Strain Rate

: This report presents the first series of conventional triaxial tests carried out on columnar first year sea ice samples obtained from the field and tested under controlled laboratory conditions using a large-capacity test machine. A total of 110 horizontal ice samples from Prudhoe Bay, Alaska, were tested on a closed-loop electro-hydraulic test machine at -10 C in unconfined and confined constant-strain-rate compression. The confined tests were conducted in a conventional triaxial cell that maintained a constant ratio between the radial and axial stress to simulate in situ loading conditions. The load ratios used were 0.25, 0.50 and 0.75. The strain rate of each test was constant at 0.01, 0.001, or 0.00001/s. Data are presented on the strength, failure strain and initial tangent modulus of the first year sea ice under these loading conditions. The effects of confining pressure, strain rate and ice structure on the mechanical properties of the ice are examined.

This research is aimed at determining the effect of thermo-mechanical ageing experimentally and numerically on the Mechanical Properties of Al-Cu Alloy by formulating a model (constitutive) to determine the nodal value of certain parameters and to simulate the obtain results using Matlab (fematiso).The development and morphology of Al-9.37Cu alloy was characterized through metallographic examination and failure rate. The alloy was obtained by employing Die -Casting Technique before being subjected to series of mechanical and materials tests. The result showed that the strength of Al9.37Cu was greatly enhanced when the alloy was under different percent of deformations between 5-15%. Constitutive model was adopted to determine the isotropic material property in which the plane stress and plain strain conditions were considered as boundary conditions. Consequently, the effect of temperature was able to influence the strain rate in which the fracture strain determined the failure rate o...

AA6010 in the F temper was investigated using a Gleeble 3800 test rig across a range of temperatures (350–550 °C) and strain rates (1 × 10−1 s−1 1 × 101 s−1) to identify optimal forming conditions. Post-forming electron back-scattered diffraction analysis was conducted to identify the mechanisms responsible for the material formability. Optimal forming conditions were observed to be 500 °C and a strain rate of 1 × 10−1 s−1, with clear evidence of dynamic recrystallisation observed, this being the dominant mechanism responsible for the increased formability. Peak yield strength of 335 MPa was achieved using a rapid aging treatment of 205 °C for one hour.

The results of a numerical simulation of meshing polymer and composite gears are presented in the paper. The numerical model used for simulations was built in Ansys Workbench 15.0, using the finite element method to obtain the solution. The results are related to the gear tests, performed by the authors and presented in the literature. A detailed stress and strain analysis of meshing gears is presented. On the basis of which gears of different polymer and composite materials can be rated and appropriate material combinations can be chosen. With the presented numerical model, root and flank stresses in each meshing point along the path of contact can be calculated. Stresses (root and flank) obtained by simulations will be compared with the stresses calculated according to VDI 2736 guideline. The numerical model takes into account friction between the tooth flanks in contact, which significantly contributes to improving the accuracy of the numerical solution. (Less)

Crashworthiness, energy absorption capacity, and safety are important factors in the design of lightweight vehicles made of fiber-reinforced polymer composite (FRP) components. The relatively recent emergence of the nanotechnology industry has presented a novel means to augment the mechanical properties of various materials. As a result, recent attempts have contemplated the use of nanoparticles to further improve the resiliency of resins, especially when resins are used for mating FRP components. Therefore, a comprehensive understanding of the response of nanoreinforced polymer composites, subjected to various rates of loading, is of paramount importance for developing reliable structures. In this paper, the effects of nanoreinforcement on the mechanical response of a commonly used epoxy resin subjected to four different strain rates, are systematically investigated. The results are then compared to those of the neat resin. To characterize the mechanical properties of the nanocompo...

Introduction: The ability of cells to respond to mechanical loads is central to the concept of mechanotransduction and the maintenance of tissue homeostasis (1). In tendons and ligaments, the mechanobiological response of the cell is mediated, in large part, through the cytoskeleton, and alterations in the shape and structure of the cytoskeleton are known to influence gene expressions (2,3). A recent study has demonstrated that high (15%) strain magnitudes can increase collagenase production in ligament cells in monolayer culture (4). Conversely, numerous studies have shown that the loss of cytoskeletal tensional homeostasis of tendon cells in situ, secondary to stress deprivation, is the stimulus for collagenase mRNA expression and protein synthesis (5-10). The reason for these conflicting observations is unclear. Several studies have shown that chemically or physically induced disruptions of the actin cytoskeleton can induce an upregulation of collagenase in fibroblasts (2,3,5,6)....

