum one (8).

Investigation on in-plane shear behavior of large-size composite plates with multi-bolt joints

This paper aims to investigate the in-plane shear behavior of large-size composite plates with multi-bolt joints. A mechanical joint structure and an universal fixture were designed and in-plane shear tests were carried out. The distributed strain gauges were used to monitor the mechanical response and ultimate bearing capacity. The failure areas and failure modes of mechanical connections were studied by ultras-scanning. A non-linear finite element model (FEM) based on 2D shell element mesh was developed to predict the load distribution and failure modes of bolt joints between composite and titanium alloys. The results show that the shear failure load reaches 365.95 kN. The shear failure occurs on the outside edges of composites plate, and the delamination extends to the vicinity of the fixture bolts. The new FEM that requires very small computational cost can evaluate the structure strength and predict destruction area. The deviation between the predicted shear failure responses and the testing results is less than 10%. The failure mode and location are consistent with the testing results, which verifies the validity of the finite element model. It suggests that this model is applicable on large scale structures and suitable to use in conjunction with iterative schemes.

Determination of the in-plane shear modulus of unidirectional carbon fiber-reinforced plastics using digital image correlation and finite-element analysis

Accurate in-plane shear properties are essential to simulate the mechanical behavior of fiber-reinforced laminated composites. Herein, a digital image correlation technique was used to analyze unidirectional carbon fiber-reinforced composites by three shear-test methods (±45° in-plane, Iosipescu, and V-notched rail shear tests), focusing on the uniformity of shear deformation during each test. The V-notched rail shear test imposed the most uniform shear deformation. This test, however, still imposed non-uniformity around the deformation regime for the in-plane shear modulus calculation, which needed to be accommodated. The non-uniformity was virtually characterized by a combination of various material properties using finite-element analysis. A universal correction factor of 0.925 resolved the non-uniformity involved in the V-notched rail shear test. This enabled the in-plane shear modulus of unidirectional carbon fiber- or glass fiber-reinforced composites to be accurately determined.

Half-Scale Tests on Masonry Panels Strengthened with Pultruded FRP Frames

The research explores the capabilities of frames of pultruded FRP profiles as seismic strengthening for masonry walls. A programme is currently in progress at the IUAV University of Venice, consisting of in-plane shear tests on half-scale panels. The selected masonry type is traditional, i.e. clay bricks and lime mortar joints. The goal is to assess the effectiveness of the strengthening system with respect to the undamaged condition of masonry. A particular focus is on the connection system between the panel and the frame, i.e. epoxy adhesive connection and bolted joint. The results will be implemented in FEM analyses and analytical models to predict the system's and the joints' shear strength.

Effect of processing parameters and void content on mechanical properties and NDI of thermoplastic composites

Several consolidation cycles were performed to study the impact of processing parameters on void content, ultrasonic NDT and mechanical performance of CF/PEEK composites. A series of [+45/−45]4S laminates were manufactured by out-of-autoclave technologies including vacuum bag only, hot-press, and automatic lay-up with in-situ consolidation. A range of porosity between 0 and 19% of void content was assessed by varying the processing temperature from 340 to 500 °C and pressure from 0.25 to 1.5 MPa. Void content, shape and location were characterized by using C-scan, matrix digestion and 2D microscopy. Mechanical characterization including in-plane shear and interlaminar shear testing was performed. The results show a critical void content where properties start to decrease at a given drop-off rate. The results suggest that each processing technology should have its own quality control criteria. The proposed methodology is useful for engineering applications of thermoplastic composites and the creation of NDT acceptance criteria.

The effect of yield and failure at the corners of the specimen on strain distribution and strain direction under in-plane shear test of wood-based structural panels specified in ASTM D2719.

The effect of yield and failure at the corners of the specimen on strain distribution and strain direction under in-plane shear test of wood-based structural panels specified in ASTM D2719.

In-and-out-of plane mechanical properties of hand lay-up vegetal fiber reinforced polyester resin composites

The results presented in this paper belong to the mechanical characterization of vegetal woven fabric reinforced composites with polyester resin as the matrix and fabrics made of cotton, jute and flax fibers. Test specimens were manufactured using a simple hand lay-up molding process. A group of test specimens was reinforced with the woven fabrics as delivered by the supplier, while another group was reinforced with woven fabrics that were chemically treated with Sodium hydroxide NaOH at 6% w/v for 48 hours. The fabrics were then neutralized and dried in an oven. Mechanical characterizations were performed using traction, compression, in-plane shear and interlaminar (out of plane) shear tests. Results show that the untreated flax fiber composite has the best specific properties among the three vegetal composites.

