Non-contact Strain Measurement System Research Articles

Elevated-temperature mechanical property and constitutive model of Galfan-coated and full-locked steel cables

Steel cables are an essential stress-bearing member in pre-tensioned steel structures. Their exposure to fire may lead to prestress loss, which may cause structural failure or even overall collapse. This study used a non-contact strain measurement system to investigate the mechanical properties of 1670 MPa Galfan-coated steel cable and 1570 MPa full-locked steel cable at elevated temperatures. The test results showed that the mechanical properties of the two types of cable decayed significantly with the increase in temperature. At 700 °C, the ultimate strength of Galfan-coated steel cable was only 2.36% of that at room temperature, and that of full-locked steel cable was 3.56%. By analyzing the stress-strain relationships between the yielding and hardening stages at 9 test temperature levels, it was found that the high-temperature nominal yield strength could be taken as the stress at the strain level of 1.25% for both types of steel cables. Based on the full stress-strain curves at each temperature level, the calculation formulae for high-temperature reduction factors of elastic modulus, proportional limit, nominal yield strength, and ultimate strength of Galfan-coated and full-locked steel cables were proposed. Besides, the high-temperature constitutive models of the two cable types were also proposed based on the experimental data. The findings of this study can improve the fire safety of pre-tensioned steel structures.

Measurement and Analysis of Deformation Behavior of Polyethylene Tube Subjected to Linear Loading and Unloading Stress Paths with Large Strain

A material testing apparatus for measuring the biaxial deformation behavior of a polymer tube has been developed to quantitatively evaluate the deformation behavior of polymeric materials. The testing apparatus can apply axial force and internal pressure to a tubular specimen. A noncontact strain measurement system was also developed, and the biaxial strain components and the radius of curvature in the axial direction of the bulging specimen are continuously measured to control the stress path applied to the specimen. Polyethylene tube with an outer diameter of 17 mm and a thickness of 2 mm are used as a test sample. The tubular specimens were subjected to linear stress paths with stress ratios of σΦ:σθ =1:0, 4:1, 2:1, 4:3, 1:1, 3:4, 1:2, 1:4, and 0:1, where σΦ and σθ are the axial and circumferential stress components, respectively, applied to the central area of the bulging specimen. Loading and unloading tests were performed to determine the biaxial true stress-logarithmic plastic strain curves. The strain rate was 1×10-3s-1. From these test results, contours of plastic work and the directions of the plastic strain rates were measured to identify a proper material model for the test sample using the Yld2000-2d yield function (Barlat et al., 2003).

Influence of Contact Area Deformation Distribution of Tire on Tire Noise, Rolling Resistance and Dry Grip Performance

Most tire properties are closely related to the pattern deformation. In order to explore the relationship between tire performance and defined deformation parameters in the contact area between the pneumatic tire and road surface, ten types of 205/55R16 passenger car radial (PCR) tires were selected as the research objects. Using VIC-3D non-contact strain measurement system and by subdividing the contact area, the pattern deformation in contact area under vertical load was tested, and the relevant deformation parameters of the contact area were extracted. Correlation analysis was used to establish the relationship between the identified deformation parameters and tire performance indicators. Then an evaluation method of tire performance based on the deformation parameters was proposed, as well as clarification of the contradictory mechanism between tire noise, rolling resistance and dry grip performance. While the results indicate tire noise having a significant negative correlation with radial deformation in the contact area, rolling resistance coefficient gave a significant positive correlation with its equivalent strain in the XY plane of the contact area, and dry braking distance positively correlates with tensile strain in the Y direction of contact area and negatively correlates with tensile strain in the X direction of the contact area.

Measurement and Analysis of Deformation Behavior of Polyethylene Tube Subjected to Biaxial Tensile Stress with Large Strain

A material testing apparatus for measuring the biaxial deformation behavior of a polymer tube is developed to quantitatively evaluate the deformation behavior of polymeric materials. The testing apparatus can apply axial force and internal pressure to a tubular specimen. A noncontact strain measurement system is also developed, and the biaxial strain components and the radius of curvature in the axial direction of the specimen are continuously measured to control the stress path applied to the specimen. Polyethylene tubes with an outer diameter of 17 mm and a thickness of 2 mm are used as test specimens, that are subjected to linear stress paths with stress ratios of σφ :σθ =1:0, 4:1, 2:1, 4:3, 1:1, 3:4, 1:2, 1:4, and 0:1, where σφ and σθ are the axial and circumferential stress components applied to the center of the bulging specimen, respectively. Biaxial stress-strain curves are successfully measured for every linear stress path at a nearly constant logarithmic strain rate of 1×10-3 s-1. A maximum equivalent strain of up to 0.71 is achieved for a specimen with a stress path of σφ :σθ =2:1. The contours of equal work plotted in the principal stress space show a significant anisotropy of the test material.

Evaluation and improvement of tire rolling resistance and grip performance based on test and simulation

In order to clarify the contradictory mechanism between tire rolling resistance and grip performance, ten (10) 205/55 R16 radial tires with different tread patterns were selected as the research objects. Using VIC-3D non-contact strain measurement system, the pattern deformation in the contact area under vertical load was tested and the relevant deformation parameters of the contact area were extracted. Correlation analysis was used to establish the relationship between the identified deformation parameters and tire performance indicators. Then the contradiction mechanism between tire rolling resistance and grip performance was identified. The mechanism is such that, in order to improve the grip performance of the tire, it is necessary to reduce the transverse tensile strain of the tread in the contact area and increase the longitudinal tensile strain of the tread, but with the increase of the longitudinal tensile strain, the rolling resistance of the tire will also increase, which leads to the contradiction between tire rolling resistance and grip performance. In order to better understand and solve this contradiction, a finite element model of 205/55R16 tire with complex pattern was established. The influence of the number and width of transverse grooves in outer shoulder area on tire rolling resistance and grip performance was analyzed by numerical simulation, where it was identified that, the longitudinal tensile deformation of the tread is the main cause of contradiction between the two performances. An optimized design of concave transverse groove with narrow groove in the middle and wide groove at both ends was proposed in the outer shoulder area to resolve the contradiction. Compared with the original scheme, the rolling resistance of the optimized scheme was reduced by 2.112 N, and the grip force saw an increase of 10.196 N, and thus delivering a cooperative improvement of tire rolling resistance and grip performance.

