Modified Arcan Fixture Research Articles

Characterization of woven composite material under multiaxial loading regimes using FE-based stereocorrelation

In this paper, woven glass fiber composite samples were subjected to three different cyclic loading histories (i.e., tensile, shear and combined loading at 45° via the Modified Arcan Fixture. During the experiments, the samples were monitored by a stereovision system. Finite Element based stereocorrelation was used to measure the displacement and strain fields. The analysis of the experiments revealed different damage mechanisms. Furthermore, for the 45° experiment, the highest strain levels were reached, whereas for the tensile test, the highest stress levels were achieved.

The effect of loading rate on mixed mode I/II fracture behavior of adhesively bonded joints: Experimental and numerical approach

In this study, the use of a modified Arcan fixture to investigate the fracture behavior of adhesively bonded Al/Al joints has been discussed under rate-dependent loading in various loading conditions (mode I, mode II, and mixed mode (I/II)). It was observed that the testing speed has a significant effect on the fracture properties of the joints, especially in pure mode, II. The results indicated that failure load was increased for all three loading modes and an increase was also observed for strain energy release rate at all loading conditions. The critical fracture loads obtained from the experimental tests were used to calculate the values of the critical stress intensity factors and strain energy release rates for loading modes I, II, and mixed mode I/II at different loading rates by using the finite element method. It was shown that the values of strain energy release rate for loading mode II were higher than mode I and mixed mode at all loading speeds. Finally, scanning electron microscope analyses (SEM) were used to investigate the effects of loading speed on the failure surfaces of the adhesive in microstructural scales and it was shown that at low loading rates, the number of crazes that cause failure in the adhesive layer increases.

Numerical Investigation of Failure in Epoxy-Based Adhesive Joints

Currently, adhesive bonding has been increasingly used in various industrial applications such as in automobile lightweight structures for multi-material assembly. However, adhesive joints show a complex failure behavior. Their failure modes can be either adhesive failure, cohesive failure, or mixed mode failure depending on their interfacial strength and also the strength of adhesive layer which also varies with hydrostatic pressure. In this study, the failure of the adhesive joints with an epoxy-based adhesive bonded to metallic substrates are investigated numerically using FEA. The damage evolution model is implemented in the finite element model to predict the failure of adhesive joints. The adhesive strengths under different states of stress for a damage evolution model are characterized using the modified Arcan fixture which is specifically designed to study of hydrostatic pressure effect on an adhesive behavior. The validation of the failure model is carried out with the results of single lap shear test. A good agreement is finally found between FEA and experiments.

On adhesively bonded joints with a mixed failure mode—An experimental and numerical study

Cohesive zone model (CZM) has been extensively used to study interfacial failure behaviors such as fracture of adhesively bonded joints (ABJs). Accurate and efficient identification of traction–separation law (TSL) in CZM signifies an important issue for design and analysis of adhesive structures. In this study, a modified Arcan fixture was developed and employed to investigate the mixed mode failure behaviors of ABJs for carbon fiber reinforced plastic (CFRP) substrates under a tensile-shear coupling load, in which the double cantilever beam (DCB) test was carried out to characterize fracture toughness for benchmark data. With the help of digital image correlation (DIC) technique, the interfacial displacement field was obtained. The virtual crack closure technique (VCCT) was adopted to decouple the mode mixture at different tension-shear angles of the Arcan specimens. Based on the traction–separation law for each mixed ratio of failure mode, a refined CZM was established. In this study, the Arcan and DCB specimens bonded with a flexible adhesive of 3M DP190 were prepared and tested. The experiments were carried out for the ABJs with two adhesive layer thicknesses of 0.3 mm and 1 mm, respectively, to investigate the influence of bonding thickness. Based on the extracted CZM parameters, a finite element (FE) analysis model was developed and validated with the experimental results. Unlike the traditional predetermined damage evolution law, a new CZM was established without a priori cohesive damage evolution; and the effectiveness of the proposed model for the TSL extraction was verified. By using this method, the mechanical response of the bonding interface under complex stress state was well predicted and the FE modeling of ABJ’s fracture was accurately achieved. The study is anticipated to gain new understanding and fundamental data on mixed failure mode, thereby enabling better design of ABJs for engineering applications.

