Repeated Tensile Test Research Articles

Highly Stretchable Strain Sensor with a High and Broad Sensitivity Composed of Carbon Nanotube and Ecoflex Composite

Wearable strain sensors with high and broad sensitivity, high stretchability and excellent mechanical endurance will be widely useful in smart wearable electronics. In this work, we developed a stretchable strain sensor fabricated with a simple stencil printing technique. The stretchable strain sensor was fabricated using a multi-walled carbon nanotubes (MWCNTs)-Ecoflex composite paste on an Ecoflex substrate. In particular, using IPA solvent, CNT particles were uniformly dispersed in the Ecoflex binder. The effect of the amount of Ecoflex resin on the stretchability and sensitivity of the sensor were also investigated. It was found that as the amount of Ecoflex resin increased, the stretchability of the sensor increased. The fabricated stretchable strain sensor showed a maximum stretchability of 1,000% with a wide sensitivity range from 3 to 12,287. The hysteresis tests indicated that the hysteresis of the fabricated stretchable strain sensor was very small, the electrical resistances of the sensors quickly returned to original value after tests. The strain sensor showed excellent mechanical durability during cyclic repeated tensile tests of 400,000 cycles. The results of the cross-cut adhesion tests indicated that the adhesion strength between the sensor composite layer and Ecoflex substrate was excellent. We also demonstrated the potential application of the stretchable sensor in wearable electronics by bending tests on a human finger and wrist.

Changes in Crystal Orientation and Surface Height after Unloading in Stepwise Load Increasing Repeated Tensile Test of Pure Titanium Thin Sheet Specimen

Changes in Crystal Orientation and Surface Height after Unloading in Stepwise Load Increasing Repeated Tensile Test of Pure Titanium Thin Sheet Specimen

Prolonging rubber fatigue life using hysteresis of strain-induced crystallization of natural rubber

Recently, soft robots have attracted considerable attention; however, they often undergo large deformations. Thus, their lifespans are critical issues. Therefore, this study proposes a novel method for extending the lives of rubber materials. We extend the fatigue life of rubber materials by focusing on the hysteresis of the strain-induced crystallization characteristics of rubber. Strain-induced crystallization is a phenomenon wherein rubber molecules exhibit crystal structures by elongation. These crystal structures are generated by elongation and disappear with relaxation. However, hysteresis occurs in both the generation and disappearance processes. Therefore, if the rubber is not completely relaxed, the disappearance of the crystal layers is slowed by hysteresis, and the formation of cracks is hindered. Herein, we select two types of rubbers: those exhibiting strain-induced crystallization characteristics (natural rubber (NR)) and those that do not (styrene-butadiene rubber (SBR)). First, wide-angle X-ray diffraction is used to confirm the formation of crystal layers under stretching for both types of rubbers. Fatigue life test is conducted using rectangular test pieces made of NR and SBR by repeated tensile tests. Subsequently, a fatigue life test is conducted for a straight-fiber-type pneumatic artificial muscle prepared by NR and SBR. The results reveal that the fatigue life is approximately 100 times longer than normal, thereby confirming the effects of prolonging the fatigue life using the hysteresis of strain-induced crystallization.

Mechanical Behavior of Q460 High‐Strength Steel under Low‐Cycle Fatigue Loading

To investigate the mechanical properties of Q460 high‐strength steel under repeat tensile loading, 45 specimens were prepared for repeated tensile tests. The specimens are tested under 16 different loading regimes. The effects of welded joints, specimen shape and dimensions, and loading modes on the mechanical properties of the steel were analyzed. In addition, a finite element model of the specimen under cyclic load was established with ANSYS and the numerical results were compared with those of the experimental tests. This finite element model can accurately simulate the deformation characteristics of Q460 steel specimens. Experimental studies have found that the welded joints have adverse effects on the mechanical properties of this material. The cumulative effect of fatigue damage on the welded specimens was significant, and the ductility of welded specimens was poor under cyclic loading. The loading mode had a major impact on the results of the material tests. As the number of loading cycles increased, the cumulative effect of fatigue damage on the specimens was more evident, and the length, size, and cross‐sectional shape of the tensile zone all affected the stiffness of the specimen. Finally, based on the experimental research and numerical analysis results, a design formula for the tensile strength of Q460 steel under repeated loading was proposed. This formula can serve as a reference for the application of Q460 steel in seismic engineering.

Application of New Energy Composites in Sports Facilities and Fitness Equipment

New energy composite is an advanced material that can replace the traditional single metal material, especially the newly developed or developed material with superior performance. At present, the material is widely used in automobile manufacturing and other fields, but there is a lack of development and application of the material in the field of sports. To solve these problems, this paper puts forward the application of new energy composites in sports facilities and fitness equipment. In this paper, the testing methods of new energy materials, including thermoelectric testing method and energy absorption testing method, can quantitatively evaluate the properties of a kind of new energy composites and point out the direction for the development of materials with high thermoelectric properties and high‐energy absorption and consumption properties. Then, through the preparation experiment of new energy materials, this paper studies the preparation process and self‐shrinkage test of carbon nanomaterials. Finally, it is proposed to use carbon nanomaterials in the sensor design of health monitoring data acquisition system. The experimental results show that when the water ash ratio is low, the self‐shrinkage value of carbon nanomaterial slurry is 74.68% lower than that under the original conditions. In the experimental study of omnidirectional monitoring characteristics, through the repeated tensile tests of rectangular sensor and omnidirectional sensor at different temperatures, it is found that the sensitivity coefficient of the sensor made of carbon nanomaterial is between 55.8 and 60.4, and the maximum fluctuation is only 5. This fully proves that the carbon nanotube omnidirectional sensor has omnidirectional detection ability.