A new model for the determination of optimum fiber volume fraction under multi-axial loading in polymeric composites

Mechanical properties of composite materials are a function of fiber volume fraction. Based on the existing micromechanical models, the in-plane shear strength of these materials is decreased as their fiber volume fraction is increased. However, their compressive strength is initially increased and then it is dropped as the fiber content increases. The fiber content in the composite of maximum compressive strength was referred to as the optimum fiber volume fraction. Experiments performed in this study revealed that in-plane shear strength variation versus fiber volume fraction was to some extent similar to that of compressive strength. Moreover, different optimum fiber volume fractions for in-plane shear strength and compressive strength were observed. Consideration of both in-plane shear strength and the compressive strength in combined loading was proposed to find the optimum fiber volume fraction. The modified Hashin failure criterion by Lessard was employed to relate the longitudinal and transverse compressive stress and strength to in-plane shear stress and strength. A safe region predicted by this failure criterion was represented by plotting longitudinal compressive and in-plane shear stress relation for different fiber contents. The fiber content corresponding to the maximum safe region was introduced as the optimum fiber volume fraction. Axial compressive and in-plane shear tests were conducted for obtaining the variation of longitudinal compressive and in-plane shear strengths with fiber volume fraction. To identify the capability of the model for multi-axial state of stress, a unidirectional off-axis test was also performed. The test results on the unidirectional and off-axis composite specimens confirmed the predictions by the theoretical model.

Experimental Techniques for Finite Shear Strain Measurement within Two Advanced High Strength Steels

There is a growing need to experimentally characterize local shear deformation in advanced high strength steels (AHSS) for the calibration of stress-state dependent fracture criteria and to better understand sheared edge cracking during secondary forming operations. Planar shear test specimens with digital image correlation (DIC) strain measurement are now commonly performed tests but may not be able to resolve the local strains during the final stage of fracture when the macroscopic shear band collapses to a micro-shear band with intense local strains. Studies of sheared edge stretching of AHSS have shown that the microstructure at the sheared edge experiences extreme local shear deformation with the shear-affected zone (SAZ) that can be much larger than the macroscopic strains reported using DIC on planar shear tests. In this work, two independent experimental techniques are proposed to characterize the residual strain distribution within the shear-affected zone for two AHSS grades with a similar strength level: a complex-phase (CP) steel, CP800, and a dual-phase (DP) steel, DP780. The first method uses finite strain theory to calculate the work-conjugate equivalent strain from grain rotations within the shear bands of interrupted in-plane shear tests. A comparison between the local DIC strain measurements and the grain rotation measurements were found to be in excellent agreement until just prior to failure. The second technique used micro-hardness measurements taken from the interrupted shear tests to develop correlations with the measured equivalent strain from the DIC system. The hardness and grain rotation techniques were then used to characterize the local strain distribution within the SAZ of hole expansion test specimens for punch clearances of 12% and 28%. Both methods provided similar strain distributions with the grain rotation method having the highest strain resolution. The residual strain field within the SAZ of both AHSS was found to be strongly dependent upon the punch clearance. Finally, a homogenization procedure was applied to the SAZ strain distributions to facilitate the length scale transition from the grain-level to length scales appropriate for finite-element modelling of sheet metal forming operations with sheared edges.

A novel discrete method of shear angle measurement for in-plane shear properties of thermoset prepreg using a point-tracking algorithm

Determining accurate in-plane shear properties of dry and prepreg fabrics is dependent upon the correct measurement of actual shear angle values. This paper presents a novel discrete method of shear angle measurement for in-plane shear properties of thermoset prepreg using a point-tracking algorithm. Two different reinforcement forms of woven and unidirectional with the same rapid-cure resin system are used in this study. In-plane shear tests of picture-frame and bias-extension are employed to evaluate the new discrete method under conditions representative of high-volume manufacturing, i.e. fast deformation rate and elevated temperature. This study demonstrates that the proposed discrete method is capable of measuring the shear angle correctly until large shear deformation, unlike traditional methods such as digital image correlation and the pin-jointed network approach. Furthermore, the normalised shear force data presents a better correlation of the two tests based on the actual shear angle measurement obtained from this novel discrete method.