Short Beam Shear Test Research Articles

Asymmetric Four Point Bend Test Method for Interlaminar Shear Strength in Ceramic Matrix Composites

Asymmetrical Four Point Bend test method is proposed for measurement of interlaminar shear strength in continuous fiber reinforced ceramic composites. The current standard ASTM test method (ASTM C1425) for interlaminar shear strength of composites uses a double edge notched compression (DNC) coupon. Large variation in measured strength is observed with the standard ASTM test method, possibly due to machining variability and damage at the notches. The proposed test AFPB method for ILSS is adapted from ASTM C1469 Standard Test Method for Shear Strength of Joints of Advanced Ceramics. This test method does not require any machining of notches and the sample size requirement is much smaller than the ASTM test method. The shear loading in this method is similar to the standard short beam shear test (ASTM D2344) with higher shear to tensile ratio compared to SBS with AFBP. Using finite element analysis, coupon geometry and the distance between the loading and support pins was optimized to maximize shear and minimize tensile and compressive stresses on the specimen. It was found that the variability in the measured ILSS strength was lower with this method compared to the ASTM standard method using the DNC specimen. In addition, the value of ILSS measured using AFPB method was found to be consistently higher than that measured using DNC coupons. It was also found that specimen preparation (cutting, polishing, etc.) did not have significant effect on the measured strength.

Fabrication and braiding angle effect on the improved interlaminar shear performances of 3D braided sandwich hybrid composites

While the interlaminar hybrid composites have been used widely and still remain in great demands, interlayer delamination, undesirable in most cases, keeps a common defect, due to the lack of interlaminar fiber-connection. Here, on the basis of the yarn interlacing rule in three-dimensional (3D) four-step braiding technology, 3D braided carbon fibers/Kevlar fibers sandwich (S_) hybrid composites with different braiding angles (S_20°, S_30° and S_40°) have been designed and fabricated with interlaminar fiber-connection. Short-beam shear tests were applied to evaluate the interlaminar shear performances of specimens. The in-situ strain maps during tests were characterized by digital image correlation (DIC) technique and specimen damages were observed via scanning electron microscope (SEM) and computed tomography (CT). Results showed that, comparing to the conventional co-cured laminated hybrid composites, 3D braided sandwich hybrid composites resisted the delamination effectively by the fiber-connection hybrid region. Braiding angle effect of 3D braided sandwich hybrid composites revealed that S_20° showed better deformability and higher structural toughness than their counterparts in S_30° and S_40°. The results presented in the current work would be helpful for the design and manufacturing of well structured hybrid preforms and composites with dramatically improved interlaminar shear properties.

Proposal and verification of a thermoplastic surface shear-strength evaluative method

A method for evaluating the surface shear strength of thermoplastics is proposed and validated. Thermoplastics are commonly used for their mass production and solid properties, but their surface properties, specifically friction and wear, are also required in some cases. The surface strength against shear loading, which has not been evaluated quantitatively as a material mechanical property, must be ascertained to elucidate these properties. We propose the overlapped short-beam shear tests to evaluate the surface shear strength of injection-molded thermoplastics. We also perform ball on disk testing to validate the results obtained from the overlapped short beam shear tests. Results show that the surface shear strength obtained from the proposed test is related to the frictional force obtained from the ball on disk tests, thereby validating the proposed method.

Z-direction performance and failure behavior of 3D printed continuous fiber reinforced composites with sinusoidal structure

The 3D printing process for continuous fiber reinforced composites (CFRCs) has many benefits, but it still faces an unsolved issue: poor performance in the Z-direction (through-thickness). To address this problem, a novel Z-direction enhancement method was proposed to optimize the fiber arrangement in the Z-direction within parts by altering the in-plane structure and out-of-plane configuration of CFRCs. Based on the bioinspired structural design and the 7-axis 3D printing robot, the sine-surface-layered CFRCs (Sin-CFRCs) were fabricated. Then, the Z-direction load-bearing capacity of Sin-CFRCs was characterized by the short-beam shear test and the three-point bending test, and the effect of structural parameters on the Z-direction performance were further examined. Moreover, Z-direction enhancement mechanisms were summarized by studying the mechanical behavior and the fracture mechanism. Finally, the results revealed a substantial improvement in the Z-direction performance of Sin-CFRCs compared to plane-layered CFRCs. The interlayer shear strength (ILSS) increased by 51.7% from 18.5 MPa to 28.1 MPa, and the flexural modulus rose by 22% from 13526 MPa to 16506 MPa. Moreover, the flexural fracture energy showed a significant improvement of 126%. These enhancements in performance can be attributed to the force field redistribution and the multiscale periodic modulus mismatch of Sin-CFRCs. As a result, the Z-direction load-bearing capacity and the energy absorption capability of Sin-CFRCs were significantly enhanced. This research opens up new possibilities for enhancing the Z-direction performance or even controlling the anisotropy of 3D printed CFRCs.

