Tensile Test Rig Research Articles

Microscopic damage behavior in CFRP cross-ply laminates at cryogenic temperature

For the practical use of cryogenic propellant tanks made of CFRP laminates, experimental elucidation of the laminates’ microstructural damage propagation behavior at cryogenic temperatures is important. This paper presents a newly developed tensile test rig that enables in-situ observation of microscopic damage using an optical microscope at cryogenic temperatures using a Gifford–McMahon refrigerator. In-situ observations of microscopic damage under uniaxial tensile loading were done at room temperature (290 K, 17 °C) and at 30 K (−243 °C) on cross-ply thin-ply CFRP specimens of three kinds with different 90° layer thicknesses. The results demonstrated that the crack propagation behavior is independent of temperature, that the matrix crack density is higher, and that the onset of matrix crack initiation strain is lower at 30 K than at 290 K. Furthermore, the thermal strain within 90° layer at 30 K and at 290 K was estimated using finite element analyses (FEA). The FEA results suggest that the decrease in onset strain of matrix crack initiation at 30 K is mainly attributed to the increase in the thermal strains within the 90° layer.

In situ X-ray tomography study on internal damage evolution of solid propellant for carrier rockets

Nitrate Ester Plasticized Polyether (NEPE) propellant has been widely used for carrier rockets. However, the propellant is usually subjected to complex loads, changing the microstructures, which eventually affects its structural integrity. To elucidate the damage mechanism of the propellant, an in situ tensile testing rig with a maximum strain rate of 0.1 s−1 was developed with high-resolution synchrotron X-ray tomography. The internal microstructure and the resultant damage evolution have been characterized quantitatively. The mechanical behaviour of sampled propellant was extracted from the dynamic mechanical analysis. In addition, numerical simulation in terms of the spatial geometry of filler particles was performed in the framework of the micromechanical approach. To visualize the debonding process, a cohesive-zone model was employed to trace the debonding at the filler/matrix interface and then the damage evolution was characterized according to the cohesive behaviour. The results can assist in correlating the cohesive behaviour due to local heterogeneity with the macroscopic mechanical response for the NEPE propellant.

Influence of the Ductility Exponent on the Fatigue of Structural Steels

Fatigue models using the strain-life method do not show exact conformity with the empirical results. Therefore, the use of the mean-stress correction approach is to be evaluated, with a particular focus on mild and higher-strength steel. The influence of the ductility parameters will be studied. A potential favorable development of structural steels with regard to ductility will be checked. The paper will focus on two types of structural steel: S355 and S700. Initially, the mechanical properties of the steel test specimens were measured via a tensile testing rig. In addition, a fatigue test was carried out by applying various mean-stresses. Surface roughness was measured at the notch and introduced into the initial model. The strain amplitudes were determined using the Ramberg-Osgood and Masing material models. Subsequently, a curve fitting was applied to the strain-life data for the fatigue ductility exponent. The multiparameter model was fitted with only one parameter. The resulting model showed a good fit between the strain-life curve and the test results. During the course of the optimization, the error and the scatter were calculated separately for steel types S355 and S700. Based on the ductility exponent, a favorable behavior of the materials was determined.

Evaluation of Buckling of 2024-T3 under High Temperatures

The mechanical and buckling behavior of AA 2024 – T3 at high temperatures has been presented. The material was examined by thermal tensile test rig with 400℃ capacity. While buckling tests were carried out using a thermal rotating buckling test machine. Several observations were drawn from the experimental results, such as the mechanical and buckling properties are reduced by application of high temperatures. The experimental results of (UTS), (YS), (BHN) and (E) were decreased by 13.77%, 19.76%, 28.8% and 24.65% respectively due to application of 250c comparing to that at room temperature. The critical buckling load (Pcr) is increased when the column length and (SR) are reduced. The critical buckling load (Pcr) results were reduced from 910N to 610N when the applied temperature increased from (RT) to 250℃. Therefore, using a high temperature true of 250℃ gives a reduction percentage of 33% in critical buckling load result. The estimation of Euler theory was overestimated the buckling properties, but when using a safety factor the estimation seems to be resemble.

