Arcan Test Research Articles

The Effects of Loading Angles on the Failure of Cross-Ply Notched Bio-Basalt Composites

A cross-ply basalt V-notched butterfly specimens were subjected to pure tension, combined tension-shear, and shear stress-strain state using a modified Arcan test fixture with loading angles from 0° to 90° with 15° increment. Multiaxial stress and strain states were studied using the principal stress and strain ratio, from which the principal angle was determined and used to represent principal states in the gauge section. The quasi-elastic to non-linear transition stresses were determined for each loading angle. In biaxial stress-strain states and pure shear, the deformation and consequently the shear-induced damage start to accumulate significantly. Also, in biaxial stress-strain states between 15°-75°, the shift from tension-shear to pure shear was observed after the transition to the non-linear part of the stress-strain curve. The digital image correlation (DIC) images and microscopic evaluation show that a large extent of damage is the consequence of the shear deformation after the rotation of 0° clamped fibres, while the 90° fibres maintained their original straight form. In off-axis tests, the principal strain axis rotates towards the weakest material axis even at small off-axis angles. This causes a transition from a tension-shear biaxial state in the linear loading part to shear in the non-linear part, leading to irreversible damage beyond the transition point.

Development of a Creep Mechanical Frame Setting Based on Arcan Test

Abstract Structural adhesive bonding has several advantages compared to other assembly techniques such as welding and riveting. Yet, creep is an important long-term phenomenon that needs to be considered for the design of such joints. To investigate this aspect, experimental investigations are needed at the scale of the adhesive layer. At such a scale, Arcan setting presents several advantages compared to other existing tests (analysis of different loads, limited edge effects) and was thus chosen for the development of an experimental approach aiming at providing creep characterization of adhesive layers. A mechanically operated testing machine was thus developed and is presented herein. To measure local strains of the adhesive layer, two linear variable differential transformer sensors are fixed on a support placed on the beaks of the Arcan sample according to two directions: normal and tangential to the bonded surface. The developed system (mechanical system and strain measurement) proved to be successful in investigating the creep behavior of adhesive layers while varying several parameters (load levels, type of load, temperature, adhesive thickness).

Methodology for evaluating the mechanical performances of a bonded assembly through complementary mechanical tests

ABSTRACT Bifunctional polymers have been studied as bonding layers (BL) on aluminum surfaces to promote adhesion of adhesives for structural bonding applications. The BL are located at the interface between the aluminum substrate and the adhesive. The mechanical performances of the BL in a bonded assembly were evaluated via several complementary mechanical tests, before and after ageing cycle: single lap shear, Arcan test, three-point bending test, and micro-scratch. The results of these four mechanical tests were compared with those of a raw reference (without any treatment) and a reference that had undergone standard surface preparation (cleaning and etching), in order to assess the mechanical performances of the surface treatment products (BL), and to value these products on the surface treatment market. In order to follow a methodology for selecting the best surface treatments, the mechanical results were compared with each other, and even correlated for samples with bonding layers (containing phosphorus and carboxylic acid functions). The correlation of the results obtained from the four mechanical tests (single lap shear, Arcan, three-point bending, and micro-scratch tests) therefore makes it possible to validate the methodology for evaluating these surface treatments.

Experimental investigations on parameter identification and failure predictions of titanium alloy by Gurson–Tvergaard–Needleman model

This study focused on the experimental investigations on parameter identification and failure prediction of Ti-6Al-4 V by Gurson–Tvergaard–Needleman (GTN) model. Two approaches, i.e., direct (by image processing of SEM observations) and indirect measurements (by the reduction of effective Young’s modulus or FE trail-and-error), were used to determine the GTN parameters. Through digital image processed SEM micrographs of uniaxial tensile specimens at different deformation stages, the developments of void volume fraction (VVF) were obtained and compared with that from indirect measurements. The three nucleation parameters can then be analytically derived from this experimentally obtained VVF developments. The critical VVF at void coalescence was directly measured through a SEM observation of the section surface around the fracture region of uniaxial tensile specimen, and this value is also consistent with that from indirect measurement. However, as the matrix of a fracture surface is characterized with an obvious varying grayscale due to its dimple morphology, the VVF at final fracture is suggested to be determined from FE trial-and-error rather than a direct measurement of the fracture surface to avoid error induced by subjective judgements. Consistency of the determined GTN parameters was verified through failure predictions on notched tension (R = 6, 20, 100), notched Arcan tests (R = 1, 3, 5), and cracked Arcan tests (SECS, DECS, and CCS), which proved that GTN model with parameters from this experimental investigation cannot only predict the macroscopic mechanical behavior of ductile metals, but also well match the entire damage evolution, from void nucleation to final fracture.

