Short Beam Shear Research Articles

A novel method for the characterization of through-thickness shear constitutive behavior of composites

This work presents a novel experimental method to characterize the through-thickness shear response for fiber-reinforced polymer composite materials. A sandwich short-beam shear specimen with a thin 0° laminated face sheet bonded with a thick 90° laminated core is proposed. A combination of a finite element model-based stress calculation and a full-field surface strain measurement in a custom sandwich specimen under bending is used in the method. An entire interlaminar shear response in the 2–3 principal material plane has been generated using a regression of FEM-calculated shear stress and DIC-measured shear strain. The measured 23-plane interlaminar shear stress–strain response was very close to the 23-plane Iosipescu test and the plate-twist shear test, but a higher ultimate shear strain was achieved. Transverse tensile failure with a 45° fracture angle originated from the transverse shear stress on the neutral surface. A full set of the three-dimensional stress–strain constitutive relations has been assessed using one short-beam-shear test method, and identical nonlinear shear stress–strain responses with distinct ultimate shear strengths have been observed in the three principal material planes for the generic FRP tape material in this work for the first time.

Thermo-mechanical characterization of sea water immersed GO based GRE hybrid composite

The present work is aimed to investigate the durability of graphene oxide (GO) dispersed GFRP hybrid polymer composite subject to exposure in natural sea water for 4 weeks. Conventional GFRP and GO (0.5 wt%) based GFRP were fabricated by taking 12 layers of woven E-glass fibre as reinforcement and epoxy thermosetting polymer as matrix. GO was synthesized in laboratory by modified Hummer’s method. Synthesis of GO was confirmed through XRD and Raman spectroscopy. Short beam shear (SBS) specimens of all types (both conventional and hybrid) of as-cured composites in desired dimension were immersed in natural sea water for various lengths of duration (maximum up to 4 weeks). All the sea water treated composite samples were characterized through 3-point bend test to reveal inter laminar shear strength (ILSS). About 35 % decrease in ILSS was reported for conventional GRE composite after 4 week of sea water immersion. Decrease in ILSS for GO reinforced GFRP composite was found to be 24.8 %, which is lesser than that compared to conventional GFRP composite. Low temperature Differential scanning calorimetry (DSC) test was conducted to access the glass transition temperature (Tg) of sea water immersed composite samples. After 4 weeks of sea water immersion, conventional GRE and GO-GRE composite exhibited 16% and 15.2% of decrease in Tg. Mechanism of bonding across fibre–matrix interface embedded with GO filler was investigated through the fractographic images, as obtained by scanning electron microscope (SEM).

Mechanical properties of graphene nanoplatelets reinforced glass/epoxy composites manufactured using resin film infusion process

<abstract> <p>Nanofillers as secondary reinforcement in polymeric composites have shown promising results on improvement of mechanical properties of the polymeric composites. However, due to the in-plane resin path, filtration of the nanofillers through fabric during processing is a major challenge in liquid infusion processes such as resin transfer molding. In resin film infusion process, the resin travels in thickness direction and due the shorter resin path, the possibility of filtration is minimal. In this study, resin film infusion (RFI) process is used to fabricate graphene platelets reinforced glass/epoxy hybrid composites. First, the resin films with 0.4 and 0.8 percent of graphene nanoplatelets (GNPs) were manufactured using solvent casting process. Then, these films were used to fabricate composites using resin film infusion process. Mechanical characterization tests, namely tensile, flexural and short beam, were performed. Tensile strength of the 0.4% and 0.8% GNPs reinforced composites was 36.13% and 22.23% higher, respectively, than that of baseline composites. Flexural strength 0.4% and 0.8% GNPs modified composites was 24.96% higher and 32% lower, respectively, compared to baseline composite. Lastly, minimal change was observed in short beam shear strength due to GNPs reinforcement. Higher void volume fraction of 1.7% and 4.5% as compared to baseline composites observed in 0.4% and 0.8% GNPs modified composites respectively.</p> </abstract>

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.