Evaluation of aluminum to composite bonded lap joints

Adhesive bond is one of the best suitable joining technique for fiber reinforced polymer (FRP) composite structures used in aerospace applications. The weight of the composite structure greatly reduces by using structural adhesives for the joining processes. The surface preparation plays a major role for achieving the better bond strength. The present work deals with the validation of the bond strength of single lap joint(SLJ) with dissimilar adherends. The Al adherend has been considered for the surface treatments such as sand paper, NaOH and Resin pre-coating (RPC) for SLJs. The angle of contacts for the different surface treated specimens has been measured using the Young–Laplace method. X-Ray radiography and ultrasonic testing has been carried to verify the internal defects of bonded joint. The bonding strength was evaluated using a tensile and flexural test rig in polymer UTM. The bond strength of the RPC surface treated bonded joints showed better performance in terms of peak load and shear strength. The maximum shear strength has been increased up to 154.63 percentage when compared to untreated surface specimens, similar trend was observed in flexural strength. A numerical simulation model has been developed for validating the results. The comprehensive analysis for the de-bonded joints at maximum loading conditions has been done with morphological studies.

Forming analysis and process study for a 6082 aluminum alloy automobile control arm in the process of forging

To reduce the weight of vehicles and save on fuel consumption, the forming analysis and process study for a 6082 aluminum alloy automobile control arm were conducted, and the results are reported here. First, the parameters of the constitutive equation of the 6082 aluminum alloy are determined, and the forming process and the dies of the stretch rolling, bending, and die-forging are proposed and discussed according to the given contours of the control arm. Then, the control arm is simulated by means of Deform-3D, the experiment results of the automobile control arm are compared with the simulation results, and the tensile strength, yield strength, and elongation of the test bars obtained from the control arm can meet the mechanical performance requirements based on the tensile test rig. Finally, the relationship of the die load, die wear, workpiece damage, and workpiece equivalent stress with different processing parameters are analyzed, and the effects of different solid solution times on the strength of control arm are discussed. The results show that when the friction coefficient is 0.3, the die temperature is 250°C, the forging velocity is 230 mm/s, the strain rate is 1s−1 and the solid solution time is 30 min, the die load, die wear, workpiece damage, workpiece equivalent stress, and the mechanical strength are then in a good state. The results of this research provide a reliable basis and analysis method for the forging of aluminum alloy automobile control arms.

High throughput mechanical testing platform and application in metal additive manufacturing and process optimization

Agility of additive manufacturing (AM) warrants a development of an equally agile, high-throughput properties evaluation technique that can efficiently assess properties of AM specimens as functions of materials and process variables. High throughput (HTP) tensile testing rig has been developed, enabled by miniature sample design and Python based control codes for a full automation of testing and data processing. The rig is capable of testing 60 specimens per hour, much faster than conventional tensile testing. To luminate the merit of its use, an efficient process optimization workflow based on HTP testing is proposed and demonstrated on laser powder bed fusion (LPBF) built stainless steel 316 L. A total of 40 miniature specimens were built with various LPBF parameters (i.e., power and scanning speed) by design of experiment (DoE) incorporating 2 factors, 3 levels, and 4 repeats. Ultimate tensile strength (UTS) and elongation at fracture (EL) were used to study sensitivity of processing parameters. An analytical model was employed to optimize the LPBF parameters to maximize UTS or EL or both. In addition, the as-printed microstructure and post-testing fracture surfaces were examined by optical and scanning electron microscopy. Rapid assessment of properties enabled to efficiently optimize the AM processing parameters, and to establish a more robust processing-structure-property relationship, which would ensure and promotereliable application of AM components.

High throughput testing platform and application in wire arc additive manufactured superalloy: Anisotropy investigation and component qualification

The rapid development of additive manufacturing requires quick and cost-effective testing techniques for efficient materials, process, and product qualification. In this study, a high-throughput (HTP) tensile testing rig with capability of automatically testing 60 specimens per hour is developed, which is orders of magnitude faster than traditional one-at-a-time tensile testing. The HTP testing was utilized to investigate the anisotropy and intrinsic scattering of the mechanical properties for superalloy IN617 manufactured by wire arc additive manufacturing (WAAM), in an effort to qualify the WAAM process and an actual component. 120 samples were extracted from WAAM-built qualification bulk at 3 heights (bottom, middle, and top) and 2 orientations (Y and Z) and 40 samples were extracted from a load collar (an actual gas turbine component) for HTP testing. This large dataset was statistically analyzed and revealed that the Z-direction had significantly higher elongation than Y-direction, but slightly lower ultimate tensile strength. Intrinsic scattering in the Y-direction was higher than in the Z-direction and increased with height, which agreed with microstructure variations examined by optical microscopy and scanning electron microscopy (SEM). It was concluded that the WAAM process and product met the internal design requirements with the consideration of the anisotropy and intrinsic scattering of tensile properties. Qualification requirements of AM material, process and components, and potential applications of HTP testing are also discussed.

