Vacuum Assisted Resin Injection Research Articles

Vertical compression performance of fiber-reinforced polymer (FRP) foam sandwich composites in hygrothermal environment

The safety of utilizing composites has garnered significant attention due to their widespread application in civil engineering, aerospace, and other fields. In the present investigation, fiber-reinforced foam sandwich composites were fabricated using the vacuum-assisted resin injection (VARI) process. The constant temperature and humidity test chamber is used to carry out damp-heat aging experiments on the specimen, and the mechanical properties after damp-heat aging are studied. The present study aims to examine the vertical compression characteristics of fiber-reinforced foam sandwich composites under the influence of hygrothermal aging. This paper also elucidates the mechanism by which the hygrothermal environment affects these composites. The results indicate that the mechanical properties of the specimens decrease after damp-heat aging. The unidirectional stacked fibers exhibit better resistance to the damp-heat environment compared to the orthogonal stacked fibers. Additionally, the inclusion of drainage holes in the setup can enhance the resistance of the specimens to the damp-heat environment.

Mechanical Degradation and Failure Analysis of Different Glass/Basalt Hybrid Composite Configuration in Simulated Marine Condition.

This work aims to evaluate the failure mechanisms of plain glass and basalt fiber reinforced composites and a selected glass/basalt hybrid composite sequence subjected to artificial seawater conditions. Sets of plain and five hybrid composite configurations were fabricated by vacuum assisted resin injection technique (VARI), and subjected to seawater aged for 258 days at 30 °C and 70 °C followed by tensile, flexural and charpy impact testing, respectively. Failure analysis for dry and seawater-aged composites were undertaken using scanning electron microscopy (SEM). Results showed that some hybrid laminates with sandwich-like and alternating sequencing exhibited superior mechanical properties and ageing resistance than plain laminates. GB3 ([B2G2]S) type hybrid composite with basalt fiber outer plies retained 100% tensile strength and 86.6% flexural strength after ageing, which was the highest among all the laminates. However, GB4 ([BGBG]S) type specimen with alternating sequencing retained the highest residual impact strength after ageing. SEM analysis on the failed specimens showed fiber breaking, matrix cracking and debonding caused by fiber–matrix interface degradation due to seawater exposure. However different hybrid configurations to a considerable extent prevented crack propagation across specimens, hence altering the overall damage morphology among different specimens.

Resin Flow Analysis for the Foam Core Sandwich Spoiler by Vacuum-Assisted Resin Injection Process

This article presents the numerical analysis and experimental investigation for the manufacturing of a foam core sandwich spoiler by vacuum-assisted resin injection (VARI) process. To find an injection scheme that guarantees both a good impregnation of the preform and a filling time compatible with the process window, the finite element model (FEM) was applied to analyze the effect of different injection schemes on the resin flow front patterns. Based on the obtained results, two optimal injection schemes are selected to form the spoiler structure. The experimental results show that the best molding quality can be achieved from the thick-end injection with a thin-end exit scheme. The comparison between simulation and experimental results shows that the overall deviation of the numerical analysis on resin flow time is 15.9%.

Assessing the mechanical behavior of glass and basalt reinforced vinyl ester composite under artificial seawater environment

Glass and basalt fiber reinforced vinyl ester epoxy (GFRP and BFRP) composites offer considerable potential for underwater and deep sea applications. In spite of their increasing usage in various sectors, there are still questions concerning their long term reliability in marine environment. In this article, the response of GFRP and BFRP to seawater ageing and their subsequent mechanical properties were evaluated. The composites were fabricated by vacuum assisted resin injection technique and seawater aged at 30 0C for 18, 28, 38, 258 and 305 days. By using scanning electron microscope (SEM), the failure of dry and seawater aged specimen after mechanical testing showed fiber breaking, debonding and sporadic fracturing along the laminate. This was due to higher moisture concentration in these areas during ageing. The results also revealed an overall steady decrease in tensile, flexural and impact strengths of seawater aged laminates with increasing ageing duration. Overall, the seawater ageing property of BFRP composites is almost identical to that of GFRP. The use of different nano-materials could also be explored in future works to address some drawbacks in the fiber–matrix interface durability after seawater ageing.

Impact and CAI behavior of SGF mat filled sandwich panels made from foam core and FRP facesheet

The interlaminar bonding property between the facesheet and foam core plays an important role in enhancing the impact damage resistance ability of sandwich panels. In this paper, we filled short glass fiber (SGF) mat between the facesheet and foam core to enhance their bonding strength. The newly designed sandwich panels were manufactured by vacuum-assisted resin injection processing. A series of SGF mat filled sandwich panels with glass and/or carbon fiber facesheets were manufactured. The low-velocity impact as well as the compression-after-impact (CAI) performence were investigated. Failure modes of the sandwich panels were analyzed. Low-velocity impact results show that SGF mat filled sandwich panels with pure glass fiber facesheet displayed the maximum contact force. In the CAI test, wrinkling of the facesheet, buckling of the foam, and debonding between them are the major failure modes. Compared with contrast samples, SGF toughened sandwich panels show the highest strength increase rate.