Mechanical Properties of BaHfO3-Doped EuBCO Coated Conductors Fabricated by Hot-Wall PLD on IBAD Template

We have developed BaHfO3 (BHO)-doped EuBa2Cu3Ox (EuBCO) coated conductors (CCs) using a hot-wall type pulsed-laser-deposition (PLD) with a high throughput condition on ion-beam-assisted-deposition (IBAD) template with a thickness of 50 μm including Hastelloy substrate. Although we have investigated the in-field Jc properties, mechanical properties are also one of the most important issues for high field magnet applications. In this article, we investigated the degradation characteristics of REBa2Cu3Ox (REBCO) CCs including the BHO-doped EuBCO CCs under uniaxial tensile strain and bending strain. As a result, dependences of irreversible strain on the REBCO film thickness were clarified. In addition, longitudinal fatigue properties of the CC were investigated by repeated tensile tests, and a fatigue behavior of metallic components of the CC was confirmed in more than 100 000 cycles.

Experimental and numerical investigations on the energy-absorption of a bending-straightening structure

This paper introduces an energy-absorption structure which dissipates energy utilising the ‘bending-straightening’ process and the friction of a thin metal plate. Three repeated tensile tests were carried out to investigate the force and energy characteristics of the structure. Different loading methods and loading rates of the simulation were studied and the numerical model was verified. Furthermore, the effects of the metal plate thickness, width, the central distance of the structure and the friction coefficient on the energy-absorption of the absorber were studied systematically. The results show that the structure is of good test reproducibility and the loading process is steady. The stable tensile force (STF) and the dissipated energy increase with the rising of the structural parameters significantly. With some of the engineering improvements, the absorber can be implemented in the seat anti-impact structure and this work can provide guidelines for the design and analysis for engineering applications.

Intrinsic tensile properties of cocoon silk fibres can be estimated by removing flaws through repeated tensile tests.

Silk fibres from silkworm cocoons have lower strength than spider silk and have received less attention as a source of high-performance fibres. In this work, we have used an innovative procedure to eliminate the flaws gradually of a single fibre specimen by retesting the unbroken portion of the fibre, after each fracture test. This was done multiple times so that the final test may provide the intrinsic fibre strength. During each retest, the fibre specimen began to yield once the failure load of the preceding test was exceeded. For each fibre specimen, a composite curve was constructed from multiple tests. The composite curves and analysis show that strengths of mass-produced Muga and Eri cocoon silk fibres increased from 446 to 618 MPa and from 337 to 452 MPa, respectively. Similarly, their toughness increased from 84 to 136 MJ m(-3) and from 61 to 104 MJ m(-3), respectively. Composite plots produced significantly less inter-specimen variations compared to values from single tests. The fibres with reduced flaws as a result of retests in the tested section have a tensile strength and toughness comparable to naturally spun dragline spider silk with a reported strength of 574 MPa and toughness of 91-158 MJ m(-3), which is used as a benchmark for developing high-performance fibres. This retesting approach is likely to provide useful insights into discrete flaw distributions and intrinsic mechanical properties of other fatigue-resistant materials.

INFLUENCE OF ALLOY COMPOSITION ON WORK HARDENING BEHAVIOR OF ZIRCONIUM-BASED ALLOYS

Three types of zirconium base alloy were evaluated to study how their work hardening behavior is affected by alloy composition. Repeated-tensile tests (5% elongation at each test) were performed at room temperature at a strain rate of 1.7 × 10−3 s−1 for the alloys, which were initially controlled for their microstructure and texture. After considering the yield strength and work hardening exponent (n) variations, it was found that the work hardening behavior of the zirconium base alloys was affected more by the Nb content than the Sn content. The facture mode during the repeated tensile test was followed by the slip deformation of the zirconium structure from the texture and microstructural analysis.

Influence of Air Voids on Mechanical Properties of Asphalt Mixtures

ABSTRACT Air voids play an important role in influencing the performance of asphalt mixtures. This study utilized several mechanical tests to characterize the influence of air void distributions on mechanical properties and response of asphalt mixtures. The overlay tester, Hamburg Wheel-Tracking Test (HWTT), and a repeated tensile test were used to characterize the resistance to fatigue cracking, permanent deformation, and moisture damage, respectively. The overlay test results showed that specimens with more uniform air void distribution had less variability in terms of resistance to fatigue cracking compared with specimens with less uniform air void distribution. Consequently, recommendations were made to improve air void distribution and reduce the test variability. The HWTT results were found to be insensitive to the air void distribution. The repeated tensile test was used to measure material properties that were required inputs to a fracture-based model for the analysis of moisture damage. The repeated tensile test and model results showed that the detrimental effect of moisture was the highest for specimens with the highest percent of air voids. In addition to the characterization of mechanical properties, this study evaluated the effect of temperature distribution in Superpave Gyratory Compacted (SGC) specimens on air void distribution. It was possible to make some minor changes to the compaction procedure in order to improve the uniformity of temperature distribution and, consequently, enhance the uniformity of air void distribution.