Effects Of Loading Strain Rate Research Articles

Effect of loading strain rate and short PVA fibers on the tensile mechanical performance of carbon TRM

AbstractTextile reinforced mortar (TRM) is an alternative reinforcement material in terms of fiber reinforced polymer (FRP) intervention due to the excellent compatibility with the substrate. The coupling effect of the seismic strain rate (10−4−10−1 s−1) and short polyvinyl alcohol (PVA) fibers on the mechanical properties of carbon TRM was studied under the uniaxial tensile load. Forty groups of tensile samples were designed to obtain the relationships between the strain rate and the volume content of PVA fibers, as well as the number of grids and types of matrices. The crack distribution, failure mode and stress–strain responses of the tensile samples were presented. The results showed that the crack and peak strength can be enhanced to 4.0–7.2 MPa and 10.1–17.3 MPa when the strain rates ranged from 10−5 to 10−1 s−1, respectively. The strain‐rate sensitivity in the crack and peak strength was confirmed. Short PVA fibers and reinforced textile grids can effectively enhance the crack and peak strength and improve the crack pattern under the static and seismic strain rates. Finally, based on the strain rate and short fibers index, a quantitative model was proposed to estimate the tensile strength of TRM under the static and dynamic strain rates.

Effect of loading strain rate on nano-indentation response of an aerospace grade epoxy polymer

Effect of loading strain rate on nano-indentation response of an aerospace grade epoxy polymer

An experimental study and failure mechanism analysis on dynamic behaviors of plain concrete under biaxial compression-compression

In order to explore the dynamic mechanical properties of concrete under biaxial compression-compression, a true triaxial instrument was used to conduct an experimental study on the dynamic mechanical properties of plain concrete under biaxial compression-compression. Eight different lateral compressive stresses (0 MPa~14 MPa) and four strain (10−5/s, 10−4/s, 10−3/s and 10−2/s) rate were considered. From this, the effects of lateral compressive stress and loading strain rate on the biaxial compression-compression properties of concrete were compared and analyzed by obtaining the failure modes, principal compressive stress-strain curves and related mechanical characteristic parameters of plain concrete under different loading conditions. The research results show that: with the increase of lateral compressive stress, the failure modes of concrete were developed from columnar failure at low lateral compressive stress to sheet-like failure at high lateral compressive stress. With the increase of lateral stress, the development trend of concrete failure mode decreased gradually under the influence of strain rate. With the increase of lateral compressive stress, the variation range of concrete principal compressive stress decreased first and then tended to be relatively stable under the influence of strain rate. With the increase of strain rate, the increase range of concrete principal compressive stress decreased under the influence of lateral compressive stress. The influence mechanism of lateral compressive stress and strain rate on biaxial compression-compression performance of concrete was analyzed. Meanwhile, based on Kupfer biaxial compression failure criterion, a biaxial compression dynamic failure criterion model considering the effect of loading strain rate on plain concrete was proposed. The research results provided an important theoretical basis for the application and development of concrete engineering.

Rate-dependent indentation size effect on hardness and creep behavior of a titanium metallization film on alumina substrate

Nanoindentation tests were performed at room temperature to investigate the indentation size effect (ISE) and creep behavior of a titanium metallization film on alumina substrate. The ISE of hardness was examined at different loading strain rate (LSR). The effects of LSR and penetrating depth on nanoindentation creep were evaluated at the steady creep state. Inverse ISE in titanium film was observed at indentation depth below 200 nm while normal ISE was observed at penetrating depth ranging from 200 nm to 1000 nm. Elastic contact theory and strain gradient plasticity theory were applied to interpret the variation trends of hardness respectively. In addition, the intrinsic hardness and characteristic length were found to be strongly dependent on LSR. Except for creep strain rate, creep displacement and creep stress exponent showed relatively conspicuous correlations to LSR and/or penetrating depths.

Experiments on the one-dimensional spall strength of SFRC

In this paper, the influence of concrete strength, aggregate size and steel fiber content on spalling strength of concrete is studied by means of split Hopkinson pressure bar test system and chemical explosion test. The typical failure mode and dynamic parameters of steel fiber reinforced concrete are analyzed. The range of strain rate of concrete (steel fiber reinforced concrete) response law is widened. The test results show that the steel fiber reinforced concrete has a good effect on the spalling strength of concrete When the fiber content is increased by 1%, the spalling strength of concrete increases by about 2 times, and the effect of loading strain rate on spalling strength of concrete is approximately linear.

