In-plane Shear Strength Research Articles

Digital Image Correlation Analysis of Strain Fields in Fibre-Reinforced Polymer–Matrix Composite under ±45° Off-Axis Tensile Testing

This study presents an experimental investigation of an in-plane shear of a glass lamina composite using a ±45° off-axis tension test. Typically, the shear stress curve, shear modulus, and in-plane shear strength for composite lamina-type materials are identified. Previous research indicated that a loading rate affects the strength of this composite. This study extends the existing literature by utilising a non-contact optical digital image correlation (DIC) method to measure strain distribution during the test. Two cross-head displacement rates were examined. The obtained strain maps reveal an uneven distribution resembling fabric texture. As the deformation progresses, the differences in the strain pattern increase. Subsequently, a quantitative analysis of the differences between regions with extreme (minimum and maximum) strain values and regions with average values was conducted. Based on these measurements, shear stress–strain curves, indicating variations in their courses, were constructed. These differences may reach several percent and may influence the analysis of numerical simulations. The DIC results were validated using strain gauge measurements, a commonly utilised method in this test. It was demonstrated that the location of the strain gauge installation impacts the results. During the tests, the occurrence of multiple microcracks in the resin was observed, which can contribute to the nonlinearity observed in the shear stress–shear strain curve.

Failure Mode Prediction of Unreinforced Masonry (URM) Walls Retrofitted with Cementitious Textile Reinforced Mortar (TRM)

The brittle failure of unreinforced masonry (URM) walls when subjected to in-plane loads present low shear strength remains a critical issue. The investigation presented in this paper touches on the retrofitting of URM structures with textile-reinforced mortar (TRM), which enables shifting the shear failure mode from a brittle to a pseudo-ductile mode. Despite many guidelines for applying composite materials for retrofitting and predicting the performance of strengthened structures, the application of TRM systems in masonry walls is not extensively described. A thorough retrospect of the literature is presented, containing research results relating to different masonry walls, e.g., bricks, cement, and stone blocks strengthened with TRM jackets and subjected to diagonal compression loads. The critical issue of this study is the failure mode of the retrofitted masonry walls. Available prediction models are presented, and their predictions are compared to the experimental results based on their failure modes. The novelty of this study is the more accurate failure mode prediction of reinforced masonry with TRM and also of the shear strength with the proposed model, Thomoglou et al., 2020, at an optimal level compared to existing regulations and models. The novel prediction model estimates the shear failure mode of the strengthened wall while considering the contribution of all components, e.g., block, render mortar, strengthening textile, and cementitious matrix, by modifying the expressions of the Eurocode 8 provisions. The results have shown that the proposed model presents an optimum accuracy in predicting the failure mode of all different masonry walls strengthened with various TRM jackets and could be taken into account in the regulations for reliable forecasting.

About Shear Properties of Plain Weave Fabric CFRP at High Temperatures: Analytical and Experimental Approaches

The in-plane and interlaminar characteristics of plain weave fabric Carbon Fibre Reinforced Polymer (CFRP) composites are studied. The influence of the temperature exposure, below the glass transition state of the composites, on these properties are studied. The in-plane shear properties, shear strength and shear modulus are affected by the temperature exposure. The in-plane shear strength has dropped by 44.36% for the specimens tested at 120 °C compared to the specimens tested at room temperature. The interlaminar shear strength, however, are largely unaffected by the temperature exposure. The interlaminar shear strength of the plain weave fabric CFRP largely depends on the cross-sectional area of the specimen than the temperature exposure. Finally, several prediction models are used for estimating the shear properties of the composites exposed to different temperatures. Among them, Hawileh model fits very well with the experimental data for predicting the in-plane shear strength, while Wang model fits well for the shear modulus. In addition to these, fracture surfaces of the in-plane shear and interlaminar shear specimens are characterized under optical microscopy to understand the failure modes and how they are influenced by the temperature exposures.

