Modified 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.

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.

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.

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.

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.

Calibration of the modified Mohr-Coulomb fracture model by use of localization analyses for three tempers of an AA6016 aluminium alloy

This paper presents a novel calibration procedure of the modified Mohr-Coulomb (MMC) fracture model by use of localization analyses and applies it for three tempers of an AA6016 aluminium alloy. The localization analyses employ the imperfection band approach, where metal plasticity is assigned outside the band and porous plasticity is assigned inside the band. Ductile failure is thus assumed to occur when the deformation localizes into a narrow band. The metal plasticity model is calibrated from notch tension tests using inverse finite element modelling. The porous plasticity model is calibrated by use of localization analyses where the deformation histories from finite element simulations of notch and plane-strain tension tests are prescribed as boundary conditions. Subsequently, localization analyses are used to establish the failure locus in stress space for proportional loading conditions and thus to determine the parameters of the MMC fracture model. Finite element simulations of notch tension and in-plane simple shear tests as well as two load cases of the modified Arcan test are used to validate the calibrated fracture model. The predictions by the simulations are in good agreement with the experiments, even though some deviations are seen for each temper. The results demonstrate that localization analyses are a cost-effective and reliable tool for predicting ductile failure, reducing the number of mechanical tests required to calibrate the MMC fracture model compared to the hybrid experimental-numerical approach usually applied.

Modelling-assisted description of anisotropic edge failure in magnesium sheet alloy under mixed-mode loading

An uncoupled fracture criterion based on a simple damage indicator computed using a mean-field crystal plasticity framework is proposed and applied to predict failure of an AZ31 sheet originating from the edges. The damage indicator quantifies the contribution of strain components along the axes of orthotropy leading to material failure. The model is calibrated by uniaxial tension tests. The damage indicator is validated for various mixed-mode deformation histories realized by modified Arcan tests in various loading configurations. The loading history of respective fracture sites obtained from DIC analyses is directly employed to a visco-plastic self-consistent crystal plasticity model to obtain the stress responses. The results indicate that the damage indicator requires – beside the strain history – an input of stress triaxiality, by which an improved predictive accuracy can be achieved. This effect is quantified for various loading scenarios, in which cracks are initiated near or at the edge of the sample.

A modified Arcan test for mixed-mode loading of bolted joints in composite structures

A novel modified Arcan test rig has been developed for testing the combined loading performance of bolted joints in composite laminates. The fixture was designed to complement existing bearing test standards (ASTM D5961) and pull-through test standards (ASTM D7332) for fastened joints in composite laminates. The new mixed-mode loading fixture fills a crucial niche, as interaction between pull-through and bearing failure modes can potentially reduce the overall joint performance and lead to anti-conservative designs.The test fixture was benchmarked against ASTM standards and was found to reliably reproduce pull-through failure behaviour observed during D7332-B testing. The comparison with D5961-B was less favourable, but the test specimens and configurations differ considerably. Work is underway to benchmark the new rig against D5961-C, which is a more comparable specimen configuration.Two mixed-mode test programs are reported in which joints were loaded at mixed-mode ratios between pure bearing and pure pull-through. It was found that the ‘failure’ load was well predicted by a quadratic mode-mixing rule. Conversely, the ‘maximum’ joint load was considerably over-predicted by a quadratic mode-mixing rule which could lead to anti-conservative predictions, particularly for dynamic systems in which joint damage is considerable.Based on the success of the preliminary testing, there is a strong case for further development and benchmarking of the new test fixture. There is scope for this fixture to be added to the suite of accepted test standards for bolted joints in composite structures.

