Rail Shear Research Articles

Characterization of bauxite residue filled sisal/glass fiber reinforced hybrid composites for structural applications

Abstract Composite materials with high compressive, flexural, and shear strength are essential for constructing various structural elements in automotive, aerospace, marine, and construction sectors. The present research aims to create bauxite residue filled sisal/glass fiber reinforced polyester composites. The different weight percentages of sisal fiber (35 %, 30 %, 25 %, and 20 %), red mud (0 %, 5 %, 10 %, and 15 %), glass fiber (5 %), and polyester matrix (60 %) were used to fabricate composites. The combined use of compression molding and hand layup technique was employed in the creation of composite materials due to its frequent utilization in the manufacturing of large-scale components found in various sectors, including automotive, aerospace, marine, and construction. In this work, investigated the physical, compressive, flexural and v notch rail shear strength of the fabricated composites. Results revealed that the composites with 30 % of sisal fiber and 5 % of red mud has the highest compressive, flexural, and v notch rail shear strength of 83.45 MPa, 182.74 MPa, and 10 MPa, respectively. Further, this composite showed high density, less void content, and less thickness swelling than other composites. According to the outcomes, this composite material demonstrates suitability for various structural applications across automotive, aerospace, marine, and construction sectors.

Effect of adding silanized cassava periderm biosilica on mechanical, V-notch rail shear, wear, and UL-94 flammability behavior of spinach stem fiber epoxy composite

Effect of adding silanized cassava periderm biosilica on mechanical, V-notch rail shear, wear, and UL-94 flammability behavior of spinach stem fiber epoxy composite

V‐notched rail shear test applied to geopolymer composites

AbstractThis work presents a systematic study of the shear properties of a potassium‐based geopolymer reinforced with distinct types of fibers. Chopped basalt reinforcements in lengths from 3 mm up to 50 mm and 13 μm in diameter were compared with thicker 20‐mm length, basalt mini bars, sand‐coated basalt mini rods, and steel fibers. The samples were tested under a V‐notched rail shear tests (ASTM D7078), coupled with optical measurements, namely, digital image correlation, allowing a novel study of their crack patterns and failure modes under shear loading. In general, the use of chopped fibers resulted in shear strengths of up to 9 MPa and shear moduli of 4.3 GPa, with no significant variation with fiber length increments, neither in shear stress nor strain at peak load (0.1%). Mini bars and steel fiber reinforcements resulted in slightly lower shear stresses of 7.1 and 8.4 MPa, respectively. They exhibited greater strain values at peak loads, up to 2.1% which were attributed to fiber‐matrix enhanced adhesions, thereby allowing gradual debonding and increased ductility. This effect was also recorded for mini rods, but at much lower strength levels, which did not contribute to their multiple cracking capacities. The alignment of the mini rods in 45° directions resulted in a 50% increase in shear stress, showing the feasibility of tailoring the manufacturing process to attend to distinct demands.

Design of a Shear Test Fixture System and Optimization of a Metal Shear Specimen for Cyclic Loading

Abstract The objective of the present paper is to investigate the optimization of the existing sheet metal specimen geometry and the optimization of fixtures for fatigue shear tests. Simple static shear tests are used for the material characterization of sheet metal and composite materials. It is well known that it is difficult to achieve pure shear conditions in the specimens because of stress concentrations. Moreover, buckling must be prevented during cyclic tensile and compressive loads, which can be achieved with suitable fixtures. This paper proposes a symmetric specimen geometry for alternating in-plane loads, where the location of crack initiation is predicted and stress concentration is minimized. The design of the geometry was supported with numerical simulations. According to the final specimen geometry, unique fixtures were developed, based in part on the standard ASTM D7078, Standard Test Method for Shear Properties of Composite Materials by V-Notched Rail Shear Method, solution. The fixtures allow operation at elevated temperatures, easy specimen change, universal use on different test rigs, and possible extension to other specimen shapes. By the proposed fixture system, any type of cyclic test can be performed (i.e., alternating, pulsating, or variable). The fixtures are suitable for measuring strain with mechanical extensometers, video extensometers, or digital image correlation. The experimental shear tests on aluminum 6061 specimens showed comparable shear strain fields as calculated by the finite element method.

