Vacuum Assisted Resin Infusion Research Articles

Applied computer vision for composite material manufacturing by optimizing the impregnation velocity: An experimental approach

The application of the cutting edge industrial solutions in composite manufacturing are optimizing the processes, quality control and resources usage. Computer vision is currently used in many quality control stages, although its potential advantages have not been applied in the process control. In this paper, computer vision is used to control the impregnation velocity in VARI (Vacuum Assisted Resin Infusion) process. As it is known, there is a relationship between the impregnation velocity and the final mechanical properties in LCM (Liquid Composite Manufacturing) processes. Constant and optimum flow front velocity mean optimum mechanical properties, although the nature of the process makes it difficult to keep these conditions. Then, a methodology has been proposed to identify and use the optimum velocity during the manufacturing process. Firstly, the flow front recognition algorithm was calibrated to be used in different reinforcement and fluid systems. Then, tensile and impact specimens have been manufactured and tested at different controlled and uncontrolled velocities. As a result, the tensile modulus has been increased up to 12.6%, as the tensile strength has increased up to 8.7%. Similarly, the maximum reaction force during the impact test has been increased up to 6.5%, as the damaged area has been reduced by 8.8%. For stitched laminates, force results increase up to 3.2%, as the damaged area has been reduced up to 31% when the optimum velocity is used. The experimental results have demonstrated the advantage of using mechanisms to control the impregnation process to achieve improved mechanical properties of composite materials.

Life-cycle health monitoring of composite structures using piezoelectric sensor network

The vacuum-assisted resin infusion (VARI) technique provides considerable advantages in manufacturing large-scale composite structures. An accurate and consecutive structural health monitoring system is urgently required to determine the initial quality and assess the structural integrity of a composite structure. In this paper, a real-time active smart diagnostic system (SDS) based on piezoelectric sensor network is proposed to monitor the whole life-cycle of composite structures. Experiments were conducted on carbon fiber reinforced plastic specimens with different thicknesses to investigate the monitoring capability of piezoelectric lead-zirconate-titanate (PZT) sensors used in the SDS approach. The PZT sensor networks inserted inside the composite structures during the VARI process are used to monitor not only the curing parameters, but also the health status of composite structures when they are in service after curing. To monitor the curing process only, the sensor network can also be installed on the bottom of the mould. Experimental results demonstrate that both 3D resin flow and degree of cure in the VARI process can be effectively monitored by the PZT sensor network. Meanwhile, the embedded PZT sensor network has the potential to identify the different stages in the curing process. It is obvious that the piezoelectric sensor network will provide important technical support for composite materials with the structure and function integrated.

Fabrication and Mechanical Performance of Graphene Nanoplatelet/Glass Fiber Reinforced Polymer Hybrid Composites

Glass fiber reinforced polymer (GFRP) composites are promising alternatives for the traditional carbon steel pipes used in the oil and gas industry due to their corrosion and chemical resistance. However, the out-of-plane mechanical properties of GFRPs still need further improvement to achieve this goal. Hence, in this work, two methods combining either vacuum mixing or spray coating with vacuum-assisted resin infusion were studied to fabricate graphene nanoplatelet (GNP)/GFRP hybrid composites. The former method resulted in a severe filtering effect, where the GNPs were not evenly distributed throughout the final composite, whereas the latter process resulted in a uniform GNP distribution on the glass fabrics. The addition of GNPs showed no modest contribution to the tensile performance of the GFRP composites due to the relatively high volume and in-plane alignment of the glass fibers. However, the GNPs did improve the flexural properties of GFRP with an optimal loading of 0.15 wt% GNPs, resulting in flexural strength and modulus increases of 6.8 and 1.6%, respectively. This work indicates how GNPs can be advantageous for out-of-plane mechanical reinforcement in fiber-reinforced composites.