The effect of laminate lay-up on the multi-axial notched strength of CFRP panels: Simulation versus experiment

The effect of laminate lay-up upon the evolution of damage and upon the multi-axial failure locus of notched carbon fibre reinforced polymer (CFRP) panels is investigated experimentally and numerically. The proportion of 0° plies and ±45° plies is varied, and combined tensile and shear loading (and direct compression) is generated by a modified Arcan test rig. The failure surface is measured for panels containing a central hole or sharp notch, and the evolution of sub-critical damage is observed by X-ray CT and sectioning of the specimens. Three distinct damage modes are evident, depending upon the applied stress state, lay-up and geometry of the stress-raiser. The open-hole and open-notch values of tensile and compressive strength increase with the proportion of 0° plies, whereas the shear strengths do not scale with the proportion of ±45° plies. Inter-fibre splitting of the main loading bearing plies reduces the stress concentration, but the degree of splitting varies with loading direction and lay-up. The Finite Element (FE) method is used to predict not only damage development within each ply but also inter-ply delamination by the use of cohesive interfaces using a traction-separation law. The predicted failure envelopes and damage evolution are in good agreement with the observations, provided the mesh aligns with the fibre direction. This supports the adopted ply-by-ply FE strategy as a useful predictive tool for composite failure.

A new method to measure the adhesion capability of the metallic surface under shear loading using a modified Arcan test

ABSTRACTThe single lap shear test is considered by carmakers as a standard test to control the adhesion of a bonded assembly. In some special cases, when thin steel surfaces are bonded to a structural toughened epoxy-based adhesive, interfacial failure could occur using this mechanical test. Understanding the contribution of the steel surface on the failure mechanisms using the single lap shear test is complex: heterogeneous distribution of stresses, contributions of edge effects, plasticity of the sheet metal, and stiffness of the specimen. It is very difficult to determine failure criteria using the single lap shear test for the interfaces.This work proposes a new method to measure the adhesion capability of the metallic surface under a well-controlled loading. The method is based on the modified Arcan test in shear loading which is adjusted to steel plates. Three different types of surfaces were characterised experimentally and numerically with different adhesion behaviours regarding their failure patterns. The new modified Arcan test is a suitable test to identify the properties of the interfaces in the bonded assemblies using strain and energy criteria.

Equivalent modelling strategy for a clinched joint using a simple calibration method

Clinching is a mechanical joining technique that involves severe local plastic deformation of two or more metal sheet parts resulting in a permanent mechanical interlock. Today, it is a reliable joining technique used in heating, ventilation and air conditioning (HVAC), automotive and general steel constructions whilst still gaining interest. As it is not computationally feasible to include detailed sub models of these type of joints in FE simulations of clinched assemblies during the design stage, this paper proposes a simple methodology to represent these connections with simplified elements. The key point of the method is the use of uncoupled plastic behaviour to model the joint plastic properties. In order to calibrate the parameters governing the equivalent model, a simple shear lap and pull-out reference test of a single clinched joint was used. The presented methodology is validated using a modified Arcan test of a single joint, which enables to exert a combination of shear and pull-out loads. Finally, a peel test is conducted to study the influence of bending moments on the behaviour of the joint.

Failure mode dependent load bearing characteristics of mechanical clinching under mixed mode loading condition

Abstract The purpose of this study is to investigate the failure mode dependent the load bearing characteristics of the mechanical clinching under the mixed mode loading condition. The joint strength of the mechanical clinched joint was determined by the geometrical interlocking shape parameters, such as the neck thickness and undercut. The load bearing tests under the pure normal and shear mode loading condition were carried out to investigate the influence of the geometrical interlocking shape parameters on the failure mode of the mechanical clinching and its joint strength by analytical approach. The Arcan test apparatus was modified to realize the mixed mode loading condition on the cross-tension specimen. For each angular positions(α=0,15,30,45,60,75,90° ), the failure mode and strength of the mechanical clinched joint was evaluated by the cross tension specimen with the modified Arcan test apparatus. Based on the experimental result, an analytical expression was derived to describe the joint failure criterion under the mixed mode loading condition.