Improvement of impact resistance of plain-woven composite by embedding superelastic shape memory alloy wires

Carbon fiber reinforced polymer (CFRP) composites have excellent mechanical properties, specifically, high specific stiffness and strength. However, most CFRP composites exhibit poor impact resistance. To overcome this limitation, this study presents a new plain-woven CFRP composite embedded with superelastic shape memory alloy (SMA) wires. Composite specimens are fabricated using the vacuum-assisted resin injection method. Drop-weight impact tests are conducted on composite specimens with and without SMA wires to evaluate the improvement of impact resistance. The material models of the CFRP composite and superelastic SMA wire are introduced and implemented into a finite element (FE) software by the explicit user-defined material subroutine. FE simulations of the drop-weight impact tests are performed to reveal the superelastic deformation and debonding failure of the SMA inserts. Improvement of the energy absorption capacity and toughness of the SMA-CFRP composite is confirmed by the comparison results.

Experimentation of the Bilinear Elastic Behavior of Plain-Woven GFRP Composite with Embedded SMA Wires.

In this paper, a plain-woven glass-fabric-reinforced polymer (GFRP) composite with embedded shape memory alloy (SMA) wires is investigated by means of experiments. The vacuum-assisted resin injection (VARI) method is utilized to fabricate the composite specimens. Quasi-static uniaxial tensile tests are then carried out to evaluate the influence of SMA reinforcement on the stress–strain behavior of the composite. Only the elastic behavior of the composite is considered in the present study. The tensile strain in all the experiments is kept below 2.5% to avoid debonding of the SMA-resin interface, which would lead to failure of the composite. Stress–strain curves are obtained and shown to present a bilinear behavior due to phase transformation taking place in the SMA wires beyond a certain stress threshold.

Investigation on the Mechanical Properties of SMA/GF/Epoxy Hybrid Composite Laminates: Flexural, Impact, and Interfacial Shear Performance.

In this article, hybrid composite laminates with shape memory alloy (SMA) and glass fiber (GF) as the reinforced phase, and epoxy resin as the host material, were manufactured by vacuum-assisted resin injection (VARI) processing. The SMA wires were embedded into the GF/epoxy composites with three kinds of modes. The effect of SMA content and the position on the flexural, low-velocity impact performance of the hybrid composite laminates was investigated. It was found that the bonding performance between the SMA wire and the host material is the key factor that determined the final overall performance of the hybrid composite laminates in both the static and dynamics tests. Based on these experimental phenomenon, we further carried out the fiber pull-out experiment to improve the interfacial shear strength between the SMA and epoxy resin. It was found that the interfacial performance could be enhanced significantly by adding nanoparticles in the interface phase.

Experimental investigation of GF/epoxy laminates with different SMAs positions subjected to low-velocity impact

In this paper, the impact response of unidirectional cross-ply GF/epoxy laminates with different shape memory alloys (SMAs) positions was investigated. According to vacuum assisted resin injection (VARI) process, we manufactured the laminates without SMAs, the laminates with one layer of SMAs were inserted in 1/8 thickness, in 1/2 thickness, in 14/16 thickness, and in 15/16 thickness of specimen, respectively, the laminates with two layers of SMAs were inserted in the 15/16 and 14/16 thickness, in 15/16 and 1/2 thickness, in 15/16 and 1/8 thickness, in 14/16 and 1/2 thickness, in 14/16 and 1/8 thickness, and in 1/2 and 1/8 thickness of specimen, respectively. The low-velocity impact experiment was performed by Dynatup 9250HV Drop Weight Impact Testing Machine under the impact energy of 28J to analyze the impact response, and the impact parameters such as contact force (F), displacement (D) and energy (E) of the laminates were obtained. To further observe and analyze the impact damage morphology, we also adopted visual inspection and scanning electron microscope (SEM) technology. The experimental results showed that impact performance of laminates improved by embedding SMAs. By contrast, the impact performance of the laminates with two layers of SMAs was optimum.