Mixed-mode loading tests for determining the mechanical properties of clinched joints with an additional rivet used in the assembly of thin-walled structures

This publication presents the possibility of forming a clinched joint with the use of a deformable element such as a full rivet. An analysis of the joint load capacity was also performed for three values of the hardness of the rivet. The joints were formed in the same sheet with thickness t=1.5 [mm] made of DX51D+Z275 steel (which is commonly used for thin-walled structures). Additional rivets with hardness values 350HV1, 400HV1, and 420HV1 were used. The joints were made with a uniform punch and a die with movable elements. Load capacity tests were carried out in order to demonstrate the influence of the angle between the load force and the axis of the clinch riveted joint. H-shaped samples were made for load tests with the use of a modified Arcan test device. All joints were tested under the same static test conditions (the traverse speed of the testing machine was 10 mm/min). In addition, the characteristic geometric parameters of the interlock were measured on the joint cross-sections.In the case of connecting the sheets with a rivet of three different hardnesses: 350HV1, 400HV1, and 420HV1, the largest surface deviations of the sheets were observed for the connection with the 350HV1 rivet hardness. Increasing the hardness of the rivet from 350HV1 to 400HV1 and 420HV1 resulted in a reduction in sheet deviations. The deviations for the largest distance from the rivet axis in the case of the 400HV1 and 420HV1 rivet hardness were at a similar level. The highest value of the interlock parameter, which determines the joint load capacity, was obtained for the rivet with the highest hardness value (420HV1). The highest joint load capacity was obtained when using a rivet with a hardness of 420HV1 and the lowest for the rivet hardness of 350HV1.

Mixed-mode I/II fracture performances of glued laminated bamboo in the in-plane longitudinal direction

Considering that glued laminated bamboo components usually fail because of the longitudinal cracks under combined tensile/shear loading, mixed-mode I/II fracture tests were conducted on two kinds of glued laminated bamboo boards in the in-plane longitudinal direction by Arcan test method: laminated bamboo lumber (LBL) with thick-layer unidirectional-arranged bamboo strips and glued laminated bamboo (glubam) with thin-layer bidirectional-arranged bamboo strips. on the basis of Wu criterion for mixed mode fracture of wood, the mixed-mode I/II fracture envelops of LBL and glubam are constructed by curve fittings on the calculated fracture toughness components and the pure mode-I and mode-II fracture toughness. The results show that the small quantity of transverse bamboo fibers change the fracture mode in the in-plane longitudinal direction from short and quick matrix-dominated brittle failure of LBL specimens into long and slow fiber and matrix-dominated quasi-ductile failure of glubam specimens. In response to the in-plane longitudinal crack, only 1:4 of transverse fibers to longitudinal fibers can provide about 6 times of the pure mode-I fracture toughness, 1.4 times of the pure mode-II fracture toughness and more than 6.5 times of the area within the mixed-mode I/II fracture envelope.

Experimental and numerical characterization of adhesive joints with composite substrates by means of the Arcan test

An experimental and numerical investigation on adhesive joints subjected to three different loading conditions (pure shear, combined shear-tensile load and pure tensile) has been carried out through the Arcan test. The aim of this work is to investigate the effect of compliant substrates on the mechanical performances of the adhesive. Differently from traditional Arcan tests, where highly rigid substrates are used, U-shaped specimens made of carbon prepreg, final thickness 1 mm and 2 mm, have been bonded with a stiff epoxy and polyurethane adhesives. Nonlinear finite element analyses were performed to assess the stress state in the adhesives obtained by the experimental tests and showed a good correlation with the experimental results. In particular, the shear and tensile tests with the thicker substrates were used to determine the properties of the adhesives, while the 45° loading case combined with the thinner substrate results were used for validation. Results show that the compliance of the substrates significantly affects the fracture propagation of both adhesives in Mode I, as well as the maximum load of the epoxy-based joint for all the loading conditions. The results suggest that the Arcan test is suitable for the complete characterization of this type of adhesive joints.