Thermomechanical performance of continuous carbon fibre composite materials produced by a modified 3D printer

First of all, this article aimed to evidence the role of a modified printer developed for continuous carbon fibre reinforced PolyAmide (cCF/PA6-I) together with the use of a fully open slicing step on the printing quality and the longitudinal/transverse tensile and in-plane shear properties. A comprehensive assessment of the microstructure and properties with a similar material (cCF/PA6-I), but produced with a commercial printer (i.e., Markforged® MarkTwo) has been achieved. Our customised printer and the open slicer used have made possible to better control the print conditions (i.e., layer height and distance between filaments), to reduce the porosity from more than 10% to about 2% and improve the mechanical properties.Moreover, the understanding of the behaviour of these 3D printed composites with wide-ranging external temperatures is mandatory for future use in a severe environment and/or development of new thermally active 4D printed composites.The 3D printed cCF/PA6-I composites have been then thermomechanically characterised along different printing directions (0, 90 and ± 45°) from −55 to +100 °C. Unlike the longitudinal properties that hardly change with temperature, the transverse and in-plane shear stiffness and strength of these 3D printed composites were particularly sensitive to temperature variations, with decreases of 25–30% and 30–55%, respectively. This was due to the high sensitivity of the polymer matrix, the fibre/matrix and interfilament interfaces when the composites were loaded along those directions, because damages induced by internal thermal stresses. Fractography has also been carried out to reveal damage mechanisms.

Jute-basalt reinforced epoxy hybrid composites for lightweight structural automotive applications

The utilization of lightweight construction is one of the keys to increase the fuel efficiency and reduce the environmental effect of automobiles. Natural fiber composites are replacing expensive synthetic fibers increasingly commonly in the automotive sector. To further lower the weight and price of the vehicle without losing rigidity and strength, basalt (B) fiber could be incorporated into jute (J) fiber composites. For the generation of hybrid composite laminates, woven textiles made of J-fiber and B-fiber were combined with an epoxy matrix. The primary mechanical features of the J-B/epoxy composite laminates, including tensile, bending, shear, and bearing characteristics, were investigated. Hand lay-up approach was used to prepare the hybrid composite laminates. The impact of the number of J-plies relative to the number of B-plies on the mechanical properties was explored. The findings proved that the basalt/epoxy composite has the maximum ultimate tensile strength, young’s modulus, toughness modulus, bending strength, bending modulus, in-plane shear strength, and bearing strength. Whereas the J/epoxy composite showed the maximum failure strain and bending strain. Hybridizing J-fiber with B-fiber improved the tensile, bending, in-plane shear, and bearing characteristics of the prepared composite. The maximum specific tensile, bending, in-plane shear, and bearing strengths are displayed by 3B-2 J-3B, followed by 2B-4 J-2B.

Identification of damage properties of glass/epoxy laminates using machine learning models

In the present research, the possibility of estimating damage properties of Glass/Epoxy woven laminates using machine learning (ML) models is investigated. The dynamic response of laminates under low-velocity impact (LVI) was characterized and used as training data sets for ML models. The suitability of four numerical models was investigated for LVI modeling, and based on their accuracy and simulation run-time, an appropriate method was selected. The MAT054 material model was selected for LVI simulations for two energy states (15 J and 20 J). After characterizing the results of these simulations a set of 13 dynamic characteristics were extracted from the dynamic response of each simulation. Moreover, for each energy state, four ML regression models, namely MLP, KNN, DT, and SVR, were performed with the numerical input sets and the random laminate damage properties in each simulation as the output sets. For each ML model the input vector was the same however only one damage property was set as an output vector. The trained ML models were able to estimate 4 out of 6 damage properties of Glass/Epoxy woven laminates namely Longitudinal modulus, Longitudinal tensile strength, Longitudinal compressive strength, In-Plane shear strength. Additionally, the output of the trained ML models was compared with damage properties obtained from experimental results and it was found that the trained models were able to estimate the said damage properties within 4% – 6% of the experimental results.