An Integrated Multiscale Simulation Routine to Predict Mechanical Performance from Manufacturing Effects

Structural performance of unidirectional composites (UD) is directly dependent on its ingredient’s properties, ply configurations and the manufacturing effects. Prediction of mechanical properties using multiscale manufacturing simulation and micromechanical models is the focus of this study. Particular problem of coupled dual-scale deformation-flow process such as the one arising in RTM, Vacuum-Assisted Resin Infusion (VARI) and Vacuum Bag Only (VBO) prepregs is considered. A finite element formulation of porous media theory framework is employed to predict the element-wise local volume fractions and the deformation of a preform in a press forming process. This formulation considers coupling effects between macro-scale preform processes and mesoscale ply processes as well as coupling effects between the solid and fluid phases. A number of different micromechanical models are assessed and the most suitable one is used to calculate mechanical properties from volume fractions. Structural performance of the “deformed” geometry is then evaluated in mechanical analysis. An integrated platform is designed to cover the whole chain of analysis and perform the properties’ calculation and transfer them between the modules in a smooth mapping procedure. The paper is concluded with a numerical example, where a compression-relaxation test of a planar fluid filled prepreg at globally un-drained condition is considered followed by a mechanical loading analysis. The development is user friendly and interactive and is established to enable design and optimization of composites.

Design, Development, and Characterization of Advanced Textile Structural Hollow Composites.

The research is focused on the design and development of woven textile-based structural hollow composites. E-Glass and high tenacity polyester multifilament yarns were used to produce various woven constructions. Yarn produced from cotton shoddy (fibers extracted from waste textiles) was used to develop hybrid preforms. In this study, unidirectional (UD), two-dimensional (2D), and three-dimensional (3D) fabric preforms were designed and developed. Further, 3D woven spacer fabric preforms with single-layer woven cross-links having four different geometrical shapes were produced. The performance of the woven cross-linked spacer structure was compared with the sandwich structure connected with the core pile yarns (SPY). Furthermore, three different types of cotton shoddy yarn-based fabric structures were developed. The first is unidirectional (UD), the second is 2D all-waste cotton fabric, and the third is a 2D hybrid fabric with waste cotton yarn in the warp and glass multifilament yarn in the weft. The UD, 2D, and 3D woven fabric-reinforced composites were produced using the vacuum-assisted resin infusion technique. The spacer woven structures were converted to composites by inserting wooden blocks with an appropriate size and wrapped with a Teflon sheet into the hollow space before resin application. A vacuum-assisted resin infusion technique was used to produce spacer woven composites. While changing the reinforcement from chopped fibers to 3D fabric, its modulus and ductility increase substantially. It was established that the number of crossover points in the weave structures offered excellent association with the impact energy absorption and formability behavior, which are important for many applications including automobiles, wind energy, marine and aerospace. Mechanical characterization of honeycomb composites with different cell sizes, opening angles and wall lengths revealed that the specific compression energy is higher for regular honeycomb structures with smaller cell sizes and a higher number of layers, keeping constant thickness.

Effect of graphene nanoplatelets on the mechanical and gas barrier properties of woven carbon fibre/epoxy composites

Carbon-fibre-reinforced polymer (CFRP) composites are promising materials for non-metallic pipe applications in the oil and gas industry owing to their high corrosion resistance, specific strength and stiffness. However, CFRP has poor gas barrier performance meaning that a liner has to be inserted. Graphene-based nanomaterials have been demonstrated to improve gas barrier properties in thermoplastic polymers, and thus, a CFRP–graphene hybrid composite could provide an alternative to lined pipes. In this work, a method combining spray coating with vacuum-assisted resin infusion was developed to fabricate CFRP hybrid composites with preferred in-plane aligned graphene nanoplatelets. Tensile and flexural properties, as well as CO2 gas permeability, were evaluated. It was illustrated that both tensile and flexural properties performed better under relatively low GNP loadings (< 0.2 vol%), while gas barrier property was significantly improved with the increasing GNP loadings which fits the Nielsen model with an effective GNP aspect ratio of 350.Graphical abstract

Effects of stacking sequence of pineapple leaf-flax reinforced hybrid composite laminates on mechanical characterization and moisture resistant properties