Experimental and numerical investigation on the crushing behavior of sandwich composite under edgewise compression loading

Abstract In present study, the buckling and crushing behavior of foam-filled glass-fiber reinforced sandwich composite column under edgewise compression were investigated by experimental, theoretical, and finite element analysis (FEA) methods. Various ratios of slenderness columns were manufactured by the vacuum assisted resin injection (VARI) process. A simple theoretical model was introduced to predict the critical collapse load taking into account the various failure modes. A user subroutine VUMAT were implemented in commercial Abaqus software based on the Hashin failure criteria. The geometrical imperfection was considered in FEA model. The experimental results revealed that the critical collapse load would be significantly reduced with the increase of slenderness, especially for the columns with the same length. Through the observing of failure morphologies and the analysis of buckling, it can be found that the first- and second-order buckling mode would play a dominant role in the crushing failure process. The FEA results simulated by present model were in good agreement with the experimental results. The results obtained in present study will be useful for the design and application of foam-filled sandwich composite.

Study on the low-velocity impact response and CAI behavior of foam-filled sandwich panels with hybrid facesheet

Foam-filled sandwich panels with six types of facesheets were manufactured by vacuum-assisted resin injection (VARI) process. Low velocity impact test and compression after impact (CAI) test of the prepared panels were performed. Failure modes of different sandwich panels were analyzed by observing the contact surface and the cross section through damage region. Scanning electron microscope (SEM) was carried out to study the microstructure of the impacted specimens. It is found that matrix cracking, fiber breaking, foam cracking and debonding are the damage modes of sandwich panel with pure carbon facesheet, while other specimens merely show some of these modes after impact test. Panels with pure carbon facesheet have poor impact resistance properties, while panels with pure glass facesheet have preferable properties among all the specimens. Hybrid panel with ply mode of [C2/G2/Foam core/G2/C2] could provide higher maximum contact force and absorb more impact energy by carbon fiber breaking on the contact surface. In CAI test, wrinkling of facesheet and buckling of foam and skin are the two main damage modes. [C4/Foam core/C4] shows highest compress strength decline rate, while [G4/Foam core/G4] shows lowest rate. Decline rate of [C2/G2/Foam core/G2/C2] is very low but the compress strength of its undamaged specimen is not high.

Finite Element Analyses of Face/Core Interfacial Fracture Toughness of Composite Sandwich with Reinforced Chopped Fibers

The reinforced mechanism is proposed to describe the energy dissipation of chopped fiber peeling and pull-out as the crack grows. Then, a finite element model (FEM) is established to simulate the process of the interfacial crack growth for a double cantilever beam.The energy release rate is calculated by the virtual crack closure technique (VCCT).Thenonlinear spring element is employed to account for bridging effect caused by the chopped fiber. In addition, the foam core composite sandwiches with and without reinforced chopped fiber are manufactured by using the vacuum assisted resin injection process. The experimental investigation is performed to determine the interfacial fracture toughness for the sandwich specimens. Furthermore, the typical numerical examples are performed to simulate the interfacial crack of composite sandwich beams. The influence of the energy dissipation on the interfacial toughness is also discussed. The experimental and numerical results indicate that the reinforced chopped fiber is an effective technique to improve the interfacial toughness of the sandwich composites.

Effects of Preheating Temperature of the Mould on the Properties of Rapid-Curing Carbon Fibre Composites Fabricated by Vacuum-Assisted Resin Infusion Moulding

Shortening the curing time is critical to improve the processing efficiency of composites. In this paper, unidirectional carbon fibre-reinforced rapid curing epoxy composite laminates were fabricated by vacuum-assisted resin injection moulding (VARIM). Different rapid curing processes (namely P80, P85, and P90) were employed, which preheating temperatures were 80, 85 and 90 °C, respectively. Different preheating temperatures of mould and fibre preform were conducted, to demonstrate the effects on the properties and processing time of the composites. In addition, a slow curing process (N80) was investigated to verify the effect of rapid curing on the mechanical properties of the composites. The relationships among preheating temperature, curing cycle and properties of the composites were analyzed. The results showed that the preheating temperature had obvious effects on the total cycle time and properties of the composites. The cycle time of the P80 process was 947 s, whereas that of the P90 process was 702 s. However, nonuniformity of the mechanical properties along the resin flow direction was more obvious for the P90 process, and more voids formed in the resin outlet region. Composites fabricated by the P80 process showed comparable mechanical properties and processing quality to those from the N80 process. It is suggested that a rapid curing process with proper preheating temperature is acceptable to improve the processing efficiency.

Experimental and numerical investigation on bolted joint in glass–fiber reinforced composites

In this paper, vacuum assisted resin injection technique was employed to prepare the composite laminates with different plies ways. The macro-mechanical performances of the bolted joint of the composite laminates were investigated by experimental and finite element simulation. The influence mechanism of different parameters on the joint performance and failure models of the composite laminates were analyzed. A VUMAT subroutine was developed, according to the failure criteria and corresponding stiffness degradation criteria, to describe the progressive damage process of bolted joint composite laminates through finite element analysis method. The results indicated that the failure strength of composite laminates would be improved with the increasing of tightening torque, and the strength of three-ply-way hybrid composite laminates is higher than that of two-way hybrid laminates. The comparisons between numerical simulation results and experimental results showed that the developed subroutine can effectively predict the macroscopic response of bolted joint glass–fiber reinforced composite laminates.