Non-linear material characterization of CFRP with FEM utilizing cohesive surface considerations validated with effective tensile test fixturing

Modelling the effect of fibre orientation in carbon fibre reinforced plastic (CFRP) on mechanical behaviour is critical for component design and manufacturing process optimization. The objectives of this paper are to simulate the mechanical properties of CFRP to fracture and design a tensile test rig that could induce fracture at the specimen gauge section consistently. Finite element solver ABAQUS Explicit was used to simulate the effects of mass/time scaling, different failure models and cohesive surfaces. Failure models evaluated were Hashin, MCT, LaRC02, maximum strain, Tsai-Wu, Tsai-Hill, Christensen and Puck. The fibre orientations investigated were parallel, 45° and perpendicular to the tensile loading condition. Extensive design of the tensile test rig was briefly described. Experimental results showed that with the newly designed test rig, the failure occurred in the gauge region, regardless of the fibre orientation. When the fibre orientation was parallel to the tensile load, all the failure models show similar rate of force increment with respect to displacement. Puck's failure model most accurately predicts the fracture force and displacement versus experimental data. With fibre orientations at 45° and 90°, the maximum strain and LaRCO2 failure models were more suitable in terms of accuracy and simulation convergence. Incorporating cohesive surfaces between instances to predict nonlinearity in the loading response is critical. Significant reduction in failure force was predicted when test was setup at angles between parallel to 45°. The model was capable of predicting the effects of fibre orientation and laminate thickness on fracture force agreeing with published experimental results.

Plastic flow anisotropy drives shear fracture

Fracture of initially crack-free bodies often occurs due to plastic instabilities known as shear bands. Previous computer simulations advanced a myriad of mechanisms to rationalize shear banding. However, they were restricted to planar geometries. We investigate the relevance of anisotropic plasticity by picking an axisymmetric tensile test rig, in which shear localization is rarely observed. The three-dimensional finite-element simulations of shear banding in this type of specimens are the first of their kind. The micromechanical modeling covers a range of competing mechanisms believed to be responsible for such failure. We show that anisotropic plasticity can effectively trigger shear bands thereby causing failure of ductile solids. Our results enable shear fracture to be rationalized in ductile rocks and mitigated against in designing advanced materials.

Assessment of Wear Form Weights in the Fretting Wear of Spline Couplings with BP Neural Network

This paper investigates the fretting wear behavior of spline couplings under grease and oil lubrication conditions, which includes coupling eccentricity measurement and wear intensity measurement at a tensile test rig. Mechanism analysis of worn splines was also studied to understand the wear forms of the tested splines. Firstly, the wear intensities of spline couplings DIN 5480 45×2×21 8f/9Hlubricated with grease Gleitmo 805 and ISO VG 320 gearbox oil Mobilgear XMP 320 were measured. Test results showed that the wear intensity reduced rapidly in the running-in phase till 3-5×106 load cycles (rotations), depending on the lubrication conditions. After that the spline couplings had a stable wear behavior till 10×106. Secondly the influences of lubrications on splines wear intensities and wear mechanism were studied. It indicated that the spline with grease lubrication had best wear behavior in comparison with oil and not lubricated ones. Finally, a fretting wear intensity calculation method which integrated the weights of adhesive wear, abrasive wear and oxidation wear was developed to calculate the wear intensity of splines.1 BP neural network model was employed for assessment of the weights of each wear form. The BP results showed that mixed adhesive, abrasive and oxidation wear happened in the tested spline couplings, which was verified through chemical composition analysis of the spline teeth faces after different load cycles. The calculated fretting wear agreed well with the tested value, indicating that the developed fretting wear intensity calculation model including wear form weights evaluated via BP neural network simulation had high accuracy on predicting the fretting wear of involuted splines.

