Strain Distribution In Specimens Research Articles

Mechanical properties of geopolymer recycled concrete infilled steel tubes with three sectional types

The steel tubes with geopolymer recycled concrete (GRC) infill are actively seeking environmentally friendly and low-carbon building materials as alternatives in the process of promoting sustainable development, maximizing the use of waste materials and resources, and reducing consumption of natural resources and environmental pollution. In this paper, three types of steel tube specimens with GRC infill were proposed, i.e., the geopolymer recycled concrete-filled steel tube (GRCFST), geopolymer recycled concrete-filled double skin steel tube (GRCFDST), and geopolymer recycled concrete-filled double section steel tubes (GRCFDSST). These GRC-steel tube structures were tested under axial compressive loading, and the influence of some crucial factors on bearing capacity, ductility and strain distribution of specimens was considered, such as the slag content, and the types of steel tube section and the replacement rate of recycled aggregate. The experimental results show that the steel tube can provide effective confinement for geopolymer recycled concrete and thus compensate for the adverse effect induced by recycled aggregate. The slag content has less effect on the bearing capacities of the GRCFDSST specimen compared with the GRCFST and GRCFDST specimens due to the stronger confinement effect of the former. The ductility of GRCFDSST specimens is better than the other steel tube specimens under the same parameter conditions. This study, building on existing literature, provides new insights and design recommendations for the mechanical performance of concrete-filled steel tube structures by using geopolymer recycled concrete as a filling material.

Overall buckling behaviour of welded π-shaped compression columns

The overall buckling behaviour of welded π-shaped columns have been investigated in this study. Twenty-five pin-ended specimens made of Q345 steel with several cross sections and a wide range of lengths were tested under axial compression. The material properties, initial imperfections and longitudinal residual stresses were all examined. The deformed shapes of test specimens involved overall flexural buckling and overall flexural-torsional buckling. The ultimate strengths, deformations and strain distributions of specimens were obtained in the test. The finite element models were established and validated by test results, and then were adopted to carry out a series of parametric studies. The buckling strengths were compared with the design strengths predicted by the current design specifications for steel structures. Reliability analyses were conducted to evaluate the existing design column curves and π-shaped column curve. It is shown that column b-curves in both Eurocode 3 and Chinese standard provide generally conservative predictions for the strengths of π-shaped members, whereas ANSI/AISC specification provides marginally unsafe predictions. A new column curve is proposed and can provide more accurate and reliable predictions for the strengths of welded π-shaped members.

Strain measurement and error analysis in thermo-mechanical tensile tests of sheet metals for hot stamping applications

In order to conduct uniaxial tensile tests for hot stamping applications, tests are normally performed by using a Gleeble thermo-mechanical materials simulator so that rapid heating and cooling processes can be obtained. However, temperature gradients in a specimen tested on Gleeble are inevitable due to resistance heating principles and heat loss to grips and water-cooled jaws. In this research, a pair of purpose-built grips made of stainless steel with low thermal conductivity and significantly reduced contacting area for clamping, as well as a flat dog-bone specimen with maximised parallel length (80 mm) were designed, for the purpose of improving the temperature uniformity within the concerned gauge section area of the specimen. Uniaxial tensile tests on AA6082 were performed, after controlled heating and cooling processes, at constant deformation temperatures in the range of 400 ℃–500 ℃ and at constant strain rate in the range of 0.1–4/s, to simulate its hot stamping conditions. The digital image correlation system was adopted to enable strain distributions in specimens to be measured. The temperature distributions in specimens were investigated and an effective gauge length of 14 mm was specified accordingly to ensure temperature gradients less than 10 ℃ within it at all tested temperatures. True stress–true strain curves of AA6082 were obtained based on results of strain measurements along the defined effective gauge length and used to calibrate a set of advanced material model. Error analysis was carried out by using thermo-electrical and thermo-mechanical FE models on ABAQUS, in which the calibrated material constitutive equations were implemented via subroutines. The error of stress–strain curves of AA6082 measured based on the specified gauge length was investigated and quantified by analysing the distribution of axial strain and axial stress.

Application of Magnetorheological Fluid in Bulge Tests of Sheet Metal

Magnetorheological (MR) fluid is a kind of smart material. In this paper, magnetorheological (MR) fluid is applied as a flexible-die, the rheological properties of which can be changed rapidly under a magnetic field, in sheet metal forming process. Bulge tests using a kind of MR fluid, MRF-J01T, are carried out on self-designed experimental device. Stainless steel 1Cr18Ni9Ti combined with different process parameters are adopted to investigate the effect of property of MR fluid on the formability of material tested. The results showed that MR fluid can be utilized successfully as a pressure-carrying medium in sheet forming process. The rheological properties of MR fluid can greatly influence the dome height and thickness strain distribution of specimens.

Influences of tensile direction and plastic strain on ultrasonic parameters measured with rolled brass plates

Cu-40 wt% Zn alloy plates were pulled parallel or perpendicular to the rolling direction and ultrasonic measurements were carried out with a probe generating shear wave of 4 MHz in frequency polarizing parallel or perpendicular to the tensile direction to examine the relationship between ultrasonic parameters, tensile direction and plastic strain. Ultrasonic echoes reflected from the bottom of specimens were Fourier transformed and an inverse transfer function was obtained as a ratio of the Fourier spectra of the first two echoes. The inverse transfer function changed complicatedly with plastic strain, and was analyzed with the subspace method to obtain a major parameter called the primary component. The primary component changed with the plastic strain, and was dependent on combination of the polarization direction of the shear wave, the rolling direction and the tensile direction. Specimens with curved sides were pulled and the primary component was obtained by the ultrasonic measurement to estimate the plastic strain distribution in specimens with the ultrasonic parameter. The estimated plastic strain was in good agreement with the measured plastic strain.

Effect of method of reinforcement and nominal stress level on the stress and strain concentration around holes in glass-reinforced plastics

The stress and strain distributions in specimens weakened by a stress raiser has been investigated by the moire fringe method in tension.