Fracture behaviour of fibre-reinforced composite materials subjected to shear loading: An experimental and numerical study

Compared to fibre-dominated behaviour, a response dominated by the matrix under shear loading can considerably limit the load-bearing capability and restrict the utilisation of composite materials. It is therefore practically significative to understand the shear response of composite materials. This paper presents a detailed experimental and numerical investigation on the fracture behaviour of composite laminates subjected to shear-dominated loading. Composite specimen with a lay-up of [(0/90)4/0]S are tested using the V-Notched Rail (VRS) shear test method. Subsequently, the Scanning Electron Microscope (SEM) investigation is also conducted on the fracture surfaces of the tested specimens to get insights into the damage mechanisms due to shear loading. In addition, a high-fidelity computational damage model is developed to predict the shear fracture behaviour of fibre-reinforced composites. Simulation results, including loading response, strain distribution and shear fracture, well correlated with experimental results, which demonstrates the predictive capability of the developed elastic-plastic damage model.

Effect of poly ether ether ketone particles on v‐notched shear and drop weight impact behavior of carbon/epoxy composite

AbstractDue to the intrinsic brittleness, low velocity impact (LVI) causes internal invisible damages that drastically degrade the structural qualities of carbon/epoxy composites. The addition of pre‐formed immiscible thermoplastic filler in thermoset matrix offers various advantages over miscible phase separated thermoplastic filler. In this work, poly ether ether ketone (PEEK) micro particles were used to improve the toughness of the carbon/epoxy composite. Mechanical stirring was used to disperse the particles. Composite was fabricated using hand lay‐up process followed by compression molding. The effect of PEEK particles was assessed using in‐plane v‐notched rail shear characteristics, drop weight impact, and compression after impact strength. The addition of PEEK particles significantly improved the in‐plane shear strength and damage tolerance of the carbon/epoxy composite, according to the results.

A modified three rail shear test procedure for rigid foamed materials

In this study, a modified three rail shear test (or double shear test) procedure is described for the determination of the shear moduli and the shear strength values of rigid foamed materials and test results are presented for light extruded polystyrene, which is a typical core material used in sandwich construction. The main idea is to obtain a nearly uniform shear stress distribution in the shear test specimens by strengthening them against bending. First, using a finite element model, it is numerically shown that a nearly pure shear stress state may be obtained in the strengthened three rail shear test specimens. Then, it is shown that the finite element numerical results obtained for the strengthened specimens are in excellent agreement with the analytical results. Next, three rail shear tests are performed on bare and strengthened specimens and the experimental results obtained are presented in comparison with the analytical results. Also, clamped beam vibration and three-point bending tests are conducted to validate the shear modulus values obtained. The results obtained show that, the strengthened three rail shear test specimens yield more accurate results for both shear modulus, and strength comparing with the bare specimens.

Behaviour of hybrid glass fibre-reinforced polymer and timber composite laminates under shear loading: Importance of fibre rotation

This paper presents a study aimed at investigating the behaviour of hybrid glass fibre reinforced polymer (GFRP)-timber (HFT) composite laminates under shear loading. A series of V-notched rail shear tests were carried out to determine the properties of HFT laminates, both in perpendicular and parallel to timber grain direction. In addition, shear tests were also conducted for pure timber and GFRP specimens. Except for pure timber specimens loaded parallel to grains, all specimens showed significant non-linear behaviour. During the testing, significant rotation of the glass fibres was observed. To further investigate the behaviour of the shear test specimens, a numerical model was developed. A numerical simulation approach that combines the progressive damage modelling of GFRP and timber with advanced fibre rotation modelling was developed. The simulation approach was implemented in finite element (FE) software program ABAQUS\\Explicit via a vectorized user-defined material model (VUMAT). FE results showed a good agreement with the test results and confirmed the significant influence of fibre rotation on the post peak behaviour of the HFT specimens under shear loading.

