Tensile Apparatus Research Articles

On the Dynamic Mechanical Characteristics of LIGA Nickel

The dynamic mechanical characteristics of LIGA nickel material are investigated by using a small split Hopkinson tensile bar apparatus (SSHTB). The strain rate related stress-strain curves of LIGA nickel are obtained and with which the dynamic mechanical characteristic parameters of LIGA nickel material under different strain rate are acquired. Meanwhile, the paper draws the conclusion that the dynamic mechanical characteristic parameters of LIGA nickel material increase with the increasing of strain rate by the experiment, which provides a theoretical basis for better application of LIGA nickel material under dynamic load conditions in Micro-electromechanical Systems (MEMS).

Dynamic tensile necking: Influence of specimen geometry and boundary conditions

This paper examines the effects of sample size and boundary conditions on the necking inception and development in dynamically stretched steel specimens. For that task, a coordinated systematic experimental–numerical work on the dynamic tensile test has been conducted. Experiments were performed using a tensile Kolsky apparatus for impact velocities ranging from 10 to 40m/s. Three different sample-gauge lengths – 7, 30 and 50mm – were considered for which the cross section diameter is 3.4mm. The experiments revealed that the specimens’ ductility to fracture depends on strain rate and sample length. Furthermore it was observed that, for those specimens having gauge lengths of 30 and 50mm, the necking location varies with impact velocity. Numerical simulations of the dynamic tensile tests were carried out in order to characterize the dynamics of neck inception and development. For each specimen calculated, three types of boundary conditions were used, all of which match the experimentally measured strain-rate. It was pointed out that, while boundary conditions hardly affect the calculated stress–strain characteristics, they strongly affect the wave propagation dynamics in the specimen thus dictating the necking location.

Mechanical characterization of epoxy moulding compound in pressurized steam

Epoxy Molding Compounds (EMCs), commonly based on epoxy resin, are used widely for encapsulation of chips in electronic devices for protection against mechanical, environmental, and chemical attack. The thermo-mechanical properties of these compounds are important for the assessment of package reliability. These properties are highly dependent on the temperature and moisture.EMCs absorb water when exposed to a humid environment. The trapped water generates steam in the compounds during the soldering reflow part of the packaging assembly process, which may drastically change the viscoelastic and adhesion behavior of the compound.The present research focuses on the characterization of mechanical properties of an epoxy molding compound in steam at elevated pressure (temperature above 100°C and relative humidity equal to 100%). A special steam chamber with a highly accurate tensile setup for force and displacement measurements is designed and manufactured. The chamber is equipped with a 3 Point Bending (3PB) loading setup. The setup can also be modified to mixed mode bending for investigating the effect of temperature and steam on the molding compound-to-lead frame interface strength.In this paper, the viscoelastic creep compliance of a molding compound in dry and wet environment is measured in 3 point bending mode. It is shown that steam significantly affects the thermo-mechanical properties of the molding compound. The glassy and rubbery modulus of the molding compound were seen to decrease almost by 20%. Furthermore the glass transition temperature decreased by about 30°C and the creep process was seen to be about a factor 40 faster in a hot steam environment.

Size-Dependent Bandgap Modulation of ZnO Nanowires by Tensile Strain

We quantified the size-dependent energy bandgap modulation of ZnO nanowires under tensile strain by an in situ measurement system combining a uniaxial tensile setup with a cathodoluminescence spectroscope. The maximal strain and corresponding bandgap variation increased by decreasing the size of the nanowires. The adjustable bandgap for the 100 nm nanowire caused by a strain of 7.3% reached approximately 110 meV, which is nearly double the value of 59 meV for the 760 nm nanowire with a strain of 1.7%. A two-step linear feature involving bandgap reduction caused by straining and a corresponding critical strain was identified in ZnO nanowires with diameters less than 300 nm. The critical strain moved toward the high strain level with shrunken nanowires. The distinct size effect of strained nanowires on the bandgap variation reveals a competition between core-dominated and surface-dominated bandgap modulations. These results could facilitate potential applications involving nanowire-based optoelectronic devices and band-strain engineering.