Underwater acoustic emission monitoring – Experimental investigations and acoustic signature recognition of synthetic mooring ropes

Mooring ropes are essential components of offshore installations, and synthetic ropes are increasingly preferred because of their favourable cost to weight ratios. In-service condition of these materials is traditionally monitored through costly visual inspection, which adds to the operating costs of these structures. Acoustic Emissions (AE) are widely used for condition-monitoring in air, and show great potential underwater. This paper investigates the AE signatures of synthetic mooring ropes subjected to sinusoidal tension-tension loading in a controlled environment, using a large-scale dynamic tensile test rig. With a linear array of 3 broadband (20Hz to 50kHz) hydrophones, four main signatures are identified: low-to high frequency, low-amplitude signals (50Hz to 10kHz), low-amplitude broadband signals (10kHz to 20kHz), high amplitude signals (10Hz to 48kHz) and medium-amplitude signals (500Hz to 48kHz). These AE types are related to different stages of rope behaviour, from bedding-in to degradation and failure. The main findings are that the failure location and breaking load can be identified through the detection of AE. The occurrence of high amplitude AE bursts in relation to the applied tensile load allows the detection of an imminent failure, i.e. prior to the failure event. These initial results indicate that AE analyses can enable the integrity of synthetic mooring ropes to be monitored.

In situ measurement of pipeline coating integrity and corrosion resistance losses under simulated mechanical strains and cathodic protection

A novel experimental assembly consisting of a specially designed tensile testing rig and a standard electrochemical flat cell has been designed for simulating buried high pressure pipeline environmental conditions in which a coating gets damaged and degrades under mechanical strain, and for studying the influence of mechanically induced damages such as the cracking of a coating on its anti-corrosion property. The experimental assembly is also capable of applying a cathodic protection (CP) potential simultaneously with the mechanical strain and environmental exposure. The influence of applied mechanical strain as well as extended exposure to the corrosive environment, coupled with the application of CP, has been investigated based on changes in electrochemical impedance spectroscopy (EIS). Preliminary results show that the amplitude of the coating impedance decreases with an increase in the applied strain level and the length of environmental exposure. The EIS characteristics and changes are found to correlate well with variations in coating cracking and degradation features observed on post-test samples using both optical microscopy and scanning electron microscopy. These results demonstrate that this new experimental method can be used to simulate and examine coating behaviour under the effects of complex high pressure pipeline mechanical, electrochemical and environmental conditions.

Ductile to brittle failure transition of HSLA-100 Steel at high strain rates and subzero temperatures

Mechanical properties of HSLA-100 steel at room and subzero temperatures of −40°C, −80°C and −196°C were investigated in this work. Dry ice and liquid nitrogen were used to reach the low temperatures. Also, the material response to different strain rates was studied. Quasi-static tensile test rig and tensile Hopkinson split bar were employed to carry out the experiments. Furthermore, fracture behavior and the transient temperature of this steel was investigated using the curve of stress triaxiality factor (P/Y) against true fracture strain (εf) using Bridgman equation. In addition, fracture mechanisms for this steel at different testing conditions were studied. Finally, SEM observations were performed to back the results found in this research. The results indicated that the material behavior at room temperature to −40°C was quite ductile regardless of the strain rate level. Fracture mechanism transition from ductile to brittle occurred at −80°C. For −196°C, the material behavior was completely brittle for high strain rate and entirely ductile for lower strain rates. It was also found that the yield stress of material progressively increased with the decrease of temperature and the increase of strain rate. The maximum increase was 160% and occurred for −196°C at the strain rate of 10,800s−1.

Mechanical Behavior of Composite Multilayered Basalt/E-Glass/Epoxy Pipe under Internal Pressure

Pressurized composite pipes made of concentric fiber reinforced polymer layers have found much interest among researchers. These composite pipes possess mechanical and thermal properties that exceed those of their constituent materials. This development is motivated by the demand for corrosion resistant, lighter and high specific stiffness components. Natural fiber composite materials retain better flexural stiffness and are environmentally friendly. Unlike experimental testing, numerical investigations on the manufacture and performance of natural fiber reinforced pipes under internal pressure seem lacking. In this analysis, the mechanical behavior of multilayer composite pipes made of natural basalt and E-glass fibers under internal pressure were carried out numerically. The multilayered composite pipes were fabricated by employing filament winding technique with, basalt and E-glass fibers, with fiber orientation angles of ±45o, ±55o, ±65o, ±75o. The matrix epoxy resin was infused using vacuum infusion process (VIP). A longitudinal and hoop tensile test rig, designed and fabricated according to ASTM D2105 and D2299 respectively, was used to determine the hoop and longitudinal properties of the pipes. Numerical simulations were conducted to determine the stress and strain behaviors with the intention to find the effect of ply angle, basalt and glass properties and also to evaluate the performance of the new natural basalt fiber as an alternative to E-glass/Epoxy.