Analysis of vibration characteristics based on variable‐angle hybrid laminates

AbstractComposite laminates are widely used in the aerospace field. Aircraft wings are subject to strong aerodynamic interference, which produces resonance, instability and other phenomena. To avoid this resonance and reduce the vibration of laminates it is essential to adopt a variable‐stiffness laminate. Methods for changing the stiffness include designing the fiber path and inserting a damping layer. The former can increase the natural frequency but does not improve the damping performance. Here we demonstrate how, depending on the resin's agglomeration, variable‐angle hybrid laminates made of carbon fiber and Kevlar fiber increase the damping performance. By using a short beam shear test we found that sandwich hybrid samples with a hybrid ratio of 50% performed better than inter‐laminar hybrid samples, which increased by 19.5%. Based on the results of interlayer properties, 8 layers of pure carbon fiber (CF) laminates and carbon fiber‐kevlar fiber (CF‐KF) hybrid laminates with variable angles were manufactured. Modal tests demonstrated that the change in fiber angle had a greater impact on the natural frequency, the maximum result of which was seen at an angle of <60|75>. By inserting, the KF layer the damping ratio of the <15|30> hybrid laminate increased by 5.45% more than pure CF laminates. These results can be referenced to improve the damping parameters of variable‐angle laminates.

Low-velocity impact and compression after impact modeling of composites using modified mesoscale model

Present article demonstrates the virtual certification methodology of composite laminates according to ASTMD7136 (low-velocity impact, LVI) and ASTM D7137 (compression after impact, CAI). Intraply behavior is described using modified mesomodel. Interply behavior is captured using cohesive elements. Intraply and interply models are implemented in commercial finite element (FE) software LS-Dyna.Unidirectional AS4/8552 material is considered in the present study. Ply and interface material properties are measured in the present work. The adopted test campaign consists of tension tests, curved beam bend, short beam shear, double cantilever and end-notch flexure tests. The LVI and CAI studies on quasi-isotropic laminates with ply scaling effects are studied. Each laminate is subjected to three levels of impact energies.Present FE models with material-aligned mesh are able to capture the diagonal matrix splits at the back face, impact duration, peak forces, delamination zones and compressive residual strengths accurately in comparison with tests.

Effects of silane‐modified nano‐CaCO3 particles on the mechanical properties of carbon fiber/epoxy (CF/EP) composites

AbstractIn this study, the effects of silane‐treated nano‐CaCO3 particles on the flexural, Mode‐I, Mode‐II and interlaminar shear strength (ILSS) properties of carbon fiber/epoxy composites are investigated experimentally. The surface of nano‐CaCO3 particles is treated with a silane coupling agent, namely, (3‐Glycidyloxypropyl) trimethoxysilane (GPTMS). Three‐point bending, double cantilever beam (DCB), end‐notch flexure (ENF), and short beam shear (SBS) tests are carried out on the prepared composite specimens according to the relevant ASTM requirements. The results show that with the dispersion of 5 wt% silane‐treated nano‐CaCO3 particles the flexural modulus, flexural strength, Mode‐I fracture toughness, Mode‐II fracture toughness, and ILSS values can be enhanced by 16.8%, 13.6%, 25.7%, 19.6%, and 19.8%, respectively, compared to reference composites. The storage modulus is also increased by about 15.3% with the silane‐treated nano‐CaCO3 particles. The silane‐treated nano‐CaCO3 particles had no significant effect on the glass transition temperature of the composites.

Investigation on tempering process parameters of in-situ consolidation CF/PEEK thermoplastic composites

In this paper, the effect of in-situ consolidation (ISC), hot-press (HP) tempering, and vacuum-bag-only (VBO) tempering process parameters on interlaminar shear strength (ILSS) of CF/PEEK laminates is investigated. Short beam shear (SBS) tests are performed on the prepared samples to characterize the load-displacement response, the ILSS trend, and the microscopic influence mechanism of different preparation processes on the ILSS. The experimental results show that the highest ILSS of the HP tempered samples reached 73.07 MPa, which is 132.04 % higher than the ILSS of the ISC samples. Furthermore, the highest ILSS of the VBO tempered sample is only 66.11 % of the HP tempered sample. Microscopic mechanism analysis revealed that the most direct reasons for the improved ILSS are stronger CF and PEEK binding interfaces, more stable crystal structures, and more uniform fiber distribution. The proposed method provides an important reference for green thermoplastic composites (TPC) for highly reliable and low-cost applications in aerospace skin types.