EFFECT OF ADDING GRAPHENE OXIDE NANOPLATELETS ON THE ARALDITE ADHESIVE FRACTURE STRENGTH UNDER MIXED-MODE I/II LOADING

In the present paper, the effect of adding graphene on the fracture strength of the Araldite adhesive was studied. Experimental specimens were made of PMMA and then were bonded using a thin adhesive layer. Different loading modes were created by using the modified Arcan fixture. The effect of adding graphene to the adhesive layer was studied at four different weight ratios of graphene, including 0.00, 0.25, 0.50, and 1.00%. The results derived suggest that the experimental specimens with 0.5 wt % graphene have the highest fracture force. For specimens with the same amount of graphene, the highest fracture force was obtained under the mode II loading condition. The experimental results were compared with the results of the finite element model. The fracture behavior of an adhesive layer was modeled using the cohesive zone model. The maximum nominal stress criterion and the quadratic power law criterion were used for the crack initiation and propagation in the adhesive layer, respectively. The comparison between the numerical and experimental results shows overall good agreement.

Finite Element Implementation of the Exponential Drucker–Prager Plasticity Model for Adhesive Joints

This paper deals with the numerical implementation of the exponential Drucker-Parger plasticity model in the commercial finite element software, ABAQUS, via user subroutine UMAT for adhesive joint simulations. The influence of hydrostatic pressure on adhesive strength was investigated by a modified Arcan fixture designed particularly to induce a different state of hydrostatic pressure within an adhesive layer. The developed user subroutine UMAT, which utilizes an associated plastic flow during a plastic deformation, can provide a good agreement between the simulations and the experimental data. Better numerical stability at highly positive hydrostatic pressure loads for a very high order of exponential function can also be achieved compared to when a non-associated flow is used.

Investigating the failure behavior of hygrothermally aged adhesively bonded CFRP-aluminum alloy joints using modified Arcan fixture

Composite adhesively bonded structures used in automobiles usually withstand the harsh environment and complex stress during long service. To further popularize the carbon fiber reinforced polymer (CFRP), it is necessary to study the failure behavior of environmentally aged CFRP-aluminum alloy joints under complex stress state and establish a mechanical performance prediction method. In this work, quasi-static tensile tests on hygrothermally (80 °C and 95% relative humidity) aged adhesively bonded CFRP-aluminum alloy butt joints were carried out using a modified Arcan fixture. The stress distribution in the adhesive of Arcan tests was analyzed by the FEM, which proved the rationality of the designed fixture. After exposure to hygrothermal aging for a maximum of 30 days, the mechanical performance of the joints under different stress states decreased remarkably at a rapid degradation rate during the early stage. For unaged joints, mixed adhesive–cohesive​ failure and CFRP fiber tearing were observed when normal stress was predominant, whereas complete cohesive failure in the adhesive occurred when shear stress was more significant. For the hygrothermal aged joints, the failure modes under different stress states were adhesive–cohesive failure because of the significant degradation in adhesive performance. The q-stress failure criteria and environmental degradation factors of the CFRP-aluminum alloy bonding structure before and after aging were established, and both were embedded into the constitutive laws of the cohesive zone model (CZM) by the user-defined material subroutine. The failure prediction method was verified by the single lap joint experiment and numerical analysis before and after aging.

Comparison of three different adhesive joints using static and dynamic impact tests : Development of a new drop weight impact test rig incorporating a modified Arcan fixture

The paper proposes to compare static and dynamic properties of three structural adhesives selected for the integration of optical space systems. These comparisons are based on an original methodology using static test and drop weight impact test to determine the best shock-strength candidate. In a first section, the design of the drop weight impact rig integrating a modified Arcan fixture is described. Then validity of the impact test rig is discussed on a simplified case thanks to an analytical model of “soft impact” available in literature. In a second section, static tests results are presented and the adhesive's critical stresses are identified with a point stress criterion. Finally, impact tests results are used to discuss the dynamic tensile and shear behaviour of each adhesive with different stress concentrations. Static critical stresses and impact strengths of the adhesives are reported. In conclusion a strategy of adhesive choice is discussed.

Effect of Service Temperature on Mechanical Properties of Adhesive Joints after Hygrothermal Aging.