Experimental and numerical analysis of local reinforced bolted composite joint

Bolted composite joint is a common composite connection technology. In this paper, failure responses of four local reinforced bolted joints are investigated by experimental and numerical method. Composite laminates of joints are made by vacuum assisted resin injection (VARI) process. Three reinforced materials are Aluminum, rigid foam and composite laminate, respectively. To predict failure response of local reinforced bolted joints, a progressive failure model in ABAQUS is developed in this paper. User subroutine VUMT using Hashin and Álvaro criteria is used to simulate progressive damage of composite laminate, and cohesive layer is used to simulate delamination between reinforced material and laminate. The results of the numerical analysis provide a more detailed insight into the progressive failure process of joint. Finite element model using two kinds of failure criteria showed an excellent agreement with experimental results.

Macroscopic Mechanical Characterization of SMAs Fiber-Reinforced Hybrid Composite Under Uniaxial Loading

This paper presents an experimental and theoretical investigation on the macroscopic mechanical behavior of shape memory alloys (SMAs) fiber-reinforced glass/resin composite subject to uniaxial loading at ambient temperature. A series of unidirectional SMAs reinforced composite laminates is fabricated through vacuum-assisted resin injection. Scanning electron microscopy is conducted to evaluate the interfacial cohesive quality between SMAs fiber and matrix. A theoretical model is proposed based on the SMAs phase transformation model and rule of mixture. Uniaxial tensile tests are performed to study the effects of weak interface and SMAs fiber volume fraction on the effective modulus of composite. Failure morphology of composite is discussed based on the observation using digital HF microscope. Due to the effects of phase transformation and weak interface, the overall stiffness of SMAs composite at the second stage is on average 10% lower than theoretical results. The rupture elongation of experimental result is approximately 13% higher than theoretical result. The local interfacial debonding between SMAs fiber and glass/resin matrix is the main failure mode.

Experimental and numerical investigation on the macroscopic mechanical behavior of shape memory alloy hybrid composite with weak interface

This paper presents an experimental and numerical investigation into the macroscopic mechanical behavior of shape memory alloy hybrid composites (SMAHCs) subjected to quasi-static loading taking into account of weak interface effect and damage evolution. SMA fiber reinforced hybrid laminates were fabricated by vacuum assisted resin injection (VARI). Scanning electron microscopy was used to evaluate the quality of SMA–matrix interface. Uniaxial tensile tests were performed to study the effects of weak interface on the effective modulus of hybrid composite. Failure morphology was discussed based on the observation using digital HF microscope. Owing to the embedding of SMA fiber, the material exhibited a bilinear mechanical behavior, and the overall stiffness of composite at the second stage was lower on average 32.7% than that of the first stage. Ultimate strength was improved by 3.4% for the three-SMA-fiber composite, and rupture elongation was slightly decreased (∼0.1%). A script program was developed to generate the hybrid composite model by using ANSYS Parameter Design Language (APDL). Uniaxial tensile test was simulated using finite element method to study the macroscopic behavior of hybrid composite based on a bilinear cohesive zone model (BCZM). The effects of embedded SMA fiber number and fiber ratio were respectively discussed.

Experimental and numerical investigation on bolted composite joint made by vacuum assisted resin injection

In this paper, experiments and finite element simulation were used to investigate the influence of geometric parameters on failure response of bolted single-lap composite joint. Specimens used for testing material stiffness, strength and failure of bolted single-lap composite joints were made by vacuum assisted resin injection (VARI). Two kinds of progressive failure models developed in ABAQUS/Standard and Explicit were used to simulate failure of joints. User subroutines USDFLD and VUMAT were used in these two models, respectively. Two finite element models showed an excellent agreement with experimental results. The results of the numerical analysis were presented with a focus on providing a more detailed insight into the progressive failure process, and the influence of the geometric parameter on failure of bolted composite single-lap joint. Failure model developed in ABAQUS/Explicit was found to be robust, accurate and highly efficient.

Effect of water absorption on the mechanical properties of glass/polyester composites

Laminates were developed by glass fibre fabric and unsaturated polyester. The fabrication was conducted by using the VARI (Vacuum Assisted Resin Injection) technique. The effect of water immersion on the tensile strength and bending behaviour of the composites was experimentally investigated. After immersed in water at a temperature of about 30 °C for various periods, the composites experienced significant reduction of the tensile strength, meanwhile the bending behaviour was improved. These are attributed to the function of the water molecules penetrated in the composites. The failure mode of the samples was shown.