The present study aims to investigate the effects of stacking sequence on physical, mechanical and moisture resistant properties of pineapple leaf fiber (PF) and flax fiber (FF) reinforced composite laminates. The non-hybrid and hybrid composite laminates are fabricated by using vacuum assisted resin infusion molding process (VARIM) with an inter-ply configuration. From the results, the maximum tensile strength (219.3 MPa), flexural strength (132.4 MPa), shear strength (39.1 MPa) and impact energy (50.2 J) have been recorded for FFRP composites while the minimum for PFRP (124.7 MPa, 52.3 MPa, 4.3 MPa, and 23.3 J) respectively. For hybrid composite laminates, the increase in volume fraction of flax fiber, improved the mechanical and moisture resistant properties while an increase in the volume fraction of PALF enhanced the elongation and flexibility of the developed composites. Furthermore, it observed that, stacking sequence configuration of flax fibers as outer layer exhibited better tensile, flexural, impact and moisture properties while flax fibers at inner layer examined maximum shear properties. Therefore, among hybrid composites, H7 recorded maximum tensile strength, flexural strength and impact energy (207.7 MPa, 121.7 MPa and 48.8 J) while H5 recorded maximum shear strength (24.2 MPa). The water absorption and chemical resistant behaviour of fabricated laminates with five different combinations of solution (distilled water, seawater, hydrochloric acid, sulphuric acid and sodium carbonate) are examined and revealed that hybrid composite laminates have better resistance to water and chemical uptake. The morphology and fracture analysis of composite laminates are analyzed with scanning electron microscopy (SEM). Overall, the developed hybrid composite laminates have lighter weight, economical and better interfacial bonding with improved mechanical and moisture properties for distinct load-bearing applications.

Numune Boyut Etkisinin Aramid/Epoksi Kompozitlerin Hidrotermal Yaşlanma Davranışına Etkisi

An investigation was carried out concerning the hydrothermal aging effect on the water intake character of aramid/epoxy composites based on the dimension effect. The aramid/epoxy composites were manufactured by the vacuum assisted resin infusion method (VARIM) kept in distilled water and sea water at 25 °C and 70 °C for 6 weeks in a controllable aging cabin. The water absorption behavior of composite samples cut with different length/width (L/w) ratios was assessed according to different water types and temperatures. Besides, the water intake character of aramid/epoxy samples was interpreted theoretically according to the Fick model. The experimental and theoretical results showed that aramid/epoxy composites displayed a tendency consistent with the Fickian model. Further, the water intake character of aramid/epoxy samples was affected by criteria such as sea water, distilled water, temperature, and different L/w ratio. The temperature increase was caused to more water absorption. Further, the increase of L/w ratio was caused to more water intake for both water types.

Impact of hydration on the mechanical properties and damage mechanisms of natural silk fibre reinforced composites

Silk fibres exhibit good biodegradability, biocompatibility and balanced strength and toughness, which are useful for toughness/impact-critical composites in the biomedical field. However, the impact of hydration has not been studied for silk fibre-reinforced polymers (SFRPs). In this work, SFRPs fabricated vacuum-assisted resin infusion (VARI) were treated under three hydration conditions. A hydration condition of 40 °C at 89% relative humidity (RH) was sufficient to induce a reduction in the tensile and flexural modulus and yield strength of SFRPs. Acoustic emission (AE) analysis showed that interface failure played a key role in the damage modes of SFRPs. Although mild hydration treatment appeared not to affect SFRPs, high hydration led to more susceptible interfacial failure. This work is intended to reveal the structural mechanisms of SRPPs under hydration, and to provide a useful reference for potential biomedical applications.

Reducing the raw material usage for room temperature infusible and polymerisable thermoplastic CFRPs through reuse of recycled waste matrix material

In this work, a closed loop recycling process is investigated, which allows polymerised bulk thermoplastic matrix (Elium 150) from production waste (also referred to as recyclate) to be reused as additive in composite manufacturing by vacuum assisted resin infusion (VARI) of virgin Elium 150 monomer. It is shown that this process can save up to 7.5 wt% of virgin material usage in each processing cycle. At the same time, the thermal stability and stiffness of the composite increases with the proportion of recyclate introduced. Contemporarily, the shear and bending properties have also been observed to improve. Gel permeation chromatography (GPC) showed that the changes observed are due to an increase in molecular weight with the recyclate content. In particular, a correlation between the molecular weight and the shear properties of the composite was discovered using single fibre push-out tests.

Multi-scale Design, Prototyping and Validation Testing of a Composite Anti Roll Bar

Lightweighting in automotive has already been a key research area for decades, and more recently this research driver has been augmented with electrification and sustainability of new mobility solutions. This contribution focuses on the redesign of a passenger vehicle anti-roll bar from the traditional steel design into a braided glass fiber reinforced composite solution. This work focuses on the functional, central part of the anti-roll bar, targeting a significant weight reduction and sustainability improvement. In terms of design and engineering using finite element methods, a multiscale approach of the composite design has been considered. At microscale the braid unit cell and at macro scale a component were modelled. For the microscale of the braided structure, a selection of design variables has been scrutinized, notably the effect of the braiding angle on the shear stiffness. On the macro scale, finite element modelling is adopted to relate the overall performance to the composite structure and part dimensioning. Additionally, high-potential designs have been prototyped by overbraiding and Vacuum-Assisted Resin Infusion processes. Functional performance testing on the prototypes evaluates the adopted simulation strategies and validates the design.