Polyurethane adhesive and aluminum alloy were selected to make adhesive joints. Butt joints tested at different loading angles (0°, 45°, and 90°) using a modified Arcan fixture were selected to represent three stress states (normal stress, normal/shear combined stress, and shear stress, respectively). Firstly, the accelerated aging tests were carried out on the joints in a hygrothermal environment (80 °C/95% RH). The quasi-static tests were carried out at different temperatures (−40 °C, 20 °C, and 80 °C) for the joints after hygrothermal aging for different periods. The variation rules of the joints’ mechanical properties and failure modes with different aging levels were studied. The results show that the failure load of the joints was obviously affected by stress state and temperature. In the low-temperature test, the failure load of the joints decreased most obviously, and the BJ was the most sensitive to temperature, indicating that the failure load decreased more with the increase of the normal stress ratio in the joint. Through macroscopic and SEM analysis of the failure section, it was found that the hydrolysis reaction of polyurethane adhesive itself and the interface failure of the joints were the main reasons for the decrease of joint strength. The failure models were established to characterize the adhesive structure with different aging levels at service temperature.

Prediction of deformation and failure anisotropy for thin magnesium sheets under mixed-mode loading

The plastic deformation and the failure behavior of a third generation magnesium AZ31 sheet is studied under quasi-static tensile, compressive, and mixed mode loading conditions at room temperature. While the deformation anisotropy is found to be less pronounced compared to previously investigated rolled sheets of this alloy, a strong dependence of the failure strain on the sheets orientation is experienced. This failure anisotropy is further studied and quantified using mixed-mode tests realized using a modified Arcan fixture. The irreversible deformation is modeled in the framework of finite elements using two coupled anisotropic plastic potentials. The model parameters are calibrated using the global force-elongation record of the tested samples. For the prediction of failure, an uncoupled damage model based on transformation of strain rates is developed and applied. It is shown that this model is able to predict the observed edge failure of notched specimens with good accuracy. The model predictions for the smooth tensile tests are analyzed in detail by full-field FE analyses to understand the interaction between strain localization and predicted damage evolution.

Experimental investigation on the mixed mode fracture behaviour of nano modified glass epoxy three phase laminated composite through Modified Arcan Fixture

This paper investigates carbon nano tube’s (CNTs) effect in the mixed-mode inter-laminar fracture response of glass fibre reinforced epoxy laminates. Laminates are prepared by adding 1%, 2% and 3% of CNTs with matrix by weight. Modified arcan fixture has been employed to generate the data for Mode I, Mode II, and various mixed-mode ratios. Loading angle has varied from 0° to 90° in steps of 15°, and the generated data was reduced by applying correcting factors to get toughness value. Periodic function model was employed to estimate the elastic constants for data reduction. Loading angle, Proportion of Carbon Nano Tube, Crack length ratio, Stress intensity factor and Energy release rate are taken as the variables for discussion. Fractured surfaces are also captured with scanning electron microscopy to study the influence of Carbon Nano Tube in inter-laminar fracture. Genuineness of specimen and fixture on exhibiting mixed mode fracture load at crack tip, was verified before proceeding the characterization. Fracture resistance was enhanced from 2.95% to 5.24% and critical load at fracture was increased from 17.47% to 22.79% with Carbon Nano Tube addition compared to the neat GFRP specimens. Enhancement is high for 1% addition, and enhancement rate decreases after further reserves. Failure assessment study was also conducted on specimens and elliptical failure criteria was noted as the best one for defining mixed mode fracture of CNT filled glass epoxy specimens.

Modelling damage in multidirectional laminates subjected to multi-axial loading: Ply thickness effects and model assessment

A meso-scale damage modelling framework for composite laminates is assessed against multi-axial experimental data obtained from specimens subjected to combined tension/compression and shear loading using a modified Arcan fixture (MAF). Two laminates made from unidirectional carbon fibre-reinforced epoxy plies of different thickness are considered to investigate the ply thickness effect on the damage behaviour of modified open-hole specimens. Intra-laminar damage is predicted using a continuum damage model combined with a fibre-aligned mesh, while cohesive zones are used to account for inter-laminar damage. The multi-axial open-hole specimen strength is predicted with a mean relative error of 15% across all the investigated lay-up and loading configurations, while the predicted damage maps show encouraging agreement with full-field measurements obtained using digital image correlation (DIC). However, the assessment reveals limitations of the assumption of small strains and rotations in the formulation of the model that lead to spurious model behaviour for shear-dominated damage modes.