Modeling strategy for clinched joints in assemblies

Clinching is a mechanical joining technique which involves severe local plastic deformation of two or more metal sheet parts resulting in a permanent mechanical interlock. Today, it is a reliable joining technique used in automotive, HVAC and general steel constructions whilst still gaining interest. As it is not computationally feasible to include detailed sub models of these type of joints in FE simulations of real-life clinched assemblies, this paper proposes a methodology to represent these connections with simplified elements. In order to calibrate the parameters governing the equivalent model, a simple shear lap and pullout test is used. This methodology is applied to clinched configurations and validated using a modified Arcan test in which both shear and pull-out loads are considered.

Analysis of the moisture effect on the mechanical behaviour of an adhesively bonded joint under proportional multi-axial loads

The objective of the study is to identify the 3D behaviour of an adhesive in an assembly, and to take into account the effect of ageing in a marine environment. To that end, three different tests were employed. Gravimetric analyses were used to determine the water diffusion kinetics in the adhesive. Bulk tensile tests were performed to highlight the effects of humid ageing on the adhesive behaviour. Modified Arcan tests were performed for several ageing times to obtain the experimental database which was necessary to identify constitutive models. A Mahnken–Schlimmer type model was determined for the unaged state according to a procedure developed in a previous study. This identification used inverse techniques. It was based on the unaged modified Arcan results and on a coupling between an optimisation routine and finite-element analysis. Then, a global inverse identification procedure was developed. Its aim was to relate the unaged parameters to the moisture concentration and overcome the difficulties usually associated with ageing of bonded assemblies in a humid environment: a non-uniformity of the stress state and a gradient of mechanical properties in the adhesive. This procedure was similar to the one used in the first part but needed modified Arcan results for several ageing times. It also required an initial assumption for the evolution of the Mahnken–Schlimmer parameters with the moisture concentration.

Determination of the 3D failure envelope of a composite based on a modified Arcan test device

This paper describes a 3D failure criterion identified through Arcan tests, to analyze the behavior of a laminate composite subjected to out-of-plane loadings. The proposed criterion is based on the Hashin’s hypothesis and the interactions between tensile and shear out-of-plane loadings are taken into account. The out-of-plane stresses generated in the composite subjected to an Arcan test are studied using 3D Finite Element calculations in order to determine the stack sequence influence. Using different angles of the loading and different stacking sequences allows the ply to be subjected to complex 3D stress state. Using the experimental results and an inverse identification procedure, it is possible to identify the out-of-plane failure envelope. It is shown that a quadratic failure envelope, which takes into account a decrease of the apparent shear strength in the presence of out-of-plane tensile stress, permits the model to describe in a correct manner the experimental results.

A stress concentration-free bonded arcan tensile compression shear test specimen for the evaluation of adhesive mechanical response

Adhesively bonded structures are increasingly used in the industry: aerospace, aeronautics, automotive and nautical fields. It is thus necessary to characterize the behavior of an adhesive in an assembly from an experimental point of view to a modeling one. The development of reliable models needs very good tests to define the performances of the adhesive used. The modified Arcan test developed by Cognard et al. is an interesting test. However it is difficult to use. The work presented in this paper deals with an evolution of this test called the Arcan Tensile/Compression–Shear Test (Arcan TCS). It simplifies the previous approach taking also into account the influence of the edge effects with the development of a new geometry of the beaks close to the adhesive. It is suited to apply tensile/compression–shear loadings to the adhesive. The test specimen proposed was designed and manufactured to improve the modified Arcan test without reducing the efficiency of the results also including an improvement of the bonding procedure. This new specimen is validated with finite element simulations and tested with an epoxy adhesive to determine the load–displacement behavior and the envelopes at failure.