Impact of auxeticity on mechanical properties of3Dwoven auxetic reinforced thermoplastic composites

Abstract3D woven composites are currently used in high‐tech applications due to their better mechanical properties than 2D laminated composites. To further enhance the mechanical performance of 3D woven composites, auxetic structures can be used as reinforcement. The auxetic structures showed better mechanical properties due to bidimensional energy dissipation capability. Orthogonal 3D woven structures showed inherent auxetic nature, however, the use of brittle thermoset resins in composites fully limits their auxeticity. To overcome this issue, three types of 3D woven auxetic structures (warp, weft, and bidirectional interlocks) were developed and used as reinforcement with thermoplastic resins (PC and PVB). Auxeticity of woven reinforcement, and tensile, flexural (3‐point), and short beam shear (SBS) tests of composites were conducted. Auxeticity results revealed that the warp interlock structure showed the highest auxeticity, while the bidirectional interlock structure exhibited the least auxeticity due to the high number of intersections and crimp %. Furthermore, warp interlock composite structure showed 47%, 49.5%, and 37% higher tensile, flexural, and shear strength values, respectively than bidirectional interlock structure in warp direction with PC resin. The overall results showed that auxetic reinforcement improved the mechanical performance of 3D woven composites.

On improvement of the interlaminar shear strength of carbon fiber/epoxy laminates with magnetically guided steel particles

To enhance the interlaminar shear strength of carbon fiber/epoxy resin laminate, stainless steel particles were filled between laminas and uniformly arranged along the thickness direction by the outside magnetic field during manufacturing the composites. Specimens with five particle densities of 15 g/m2, 30 g/m2, 45 g/m2, 60 g/m2, and 75 g/m2 were prepared for testing. The interlaminar shear strength was obtained by short beam shear test and compared with the one of specimens without particles and with the randomly distributed particles between layers. Both modified equivalent stiffness predicting model and bridging model were established. A segmented prediction model was proposed by combining the two models. The error between results obtained by the proposed model and test was less than 10%. Results showed that the interlaminar shear strength of all specimens filled with particles was improved except for the one with particle density of 15 g/m2. The interlaminar shear strength of the specimens with randomly distributed particles between layers increased by 6.12%, 7.29%, 7.43%, and 6.01% for specimens with particle densities of 30 g/m2, 45 g/m2, 60 g/m2, and 75 g/m2. The interlaminar shear strength of the specimens with magnetically guided particles aligned along the thickness direction increased by 9.78%, 14.39%, 17.93%, and 20.39% for the four particle densities. This indicated that the interlaminar shear strength of the carbon fiber/epoxy laminate could be effectively enhanced by aligning the particles between laminas along the thickness direction using the outside magnetic field guidance during manufacturing the composites.

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.

Damage mechanism of Al2O3f/Al2O3 composites by acoustic emission technology

Continuous alumina fiber-reinforced alumina matrix composites (Al2O3f/Al2O3 composites) were produced via sol-gel process, the structure, micromorphology, and matrix properties of the composites were characterized, and then the damage mechanism was investigated using acoustic emission (AE) technology. The results showed that the composites were mainly composed of α-Al2O3. When the load first increased with time in the tensile test, the composites showed low AE signal energy, and cracks started and expanded in Al2O3 matrix. When the load reached its peak and abruptly declined, the number of AE signal events and accumulated energy increased dramatically. The proportion of AE signal events in the Al2O3f/Al2O3 composites was 0.37, and the proportion of accumulated energy was as high as 0.79, indicating that most of the fibers and the matrix were destroyed at this time. During the short-beam shear test, almost no AE signal was generated when the load rise reached the peak, and the crack instability expanded along the interlayer, resulting in delamination failure. After the initial load decreased, numerous high-energy AE signals were generated with increasing specimen deformation, and many fibers in Al2O3f/Al2O3 composites were crushed synchronously with the matrix.

Constructing a Superior Interfacial Microstructure on Carbon Fiber for High Interfacial and Mechanical Properties of Epoxy Composites.