Effect of dispersing CTBN into Diglycidyl Ether of Bisphenol-A on Mixed mode Loading

Delamination of polymer composite is one of the major failure characteristic, in this context the fracture behavior of the tailored composites in combination of opening mode and shearing mode is assessed and its fracture robustness of the glass fiber reinforced laminate are determined experimentally, in this present work by developing a modified Arcan fixture using a single edge notched specimen for characterizing in various loading conditions, The fixture was made of industrial grade Aluminum ingot machined to an outer diameter of 150 mm, having a thickness of 10 mm. The fixture had provision to load the sample at different oblique angles up to 90 degrees in steps of 15 degrees. The samples were attached to the fixture by means of fasteners and were tested in tensile mode using a 40 KN Instron tensile tester at constant displacement and ambient conditions. Further, the resin was strengthened with Carboxyl Terminated Butadiene Arenonitrile (CTBN) and its effect on fracture parameters was studied by varying the loading angles. Results indicate that the fracture parameters vary with loading and at angles greater than 45 degrees, the GFRP sample’s behavior changes from opening mode to shearing mode and the converse is also true. This pattern is similar, with the specimens even after modifying the resin with CTBN however, it was found that stress intensity factor increased corresponding to the increase of CTBN infusion. CTBN was dispersed into the Bisphenol base A (LY566– A general purpose thermoset epoxy resin) in three different percent: 1%, 3% and 5% by weight. The layup sequence used in this work was cross ply. The effect of varying the loading angles on the stress intensity factors were studied.

Experimental Investigation and Finite Element Modelling of the Influence of Hydrostatic Pressure on Adhesive Joint Failure

Structural adhesives have been increasingly used in automotive industries in conjunction with lightweight structural components to maximize weight reduction in modern car design. They are used to bond various kind of lightweight materials such as FRP composites or metallic alloys and provide a good distribution of force across joining area without damaging the substrates. For automotive applications, bonded components have been often used in complex loading environments which brings failure prediction of adhesive joints a key of success for this technology. As polymer-based materials, hydrostatic pressure can have a major impact on adhesive joint failure in addition to temperature and strain rate. Its influence can be investigated using a specific test fixture known as a modified-Arcan fixture. This article presents the characterization of epoxy-based adhesive using a series of modified-Arcan tests to apply different loading taking in account effect of hydrostatic pressure onto adhesive joints. A high-order exponential Drucker-Prager failure criterion is chosen to interpret the yield and failure surface. Finally, the non-linear behaviour of adhesive is identified via 0° and 90° Arcan tests which correspond respectively to tri-axial and shear modes and the validation of this behaviour is carried out by mix-mode 60° and 120° Arcan tests. The simulation shows a good agreement only with the result in direction 60° while in direction 120° the divergence is obvious due to the different in damage mechanism of this mode.

Ply thickness and fibre orientation effects in multidirectional composite laminates subjected to combined tension/compression and shear

The effects of laminate lay-up and multiaxial loading on the failure of multidirectional laminates can be significant. Thus, ply thickness and fibre orientation effects in quasi-isotropic carbon/epoxy laminates subjected to combined tension-shear and compression-shear loading are investigated. Three laminate lay-ups with equivalent thickness and homogenised elastic properties, but with different ply thicknesses and ply orientation angles are studied using open-hole specimens. Combined tension/compression-shear loading is applied using a new Modified Arcan Fixture (MAF). A methodology for identifying the failure behaviour based on stereo Digital Image Correlation (DIC) is devised. The results show that ply thickness has a strong effect on the failure behaviour in combined tension-shear, whereas the effect is small in compression-shear loading. No significant effect of the relative fibre orientation angles is observed under either loading regime. The experimental approach provides a new tool to investigate composite laminates under the full tension/compression-shear loading regime.

