Tensile deformation strain control

Mechanical properties of the composite materials were tested by a hydraulic-driven MTS tensile tester manufactured by MTS Systems Corporation, Minneapolis, Minnesota. A strain-rate of 5x 10 5 s 1 was used. During deformation, the linear actuactor position was monitored and controlled by a linear variable differential transformer (LVDT), while strain was measured using MTS-brand axial and diametral strain-gauge extensometers. The axial extensometer serves to measure the tensile deformation in the direction of loading while the diametral extensometer serves to measure the compressive deformation at 90° to the loading axis due to Poisson s contraction. All tensile tests were performed at 23 °C and in accordance to ASTM D3518-76. 

As in externally induced deformation, we should distinguish between strain-controlled and stress-controlled molecular systems. For example, deformation induced by a well-defined conformational transition (Fig. lb, bottom) can be considered as strain-controlled, where the strain is encoded by the new molecular configuration. In contrast, extension of the backbone in molecular bottlebrushes (Fig. Ic, middle) occurs at a constant tensile force controlled by steric repulsion of the densely grafted side chains. In addition to the strain distribution, it is important... 

Besides that, compressive force can be manipulated to facilitate cell lysis and collect their cellular components for later cell-based assay. Similarly, Wang et al. fabricated a micromechanical stimulator fliat is capable of providing controlled compressive or tensile strain to the cultured cells in vitro (Fig. 4). Experimental characterization of its PDMS membrane deformation showed that the microdevice can provide —6 % compressive to 25 % tensile radial strain to the cultured cells within the membrane center [6], which allowed simultaneous investigation of both mechanical strains on the same cells. Zhou et al. developed a microchip platform with microchannels that resembles the mechanical environment of small blood vessels in vivo (Fig. 5). They demonstrated that the deformation of the membrane by hydraulic pressure induced cyclic circumferential strains on the adhered mesenchymal stem cells and thus caused significant stmctural and biochemical changes to the cells [7]. 

On the macroscopic level the extent to which a temporary deformation can be fixed and the recovery of the permanent shape or the recovery stress are the most important characteristics of the shape-memory effect (SME), which can be quantified in cyclic, thermomechanical tensile tests or bending tests. Such cycUc tests consist of a SMCP module that can be performed either under stress or strain control... 

Al-Hussein, M., Strobl, G. Strain-controlled tensile deformation behavior of isotactic polyfl-butene) and its ethylene copolymers. Macromolecules 2002,35, 8515-8520. 

An important issue is the influence of an electrochemical environment on the cyclic deformation behavior of metals [74,33-35]. As illustrated by the data in Fig. 1 for a carbon-manganese steel in high-temperature water, environment does not typically affect the relationship between stresses and strains derived from the maximum tensile (or compressive) points of steady-state (saturation) hysteresis loops [36]. Such loops should relate to elastic and plastic deformation prior to substantial CF microcracking. CF data of the sort shown in Fig, 1 are produced by either stress or total strain controlled uniaxial fatigue experiments, identical to the methods... 

Vanden Eynde, S., Mathot, V., Koch, M.H.J., Reynaers, H., Thermal behaviour and morphology of homogeneous ethylene-propylene and ethylene-1-butene copolymers with high comonomer contents. Polymer 2000,41 3437-3453. Al-Hussein, M., Strobl, G., Strain-controlled tensile deformation behavior of isotactic poly(l-butene) and its ethylene copolymers. Macromolecules 2002, 35 8515-8520. 

Alexander LE (1979) X-ray diffraction methods in polymer science. Wiley, New York Al-Hussein M, Strobl G (2002) Strain-controlled tensile deformation behavior of isotactic poly (1-butene) and its ethylene copolymers. Macromolecules 35(22) 8515-8520 Allegra G (1974) Role of internal viscosity in polymer viscoelasticity. J Chem Phys 61... 

Figures 10.9 to 10.11 illustrate how stretching curves and critical strains vary with temperature, again with results for PEVA12, and with the crystallinity here polyethylenes with different crystallinities are compared. Curves demonstrate a further general property of semicr3 talline pol5oners. While the stresses vary in systematic manner, there is no effect on the critical strains for softening (en 0.1) and hardening (en 0.6) and virtually no change in the elastic-plastic composition of the strains. Hence, tensile deformation of semicrystalline polymers is strain-controlled and changes the mechanism at two critical strains that are temperature and crystallinity invariant.

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