Identification of the Elastic–Plastic Behavior of Adhesively Bonded Structures Under Multi-Axial Loadings: Comparison of a Modified Arcan Test and a Tension/Compression–Torsion Test

Structural bonding is nowadays widespread in the industry. However, characterisation methods and 3D modelling of the adhesives need to be improved. The characterisation requires an experimental procedure to obtain a large experimental database under various loading cases, which represents a significant amount of data. The 3D modelling requires advanced models with several parameters to identify and generally uses inverse identification procedures, which can be time expensive. For a good accuracy, the constitutive models need to take into account the dependency on the hydrostatic stress and be written under the non-associated formalism. In this study, the experimental database is obtained via a modified Arcan test that can cover a wide range of loadings between tension, shear, mixed tension–shear, and mixed compression–shear. A second experimental campaign is realized with a tension/compression–torsion (TCT) test that can cover a greater range of loadings: from tension to compression and mixed tension/compression–shear, with an infinite possibility of mixed loadings. The modified Arcan database is used to identify a 3D elastic–plastic Mahnken–Schlimmer type model, according to an inverse identification procedure developed in a previous study. This model identification is validated on the experimental database coming from the TCT test: a numerical/experimental comparison is realized. This allows the validation of the model and emphasizes the benefits of the TCT test. Indeed, it proves that this test is well suited to characterize adhesive joints and presents several capacities that will be really useful for further studies, like an infinite range of non-proportional loadings available.

Characterization and modelling of the viscous behaviour of adhesives using the modified Arcan device

The non-linear behaviour of an epoxy adhesive has been studied thanks to the use of a modified Arcan test device. Multilevel creep tests have been performed in order to characterize the time-dependent behaviour. A visco-elastic model has been chosen to describe the behaviour of the adhesive. This model is based on the decomposition of the visco-elastic strain into elementary viscous mechanisms. The non-linear behaviour of the visco-elasticity is taken into account thanks to a non-linear function which depends on the stress. A specific identification procedure based on a single test has been proposed. Finally, the model has been validated using tests that have not been used for the identification. The model proposed in this paper enables the time-dependent non-linear behaviour of adhesives to be reproduced in a correct manner.

A tension/compression–torsion test suited to analyze the mechanical behaviour of adhesives under non-proportional loadings

Structural adhesives are nowadays recognized to be an efficient alternative to traditional fastening methods, such as riveting or welding. However, their behaviour is complex, slowing down their spreading in the industry which requires reliable numerical models to predict their behaviour. Indeed, it is also well known that the dependency to the hydrostatic stress should be taken into account and the non-associated formalism should be considered. The identification of such models therefore requires a large experimental database under multi-axial loadings. To this end, a modified Arcan device was developed in a previous study. It enables the solicitation of an especially designed bonded sample under a wide range of proportional loadings between tension and compression–shear. A logical improvement is the development of a test that can complete the modified Arcan test by allowing loadings between compression–shear and compression as well as non-proportional loadings. This work focuses on the development of such a test: a tension/compression–torsion test. A finite element study of a specimen geometry well suited for the test was carried out. A great attention was paid to edge effects classical from adhesively bonded structures. As was done with the modified Arcan device, a geometry with beaks was proposed. The bonding device and the manufactured testing device are presented along with the first experimental campaign results which validate the test design.

Numerical Simulation of Ductile Fracture in Modified Arcan Test

In this study, the experimental results from a modified Arcan test on dual-phase steel are revisited in order to assess a numerical modelling approach for ductile fracture. This experiment is chosen since it displays a complex crack-path that undergoes three phases: fracture initiation and crack propagation with transition from Mode I to Mode II. A significantly larger amount of plastic dissipation is observed in the material at the point of fracture initiation compared to the material points along the crack-path. A numerical approach that is capable of capturing this complex crack-path is believed also to give good predictions in other complex fracture problems. The numerical simulations of the modified Arcan test are run with the nonlinear Finite Element (FE) code IMPETUS Afea Solver. Elements with tri-linear shape functions are utilized in combination with explicit time integration. The plastic behaviour of the material is modelled by the elastic-viscoplastic J2 flow theory using the Voce work-hardening rule. Both element erosion and node-splitting techniques are tested in order to simulate the crack propagation. It is shown that the node-splitting technique with a crack-tip enhancement gave the best prediction of the three different phases of the crack propagation.