Model trees and stepwise regressions for accurate in-plane shear strength predictions of partially grouted masonry walls

The behaviour of partially grouted (PG) masonry shear walls is complex due to masonry's anisotropic nature and the nonlinear interactions among its constituents. Currently available code- and research-based shear strength equations provide highly variable results when predicting the in-plane shear strength of PG masonry walls. It is crucial to develop a greater understanding in this area, as sudden shear failures of masonry walls can lead to catastrophic losses of human life and property. This study presents the development of several new in-plane shear strength models for PG masonry walls using stepwise regression and model trees with data compiled from 292 experimentally tested walls. The models are found to significantly outperform existing code- and research-based shear strength equations. It was found that, of the variables studied, the most significant ones are the axial load, wall geometry, compressive strength of mortar, and area of interior vertical reinforcement.

In-plane shear strengthening of traditional unreinforced masonry walls with near surface mounted GFRP bars

In this study, the effectiveness of Near Surface Mounted (NSM) method, for in-plane shear strengthening of traditional and historical Unreinforced Masonry (URM) walls, is investigated through a comprehensive experimental study. For this purpose, square solid clay brick masonry wallettes (42 samples) with three different types of traditional mortars including gypsum mortar, lime-cement-sand mortar and lime-sand mortar are prepared and retrofitted with NSM Glass Fiber Reinforced Polymer (GFRP) bars. Then, diagonal shear tests are conducted to evaluate the in-plane shear behavior of the masonry wallettes. The effects of some key variables such as wall thickness, the retrofitted face of the wall, reinforcement ratio, and the type of paste for mounting the reinforcing bars, on the effectiveness of the retrofitting method are investigated. The results of the tests are presented in terms of the failure modes and the lateral shear stress-drift curves of the test specimens. Accordingly, the retrofitting method can enhance the in-plane shear strength, and the ultimate lateral drift capacity of the URM wallettes. According to the test results, the type of filler paste and reinforcement ratio influence the strength enhancement of the test specimens. Furthermore, in specimens retrofitted with the one-side retrofitting scheme, due to the asymmetry of walls under in-plane loads, an unexpected out-of-plane deformation is induced in the walls under in-plane load which adversely affects its global behavior.

CRM reinforced brick masonry walls: Experimental and parametric numerical investigations

Composite Reinforced Mortar (CRM) is an innovative typology of inorganic composites for the reinforcement of existing masonry structures, consisting of bi-dimensional glass fiber grids embedded in a mortar matrix with a thickness of 30-50mm.Several experimental campaigns have been carried out using diagonal-compression loading, to evaluate in-plane shear strength increase. However, limited research is still available to define the mechanical properties of CRM and its bond behavior to masonry substrates. The lack of knowledge of mechanical parameters also prevents the possibility of numerical simulations to extend experimental results.In this paper, a series of experimental tests were performed on CRM components to provide a mechanical characterization of the system. Based on experimental results, several nonlinear numerical analyses were carried out considering reinforced and unreinforced masonry walls in shear-compression, and the effect on strength, ductility, and stiffness of specimens was pointed out. An analytical procedure was proposed using a regression of numerical results to evaluate CRM efficiency on the seismic behavior of the walls.

Effect of Aviation Turbine Fuel Exposure on Interlaminar and Inplane Shear Properties of Glass Fiber Reinforced Epoxy Composite

This study investigated the effect of aviation turbine fuel exposure on interlaminar and in-plane shear properties of E-glass/epoxy composite. The two types of test specimens, namely bare and resin-coated specimens with varying thicknesses as per the ASTM standard, were made out of E-glass/epoxy composite to evaluate their interlaminar and in-plane shear properties. These all types of specimens were immersed inside the aviation turbine fuel for two months and then afterward their effect on the reduction of mechanical properties like interlaminar and in-plane shear tests properties were experimentally investigated. Test results show that ATF fuel exposure has reduced the interlaminar shear strength by 10.04 %, 7.83 %, and 6.01 % for bare, with 0.1 mm and 0.2 mm resin coating, respectively. Similarly, in-plane shear strength was reduced by 14.75 %, 11.22 %, and 7.52 % for bare, with 0.1 mm and 0.2 mm resin coating, respectively, and in-plane shear modulus was reduced by 10.87 %, 8.94 %, and 6.52 % for bare, with 0.1 mm and 0.2 mm resin coating conditions as compared to as-received (without ATF exposure) specimens.SEM micrographs and results too showed that properties were reduced and indicated that the glass/epoxycomposite was resistive to fuel ingression. It was observed that bare specimens exhibited a reduction in shearproperties due to ATF ingression to the polymeric network and induced internal stresses, which not only degraded the matrix and fiber-matrix adherence but created micro-cracks too in the resin at interfaces. Resin-coated specimens limit fuel ingression, which has led to a reduction in properties.