Influence of the electrochemical treatment level of carbon fibers on the compression after impact property of carbon fiber/epoxy composites

AbstractIn this paper, carbon fibers (CF) with different electrochemical treatment levels were obtained by changing the parameters of electrochemical treatment, and the effect of electrochemical treatment levels on the surface properties of CF was studied by scanning electron microscope, atomic force microscopy and X‐ray photoelectron spectroscopy. The interfacial shear strength (IFSS) of CF with different electrochemical treatment levels were characterized by single fiber‐composite fragmentation. The effects of electrochemical treatment on the mechanical properties of CF were investigated by monofilament tensile test and composite laminate 0° tensile test. Finally, the carbon fibers were compounded with epoxy resin to prepare composite laminates, whose effect on the macroscopic mechanical properties of the composite, such as short beam shear strength (SBSS) and compression after impact (CAI) strength, was studied. As a result, with the increase of the level of electrochemical treatment, the surface roughness and chemical activity of CF increased first and then decreased, while the surface energy shows a gradually increasing trend. The IFSS of CF‐BX shows a gradually increasing trend, while that of the CF‐SX shows a trend of increasing first and then remaining basically unchanged, while SBSS shows the same trend. The monofilament tensile test and composite laminate 0° tensile test showed that the electrochemical treatment did not have a significant effect on the mechanical properties of CF. The compression after impact test showed that with the enhancement of the electrochemical treatment, the CAI of the composite laminates increased first and then remained roughly unchanged.

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.

Effect of Sequential Thermal Aging and Water Immersion on Moisture Kinetics and SBS Strength of Wet Layup Carbon/Epoxy Composites

This paper presents results of specific cases of sequential exposure of wet layup ambient cured carbon/epoxy composites to thermal aging and immersion in deionized water. Thermal aging is conducted at temperatures between 66 °C and 260 °C for periods of time up to 72 h whereas immersion is up to 72 weeks. Effects are characterized in terms of moisture kinetics using a two-stage diffusion model, and through short beam shear (SBS) strength. The response is characterized by a competition between the mechanisms of postcure, which results in increased polymerization and increases in SBS strength and glass transition temperature; and thermally induced microcracking and polymer degradation as well as moisture-induced plasticization and hydrolysis accompanied by fiber-matrix debonding, which results in deterioration. Thermal aging by itself is not seen to negatively impact SBS strength until the highest temperatures of exposure are considered in the investigation. However, the subsequent immersion in deionized water is seen to have a greater deteriorative effect with the period of post-thermal aging immersion being the dominant deteriorative factor.

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.

Composite Structural Supercapacitors: High-Performance Carbon Nanotube Supercapacitors through Ionic Liquid Localisation.

Composite structural supercapacitors (SSC) are an attractive technology for aerospace vehicles; however, maintaining strength whilst adding energy storage to composite structures has been difficult. Here, SSCs were manufactured using aerospace-grade composite materials and CNT mat electrodes. A new design methodology was explored where the supercapacitor electrolyte was localised within the composite structure, achieving good electrochemical performance within the active region, whilst maintaining excellent mechanical performance elsewhere. The morphologies of these localised SSC designs were characterised with synchrotron X-ray fluorescence microscopy and synchrotron X-ray micro-computed tomography and could be directly correlated with both electrochemical and mechanical performance. One configuration used an ionogel with an ionic liquid (IL) electrolyte, which assisted localisation and achieved 2640 mW h kg−1 at 8.37 W kg−1 with a corresponding short beam shear (SBS) strength of 71.5 MPa in the active area. A separate configuration with only IL electrolyte achieved 758 mW h kg−1 at 7.87 W kg−1 with SBS strength of 106 MPa in the active area. Both configurations provide a combined energy and strength superior to results previously reported in the literature for composite SSCs.

Effect of Thermal Exposure on Residual Properties of Wet Layup Carbon Fiber Reinforced Epoxy Composites.