On the mixed mode I/II/III inter-laminar fracture toughness of cotton/epoxy laminated composites

Nowadays, natural fiber reinforced laminated composites have been extensively used in order to fabricate the various structures. In this paper, a woven cotton/epoxy laminated composites system was considered. The main purpose of this investigation is to measure a full range of mixed mode I/II/III Inter-laminar facture toughness (IFT), critical strain energy release rate (CSERR) and the mechanical properties of this material. Hence, in addition to tensile, flexural and in-plane shear tests, a series of delamination tests consisting of pure modes, mixed modes I/II, I/III and II/III were carried out. The fracture tests were conducted using a modified Arcan fixture and an out-of-plane fixture. The experimental results showed that the delamination responses of cotton/epoxy system are deeply dependent on the loading conditions. It was also found that the Inter-laminar fracture toughness and CSERR under pure mode I and mixed mode II/III loading conditions have the lowest and greatest values among the delamination modes, respectively. It was also conducted that in comparison with the woven carbon/epoxy and glass/epoxy systems, the modes I, II and III CSERR of cotton/epoxy is remarkable.

Mixed-Mode Deformation and Failure of a Magnesium Sheet Quantified using a Modified Arcan Fixture

The anisotropic plastic deformation and the failure behaviour of a rolled magnesium sheet is quantified by means of a modified Arcan loading device. Combined mode I/II loadings are applied at room temperature. Anti-buckling guides enforce parallel motion of the fixture. The evolution of local strain fields during loading is analysed by means of digital image correlation. Two target functions are constructed from each test: one including the kinetic, another describing the kinematical response. The failure strain as a function of the loading direction and sheet orientation is quantified. It is shown that the failure mechanism is independent of the loading angle. Guidelines for future constitutive model developments are provided in terms of the exploration of the samples motion, the uniformity of strain fields and their respective significance.

Fracture characteristics of mixed-mode toughness of dissimilar adherends (cohesive and interfacial fracture)

This paper investigates the fracture behavior of aluminum/polymer dissimilar adhesively bonded joints at different mixed-mode ratios. For this purpose, a series of experiments were carried out using a modified Arcan fixture to obtain critical fracture load in mode I, mode II and mixed-mode, for two types of cohesive and interface starter cracks. Experimental data, along with the Virtual Crack Closure Technique (VCCT) were employed to extract the strain energy release rates. The average values of strain energy release rates were found and for cohesive cracks, and and for interface cracks. Considering the relations between the strain energy release rate and the stress intensity factor, and were also calculated for cohesive and interface starter cracks.

Development of Modified Arcan Fixture for biaxial loading response of fiber-reinforced composites

A Modified Arcan Fixture (MAF) was developed to study the biaxial mechanical behavior of fiber reinforced composites. The MAF was calibrated compared with standard ASTM tests for an epoxy/twill woven-ply laminate. Material properties obtained with ASTM tests are implemented in ABAQUS to find the optimal notch radius that creates the most uniform stress state in gauge area. The optimized configuration of Arcan specimen was adopted to design the entire fixture numerically in preload and load steps to avoid plastic deformation. Stress concentration factor was considered in Arcan specimen under tensile loading. Biaxial experimental data for woven-ply composite in different loading angles was obtain with the MAF. Failure modes under biaxial loading show that fibers rotated towards the principle tensile direction and failure was caused by excessive stress which reached fiber limit. The ultimate shear strength corrected by considering the fiber rotation effect are in good agreement with ASTM standard results.

A simple nonlinear constitutive model based on non-associative plasticity for UD composites: Development and calibration using a Modified Arcan Fixture

A simple nonlinear constitutive model based on non-associative plasticity for unidirectional (UD) composites is developed and calibrated using a Modified Arcan Fixture (MAF) and Digital Image Correlation (DIC). The plasticity model accounts for the nonlinear response of unidirectional composites subjected to multiaxial loading, assuming transverse isotropy and negligible plasticity in the fibre direction. The different responses in transverse tension and compression are accounted for by a Drucker–Prager type yield function to include transverse pressure sensitivity. It is shown that using an associative flow rule leads to the prediction of non-physical plastic strain components, whilst the use of a non-associative flow rule resolves the deficiency of the associative model. The non-associative model is calibrated and verified against biaxial test data obtained from glass/epoxy specimens using the MAF, as well as against off-axis test data available in the literature for two additional composite material systems. The nonlinear stress-strain curves for unidirectional composites subjected to multiaxial stress states predicted by the model are in good agreement with all three sets of experimental data, thus demonstrating the predictive capabilities of the proposed model.