A plastic-based model for in-plane shear strength of steel plate-concrete shear walls

The steel plate-concrete shear wall (SCSW) has great potential being used in nuclear facilities due to its high construction efficiency and excellent structural performance. Although it is not new, but only thirty-year history of study for application in nuclear facilities. Different from other ordinary structures, nuclear facilities are low-rise buildings consisting of squat shear walls, and the in-plane, out-of-plane shear capacity and their combination are of concern in design. Currently, several equations for evaluation of in-plane shear strength of SCSW element are put forward and some are adopted by design codes with some modification. However, these equations are established based on the elastic theory and do not consider the collaborative work of infilled concrete and steel plates in limit state from an overall perspective. From the ultimate limit design point of view in current design structural codes or standards, a new model for evaluating the in-plane shear strength of the SCSW element is derived based on the lower bound plastic limit theory and two of its simplified expressions are proposed for easy application. The accuracy of the proposed equations is verified by comparing the calculated results with 14 collected experimental results. In the end, a comparison between the proposed equations and those in codes AISC N690 and JEAG 4618 is conducted.

Mechanical Characterization of Hybrid Nano-Filled Glass/Epoxy Composites.

Fiber-reinforced polymer (FRP) composite materials are very versatile in use because of their high specific stiffness and high specific strength characteristics. The main limitation of this material is its brittle nature (mainly due to the low stiffness and low fracture toughness of resin) that leads to reduced properties that are matrix dominated, including impact strength, compressive strength, in-plane shear, fracture toughness, and interlaminar strength. One method of overcoming these limitations is using nanoparticles as fillers in an FRP composite. Thereby, this present paper is focused on studying the effect of nanofillers added to glass/epoxy composite materials on mechanical behavior. Multiwall carbon nanotubes (MWCNTs), nano-silica (NS), and nano-iron oxide (NFe) are the nanofillers selected, as they can react with the resin system in the present-case epoxy to contribute a significant improvement to the polymer cross-linking web. Glass/epoxy composites are made with four layers of unidirectional E-glass fiber modified by nanoparticles with four different weight percentages (0.1%, 0.2%, 0.5%, and 1.0%). For reference, a sample without nanoparticles was made. The mechanical characterizations of these samples were completed under tensile, compressive, flexural, and impact loading. To understand the failure mechanism, an SEM analysis was also completed on the fractured surface.

In-plane shear and tensile behavior of two-pass injection-molded glass fiber reinforced polypropylene composites with different fiber lengths

Glass fiber reinforced polypropylene (GF-PP) composites have proven a great potential in the designation and manufacturing of control arms, leaf springs, barriers, beams and bridge decks. Two-pass injection molding of GF-PP was investigated in this study. Polypropylene (PP) was injected with different weight fractions (w%) of chopped glass fibers (GFs) with different fiber feedstock lengths (FFSLs). The composites were then crushed and re-injected once again. Some specimens were burned out to check the actual weight fractions and fiber lengths after the injection processes. The fiber lengths dramatically decreased due to damages during two-pass injection processes and crushing. The manufactured specimens were tested in tension, and the results indicated that the tensile strength increased slightly at w = 10% of GF. Further increase of GF weight fraction leads to a drop in the tensile strength below neat PP. The results of SEM micrographs showed an increase in air voids concentrations at high GF percentages which clarifies the reason behind the drop in the tensile strength. Also, in-plane shear tests were carried out using the Iosipescu fixture where a slight increase in the in-plane shear strength was noticed by increasing fiber weight fractions. In-plane shear moduli of all specimens were measured experimentally by strain gauges and calculated theoretically. The shear modulus was enhanced by glass fiber addition and a further increase was noticed by increasing the fiber weight fractions.