Numerical analysis of mechanical performances of shape memory alloy hybrid composites

The effects of the content and position of SMA wires on the static properties of glass fiber reinforced epoxy (GF/epoxy) composite laminates prepared by vacuum-assisted resin infusion (VARI) process were investigated. According to the influence of different embedding content and position of SMA wire on mechanical performances of composite laminates, the optimal content and optimal position of SMA were found out. The static mechanical finite element models of GF/epoxy composite and shape memory alloy hybrid composites (SMAHCs) are established. The validity of the models is verified by comparing the simulation results with the experimental results. According to the finite element results, the influence of SMA embedding content and position on the mechanical performances of composites is described quantitatively.

Mechanical and acoustic emission properties of vegetable fiber‐reinforced epoxy composites for percussion instrument drums

AbstractPercussion instrument drums are traditionally made of wood, which is becoming less available as environmental concerns grow. In order to replace wood in percussion instruments, four types of epoxy resin composites reinforced with fabrics of hemp, flax, ramie, and jute, respectively, are fabricated using vacuum assisted resin infusion molding. The tensile and flexural properties of the composites are measured and compared with those of ailanthus wood. The results show that the flexural strengths and moduli of the composites are either better or in between to those of the horizontal and vertical strips of the wood. An acoustic test method is developed to test the acoustic performance of the composites and the wood. The results show that the composites have lower acoustic dynamic moduli, acoustic radiation damping coefficients, sound velocity, and higher acoustic impedance than those of the wood due to their lower flexural moduli and higher specific densities. The shapes of the acoustic spectra for the composites are somewhat similar to those of ailanthus. The acoustic performance comprehensive scores of the four composites are also in between those of the vertical and the horizontal strips of ailanthus. It is possible to match the acoustic performance of ailanthus by increasing the flexural modulus and decreasing the specific density of the composites through reducing the yarn crimp, increasing the fiber volume fraction, and introducing microvoids into the composites.

Small-diameter optical fibre sensor embedment for ambient temperature cure monitoring and residual strain evaluation of CFRP composite laminates produced by vacuum-assisted resin infusion

Out of autoclave (OoA) processing techniques, such as liquid composite moulding techniques (LCM) and, particularly, the vacuum-assisted resin infusion (VARI) technique, are being used, with increasing success, in replacement of prepreg/autoclave technologies to produce structural aircraft/aerospace polymer composite parts, due to its better cost effectiveness and competitiveness. This work aims to embed Fibre Bragg grating (FBG) sensors to monitor the VARI manufacturing of carbon fibre reinforced polymer (CFRP) composites and evaluate the associated phenomena: ambient curing and post curing reactions and resulting residual strains. The curing kinetics of the epoxy resin system alone was initially studied through isothermal differential scanning calorimetry (DSC) tests and applying the isoconversional Friedman method, and further studied by strain monitoring during ambient curing and post curing resorting to FBG sensors. The FBG sensors in the CFRP laminates were able to detect a subtle increase of strain as infusion of the CFRP started and to measure decreasing strain as resin filled in the dry fabric layers. Subtle strain decrease revealed forming crosslink bonds. Compressive strains measured by the FBG sensors during post curing show that further crosslink takes place. A comparison of resultant residual strains was made between specimens with embedded FBG sensors on small-diameter optical fibres (SDOF) and on large-diameter optical fibres (LDOF).