Comparison of the shear behavior in graphite-epoxy composites evaluated by means of biaxial test and off-axis tension test

Abstract Characterization of shear behavior in composite materials remains a not fully solved problem. In the last fifty years, many different approaches have been proposed to solve this problem (rail shear, thin-walled tube torsion, off-axis tensile, ±45° tensile, Arcan, Iosipescu, asymmetric four-point bend, plate twist, v-notched rail shear, off-axis flexural, and shear frame), although none of these approaches have achieved an unquestionable solution. For this reason, proposals of alternative methods and comparison between different experimental techniques are of interest. In the present work, the use of cruciform samples with the fiber oriented at 45° with respect to the load directions, and subjected to tension-compression (creating a pure shear stress state at the central part of the samples), is studied. The experimental results of the cruciform samples have been compared with the off-axis tests (with the fiber at 10°) for the same material (AS4/8552), finding a good agreement between the shear experimental curves, especially at the initial part of the curve, where the shear modulus is calculated. Nevertheless, the shear strength value obtained by means of the cruciform specimen has shown to be significantly lower than that obtained using the off-axis test. A Finite Element numerical model of the cruciform specimen has been developed to analyze the stress field of the samples. Numerical results have shown that there is a central area of the cruciform specimens where a pure and uniform shear stress state is developed, which is suitable for the evaluation of the shear constitutive law of the material. It has been observed that there is a (σ 22) stress concentration in the transition between the straight and curved parts of the boundary geometry of the samples, which explain some premature failures of the samples. This premature failure could be avoided with tabs extended up to the beginning of the central part of the sample.

Study on Stress Concentration and Strain Distribution in the Two Rail Shear Method for Plywood and MDF.

Study on Stress Concentration and Strain Distribution in the Two Rail Shear Method for Plywood and MDF.

Experimental determination of deformation homogeneity and shear states using the digital image correlation method

One of the great challenges in the pure shear and simple shear tests is to maintain the deformation state and deformation homogeneity of a specimen under large deformations. For this reason, the aim of this work is to investigate the state of shear deformation and degree of deformation homogeneity of three different shear specimens. A simple and easily replicable methodology was proposed to estimate the degree of deformation homogeneity of specimens, while a time-independent kinematic vorticity parameter was employed to identify pure shear and simple shear deformation states. All data were obtained from full-field displacements that were extracted with the two-dimensional digital image correlation (2D-DIC) method. Specimens of polytetrafluoroethylene (PTFE) were tested using the modified slotted shear test and the V-notched rail shear test, which are used to induce a simple shear state. The planar tensile test was used to produce a pure shear state in a thin sheet of rubber-like material. For small deformations, both slotted and V-notched shear tests induced a good degree of deformation homogeneity along the shear path between the notches of specimens, mainly in the central region. However, the V-notched specimens buckled at large deformation, producing a decrease in the degree of deformation homogeneity. In this case, the results were qualitatively assessed due to the errors associated with out-of-plane motions. High degree of deformation homogeneity was also observed in pure shear specimens. All tests demonstrated to be effective for inducing a state of pure shear or simple shear. Results show that the two approaches can be used as supplementary tools for determining the state of shear deformation and degree of deformation homogeneity.

Implementation of the modified V-Notched Rail Shear method for characterizing glass fibre thermoplastic composites at sub-zero and elevated temperatures

In the recent years, the thermoplastic-based composites are being increasingly used in a variety of industrial applications such as the automotive due to the unique features they exhibit, mainly their recyclability and their interesting capacity to be formed and produced in high volume rate. Among the most interesting categories utilized extensively in these sectors, the short fibre composites are an attractive solution to non-critical load carrying structures while the textiles are utilized in more critical components. Nevertheless, all of them are implemented into a varying service temperature range, from sub-zero up to higher temperatures than the ambient. Thus, the definition of their mechanical performance with respect to their material and fabrication characteristics is a crucial procedure. Among them, the shear properties are the most challenging due to the complexity of the standardized mechanical tests. Moreover, these properties are greatly dependent on the matrix quality and, in general, to the overall composite's quality. In the present work, presented is an experimental campaign implementing temperatures from −30 °C up to 80 °C that includes both short and textile thermoplastic based composites, fabricated with different processes. In addition, introduced is a modified testing apparatus based on the standardized one that aims to overcome some of the drawbacks observed so far.