Investigation on the Ground Pressure Induced by Hard Roof Fracturing at Different Layers during Extra Thick Coal Seam Mining

The fracturing of hard roofs in different layers would result in complex ground pressure on the working face, such as supports collapsed and severe roadway deformation. However, the mechanism of the ground pressure induced by hard roof fracturing in different layers is still unclear. In the paper, a physical model of a 20 m extrathick coal seam mined with hard roofs existing was established based on the physical simulation similarity criterion. The overburden fracturing structure, abutment stress distribution, and failure characteristics of the coal body were monitored by a noncontact strain measurement system and resistance strain gauges, to reveal the mechanism of ground pressure induced by hard roof fracturing. Furthermore, on-site measurement was used to monitor and analyze the ground pressure affected by hard roofs in different levels. The results provide a theoretical basis for the control of ground pressure in extrathick coal seam mining with hard roofs.

Study on Dynamic Strain Distribution in Rock Broken by Abrasive Slurry Jet

To reveal the stress and strain field in rock under abrasive slurry jet (ASJ) impacting, this paper carried out experiments to measure the dynamic rock strain using a novel strain measurement approach, which is the non-contact strain measurement system. Moreover, it was compared with the theoretical analysis of stress propagation in rock. The results showed that dynamic strain will propagate within rock in the form of spherical waves, whose maximum value is proportional to the jet pressure and inversely proportional to the square of the propagation distance. In the process of ASJ impacting rock, strain will increase from zero to a maximum value in milliseconds. Dynamic strain in rock is fluctuates due to the release of internal stress caused by the rock crushing, which can reflect that rock will be broken by ASJ in the form of stepped-failure. The paper reveals the dynamic strain distribution in rock broken by ASJ and provides a new idea and method for studying the rock failure mechanism under ASJ impacting.

Deformation Behavior of Hard Roofs in Solid Backfill Coal Mining Using Physical Models

Solid backfill coal mining technology has been widely applied in coal seams that are at risk of hard roof. Using actual measured strain–stress curves of the backfill body and the similarity theory, this study designed and employed four experimental models for physical simulation, corresponding to roof-controlled backfilling ratios of 0%, 40%, 82.5% and 97% using the geological conditions of Face No. 6304 in the Jining No. 3 coal mine—a solid backfill coal mining face under a hard roof. A non-contact strain measurement system and pressure sensors were used to monitor the deformation of the overlying strata and changes in abutment stress ahead of the face during mining of the models for varying roof-controlled backfilling ratios. The results indicated that the solid backfill body was able to support the roof. As the roof-controlled backfilling ratio was increased, the maximum subsidence of the roof and the maximum height of the cracks decreased. When the roof-controlled backfilling ratio was 82.5% or higher, the working face did not display any obvious initial fractures or periodic fractures, and both the value and the impact range of the abutment stress ahead of the face decreased.

1210 SiN薄膜の引張・曲げ強度特性に及ぼす微小欠陥の影響(S05-3 ナノ・マイクロ材料の強度・信頼性(3)ナノ・マイクロ材料の強度物性評価,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

The mechanical properties of SiN thin film microelements, fabricated by sputtering and CVD processes, were evaluated using specially designed testing systems for the mechanical properties of thin tensile and bending microelements. The tensile testing system consists of a tensile testing machine actuated by a PZT driven positioning stage, a micro manipulation system, and a non-contact strain measurement system with a help of a double-filed-of-view microscope. For bending tests, the testing system used is based upon a Nano Indenter with a specially designed indenter and an ultra-precise positioning stage. In order to investigate the size effects on the mechanical properties, the thickness of the sample used were 1μm and 3μm, and the specimen width was varied from 5μm to 50μm. The Young's modulus of the SiN thin film was independent of sample width and thickness: the Young's modulus was not influenced by specimen size and loading mode. However, Young's modulus of the film fabricated by sputtering was higher than that by CVD. The tensile strength and bending strength increased with a decrease in thickness, and the strength of the film fabricated by CVD was higher than that by sputtering. The fracture initiation sites were closely examined by a high-resolution field-emission type scanning electron microscope, and the strength of the thin film was revealed to be determined by stress intensity factor of the micro defect in a thin microelement.

610 SiN薄膜マイクロエレメントの強度特性と寸法効果(OS10(2) 拡大する実験力学・新領域への拡大)

The mechanical properties of SiN thin film microelements were evaluated using the previously developed testing system for the mechanical properties of thin tensile microelements. The testing system consists of a tensile testing machine actuated by a PZT driven positioning stage, a micro manipulation system, a noncontact strain measurement system with a help of a double-filed-of-view microscope. In order to investigate the size effects on the mechanical properties, the thickness of the sample used were 1μm and 3μm, and the width was varied from 5μm to 50μm. The Young's modulus of the SiN thin film was 226±11GPa, irrespective of sample size. However, the tensile strength increased with a decrease in thickness and sample width, or sample cross sections.