Addition of compatibilized nanoclay and UHMWPE fibers to epoxy based GFRPs for improved mechanical properties

Epoxy based glass fiber reinforced composite laminates containing silanized nanoclay and compatibilized ultra-high molecular weight polyethylene (UHMWPE) fibers were processed using vacuum assisted resin infusion moulding for improved mechanical properties. UHMWPE fibers are low-cost, light-weight with excellent impact strength (highest among thermoplastic fibers), tensile strength and modulus. X-ray diffraction/transmission electron microscopy validated nano-level dispersion of nanoclay. Silanization of nanoclay was validated by Fourier-transform infrared spectroscopy. UHMWPE fibers were compatibilized using three different surface treatments and their compatibilization was confirmed by energy dispersive spectroscopy. Nanocomposite reinforced with 2 phr silanized nanoclay and 0.25 phr compatibilized UHMWPE fibers (treated using the best method) showed significant improvement of 30% in impact strength over the reference sample (all other mechanical properties also showed significant improvements). SEM analysis confirmed that silanization of nanoclay and compatibilization of UHMWPE fibers through the optimum treatment resulted in enhanced interfacial bonding among different constituents of the GFRP nanocomposite system.

Upgraded Mechanical Properties of Diluent Nano-filled Glass/Epoxy Composites Fabricated by Vacuum Assisted Resin Infusion

Vacuum Resin Infusion process (VRI) is the most common method for the manufacturing of composite laminates. Unfortunately, VRI has some disadvantages such as incomplete filling of the mold and poor impregnation due to the high viscosity of the nano-polymeric resin. The high viscosity of nano-polymeric resin consumes a lot of time to complete the process. In this study, an attempt was done to decrease the viscosity of the epoxy and nanophase epoxy hence decreasing the processing time. Ethanol was added with small weight fractions (0.5 wt.% and 1 wt.%) to the epoxy resin without evaporation to decrease its viscosity. Moreover, TiO2 nanoparticles with 0.25 wt.% and 0.5 wt.% were added to epoxy resin to produce nano-filled glass fiber/epoxy composites. Two types of glass fiber reinforcements were used which are either chopped or woven glass fabric. The results showed that, as the ethanol percentage increases, the resin viscosity decreases and consequently the processing time. Adding 1 wt.% of ethanol and 0.25 wt.% of TiO2 nanoparticles to epoxy resin slightly increases tensile strength as compared with neat chopped glass fiber/epoxy composites. The tensile strength of woven glass fiber/epoxy and the flexural properties of both woven and chopped glass fiber reinforced epoxy improved significantly with the addition of 0.5 wt.% of ethanol and 0.25 wt.% of TiO2 nanoparticles.

Manufacturing and Characterization of Hybrid Composites with Basalt and Flax Fabrics and a Partially Bio-based Epoxy Resin

This research is focused on manufacturing and characterization of hybrid composite laminates obtained different stacking sequences of basalt and flax fabrics with silane treatments embedded in a partially bio-sourced epoxy resin as matrix. They were manufactured by the vacuum-assisted resin infusion molding and mechanical properties were tested in tensile, flexural and impact conditions. The effect of the coupling agent on the fiber/matrix interface was studied by FESEM. The effect of temperature on mechanical properties was evaluated by DMTA and TMA. FESEM images revealed improved fiber/matrix interactions with silane treatment, having a more satisfactory effect on basalt fibers than on flax fibers because of its silica-based structure, leading to improved mechanical properties. It is worthy to note that the hybrid stacking sequence has no remarkable influence on the elongation at break. On the contrary, the hybrid stacking sequence offered a great influence on both the elastic modulus and the tensile strength.

Effect of the orientation carbon-glass fiber reinforced polyester composite on bending strength for runner foot prosthesis applications

An alternative way for increasing the strength of the runner’s prosthesis is by utilize the direction of fiber orientation. The aim of this research is to determine the effect of the orientation carbon-glass fiber reinforced composite on its bending strength. The main materials used in this study are carbon and glass fiber. The independent variable in this study is the direction of fiber orientation (0°, 45°, 90°, 0°/90°/0° and 90°/0°/90o). The dependent variables in this study are the bending strength and fracture micro photographs. This study is controlled by the method of manufacturing composites with vacuum assisted resin infusion (VARI) and unsaturated polyester yukalac® 157 BQTN-EX with a density of 1.12 g cm−3. Polyester composite are reinforced with carbon and glass fiber with varying fiber orientation. Each composite was reinforced carbon-glass fiber with orientation 0°, 45°, 90°, 0°/90°/0° and 90°/0°/90°. The results showed that the bending strength of composite reinforced carbon glass fiber with orientation of 0°, 45°, 90°, 0°/90°/0° and 90°/0°/90° respectively 1.32 MPa, 1.65 MPa, 0.93 MPa, 1.25 MPa and 4.46 MPa. While, the deflection values for composites reinforced carbon glass fiber with orientation of 0°, 45°, 90°, 0°/90°/0° and 90°/0°/90° respectively 9.65 mm, 8.7 mm, 13.45 mm, 10.59 mm and 3.83 mm. The lowest bending strength occurs in carbon-glass fiber reinforced composites with fiber orientation 90° is 0.93 MPa with the deflection of 13.45 mm. The highest bending strength occurs in carbon-glass fiber reinforced composites with fiber orientation 90°/0°/90° is 4.46 MPa with a deflection of 3.83 mm. The results of fracture testing using scanning Electron Microscopy (SEM) showed mixed failure due to delamination and fiber pull out.