Experimental and numerical investigation of the effects of porosity on the in-plane shear properties of CFRPs using the V-notched rail shear test method

Voids occurred after the manufacturing process are a common defect of composite materials. They appear to have a negative impact on the matrix-dominated material properties, the gravity of which depends upon the porosity content, the shape and the volume of pores. In the present work, the effects of porosity on the shear mechanical properties of unidirectional carbon fiber-reinforced plastic composites are evaluated via mechanical testing and numerical simulation. In this framework, the V-Notched Rail Shear test method is applied on carbon fiber reinforced plastic specimens of four porosity levels. Moreover, two finite element methodologies are utilized for simulating this particular mechanical test namely the progressive damage model (PDM) and the Virtual Crack Closing Technique (VCCT). Double cantilever beam (mode I) and end notched flexure tests (mode II) are also conducted for the development of the VCCT model. The results from the shear mechanical tests reveal a considerable drop in both the elastic properties and strength. In addition to that, for larger porosity contents, more cracks are present and crack initiation and propagation occur at a faster pace. Finally, the advantages and disadvantages of the two numerical methods are presented and assessed revealing a satisfying consistency with the results obtained by the mechanical tests.

Assessment of the shear properties of thermoplastic composites using the ±45° tension and the V-notched rail shear methods

Composite materials consisting of thermoplastic matrix are gaining the interest of both the aeronautical and the automotive industry as they comprise a series of advantages regarding their mechanical performance, their recyclability and their ability to be produced in large quantities. Nevertheless, some notable drawbacks have been noticed related to the fabrication process affecting their in-plane shear properties the characterization of which is complicated. Among the notable number of testing methods proposed throughout the years, several advantages and drawbacks were observed, mostly related to the way the load is applied, the stress uniformity and the applicability of each method to various material architectures. In the present work, the modified V-notched rail shear and the ±45° shear testing methods are applied to short and textile glass fiber reinforced thermoplastics aiming to assess the influence of both the fabrication method and the strands direction. Consecutively, the results obtained from the two different testing methods are compared revealing a relatively good agreement while, in parallel, the stress uniformity and the local failures observed on the specimens are analyzed.

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.

Determination of In-Plane Shear Properties of Laminate with V-Notch Rail Shear Test and Digital Image Correlation

Abstract This article presents the results of the application of Digital Image Correlation (DIC) to measurements of in-plane shear modulus and strength of three different carbon fiber reinforced laminates. Three different approaches to shear strain calculations via DIC are evaluated and compared with standard strain gage measurements. Calculation of shear strain based on averaging DIC strain values of strain gages area in most cases yielded results closest to strain gages, while measurements based on single point strain measuring differed the most from strain gages. These results are attributed to shear strain distribution in the center area of the specimen. Thermoplastic matrix fabric reinforced composite had the lowest shear strength at 5% of shear strain, but the highest ultimate shear strength and strain at failure. Of thermosetting materials, laminate reinforced with unidirectional carbon fiber had shear modulus about 10% lower, than fabric reinforced laminate, but higher ultimate strength and strain at failure. This behavior is attributed to the presence of weaves in fabric reinforcing the laminate, causing shear stiffening of the material, but lowering its ability to deform under shear loading.

Use of fiber optic sensing to measure distributed rail strains and determine rail seat forces under a moving train

Rayleigh backscatter fiber optic sensing permits dynamic strains to be measured along an optical fiber with a gauge spacing and temporal resolution sufficient for rail applications. However, this sensing technology is highly sensitive to vibration. A 7.5 m long section of rail was instrumented with optical fiber and strain measurements were recorded during passage of a freight train slowed to 8–11 km/h. This strategy to minimize rail vibration was successful in permitting distributed dynamic rail strains to be measured under freight car loading. The measured rail strains were used to determine the rail shear forces, which were then used with the static wheel loads to determine the rail seat load for 14 consecutive sleepers as the train passed over the field monitoring site. These data were then combined with measurements of dynamic rail displacement captured using digital image correlation to infer the rail seat load–deflection relationships for individual sleepers. These relationships were observed to provide significantly more detailed information about unsupported voids and the sleeper contact stiffnesses than the traditional consideration of the relationship between applied load and rail deflection and highlights how track behavior at a monitored location can be dependent on the conditions and behavior of neighbouring sleeper.