The interaction of loading mode and humidity on the properties degradation of an epoxy adhesive subjected to strength, fracture, and fatigue tests

AbstractHygrothermal aging has a significant impact on the performance of adhesives and bonded joints. However, despite extensive investigations into the aging effect of bonded structures, there is still limited knowledge on how aging affects joint performance as a function of the loading type and the load angle. Accordingly, in this study, an epoxy adhesive was tested under different loading types/angles including tensile and shear standard strength tests, mode I and mode II fracture tests, and fatigue and static Arcan tests. All these experiments were performed for both aged and unaged conditions. To understand the influence of loading angle on the failure response of aged bonded joints, Arcan samples were subjected to mixed mode loading conditions as well. A fractography analysis was conducted to provide a better understanding of the failure mechanism of aged samples loaded at different modes. Based on these results, it was found that mode I (tensile loading conditions) is more sensitive to the aging conditions than mode II (shearing) for all loading types (strength, fracture, and fatigue tests). The influence of moisture on fracture toughness was however less relevant than the strength. The results also showed that for the same loading mode and for the same Arcan joints, the fatigue strength is significantly more degraded by the aging conditions than the static strength.

Modelling edge effects at the interface in bonded joints using gradient functions in the mechanical properties of the adhesive: Application of the method to the Arcan test loaded in tension and shear

The design of bonded joints requires studies of stress concentrations due to edge effects. For complex joint configurations, the finite element method can be quite costly. The objective is to develop a fast and reliable numerical design tool for bonded assemblies. Therefore, an approach to design bonded assemblies is presented which aims to meet the needs of a design office, particularly in terms of calculation costs. The latter consists in reproducing the edge effects with a single element through the joint thickness using a modulus function. The concept was tested on Arcan specimen with two loading cases: tension (γ = 0°) and shear (γ = 90°). A 2D model under the elastic assumption is developed to describe the edge effects of the joint using Abaqus subroutines (UMat). The approach is set up to solve this problem in the form of two blocks. First, mesh refinement studies for bonded specimens loaded in tension were performed, within a good level of accuracy, on the free edge with the use of local discretization error estimation. After that, the effects of local geometry and modulus ratio are investigated. Afterwards, the von Mises stress at the interface level of the adhesive joint was used to identify a modulus function to describe the behavior of a joint with straight edge geometry for tension and shear loadings. The proposed approach has improved the performance of the model. Actually, the calculation is practically three times faster than for the conventional model.

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.

Ductile crack propagation path depending on material properties: Experimental results and discussions based on numerical simulations

To ensure the structural integrity of advanced thin sheet metals in engineering applications, it is necessary to understand their ductile crack propagation behaviour. In this work, we clarified the governing factors for ductile crack propagation paths in sheet metals by the comprehensive investigation with experimental and numerical approaches. Using two types of sheet metals, a steel and an aluminium alloy, experiments with Arcan tests were performed, and the difference in the crack paths were observed and analysed. The strategy for simulating ductile fracture proposed by the authors was successfully validated with the experimental Arcan test results, and it was applied to a parametric study based on the numerical simulations for clarifying the governing factors for ductile crack propagation paths in sheet metals. The two factors, strain hardening ability and ductility diagram parameter, were confirmed to be dominant in controlling the ductile crack propagation. The findings in the parametric study explain the difference of the crack paths as observed in the experimental Arcan tests for the two materials, thus elucidating the inverse design philosophy that facilitates material design to achieve desired performance metrics in enhancing the integrity of engineering structures.

Failure Locus of an ABS-Based Compound Manufactured through Photopolymerization.

This work investigates the critical plastic strain variation with stress triaxiality and the Lode angle parameter for an Acrylonitrile butadiene styrene (ABS)-based proprietary blend compound (commercial name VeroWhitePlus™ RGD835) manufactured through photopolymerization. Various triaxial states of stress and Lode angles were obtained with the help of notched flat specimens used in tensile loadings, notched round specimens used in compression (upsetting) tests and butterfly specimens used in Arcan tests. The tests were replicated using finite element analyses in order to evaluate the aforementioned parameters.