Thermal Shock Behavior of Twill Woven Carbon Fiber Reinforced Polymer Composites

In the current research, the effect of cyclic temperature variation on the mechanical and thermal properties of woven carbon-fiber-reinforced polymer (CFRP) composites was investigated. To this, carbon fiber textiles in twill 2/2 pattern were used as reinforced phase in epoxy, and CFRPs were fabricated by vacuum-assisted resin-infusion molding (VARIM) method. Thermal cycling process was carried out between −40 and +120 °C for 20, 40, 60 and 80 cycles, in order to evaluate the effect of thermal cycling on mechanical and thermal properties of CFRP specimens. In this regard, tensile, bending and short beam shear (SBS) experiments were carried out, to obtain modulus of elasticity, tensile strength, flexural modulus, flexural strength and inter-laminar shear strength (ILSS) at room temperature (RT), and then thermal treated composites were compared. A dynamic mechanical analysis (DMA) test was carried out to obtain thermal properties, and viscoelastic properties, such as storage modulus (E’), loss modulus (E”) and loss factors (tan δ), were evaluated. It was observed that the characteristics of composites were affected by thermal cycling due to post-curing at a high temperature. This process worked to crosslink and improve the composite behavior or degrade it due to the different coefficients of thermal expansion (CTEs) of composite components. The response of composites to the thermal cycling process was determined by the interaction of these phenomena. Based on SEM observations, the delamination, fiber pull-out and bundle breakage were the dominant fracture modes in tensile-tested specimens.

Evaluation of production quality and mechanical behavior of low-cost shear connectors manufactured with perforated GFRP plates

abstract: Insulated pre-cast concrete wall panels, also called sandwich panels, consist in two external concrete layers, in which an internal layer of thermal insulation material is inserted between, aiming better acoustic and thermal performance. One of the main concerns regarding the performance of these panels refers to the elimination of thermal bridges caused by metallic connectors, which jeopardize the panels’ thermal efficiency. One of the proposals to solve this problem consists in the use of PERFOFRP connectors, which are plane plates with perforated holes through its thickness, which are embedded into the concrete plates, creating anchorage pins that enhance the shear strength and the layers’ debonding resistance. This research had the objective of evaluating the production quality of this type of connector, produced with a low-cost and easy-to-use vacuum assisted resin infusion system; considering the effects of: (a) resin plate homogeneity, by taking samples from various locations on the plate; (b) fabrication repeatability; and (c) raw production materials’ origin; on the results of: (I) ultimate tensile stress, (II) modulus of elasticity, and (III) volume fraction of fibre. Also, 18 specimens in the form of representative models of the shear connector in insulated pre-cast concrete wall panels, with six different hole configurations achieved by varying the holes’ diameter and spacing, were subjected to push-out tests, to assess the holes’ diameter and spacing effects on the mechanical performance of the connection in terms of ultimate load capacity and stiffness. The results indicated a production quality with a satisfactory level of characteristics variation, considering: the variability in different parts of a single composite plate, the variability between composite plates from different infusion process, and the variability between different production batches. Furthermore, the push-out tests demonstrated that the perforated connectors presented, when compared to non-perforated connectors: a gain in shear strength from 8% to 25%, lower relative displacements, and higher levels of stiffness. It was also observed that connectors with 25.40 mm diameter holes presented better performance than connectors with 31.75 mm diameter holes; and that the reducing the hole spacing from 2.00 to 1.75, for the 25.40 mm diameter specimens, caused a decrease in the load capacity of the connector. Thus, it was verified that variations on the hole’s diameter and spacing influenced the load carrying capacity of the connection.