The interface quality is crucial for the properties of carbon fiber-reinforced polymer- matrix composites (CFRPs). In order to improve the interfacial and mechanical properties of CFRPs, a superior gradient modulus interfacial microstructure is constructed on the carbon fiber (CF) surface by chemically grafting a self-assembly carboxyl-terminated hyperbranched polymer (HP-COOH). A monofilament debonding test, a short beam shear test, an impact test and a dynamic mechanical thermal analysis (DMTA) were conducted to investigate the properties of the modified composite. Prominent improvements of 79.6% for the interfacial shear strength, 51.5% for the interlaminar shear strength, and 49.2% for the impact strength, as well as superior heat-resistance properties are achieved for composites with the gradient modulus interface over those of the untreated CF composites. The mechanism for performance improvement is mainly attributed to the enhanced CF surface energy, mechanical interlocking, and chemical bonding interactions. In particular, an atomic force microscopy (AFM) test proved that the gradient modulus interfacial microstructure formed by HP–COOH could widen the interface layer thickness and buffer the sharp variations in the modulus from CF to resin, thereby transmitting an external force and reducing the stress concentration. This work provides a facile and efficient strategy for constructing a superior and versatile interface for high- performance composites.

Effect of addition of graphene nanoplatelets on the mechanical properties of triaxially braided composites

Braided composites possess an advantage of good out-of-plane mechanical properties, near net-shape manufacturing, impact and damage resistance. This work aims to investigate the effect of graphene nanoplatelet (GNP) addition on glass fibre triaxial braided composites (TBC). Tensile, flexural, and short beam shear tests were conducted to investigate the mechanical performance of the pristine and hybrid TBC. A numerical model was framed to estimate the material properties of hybrid TBC which were further used as input for the finite element simulation. Results indicate a 15% increase in tensile strength, a 20% increase in flexural strength and a 10% increase in interlaminar shear strength (ILSS). The experimental results were in good agreement with the analytical results. The braided architecture along with proposed GNP combination further enhances mechanical properties and enables gradual failure of the composite which is a desirable property for load bearing structures.

Interlaminar shear strength and failure analysis of composite laminates with double and triple hybrid configurations

Interlaminar shear strength (ILSS) of fiber-reinforced hybrid composites was investigated for double and triple fiber hybridizations. For this purpose, woven carbon, glass, and Kevlar fibers were used for the production of hybrid composites with different stacking sequences. Hybrid samples had a quasi-isotropic structure, and they were subjected to the short beam shear (SBS) tests according to the ASTM D2344 standard. Failure and fracture surfaces of the samples were analyzed along the loading direction with the help of microscopic photos. The degree of the hybridization effects was determined with concerning the rule of mixture in terms of ILSS and peak load, separately. Additionally, a statistical one-way ANOVA analysis for hybrid composites showing significant differences between the results was performed. The results from this study indicated that the location of fibers in the hybrid composites was a key factor regarding the ILSS and failure mechanism along the out-of-plane direction.

Shear Property and Uniform Vertical Load Capacity of Bamboo I-Beams

Bamboo oriented strand boards (BOSB) are very suitable for application in construction structures because of their excellent mechanical properties. This research investigated the shear performance of bamboo I-beams composed of BOSB to verify the structural performance of I-beams. Short beam shear tests and uniform vertical load capacity tests were performed to investigate the effects of various factors on the properties of bamboo I-beams. The results showed that shear bearing capacity and uniform vertical load capacity of bamboo I-beams exceeded the requirements for performance-rated I-Joists in APA PRI-400-2021. The shear bearing capacity, stiffness, and failure types of bamboo I-beams were determined by the web materials, flange–web joint type, and beam depth. Increasing the bamboo I-beam depth without changing the flange dimensions had no significant effect on the shear bearing capacity and stiffness of bamboo I-beams. The shear bearing capacity and stiffness of wooden orientated strand board webbed I-beams were almost half of those of bamboo I-beams with the same depth. The shear bearing capacities of specimens calculated based on the shear bearing capacity calculation formula of I-beams recommended in the Canadian standard were reasonably close to the experimental results. The uniform vertical load capacity of bamboo I-beams gradually decreased as the depth of the bamboo I-beam increased from 300 mm to 500 mm.