Digital Image Correlation in the Classroom: Determining Stress Concentration Factors with Webcams

In this study, we introduce graduate students to an experiment with digital image correlation (DIC). From an educational point of view, the aim is to get students familiar with basic aspects of stereovision and DIC, for example, speckle pattern, subset size, focus, aperture, etc. First, a homogeneous uniaxial tensile test is conducted on a rubber dogbone, allowing the determination of the hyperelastic stress—strain relationship. Next, a nondestructive 2D deformation test on a rubber specimen with a specific geometry is performed on a small tensile setup. At various load steps, images are captured with a low-cost webcam and are processed with our in-house DIC software which is available for each individual student. Assuming a Mooney—Rivlin material model based on the determined stress—strain data, one can derive stress concentration factors for the specific holes and notches present in the specimen. A comparison is made to analytical calculations of the stress concentration factors and eventually a finite element analysis of the experiment can be performed. In this way, a synergy between experiment, simulation, and theoretical calculations is achieved. Moreover, we have accomplished all stages in the engineering process of determination of material properties, simulation, and validation. The particular experimental setup is chosen to avoid the use of special equipment, for example, sophisticated tensile devices and expensive high-tech cameras, without losing the focus of the objective.

Recent developments in dynamic testing of materials

Three new testing configurations that have been developed since the last DYMAT conference in 2009 are presented. The first is high strain rate testing of Kevlar cloth and Kevlar yarn in a tensile Split Hopkinson Bar (SHB) apparatus. The Kevlar cloth/yarn is attached to the bars by specially designed adaptors that keep the impedance constant. In addition to determining the specimen’s stress and strain from the recorded waves in the bars the deformations are also measured with Digital Image Correlation (DIC). The second testing configuration is a high strain rate shear test for sheet metal. The experiment is done by using a flat notched specimen in a tensile SHB apparatus. The shear strain is measured using DIC within the notch and on the boundary. The third development is a compression apparatus for testing at intermediate strain rates ranging from 20 s −1 to 200 s −1 . The apparatus is a combination of a hydraulic actuator and a compression SHB. The stress in the specimen is determined from the stress wave in a very long transmitter bar and the strain and strain rate is determined by using DIC. The results show clean stress strain curves (no ringing).

501 リンク機構式の二軸引張り試験装置の開発(G03-1動特性評価および最適化技術,G03機素潤滑部門)

For environmental protection, the application of lightweight materials in car has increased, Lightweight materials are prone to observe forming defects such as springback during forming. In order to shorten the development period of a forming dies, it is necessary to predict these defects in advance In order to perform highly precise forming simulation, it is necessary to obtain the material data based on a biaxial tensile test. The present biaxial tensile test equipment has large-size and is expensive. Therefore, compacter biaxial tensile test equipment has been developed. In this paper, the performance of recommended location of measuring strain is examined. It is confirmed that the good results were obtained, In order to investigate the performance in the case of tensile ratio 1:0, new jig is proposed and test results were compared with servo controlled tensile apparatus.

자동차 프론트엔드모률 캐리어용 경량 복합소재의 고속인장 시험

경량복합소재의 고속인장시험을 수행하여 변형률속도에 따른 강도변화를 측정하고자 한다. 준 정적 시험인 경우 섬유강화 복합소재의 인장시험은 ASTM D3039에 따른 시편 형상이 사용되지만 고속 인장시험인 경우 표준화된 시편 형상에 대한 연구가 진행되어 있지 않다. 본 연구에서는 ASTM D638에 나타난 시편 형상을 기본으로 몇 가지 변형된 형태의 시편을 가지고 고속인장 시험을 수행하여 변형률 속도에 따른 경량복합소재의 강도 변화를 측정하였다. 낙하방식의 고속인장 시험기를 제작하여 변형률 속도 15/s, 100/s에서 시편의 형상에 따른 섬유강화 복합소재의 인장거동을 측정하였으며 시편의 폭이 6mm, 8mm, 10mm인 경우에 대하여 시험을 수행하였다. 측정 결과 시편의 폭이 8mm인 경우 섬유강화 복합소재의 강도를 정확하게 평가할 수 있는 것으로 나타났다. High strain rate tensile tests were performed to measure the strain rate sensitivity of fiber reinforced composite material. The composite material was developed for the light weight design of an automotive FEM(front end module) carrier. Standard specimens for quasi-static tests of fiber reinforced composites can be found in ASTM D3039. However, in case of high strain rate tests, it was hard to find standard specimen shapes. In this study, three kinds of tensile specimens designed based on ASTM D638 were investigated to determined the adequate gauge width of tensile specimen for fiber reinforced composite. A drop tower type of high speed tensile apparatus was developed for strain rates of about 15/s and 100/s. Gauge width of 6mm, 8mm and 10mm were investigated. Test results showed the specimen of 8mm width was adequate for the high strain rate tensile tests of fiber reinforced composite. It was found the strength of the composite material increased as the strain rate increased.