Ambient cured wet layup carbon fiber reinforced epoxy composites used extensively in the rehabilitation of infrastructure and in structural components can be exposed to elevated temperature regimes for extended periods of time of hours to a few days due to thermal excursions. These may be severe enough to cause a significant temperature rise without deep charring as through fires at a small distance and even high-temperature industrial processes. In such cases, it is critical to have information related to the post-event residual mechanical properties and damage states. In this paper, composites are subjected to a range of elevated temperatures up to 260 °C over periods of time up to 72 h. Exposure to elevated temperature regimes is noted to result in a competition between the mechanisms of post-cure that can increase the levels of mechanical characteristics, and the deterioration of the resin and the bond between the fibers and resin that can reduce them. Mechanical tests indicate that tensile and short beam shear properties are not affected negatively until the highest temperatures of exposure considered in this investigation. In contrast, all elevated temperature conditions cause deterioration in resin-dominated characteristics such as shear and flexure, emphasizing the weakness of this mode in layered composites formed from unidirectional fabric architectures due to resin deterioration. Transitions in failure modes are correlated through microscopy to damage progression both at the level of fiber-matrix interface integrity and through the bulk resin, especially at the inter-layer level. The changes in glass transition temperature determined through differential scanning calorimetry can be related to thresholds that indicate changes in the mechanisms of damage.

Study on Different Shear Performance of Moso Bamboo in Four Test Methods.

Bamboo is recognized as a potential and sustainable green material. The longitudinal-splitting and shear strengths of bamboo are weak but critical to its utilizations. To discuss the different shear performances of bamboo, the shear strength and behaviors of bamboo culm were investigated by four test methods: the tensile-shear, step-shear, cross-shear, and short-beam-shear methods. Then, the different shear performance and mechanisms were discussed. Results indicated that the shear strength was significantly different in the four test methods and was highest in the step-shear-test method but lowest in the tensile-shear-test method. Moreover, the typical load-displacement curves were different across the shear methods but were similar to the curves of the respective loading modes. The axially aligned fiber bundles played an important role in all the shear performances. In the tensile-shear method, specimens fractured at the interface of the bamboo-fiber bundles. However, compress-shear behaviors were a combination of compression and shear. Then, the cross-shear method, in compress-shear, was lower than that of the step-shear method because of oval-shaped bamboo culm sections of different thickness. In the short-beam shear method, the behaviors and shearing characteristics were like bending with the fiber bundle pulled out.

Investigation of Interlaminar Shear Properties of CFRP Composites at Elevated Temperatures Using the Lempel-Ziv Complexity of Acoustic Emission Signals.

Three-point bending tests on Short Beam Shear (SBS) specimens are performed to investigate the interlaminar shear properties of plain weave fabric CFRP composites. The tests are performed in a controlled environmental chamber at two different elevated temperatures. The interlaminar shear properties of the specimens remain largely unaffected by the testing temperature. However, the SEM micrographs show different damage progressions between the specimens tested at 100 °C and 120 °C. Fibre ruptures and longer delamination between the plies, as a result of a high temperature, are observed in the specimens tested at 120 °C, which are not observed in the specimens tested at 100 °C. In addition, the acoustic emission activities during the tests are investigated by using piezoelectric sensors. The information-theoretic parameter, the Lempel-Ziv (LZ) complexity, is calculated for the recorded acoustic signals. The LZ Complexities are used for identifying the occurrence of the first delamination failure in the specimens. Additionally, the two features of the acoustic signals, LZ complexity and Weighted Peak Frequency (W.P-Freq), are used for distinguishing the different damage sources in the CFRP specimens. The results are well-supported by the time-frequency analysis of the acoustic signals using a Continuous Wavelet Transform (CWT).

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.

Carbon fiber/epoxy composite property enhancement through incorporation of carbon nanotubes at the fiber-matrix interphase – Part II: Mechanical and electrical properties of carbon nanotube coated carbon fiber composites

A new method to achieve a uniform coating of carbon nanotubes (CNTs) onto carbon fibers (CFs) has been developed which enables the scalable fabrication of CNT modified CF/epoxy composites. In this method, CNTs are coated onto CFs by immersion into a CNT/water suspension resulting in a uniform coating of CNTs. Unidirectional CF/epoxy composites with the CNT layer of 100–200 nm were fabricated by a prepregging method and mechanical/electrical properties were evaluated. The results show that the compressive, short beam shear strengths and Mode I interlaminar fracture toughness were improved by 22 %, 11 % and 48 % respectively after the incorporation of only 0.39 wt% CNTs. Electrical conductivities in 90˚ and through thickness direction were improved by two or three orders of magnitude (Log Resistivity: 1.24 and 2.31) respectively. These results indicate the importance of designing the fiber–matrix interphase to improve fiber reinforced polymer composite mechanical and electrical properties.

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.