An experimental assessment of hybrid bolted/bonded basalt fiber reinforced polymer composite joints' temperature-dependent mechanical performances by static and dynamic mechanical analyses

Bonded joint utilization is limited under elevated temperatures because of the polymer's relaxation. The hybrid bonded/bolted (HBB) joining allows more durable joints than both methods by combining the advantages of both techniques or minimizing their disadvantages. The present research systematically manifests the temperature's effect (under various isothermal conditions from room temperature to 150 °C) on the mechanical performances of bonded, bolted, and HBB composite single lap joints (SLJs). Tensile test results showed that the HBB joint's mechanical performance at room temperature (RT) increased by 47% and 89% relative to the bolted and bonded joints, respectively. Additionally, the jointed structures’ glass transition temperature (Tg) were evaluated by dynamic mechanical analysis (DMA). The bolted, bonded, and HBB joints’ Tg were obtained as 77.8, 107.9, and 111.2 °C, respectively. Besides, strong correlations were obtained between static tensile tests and DMA results, and a simplified model was developed to estimate the maximum tensile load values of single lab joints (SLJs)

Coating graphene nanoplatelets onto carbon fabric with controlled thickness for improved mechanical performance and EMI shielding effectiveness of carbon/epoxy composites

Coating nanostructures on fiber reinforcement is a facile and scalable technique to manufacture next-generation fiber-reinforced polymer composites with tailored physical properties. Optimizing the nanomaterial coating thickness on fibers is vital in tailoring the multifunctionality of fiber-reinforced composites without sacrificing the mechanical performance since it relies on the fiber–matrix interface, where interlaminar and other physical properties are governed. This paper investigates the impact of graphene nanoparticle (GNP) coating thickness on the mechanical properties, fracture behavior, thermo-mechanical, and electromagnetic interference (EMI) shielding effectiveness (SE) of composite structures. We grafted GNPs on carbon fabrics using a solution coating method with various thicknesses (10, 20, and 30 µm), and GNPs grafted fabrics were impregnated with an epoxy resin. The 20 µm GNPs coating thickness exhibited the highest mechanical performance, increasing the tensile and interlaminar shear strength by 32% and 26%, respectively, compared to pristine samples. Storage modulus and transition (Tg) temperature values increased by 18.6% and 13.6% for 20 µm coating thickness, respectively. Besides, the unstable crack growth at the fiber–matrix interface was stabilized when the GNPs coating thickness reached 20 µm according to delamination toughness tests. While mode-I fracture toughness increased up to 22%, an improvement of 13.5% was obtained in mode-II fracture toughness. The underlying toughening mechanisms at the interfacial region were identified using scanning electron microscopy. The EMI-SE was slightly increased by the GNPs grafting, whereas thinner GNPs coatings exhibited higher shielding efficiency

Effect of long-term stress aging on aluminum-BFRP hybrid adhesive joint's mechanical performance: static and dynamic loading scenarios

Composite-aluminum hybrid adhesive joints represent an ideal solution for designing lightweight structures for the marine industry. However, seawater aging is a serious concern, limiting the safe service life of the joint. Notably, efforts to understand the impact of aging have largely focused on the short-term periods without considering actual operating conditions. Here, we report the mechanical performance of hybrid joints subjected to the long-term stress aging. Besides, we modified the epoxy adhesive with halloysite nanotubes (HNTs) to limit the aging driven adhesive degradation and improve the adhesive's rigidity. We evaluated mechanical performances of hybrid joints by performing tensile, flexural, and drop-weight impact tests. While we increased the load-carrying capacity by over 25% with the HNTs modification before the stress aging process, modified adhesive withstood almost 55% higher tensile load than the neat epoxy adhesive after six-month stress aging. The modified adhesive also absorbed 41% less impact energy, indicating the efficiency of HNTs on limiting the degradation due to the stress aging. Furthermore, the damage mode transformed from adhesion to cohesion, thanks to the improved adhesive-composite interface performance. We envisage that these exciting results will pave the way for designing robust hybrid joints for the marine industry

Fracture and dynamic mechanical analysis of seawater aged aluminum-BFRP hybrid adhesive joints

Adhesively bonded hybrid FRP-aluminium structures have recently become an efficient solution for marine engineering applications. However, polymer adhesives' bond performance is sensitive to the marine environment due to polymer and interfacial degradation. This study aims to develop mode I, mode II delamination toughness, and Tg data as a comprehensive design guideline for hybrid BFRP-aluminum modified-adhesively bonded joints subjected to seawater aging. The hybrid joints were exposed to long-term seawater aging (for 6 months) to reveal their fracture and thermomechanical performances. Besides, the adhesive was reinforced with HNTs to increase fracture resistance with additional nano-scale toughening mechanisms and to delay the water absorption. After the long-term aging, reinforced adhesively bonded joints exhibited ∼36% higher fracture toughness than neat adhesively bonded joints. Moreover, DMA was conducted on miniaturized SLJ samples, which revealed that HNT modified adhesive joints showed ∼11.5 °C higher Tg. The calculated aging rates also proved the effectiveness of HNTs modification on the epoxy adhesive's aging performance since the HNT reinforced adhesive represented 43% lower aging rates in terms of storage modulus. It is considered that experimental results will help comprehend long-term aging influences on the composite-aluminum hybrid designs’ fracture and thermomechanical performances. These exciting findings will pave the way for the safe use of high stiffness and cost-effective aluminum-BFRP hybrid structures for the marine industry

Experimental investigation on compression-after-impact (CAI) response of aerospace grade thermoset composites under low-temperature conditions assisted with acoustic emission monitoring