Background: The present study aimed to assess and compare regional strain of the right and left sides of interventricular septum in healthy subjects using velocity vector imaging analysis due to the importance of interventricular septum and limited basic information about the exact function of the interventricular septum.MethodsThe present study was conducted on 40 healthy subjects. Echocardiography was performed in the apical 4-chamber view in the left lateral decubitus position. Image analysis was done offline with velocity vector imaging; the longitudinal strain and strain rate were calculated during 3 cardiac cycles. Strain-time and strain rate-time curves in basal, middle, and apical segments of the left and right sides of interventricular septum were recorded; peak values and time to peak strain were determined. ResultsThere was no significant difference between the longitudinal strain in the right and left basal (−17.7 ± 5.10% vs. −18.2 ± 5.14%, P = .550), middle (−17.1 ± 4.53% vs. −17.9 ± 4.29%, P = .197) segments, strain rate of basal (−1.1 ± 0.36 1/s vs. −1.0 ± 0.36 1/s, P = .350), and middle (−1.0 ± 0.30 1/s vs. −1.1 ± 0.32 1/s, P =0.551) segments. However, there was a significant difference between the longitudinal strain (−22.2 ± 5.55% vs. −16.6 ± 4.45%, P < .001) and strain rate (−1.5 ± 0.46 1/s vs. −1.1 ± 0.33 1/s, P < .001) of the apical segment. Time to peak strain was significantly different only in the middle segment of interventricular septum (right side: 351.0 ±11.5 ms vs.left side: 344.4 ± 13.1 ms, P = .004). ConclusionsThe findings of this study suggest that the right and left function of the septum was comparable in the basal and middle segments of healthy subjects; this function was significantly different in the apical segments.

The application of the unified physics is the way to understand the phenomenology and mechanics of super plastic flow (SPF). In this scenery, the main proposed in this work is to establish the effect of grain size and thermomechanical conditions on the activation energy for super plastic flow (Qspf) in Zn-22Al eutectoid alloy by applying the quantum mechanics and relativistic model (QM-RM) proposed by Muñoz-Andrade. Analyses on the experimental results reported before by some authors, it is shown for grain size of 0.35 μm that the calculated Qspf by using QM-RM for grain boundary sliding is 55.669 kJ/mol at 303 K and strain rate of 1 s−1. These results are in closed agreement with the value of Qa = 54 kJ/mol reported previously by using the theoretical and conventional methodology set up by Mohamed and Langdon. However, for grain size of 0.8μm, the calculated Qspf is 67.864 kJ/mol at 473 K and strain rate of 1×10−2 s−1. Furthermore, in order to understand the phenomenology and mecha...

The mechanical properties of 2024 aluminum alloy were studied after two different tempers. The T351 temper (solution heat treatment, stress relief, and natural aging) leads to high hardness and toughness. A thermal treatment consisting of heat-treating at 280 °C for 48 h and slow cooling in a furnace, named TT temper, was performed to increase the precipitate size and their separation while minimizing the amount of solutes in solid solution, which produced the minimum hardness for an overaged Al2024 alloy and a lower tensile flow stress than for the T351 temper. The flow stress strongly decreases and the elongation to failure strongly increases for both materials above 300 °C. Differences in strain rate at a given stress in the power law regime at all temperatures for both tempers and compared with pure aluminum are attributed to the influence of solutes in solid solutions, affecting both the glide and climb of dislocations. However, the stacking fault energy, SFE, alone does not ac...

A commercial 2024 aluminum alloy was heat treated at 280 °C for 48 h and then slow cooled in a furnace to obtain minimum hardness. This material was then friction stir processed (FSP) using three sets of processing conditions. To study the effect of the processing on the microstructure and the high temperature mechanical properties, the materials were tested in tension at an initial strain rate of 10−2 s−1 and temperature range 200 to 450 °C. Processing severity was selected as the main factor for obtaining fine grain sizes right after FSP. The grain size was enormously reduced from about 50 µm to 1 µm. This grain reduction gave rise to very high elongations to failure of about 400%. Strain–rate-change tests showed a stress exponent close to 2 at intermediate strain rates, which was related to grain boundary sliding as the controlling deformation mechanism and to superplasticity, which is strongly grain-size dependent. A possible controlling deformation mechanism by solute-drag cree...

Friction stir processing (FSP) was used on coarse-grained WE54 magnesium alloy plates of as-received material. These were subjected to FSP under two different cooling conditions, refrigerated and non-refrigerated, and different severe processing conditions characterized by low rotation rate and high traverse speed. After FSP, ultrafine equiaxed grains and refinement of the coarse precipitates were observed. The processed materials exhibited high resistance at room temperature and excellent superplasticity at the high strain rate of 10−2 s−1 and temperatures between 300 and 400 °C. Maximum tensile superplastic elongation of 726% was achieved at 400 °C. Beyond 400 °C, a noticeable loss of superplastic response occurred due to a loss of thermal stability of the grain size. Grain boundary sliding is the operative deformation mechanism that can explain the high-temperature flow behavior of the ultrafine grained FSP-WE54 alloy, showing increasing superplasticity with increasing processing...

Hot torsion tests to fracture to simulate thermomechanical processing were carried out on a solution-treated Al-Cu-Mg alloy (Al 2024-T351) at constant temperature. Torsion tests were conducted to failure in the range 270 to 470°C, between 2 and 26 s-1. A peak ductility of the 2024 alloy was found at about 410°C. The high temperature data was analyzed by means of a Garofalo equation, obtaining a stress exponent of 6.1 and an activation energy for deformation of 180 kJ/mol. These high temperature deformation parameters correspond to an underlying deformation mechanism of constant substructure (n=8) but experiencing increasing microstructure coarsening with increasing temperature. The workability of the alloy was characterized by maximum energy efficiency and stability maps constructed from the torsion tests data to determine optimal conditions for the forming process, which depend on applied strain rate. A forming temperature of about 400°C is recommended.