Interfacial and Interlaminar Shear Strength of Unidirectional Viscose Fibre-Reinforced Epoxy Composites—an Overview of the Comparability of Results Obtained by Different Test Methods

In this study, the apparent interfacial and interlaminar shear strength (IFSS and ILSS) of single fibres and unidirectional (UD) viscose fibre-reinforced epoxy composites were characterised using different test methods. Microbond and pull-out tests were used to analyse the IFSS of single fibres embedded in epoxy and the transverse tensile test was applied to measure the IFSS of UD fibre-reinforced composites. The short beam shear test, single edge notched bending test (SENB), double-notched tensile test and double-notched compression test were applied to characterise the ILSS. The composites were produced from continuous tows with fibre mass fractions of 20%, 30% and 40% and fibres of different fineness (1.7, 3.3 and 28.0 dtex). The results showed that the different test procedures led to different trends of ILSS depending on the fibre mass fraction and fibre fineness used. The transverse tensile test revealed that the IFSS decreased with increasing fibre mass fraction and fibre diameter. A different trend was found with the short beam shear test and the SENB test for the ILSS. Here, higher values were detected with increasing fibre mass content, and the influence of the fineness was less noticeable. The double-notched shear tests (tensile and compression) showed a different trend: the ILSS increased with increasing fibre mass fraction from 20% to 30%. With a further increase to 40%, the ILSS tend to decrease slightly. An influence of the fibre fineness on the ILSS could not be statistically proven. The different trends of the test methods are attributed to the constitution of the composite and the different load application caused by the test procedures.

Interlaminar shear strength of vacuum pressure impregnated coils with epoxy resin for high field magnet at cryogenic temperature

The interlaminar shear properties of epoxy impregnated coils are critical parameter to the design of the high field superconducting magnets. The existing test methods of the interlaminar shear strength of the composite insulation systems for the superconducting magnet coils in cryogenic temperature were discussed. The insulation system of the niobium titanium superconductor coated with woven glass fiber reinforced polymer coil were fabricated by vacuum pressure impregnation with IR-3 and CTD-101K resins. Short beam shear tests of the impregnated coil were performed at room temperature and liquid nitrogen temperature (77K). The results show that the interlaminar shear strength of the samples used IR-3 resin are better than CTD-101K both at room and cryogenic temperature. A detailed observation of the failed specimens was also investigated to verify the failure mechanisms by optical microscopy.

Influence of graphene nanoplatelet concentration on the electrical, mechanical, and piezoresistive properties of glass fiber/epoxy composites

AbstractThis paper reports the effect of weight concentration of graphene nanoplatelets (GNPs) on the electrical, mechanical, thermo‐mechanical, and piezoresistive properties of unidirectional glass fiber/epoxy composite laminates. The neat (without GNPs) and multiscale laminates (with GNPs) were fabricated with different GNPs contents (0.25, 0.50, 0.75, and 1.00 wt%) using a simple and feasible process based on spray coating followed by vacuum assisted resin infusion. The morphological analysis on glass fiber surfaces evidenced the presence of an effective GNP network formation which tends to be denser as GNPs content increases. As a result, the electrical conductivity and gauge factor measured on top and bottom surfaces of specimens were greatly increased in laminates. Short beam shear and flexural test results showed that the addition of GNPs to the laminates causes a significant reduction in their interlaminar shear strength, flexural strength, and strain to failure with respect to the neat laminate. However, the flexural modulus of laminates does not suffer any apparent change in its reference value and the glass transition temperature was slightly increased in samples with 1.00 wt% GNPs. The fractographic analysis revealed that delamination was the main damage mechanism detected upon mechanical testing, suggesting that relative high concentrations of GNPs cause that interlaminar regions of laminated composites become weaker. In spite of this, excellent strain self‐sensing capabilities and internal damage detection were observed during flexural electromechanical tests performed in beam‐type specimens with higher GNP content.

Enhanced interfacial adhesion of CF/PEEK-titanium hybrid laminates via introducing micro-nano layers with multi-walled carbon nanotube networks

An effective and easily-handled strategy for enhancing the interfacial adhesion of CF/PEEK-titanium hybrid laminates was proposed, which was achieved by introducing micro-nano layers with multi-walled carbon nanotube (MWCNT) networks between titanium and PEEK layers via electrophoretic deposition. The optimal deposition condition was explored by setting different concentrations of MWCNTs and times of deposition. Short beam shear tests were conducted at room temperature to characterize the interlaminar shear strength of the hybrid laminates. The results showed that the optimum parameters of deposition were 0.75 mg/mL of MWCNTs concentration and 90 s of deposition time, leading to a 47.8% increase of interlaminar shear strength compared with the sandblasted-only case. The mechanisms for enhancement were explained by micromorphology, apparent contact angle, and roughness analyses, which could be utilized to guide the preparation of CF/PEEK-Ti hybrid laminates with interfacial reinforcement by MWCNTs. Besides, multiple failure modes occurred at the metal-composites interface including a mixed mode of interfacial and cohesive failures, and a large amount of PEEK and carbon fibers remaining on the surface of titanium sheet proved the excellent interlaminar properties of the hybrid laminates.