Assessing shear, tensile and fracture properties of macroporous nanocomposites using the Arcan test

Macroporous polymers and nanocomposites remain popular materials due to their low densities and unique interconnected pore structures. The determination of mechanical properties in relevant loading conditions, such as shear, remains largely underexplored due to the comparative complexity of such analysis compared to simple compression tests. We investigated the use of the Arcan test to induce uniform biaxial stress in such materials and provide insight into the effect of porosity and silica particle reinforcement on shear properties and fracture toughness of high/medium internal phase emulsion templated macroporous polymer nanocomposites, called polyHIPE/MIPEs. Increasing foam densities were associated with greatly improved tensile and shear properties. Improvements in shear strength and modulus were also noted in polyMIPEs reinforced with as little as 5 wt.% silica nanoparticles, although any increase in tensile properties was lacking. Fracture toughness was investigated using an assumed Poisson's ratio. Decreasing the porosity of macroporous polymers and increasing particle loading resulted in considerable improvements in fracture toughness. These results illustrated the potential of the Arcan test as a simple and effective method for investigating otherwise rarely reported loading conditions in macroporous polymers and nanocomposites.

Hybrid experimental-numerical strategy for efficiently and accurately identifying post-necking hardening and ductility diagram parameters

Although various effective models for simulating ductile fracture in metallic materials have been established, the methods to identify the required parameters have scarcely been clarified. The difficulty for parameters identification of ductile fracture models is the actual bottleneck for accurate numerical predictions in ductile fracture simulation. In this paper, a strategy to efficiently identify the post-necking strain behaviour and the ductility diagram parameters is proposed by a hybrid experimental-numerical procedure. In the proposed strategy, only two types of experiments are required: a conventional tensile test and a crack growth test. All the parameters to simulate the post-necking strain hardening behaviour and the ductile fracture can be uniquely identified via numerical optimisations using load-displacement curves of the two tests. The proposed strategy was applied to an A2024T3 aluminium alloy and the post-necking hardening and ductility diagram parameters were identified by a flat tensile test and an Arcan test. Two types of plate specimens with a hole were then used to validate the proposed strategy. Good agreements between the experimental results and the numerical predictions clearly show the feasibility and accuracy of the proposed strategy. The results demonstrated that the proposed strategy is simple but effective. Therefore, it can be a general basis for characterising mechanical properties of various metallic materials.

Fracture characterization of bonded composites: A comparative study

Bonded joints have important benefits over conventional joining techniques such as rivets, welding, bolts and nuts in structural applications, particularly for components prepared of composite or polymeric materials. Due to the involvement of many geometric, material and construction variables, and the complex fracture and mechanical modes offered in the bonded joints, a proper consideration of fracture behavior is required to fully achieve their benefits. The fractures in bonded joints are mainly of three types; interlaminar (delamination), adhesive (interfacial) and cohesive crack. For a particular defect, crack propagation may occur in the tensile (mode I), the shear (mode II), and the tear (mode III) and their combinations (mixed mode). This study deals with topics such as theories of bonded composite joints and repairs, finite element analysis and fracture-based analysis and tests of mixed-mode cohesive, interfacial and interlaminar fracture mechanics. By employing geometrical factors extracted from finite element analysis and experimental results obtained from a modified Arcan test fixture, the mixed-mode cohesive, interfacial, and interlaminar fracture toughness are determined and fracture surfaces obtained are discussed.

Fatigue life evaluation of adhesive joints in a real structural component

The aim of this work is to study how well fatigue life predictions, based on Arcan tests results, apply to real joint with a complex geometry, used as a structural component in industrial vehicles. Using a stress-life approach, a master stress-life curve for fatigue was constructed. By utilizing the master curve, fatigue life predictions were made for the joints and compared with the welded assembly. Experimental fatigue tests were performed to verify the predictions. The results agreed with the fatigue life predictions. It was concluded that adhesive bonding is a suitable alternative to welding in terms of longevity.