In-plane shear strength of solid clay brick masonry reinforced with near surface mounted steel bars

Structural walls made of solid brick masonry have been used for centuries in old buildings, which are vulnerable to earthquakes. Reinforcing this type of walls may increase the overall building seismic strength. In this paper, the in-plane behaviour of these types of walls, both plain and reinforced, was experimentally assessed through triplets shear tests. The reinforcement considered, with near surface mounted (NSF) steel bars, has already been studied in the scope of a broader ongoing research project. The in-plane strength of brick masonry walls is of utmost relevance for seismic resistance and strongly depends on their resistance to sliding that may occur along the horizontal mortar interfaces. The bricks and the laying mortars tested correspond to walls of buildings built between 1920 and 1950 that may be found in Lisbon and other cities. Triplet specimens (made of three stacked bricks connected by a laying mortar) were built and tested. Two types of mortar compositions were used, of an earlier and a later phase within the period referred above. Both types included unreinforced specimens and specimens reinforced with steel bars of different types. The specimens were subjected to direct horizontal shear tests to determine the relevant properties of the assemblage, namely the cohesion and friction angle of the brick mortar joints. The results obtained in this study may be used in the numerical modelling of ancient buildings with brick masonry walls granting a better correlation with real behaviour.

Fusion-bonding performance of short and continuous carbon fiber synergistic reinforced composites using fused filament fabrication

In this work, short and short continuous fiber synergistic reinforced composites (S-CFRPCs) were successfully fabricated by fused filament fabrication. The influences of short fiber content on the filament bonding properties were evaluated through short beam shear (SBS) and in-plane tensile shear tests. The data showed an increasing and then decreasing trends of interlaminar shear strength (ILSS) and in-plane shear strengths of S-CFRPCs specimens as short fiber content rose from 0 wt% to 10 wt%. Specimens with a short fiber content of 5% displayed higher load carrying capacities and significant fusion-bonding performances, with approximately 41% and 80% increase in ILSS and in-plane shear strength when compared to 0% specimen, respectively. The fracture surfaces of tested S-CFRPCs specimens indicated fiber pull-out and resin fracture as dominant bonding failure models. The use of proper amounts of short fibers effectively improved the fusion-bonding of S-CFRPCs. In sum, these findings look promising for future design of strong and tough composite structures.

Mechanically robust structural hybrid supercapacitors with high energy density for electric vehicle applications

The concept of structural energy storage devices has fascinated great attention in the past decade as they enhance system capabilities by the system weight/volume savings. The existing engineering technique is to fabricate multifunctional devices with the capacity of electrical energy storage and load-bearing functionalities simultaneously. Herein, a novel structural hybrid supercapacitor with activated carbon fabric as a negative electrode and lithium cobalt oxide coated carbon fabric through electrophoretic deposition, as a positive electrode, is assembled, for the first time, using the vacuum bagging fabrication method. Increasing the lithium cobalt oxide deposition concentration on carbon fabrics improved the electromechanical performance of structural hybrid supercapacitors. At a 10 g of lithium cobalt oxide deposition on battery-type carbon fabrics, the structural hybrid supercapacitors display an outstanding specific energy of 2.4 Wh.kg−1, a specific power of 41.3 W.kg−1, the charge density of 11.71C.L−1, specific-capacitance of 0.6 F.g−1, in-plane shear strength of 25.3 MPa, in-plane shear modulus of ∼2 GPa, bending strength of 117 MPa, bending modulus of ∼28 GPa and impact strength of 317 kJ.m−2, demonstrating the prospective applications in the military, automotive and aerospace sectors.

Experimental Investigation on Hygroscopic Aging of Glass Fiber Reinforced Vinylester Resin Composites.