Strain-rate behavior in tension of the tempered martensitic reduced activation steel Eurofer97

The tensile properties of the high-chromium tempered martensitic reduced activation steel Eurofer97 were determined from tests carried out over a wide range of strain-rates on cylindrical specimens. The quasi-static tests were performed with a universal electro-mechanical machine, whereas a hydro-pneumatic machine and a JRC-split Hopkinson tensile bar apparatus were used for medium and high strain-rates respectively. This tempered martensitic stainless steel showed significant strain-rate sensitivity. The constitutive behavior was investigated within a framework of dislocations dynamics model using Kock’s approach. The parameters of the model were determined and then used to predict the deformation range of the tensile deformation stability. A very good agreement between the experimental results and predictions of the model was found.

Effect of warm forming conditions on AZ31B flow behaviour and microstructural characteristics

The paper presents the mechanical and microstructural characterization of the magnesium alloy AZ31B through tests conducted at elevated temperature on a dedicated uni-axial tensile set-up. The samples are heated in-situ through induction heating and their actual deformation is recorded in-line through the Aramis™ system. Results from the tests in terms of flow stress, plastic properties and anisotropic coefficients are presented and commented. Additionally, the microstructural analysis on deformed samples in terms of grain size and recrystallized fraction is shown, in order to identify the fundamental mechanisms of dynamic recrystallization and grain growth and to correlate them with the testing parameters. The study provides the best combination of process parameters that can assure, at the same time, good formability and sound microstructure in the warm forming temperature range.

The study on the creep of calcium carbonate-filled polypropylene (PP/CaCO3) prepared at different vibration condition

A vibration force field had been introduced during the polymer injection processing in the article, which caused some physical properties of the articles were significantly improved. The creep behavior of calcium carbonate-filled polypropylene (PP/CaCO3) prepared at different vibration condition was studied in order to reveal the influence of vibration conditions on the creep behavior. First, the tensile creep behavior of the PP/CaCO3 prepared at different vibration conditions has been investigated with a tensile creep apparatus, and it had been observed that with the vibration frequency increasing, the tensile strain would be maximum value at 0.72 Hz. While the tensile strain of the PP/CaCO3 prepared at different vibration pressure would be decreasing with the vibration pressure increasing. Then the wide-angle X diffraction (WAXD) and the differential scanning calorimeter (DSC) were used to explore the microstructure of the PP/CaCO3 article prepared at different vibration condition. According to the WAXD and DSC data, the number of the crystal grain may play an important role on the change of the creep behaviors of PP/CaCO3 article prepared at different vibration conditions. Finally, the inner reason why the different vibration condition would cause different creep behavior could be found that if the number of the crystal grain is larger, then there would be stronger physical cross-linking structure, which causes stronger anti-creep ability.

Constitutive modeling of intrinsic silicon monocrystals in easy glide

Constitutive modeling of silicon materials is currently restricted to the very early stage of deformation. Uniaxial tensile testing of monocrystals oriented for single glide is traditionally simulated by a scalar model relying on the so-called machine equation. The present work uses a crystal plasticity framework to identify the role of secondary slip systems in the yield region. A three-dimensional finite element model of a tensile apparatus is validated by comparison of its outputs to the results yielded by a scalar formulation. Best fits of the constitutive model of Alexander and Haasen to experimental data reveal strong variations in its parameters with temperature. An improved constitutive model for intrinsic silicon monocrystals deformed in single slip is described. Its parameters are identified as analytical functions of temperature. We show its excellent agreement with the observed steady state of deformation in stage I.