Experimental analysis of orthotropic strength properties of non-crimp fabric based composites for automotive leaf spring applications

We investigated the feasibility of a transversely isotropic approach to assess the strength properties during the design of a composite leaf spring. A modified Arcan test setup was developed to test the strength properties of the used non-crimp fabric based material in all orthotropic directions. Through comparisons with standardized coupon test methods for fiber-reinforced materials, a notch stress factor for tensile and shear load was derived. Our results indicate that fabric influences the material’s strength, and the assumption of transverse isotropy behavior is invalid. The measured transverse tensile strength was lower by a factor of 2.2 in the out-of-plane direction than in the in-plane direction, possibly leading to a lower resistance of leaf springs against delamination. Process induced differences did not significantly affect the measured strength in the tested directions. These findings will be useful in developing leaf springs with increased fatigue resistance.

Effects of delamination in drilling glass/polyester composite

Considering failures during machinery processes such as drilling, a precautionary analysis involving delamination and the corresponding dissipated energy is required, especially for composite structures. In this context, because of the complexity of both the analysis procedure and experimental test setup, most studies prefer to represent mode I and III interlaminar crack propagation instead of that involving mode II. Therefore, in this study, the effect of mode II delamination and corresponding interlaminar crack propagation was considered during the drilling process of multilayered glass/polyester composites using both numerical and experimental approaches. In the experimental procedure, the mechanical properties of the glass/polyester specimens were obtained according to ASTM D3039. In addition, the interlaminar mixed-mode (I/II) loadings were determined using an ARCAN test fixture so that the fracture toughness of glass/polyester could then be identified. The mode II critical strain energy release rate (CSERR) was then obtained using an experimental test performed using an ARCAN fixture and the virtual crack closure technique (VCCT). It was determined that the numerical approach was in accordance with the experiments, and more than 95% of crack propagation could be attributed to mode II compared to the two other modes.

Determination of the Shear Modulus of Pine Wood with the Arcan Test and Digital Image Correlation.

Arcan shear tests with digital image correlation were used to evaluate the shear modulus and shear stress–strain diagrams in the plane defined by two principal axes of the material orthotropy. Two different orientation of the grain direction as compared to the direction of the shear force in specimens were considered: perpendicular and parallel shear. Two different ways were used to obtain the elastic properties based on the digital image correlation (DIC) results from the full-field measurement and from the virtual strain gauges with the linear strains: perpendicular to each other and directed at the angle of π/4 to the shearing load. In addition, the own continuum structural model for the failure analysis in the experimental tests was used. Constitutive relationships of the model were established in the framework of the mathematical multi-surface elastoplasticity for the plane stress state. The numerical simulations done by the finite element program after implementation of the model demonstrated the failure mechanisms from the experimental tests.

Damage Mechanism Evaluation of Polymer Matrix Composite Reinforced with Glass Fiber via Modified Arcan Test Specimens

Damage mechanism evaluation of polymer matrix composites reinforced with glass fibers via Arcan test has become a very vital research area for determining the weak part of composite structures in aircraft segments. So, the objective of the present article is to study the effect of changing different load angles as: α = 0°, 15°, 30°, 45°, 60°, 75°, and 90° of unidirectional glass-fiber-reinforced polymer matrix composite specimens by Arcan test. In this study, modified Arcan test specimens (butterfly shaped) are used to study the mechanical properties and the resulting fracture mode of unidirectional glass-fiber-reinforced polymer matrix composite under combined tension and shear stresses. Two cases of applied Arcan test specimens of unidirectional glass-fiber-reinforced polymer matrix composite specimens were evaluated: (1) notch-to-notch perpendicularly oriented fiber specimens are referred to as group A1, and (2) notch-to-notch longitudinally oriented fiber specimens are group A2. The results revealed that the shear modulus of A1 specimens is found to be G12 = 5.5 GPa ± 18%, which is close to the value calculated using the elastic properties of the composite components. On the other hand, the shear modulus of A2 specimens is found to be G21 = 4.2 GPa ± 8%, which is relatively close to calculated G23 value. It is observed that the fracture mode of A2 specimens is almost not affected by the loading direction. However, the number of cracks and its direction relative to the notch-to-notch line decreases as the test angle increases. Moreover, the strength of A1 specimens is much higher than that of A2 specimens at all applied loading angles, except for pure shear loading.