The Influence of Uneven Temperature Distributions on Local Shear and Interlaminar Fracture Toughness Properties of a Thick Composite Laminate

Abstract Because wind turbine blade length has increased over the years, so have the root and spar cap thicknesses. Temperature gradients and residual strains related to the manufacturing process of thick laminates are factors that determine the final laminate mechanical properties. The aim of this study is to investigate the manufacturing process influence on shear and fracture toughness properties for an epoxy glass fiber-reinforced polymer. Epoxy-infused laminates of 84 layers (55–60 mm) thick were manufactured. The laminate was manufactured using vacuum infusion on a single-sided mold. Thermocouples and strain gauges were embedded at different thickness positions to monitor temperature and residual strain during the curing process. The laminate was manufactured using the sublaminate technique: with the help of peel plies at different thickness positions, sublaminates were extracted and separately tested as standard coupons. Shear coupons were tested according to ASTM D7078-12, Standard Test Method for Shear Properties of Composite Materials by V-Notched Rail Shear Method, and fracture toughness double-cantilever beam coupons were tested in Mode I according to ASTM D5528-13, Standard Test Method for Mode I Interlaminar Fracture Toughness of Unidirectional Fiber-Reinforced Polymer Matrix Composites. Based on the extracted sublaminates, the relations between local curing cycles, residual strains, and the influence on the shear and fracture toughness were studied. This work reports temperature profiles and residual strain measurements that were monitored during thick laminate manufacturing. In addition, experimental data from shear and fracture toughness tests (static and fatigue) are correlated with the local residual strains and temperature measurements.

How important is sample alignment in planar biaxial testing of anisotropic soft biological tissues? A finite element study

Finite element models of biomedical applications increasingly use anisotropic hyperelastic material formulations. Appropriate material parameters are essential for a reliable outcome of these simulations, which is why planar biaxial testing of soft biological tissues is gaining importance. However, much is still to be learned regarding the ideal methodology for performing this type of test and the subsequent parameter fitting procedure.This paper focuses on the effect of an unknown sample orientation or a mistake in the sample orientation in a planar biaxial test using rakes. To this end, finite element simulations were conducted with various degrees of misalignment. Variations to the test method and subsequent fitting procedures are compared and evaluated.For a perfectly aligned sample and for a slightly misaligned sample, the parameters of the Gasser-Ogden-Holzapfel model can be found to a reasonable accuracy using a planar biaxial test with rakes and a parameter fitting procedure that takes into account the boundary conditions. However, after a certain threshold of misalignment, reliable parameters can no longer be found. The level of this threshold seems to be material dependent.For a sample with unknown sample orientation, material parameters could theoretically be obtained by increasing the degrees of freedom along which test data is obtained, e.g. by adding the data of a rail shear test. However, in the situation and the material model studied here, the inhomogeneous boundary conditions of the test set-ups render it impossible to obtain the correct parameters, even when using the parameter fitting method that takes into account boundary conditions.To conclude, it is always important to carefully track the sample orientation during harvesting and preparation and to minimize the misalignment during mounting. For transversely isotropic samples with an unknown orientation, we advise against parameter fitting based on a planar biaxial test, even when combined with a rail shear test.

Shear test method for and mechanical characteristics of short basalt fiber reinforced polymer composite materials

ABSTRACTIn this work, an experimental study was performed to investigate the shearing mechanical properties of short basalt fiber‐reinforced polymer composite materials (SBFRP), and an optimized test method was developed. The following findings were obtained: (1) The optimized V‐notched rail shear device and test method are reliable and valid, enabling the effective shear testing of samples similar to those tested in this study in the future. (2) The shearing failure cracks of SBFRPs can be classified into three types, namely, main cracks, coupling cracks, and micro‐cracks. The micro‐cracks, which originate from micro‐slippage at the interfaces between the short fibers and the epoxy resin, initiate prior to the main cracks. (3) The existence of a critical value of the fiber volume fraction is proposed, above which a sample possesses a nonlinear deformation capacity by virtue of the initial micro‐slippage at the fiber/matrix interfaces. Furthermore, a higher fiber volume fraction gives rise to a stronger nonlinear deformation capacity. (4) The shearing mechanical properties and other basic material attributes of SBFRPs with a fiber length of 3 mm are presented, thereby establishing a foundation for the theoretical study, finite‐element analysis, and application and dissemination of SBFRPs. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46078.