Microstructure phenomena and mechanical properties of AZ31B under warm forming conditions

The paper presents the mechanical characterization of the magnesium alloy AZ31B at elevated temperature carried out on a dedicated uni-axial tensile set-up. The samples are heated in-situ through induction heating and their deformation recorded in-line through the Aramis™ system. Results from the tests in terms of plastic properties, anisotropic coefficients, hardening and strain rate sensitivity exponents are presented and commented. At the same time, the microstructural analysis on deformed samples in terms of grain size and recrystallized fraction is shown, in order to evidence the fundamental mechanisms of dynamic recrystallization and grain growth and to correlate them with the testing parameters. The study is worth to highlight the best combination of process parameters that can assure at the same time good formability and sound microstructure in the warm temperature range.

Effect of fatigue damage on the dynamic tensile behavior of 6061-T6 aluminum alloy and AISI 4140T steel

Usually material properties are determined from damage free materials, but it is not well known how these properties vary with respect to previous fatigue damage. In the present work the dynamic response of fatigue damaged 6061-T6 aluminum alloy and AISI 4140T steel specimens subjected to impact loading was investigated. Samples subjected to previous damage under high cycle fatigue and low cycle fatigue were tested. Different fatigue damage levels were considered. In addition, the effect of previous fatigue damage on the quasi-static behavior, ductility and fracture mechanism was also evaluated for both materials. A tensile Hopkinson bar apparatus was used in this work to investigate the dynamic response of the pre-fatigued specimens. Projectile speeds ranged from 18 m/s to 30 m/s giving strains rates from 550 to 2850 s −1. The quasi-static mechanical properties of aluminum are not affected by the way the fatigue damage is induced. The dynamic properties, however, are sensitive to the previous fatigue damage, but are not affected by the strain rate. In the steel case, and when damage is induced by strain control, the mechanical properties are influenced by the previous fatigue damage. The dynamic properties are sensitive to the previous fatigue damage and depend on the strain rates. The analysis results show an increase in the ductility of the aluminum alloy when increasing the fatigue damage level; the steel exhibits an opposite behavior, a decrease in the ductility when increasing the damage level. The results show how the previous fatigue damage can modify the quasi-static and dynamic mechanical properties of the tested materials.

Influence of thermal treatment on stress corrosion of Fe–40 at.% Al alloy in water vapour environment

The paper aimed at the water vapour induced corrosion of the Fe–40 at.% Al alloy under applied constant loads using tensile apparatus. To interpret the registered experimental curves they were converted in accordance with Ternes method. Microfractographic investigations were conducted on specimens after cracking. Results reveal susceptibility of the iron aluminide to stress corrosion, and influence of heat treatment on this process.

Strain characteristics of critical current in RABiTS/Y-Ba-Cu-O coated conductors

The strain dependence of critical current I c of a commercial RABiTS (Rolling-Assisted Biaxially Textured Substrates) YBCO coated conductor tape with Cu stabilizing layers on both surfaces has been studied by two kinds of bending apparatus and a tensile apparatus at 77 K and 293 K. According to the voltage measurements using multi-taps in the longitudinal direction, local I c degradation was also observed. In the continuous bending-tension test at 77 K, in which YBCO layer was subjected to the tensile strain, I c began to decrease rapidly beyond the strain of 0.6% after initial moderate degradation. In the continuous bending-compression tests, the I c began to decrease rapidly beyond the strain of 0.4%. The strain for the beginning of degradation of I c obtained by tensile tests at 77 K was almost the same as that by the bending-tension tests. Bending test at RT using FRP holders showed I c degradation not so different from that by the continuous bending tests at 77 K. In all tests, the I c initially degraded locally irrespective of the position in the specimens. Furthermore, I c degradation by repeated bending was also studied.

EFFECT OF PRE-FATIGUE ON DYNAMIC AND STATIC TENSILE PROPERTIES OF LASER WELDED BUTT JOINTS BETWEEN DIFFERENT HIGH STRENGTH STEEL PLATES

In this research, the effects of pre-fatigue on the dynamic and quasi-static tensile properties of laser welded butt joints between three kinds of steel plates, i.e. HR270, HR590 and HR780 steels, were investigated using tensile split Hopkinson bar apparatus. There were no significant effects of pre-fatigue on the dynamic and static tensile properties of HR780-HR270 and HR780-HR590 joints. Their fracture occurred in the middle of the weaker base metal parts. However, one or two in three pre-fatigued HR780-HR780 joint specimens broke at the heat affected zone, irrespective of strain rate. Their elongation decreased dramatically from that of the virgin specimens, although there are no changes in the tensile strength.