An Experimental Study on the Compressive Dynamic Performance of Polypropylene Fiber Reinforced Concrete for Retaining Structure under Automobile Collision Magnitude

In order to examine the compressive dynamic performance of polypropylene fiber reinforced concrete to be used for the retaining structure under the automobile collision magnitude, an experimental study was carried out by using hydraulic servo on concrete specimens with 4 different polypropylene fiber contents under 6 loading strain rates. The failure modes and stress-strain curves of concrete under different loading conditions were obtained. Then, by comparatively analyzing the mechanical characteristic parameters of polypropylene fiber reinforced concrete under different loading conditions, the following conclusions are drawn: with the increase of the polypropylene fiber content, the integrity of concrete upon compressive failure is gradually improved. When the polypropylene fiber content is relatively high, the static and dynamic failure modes are basically similar. With the increase of the loading strain rate, the peak compressive stress and elastic modulus of the polypropylene fiber reinforced concrete gradually increase. The increase in the polypropylene fiber content gradually intensifies the effect of loading strain rate on the peak compressive stress dynamic improvement coefficient. The peak strain of polypropylene fiber reinforced concrete is gradually increased with the increase of polypropylene fiber content, while the effect of the loading strain rate on the peak strain shows an obvious discreteness characteristic. Meanwhile, we proposed a relationship equation for describing the peak compressive stress dynamic improvement coefficient based on the coupling effect of the polypropylene fiber content and loading strain rate and further discussed the underlying stress mechanism in detail. Our research findings are of important research significance for the application and promotion of polypropylene fiber reinforced concrete in the engineering practice of retaining structures.

Effect of loading strain rate on creep and stress-relaxation characteristics of sandy silt

Silty soil is abundant in alluvium deposits within urban areas, and determination of its long-term settlement characteristics is a crucial issue. This study aims to investigate the effect of four different strain rates (i.e., 1, 0.1, 0.01, 0.001 ​mm/min) on the creep and stress-relaxation behaviour of a natural type of sandy silt by performing a series of triaxial compression tests. In monotonic (reference) tests, the peak deviatoric stress increased and the volumetric strain decreased by increasing the shearing rate. The results in greater shearing rates showed that the deviatoric stress curves have a greater quasi-elastic behaviour followed by a slight yield point. Also, an almost uniform behaviour was recorded in the deviatoric stress of the specimens tested at lower shearing rates. The creep testing showed that the specimens tested at greater initial shearing rates have a greater axial strain than those tested at lower shearing rates. Also, the stress-relaxation testing showed that the specimens tested at higher shearing rates have a greater relaxation than the specimens tested at lower initial shearing rates. A comparison between particle breakages that occurred in each testing condition showed that the particle breakage index (PBI) in a monotonic condition is 1.25 and 1.5 times (in average) greater than the creep and stress-relaxation tests respectively.

An Experimental Study Examining the Size Effect on the Compressive Dynamic Performance of Nuclear Power Containment Concrete

To study the size effect of nuclear power containment concrete (NPCC) under compressive dynamic performance, the cube concrete specimens with 3 different cube sizes were measured at 10 different loading strain rates using a hydraulic servo, and the failure mode and compressive strength of NPCC were compared and analyzed under different loading conditions. Based on the comparative analysis of experiment results, the following conclusions can be drawn: the effect of loading strain rate has caused NPCC to develop from static strain rate, mainly cement cementitious layer damage and uniform distribution of cracks, to dynamic strain rate, where there are partial coarse aggregate failures and oblique cracks as the main crack distribution. Due to the size effect, the integrity of large-scale NPCC specimen after compression failure is relatively high. With the increase of loading strain rate and decrease of cube size, compressive strength of NPCC is gradually increased, and, with the increase of loading strain rate, the size effect on the mechanical properties of NPCC becomes more significant. Moreover, this paper quantitatively analyzes the influence of the coupling effect of strain rate and size effect on the compressive strength of NPCC, and its mechanism is discussed in depth. The research results are of great significance to the safety of nuclear power concrete containment.

Creep behavior in Virginia Beach sand

Triaxial compression tests were performed on dense specimens of Virginia Beach sand at low and high confining pressures to study time effects that relate to grain crushing due to static fatigue or delayed fracture. Experiments to study effects of loading strain rate on subsequent creep showed negligible time effects and no grain crushing at low confining pressures, while tests at high confining pressures indicated increasing amounts of creep with increasing initial loading strain rates and with increasing deviator stress at creep. Investigation of effects of grain-size distribution indicated stiffer initial response and smaller amounts of creep for more uniformly graded soils at high confining pressures. The experimental results showed that structuration effects were not present in the dense Virginia Beach sand. A long-term creep test at high confining pressure indicated continuous creep with no indication of its termination. Sieve analyses following each triaxial test showed that grain crushing, as quantified by Hardin’s relative breakage factor, was proportional to energy input and amount of creep observed for each soil specimen. The creep is due to the time-dependent static fatigue by which the grains crush and cause rearrangement of the grain structure, and this is the reason behind the time effects in granular materials.

Effect of thermal fluctuations in cyclic plasticity.

A formula to describe the creep strain-rate based on the random barriers theory was presented by considering the process in which the movable dislocations could surmount the barriers in the field of resisting force with the help of thermal fluctuations. An effect of loading strain-rate on the stress-strain curves in cyclic loading at a slow rate was discussed with a new equation combined by the above formula and the equilibrium equation between the stress-rate and the strain-rate at any stress which had been derived in the previous paper. The results simulated by the above new equation show that the hysteresis curve at room temperature may shift conspicuously to the lower stress level as the loading strain-rate comes near to the creep strain-rate.