Low-velocity impact (LVI) can provoke catastrophic failure depending on the impact energy, lay-up configuration, and the operating temperature in fiber-reinforced composite structures via damage accumulation during the service. Additionally, extreme operating temperature is an important factor affecting the damage initiation and growth mechanism and understanding the compression-after-impact (CAI) response is a promising way to predict the damage-growth dynamics. For this purpose, this study investigates the LVI response and CAI strength of composite laminates under the −55 °C temperature considering the low-temperature (LT) service conditions of aerospace applications. The experiments are performed on cross-ply ([0/90°]4s) and angle-ply ([±45°]4s) lay-up composites for impact energy levels of 1.4 J and 10 J. After LVI tests, the occurred damages are examined by infrared thermography (IRT). Furthermore, the effect of the impact damage on the failure mechanism under compression loading is elaborated using acoustic emission (AE) inspection. The CAI test results reveal that the LT increases the compressive residual strength. However, this change is directly related to the load and lay-up configuration. The alternation in the damage growth mechanism of angle-ply laminates under LT operating temperature is more significant compared to the cross-ply laminates

Effects of alumina nanoparticles on dynamic impact responses of carbon fiber reinforced epoxy matrix nanocomposites

The influence of alumina (Al2O3) nanoparticles addition upon low-velocity impact behaviors of carbon fiber (CF) reinforced laminated epoxy nanocomposites have been investigated. For this purpose, different amounts of Al2O3 nanoparticles ranging from 1 to 5 wt% were added to the epoxy resin in order to observe the effect of nanoparticle loadings. CF reinforced epoxy based laminated nanocomposites were produced using Vacuum Assisted Resin Infusion Method (VARIM). The low velocity impact (LVI) tests performed according to the ASTM-D-7136 standard under 2, 2.5 and 3 m/s impact velocities. After LVI testing, the damage formations within composites were examined by using scanning electron microscopy (SEM). The results of this study showed that addition of Al2O3 nanoparticles provided a significant improvement in impact damage resistance. The highest damage resistance and minimum energy absorption were observed for 2 wt% Al2O3 nanoparticles loadings. As a result, we can confidently claim that the addition of the Al2O3 nanoparticles in CF/epoxy composites has considerably affected the dynamic response of the nanocomposites. Keywords: Alumina (Al2O3), Carbon fiber (CF), Epoxy, Low velocity impact (LVI

Acoustic emission analysis on mechanical properties and damage evolution of multiscale Kevlar/Glass hybrid 3D orthogonal woven composites under flexural loading

Three-dimensional (3-D) woven fabrics have attracted a lot of attention due to their delamination resistance, great tailorability, and low manufacturing time. In this study, Acoustic Emission (AE) is used to investigate the effect of different fiber hybridization types of 3-D orthogonal fabrics on the flexural properties and damage evolution along the longitudinal and transverse direction of the composite plate. Three different fabric configurations, namely Baseline, Inter-ply and Intra-tow, are studied. All the fabric configurations have the same fabric architecture consisting of six warp and seven weft layers. The warps of all the fabric types are Kevlar whereas the z-binders consist of ultra-high molecular weight Polyethylene fibers. The wefts of the baseline fabric are all Kevlar while Inter-ply fabric has three Kevlar layers flanked by four glass layers. The Intra-tow fabric has three Kevlar layers in the middle with four layers of hybrid glass/Kevlar tows at the top and bottom surfaces. In-situ AE analysis is carried out to understand how damage starts and progresses in the three composite types. AE results are then verified using scanning electron microscopy

The effect of multiscale Kevlar/Glass hybridization on the mechanical properties and the damage evolution of 3D orthogonal woven composites under flexural and impact loadings

This work aims to evaluate the effectiveness of inter-ply/intra-tow hybridization in 3D woven composites to achieve an ameliorated impact and flexural performance. In this regard, inter-ply/intra-tow hybrid epoxy composites with Kevlar, E-glass, and ultra-high-molecular-weight polyethylene (UHMWPE) reinforced 3D fabrics are manufactured using the vacuum infusion method. To scrutinize the static and dynamic responses, the produced composites are subjected to flexural and low-velocity impact (50, 100, and 150 J) tests. The findings show that inter-ply hybrid composites exhibit more improved impact and flexural performance than their intra-tow hybrid counterparts. While the elastic moduli and strength values of weft-directional hybrid composites increase, on the contrary, warp-directional counterparts do not display an enhancement in flexural performance. Scanning electron microscopy (SEM) examinations and acoustic emission analysis are conducted together on the bending specimens to understand failure mechanisms leading to observed mechanical responses

Tailoring adherend surfaces for enhanced bonding in CF/PEKK composites: comparative analysis of atmospheric plasma activation and conventional treatments

Here, we propose the utilization of atmospheric plasma activation (APA), which outperforms peel-ply (PP) treatment and mechanical abrasion (MA) in achieving high-performance adhesively bonded carbon fiber/polyetherketoneketone (CF/PEKK) composites. This study covers several key aspects, including the chemical and morphological characterization of treated surfaces and mechanical performance assessments of single lap-joints (SLJs) under tensile and flexural loading conditions. In addition, in-situ acoustic emission (AE) monitoring is employed during tensile tests to determine dominant damage types and failure modes in the SLJs. Surface analysis shows that MA increases roughness, PP treatment decreases wettability, while APA enhances wettability by modifying the surface chemistry. Tensile and flexural tests reveal that APA-treated joints surpassed non-treated (NT) ones, with up to 5- and 7-times higher load-carrying performance, respectively, while fracture analysis suggests a shift from adhesive to cohesive failure. AE results show that increased AE events related to cohesive failure align with improved interface interactions