Periostin regulates atrioventricular valve maturation

Cardiac valve leaflets develop from rudimentary structures termed endocardial cushions. These pre-valve tissues arise from a complex interplay of signals between the myocardium and endocardium whereby secreted cues induce the endothelial cells to transform into migratory mesenchyme through an endothelial to mesenchymal transformation (EMT). Even though much is currently known regarding the initial EMT process, the mechanisms by which these undifferentiated cushion mesenchymal tissues are remodeled “post-EMT” into mature fibrous valve leaflets remains one of the major, unsolved questions in heart development. Expression analyses, presented in this report, demonstrate that periostin, a component of the extracellular matrix, is predominantly expressed in post-EMT valve tissues and their supporting apparatus from embryonic to adult life. Analyses of periostin gene targeted mice demonstrate that it is within these regions that significant defects are observed. Periostin null mice exhibit atrial septal defects, structural abnormalities of the AV valves and their supporting tensile apparatus, and aberrant differentiation of AV cushion mesenchyme. Rescue experiments further demonstrate that periostin functions as a hierarchical molecular switch that can promote the differentiation of mesenchymal cells into a fibroblastic lineage while repressing their transformation into other mesodermal cell lineages (e.g. myocytes). This is the first report of an extracellular matrix protein directly regulating post-EMT AV valve differentiation, a process foundational and indispensable for the morphogenesis of a cushion into a leaflet.

Dynamic Fracture of Natural Rubber

Abstract This paper illustrates how the fracture energy of a tensile strip made of unfilled and 25 phr carbon black-filled natural rubber varies with far-field strain rate in the range 0.01–71 s−1. Quasistatic and dynamic fracture tests were performed at room temperature with an electromechanical INSTRON machine, a servo-hydraulic MTS machine, and Charpy tensile apparatus, respectively. It was found that the fracture energy of the unfilled natural rubber did not vary significantly over the range of sample strain rate, but there was significant variation in the fracture energy of the 25 phr carbon black-filled natural rubber from 0.01 to 71 s−1 sample strain rate. The fracture energy of the 25 phr carbon black-filled natural rubber at a sample strain rate of 0.1 s−1 was about three times greater than it was at the 10 s−1 sample strain rate. While the carbon black fillers increased the fracture energy of natural rubber by about 200% at quasistatic sample strain rates (0.01–0.1 s−1) and at 71 s−1, the carbon black fillers did nothing to improve the fracture energy of natural rubber at sample strain rates between 5 and 29 s−1. In this strain rate range, the fracture energy of 25 phr carbon black-filled natural rubber was almost the same as that in the unfilled natural rubber. The variation in the fracture energy with far-field strain rate was due to changes in the material behavior of natural rubber at high strain rates. Finite element analysis using a high-strain-rate constitutive equation for the 25 phr carbon black rubber specimen was used to calculate the fracture energy of the specimen at a sample strain rate of 55 s−1, and good agreement was found between the test and finite element results.

Tensile Strength Characteristics of Unsaturated Sands

Tensile strength characteristics of unsaturated sands are examined through a combined theoretical and experimental study. The characteristics of tensile strength in all three water retention regimes of pendular, funicular, and capillary are examined. A simple direct tensile strength apparatus is employed to determine tensile strength for sands with a broad range of particle sizes from silty sand to fine sand and medium sand over a full range of degree of saturation. Tensile strength characteristic curves (TSCC) are established experimentally for these sands and are used to validate the existing theories for tensile strength in the pendular regime. The TSCC for sand characteristically exhibits two zeros at 0 and near 100% saturation, and two peak values occurring in the pendular and capillary regimes, respectively. A minimum tensile strength is observed in the dense fine sand, indicating that either water bridges or pore pressure contributes exclusively to the tensile strength in the funicular regime of this sand. The maximum tensile strength for the silty sand is 1,448Pa, the fine sand is 1,416Pa, and the medium sand is 890Pa. Comparison between the soil–water characteristic curves obtained for these sands indicates that the peak tensile strength in the capillary regime is highly correlated to the air-entry pressure. Photographs of the failure surfaces clearly delineate distinct geometric characteristics for different water retention regimes. Analysis of the patterns of failure surfaces in different water retention regimes indicates that the effective stress principle is valid for tensile stress failure in unsaturated sands.