The hygroscopic behavior of vinylester resin and high strength glass fiber reinforced vinylester resin composites were examined here, including weight change and the resulting degradation of mechanical properties. The prepared resin and composites specimens were immersed in deionized water and artificial seawater with an applied temperature of 70 °C, and then the specimens were weighed at specified time intervals in combination with the observation of surface morphologies using a scanning electron microscope. Identification of variations of functional groups was also carried out using Fourier-transform infrared spectroscopy. Meanwhile, the mechanical properties for resin and the composite specimens were tested periodically. The observations on surficial morphologies and the test on weight change display that the vinylester resin hydrolyzes seriously after immersion in deionized water, and that the embedment of glass fiber effectively inhibits the moisture absorption and hydrolysis for resin matrix in composites. The results from the mechanical properties test reveal that the tensile strength of pure resin decreases by 35.3% after 7 days’ immersion and keeps small fluctuation in the sequent immersion duration. However, the compressive strength of pure resin consistently dwells at 100 ± 2 MPa during immersion. After immersion for 90 days, the tensile strength decreases by 28.5% and 38.4%, the compressive strength reduces by 7.2% and 16.6%, and the in-plane shear strength reduces by 16.6% and 15.2% for the composites immersed into deionized water and artificial seawater, respectively. The main highlights of this paper are that it provides a more comprehensive mechanical properties test in combination with the microscopic characterization on a matrix and its composites to reveal the aging behavior of composites under a hygroscopic environment.

Microstructure and mechanical properties of SiCf/SiC composite prepared by chemical vapor infiltration

Continuous silicon carbide (SiC) fiber reinforced SiC ceramic matrix (SiCf/SiC) composites are widely studied for possible applications as hot sections in next-generation aeroengines because of their excellent thermo-structural properties. Their mechanical properties were comprehensively evaluated based on the interaction mechanisms among fiber, interphase, and matrix. Moreover, it was found that matrix cracking and fiber bridging mechanisms influenced the shear-dominated and tension-dominated properties, respectively, clearly indicating that the mechanical properties of the material should be correlated. In this study, mechanical properties of the two-dimensional SiCf/SiC composite were comprehensively evaluated, and the correlation laws were verified between tension and bending, tension and in-plane shear, and in-plane shear and interlaminar shear. Results showed that the ratio of shear to tensile matrix cracking stress was 0.68, while the ratio of flexural to tensile strength was 2.3, and the interlaminar shear strength was equal to the in-plane shear strength minus the fiber bridging stress. Fiber bridging is the key mechanism controlling the above-mentioned correlation by the established meso-mechanical formulas, and the interlaminar shear mechanism is controlled by matrix cracking and influenced by interlaminar pores.

Impact and fatigue tolerant natural fibre reinforced thermoplastic composites by using non-dry fibres

This article introduces stiff and tough biocomposites with in-situ polymerisation of poly (methyl methacrylate) and ductile non-dry flax fibres. According to the results, composites processed with non-dry fibres (preconditioned at 50% RH) had comparable quasi-static in-plane shear strength but 42% higher elongation at failure and toughness than composites processed with oven-dried fibres. Interestingly, the perforation energy of flax–PMMA cross-ply composites subjected to low-velocity impact increased up to 100% with non-dry flax fibres. The in-situ impact damage progression on the rear surface of composites was evaluated based on strain and thermal field maps acquired by synchronised high-speed optical and thermal cameras. Impact-induced delamination lengths were investigated with tomography. Non-dry fibres also decreased the tension–tension fatigue life degradation rate of composites up to 21% and altered the brittle failure mode of flax–PMMA to ductile failure dominated by fibre pull-out.

Reinforced Effect on Brick Wall Using Timber Wall as a Retrofitting Method

The purpose of this study is to utilize timber material to enhance the in-plane shear strength and deformation capacity of a brick wall. The proposed strengthening method is light-weight and easy to assemble and includes a timber frame, plywood panel, M12 threaded rod with chemical epoxy, and the hold-down anchor. To evaluate the effectiveness of the reinforced brick wall, three walls were tested under a cyclic horizontal load and static compression stress: the brick wall (BW wall), the reinforced brick wall with timber (BW-T wall), and the reinforced brick wall with timber and the hold-down anchor (BW-TA wall). The proposed prediction method of the Kamiya and Inayama Murakami models assessed the BW-TA wall. The rocking was caused by the failure of BW and BW-T walls. However, because the BW-T wall failed in the lowest part of the wall, the timber part retained the original shape of the brick wall. When the diagonal on the BW-TA wall failed, the horizontal load at maximum load increased by 22%, and the drift angle calculated from the diagonal measurement increased 4.6 times.