A Novel Experimental Design to Obtain Forming Limit Diagram of Aluminium Alloys for Solution Heat Treatment, Forming and In-Die Quenching Process<sup></sup>

Solution heat treatment, forming and in-die quenching (HFQ) is a patented process to form complex shape metal components at a high efficiency and a low cost. Conventional experiment approaches to determine forming limit curves (FLCs) at different strain paths are not applicable for the HFQ forming process. A novel biaxial tensile test rig is designed to overcome the difficulties and determine the FLCs at high temperatures based on the commercial Gleeble machine. This test device employs the circle plate and connecting rod mechanism in order to achieve different strain states, such as uniaxial tension, plane strain and biaxial tension. Resistance heating and air cooling are adopted to obtain an isothermal environment and to control cooling rates in Gleeble respectively. The designs of the cruciform specimen for this test are also introduced in this paper.

Mechanical Property of HVOF Inconel 718 Coating for Aeronautic Repair

The module of elasticity is one of the most important mechanical properties defining the strength of a material which is a prerequisite to design a component from its early stage of conception to its field of application. When a material is to be thermally sprayed, mechanical properties of the deposited layers differ from the bulk material, mainly due to the anisotropy of the highly textured coating microstructure. The mechanical response of the deposited layers significantly influences the overall performance of the coated component. It is, therefore, of importance to evaluate the effective module of elasticity of the coating. Conventional experimental methods such as microindentation, nanoindentation and four-point bending tests have been investigated and their results vary significantly, mainly due to inhomogeneous characteristics of the coating microstructure. Synchrotron radiation coupled with a tensile test rig has been proposed as an alternative method to determine the coating anisotropic elastic behavior dependence on crystallographic orientations. The investigation was performed on Inconel 718 (IN718) HVOF coatings sprayed on IN718 substrates. Combining these experimental techniques yield a deeper understanding of the nature of the HVOF coating Young’s modulus and thus a tool for Design Practice for repair applications.

The development of a high temperature tensile testing rig for composite laminates

This study aimed to develop a high temperature tensile test capable of testing fibre reinforced composites up to 1000°C, in order to understand the behaviour of certain composites at these temperatures and produce data suitable in the design of high temperature structures. The test design was assessed using finite element analysis before validating at ambient temperatures against conventional tensile test equipment. The chosen design achieved reliable tensile results and high temperature testing was then successfully conducted, using polysialate composite materials, establishing high temperature mechanical data which was previously unknown. The test setup and data achieved in this study are vital in the design of next generation high temperature structures.

An in situ tensile tester for studying electrochemical repassivation behavior: Fabrication and challenges

An in situ tensile rig is proposed, which allows performing electrochemical (repassivation) experiments during dynamic mechanical testing of wires. Utilizing the basic components of a conventional tensile tester, a custom-made minitensile rig was designed and fabricated. The maximal force that can be measured by the force sensor is 80 N, with a sensitivity of 0.5 mV/V. The maximum travel range of the crosshead induced by the motor is 10 mm with a minimum step size of 0.5 nm. The functionality of the tensile test rig was validated by investigating Cu and shape memory NiTi wires. Wires of lengths between 40 and 50 mm with varying gauge lengths can be tested. An interface between wire and electrochemical setup (noncontact) with a smart arrangement of electrodes facilitated the electrochemical measurements during tensile loading. Preliminary results on the repassivation behavior of Al wire are reported.

Determination of the high strain rate fracture properties of ductile materials using a combined experimental/numerical approach

The ‘flying wedge’ is a dynamic tensile test rig for determining the fracture properties of ductile materials over a range of strain rates from 102–104s−1. To accurately interpret the results from these tests, finite element simulations of the complete experiment as well as detailed models of the specimen subjected to different loading conditions are conducted using advanced materials constitutive relations. A new technique to carry out interrupted tensile testing at high strain rates on the flying wedge has been developed. Some typical results of the combined experimental and numerical technique are used to compare the predictions of different numerical ductile failure models which are also briefly reviewed in this paper.