Mechanical properties contraction

To imrove mechanical properties, increased axial molecular orientation was required. Union Carbide workers under government contract worked on... 

W.D. Claus et al, Evaluation of the Mechanical Properties of Yarns for Ballistic Applications , Rept No USA-NLabs, C/PLSEL-TR-73-60-CE, 113, Contract DAA G17-70-C-0086, Fabric Research Labs Inc, Dedham (1973)... 

Resilin has a remarkably high fatigue lifetime (probably >500 million cycles) and our aim is to reproduce this desirable mechanical property in synthetic materials derived from our studies of resilin structure and function. We believe that recombinant resilin-like materials may be used, in the future, in the medical device field as components of prosthetic implants, including spinal disks and synthetic arteries. Spinal disks, for example, must survive for at least 100 million cycles of contraction and relaxation [30]. 

As described above, protein domains that provide discrete biological cues (e.g., cell binding) or mechanical properties (e.g., expansion or contraction with temperature changes) can be borrowed from nature and designed into synthetic polypeptides or joined with other polymers to provide bio-inspired function in new... 

Modern representations of the virtual heart, therefore, describe structural aspects like fibre orientation in cardiac muscle, together with the distribution of various cell types, active and passive electrical and mechanical properties, as well as the coupling between cells. This then allows accurate reproduction of the spread of the electrical wave, subsequent contraction of the heart, and effects on blood pressure, coronary perfusion, etc. It is important to point out, here, that all these parameters are closely interrelated, and changes in any one of them influence the behaviour of all others. This makes for an exceedingly complex system. 

Purely electrical models of the heart are only a start. Combined electromechanical finite-element models of the heart take into account the close relationship that exists between the electrical and mechanical properties of individual heart cells. The mechanical operation of the heart is also influenced by the fluid-structure interactions between the blood and the blood vessels, heart walls, and valves. All of these interactions would need to be included in a complete description of heart contraction. 

The low-temperature thermal conductivity of different materials may differ by many orders of magnitude (see Fig. 3.16). Moreover, the thermal conductivity of a single material, as we have seen, may heavily change because of impurities or defects (see Section 11.4). In cryogenic applications, the choice of a material obviously depends not only on its thermal conductivity but also on other characteristics of the material, such as the specific heat, the thermal contraction and the electrical and mechanical properties [1], For a good thermal conductivity, Cu, Ag and A1 (above IK) are the best metals. Anyway, they all are quite soft especially if annealed. In case of high-purity aluminium [2] and copper (see Section 11.4.3), the thermal conductivities are k 10 T [W/cm K] and k T [W/cm K], respectively. 

Mechanical properties of the sample In the simplest case, the sample stands alone (it is fixed by a screw as in measure of Section 11.5.2), or a support may be necessary as in the examples of Section 11.3.2 and Section 11.4.2. In the latter case, the support represents again a thermal conductance in parallel with the sample. Such shunt conductance must be taken into account for low-conductance samples. Contractions (or dilatations, see Chapter 13), which take place when the sample is cooled, not only change the geometrical factor, but also influence the mechanical joints and hence the thermal contact resistance. Various mechanical solutions, some of them very exotic , have been used in the measure of the thermal conductivity [2-4]. 

One of the more recently exploited forms of thermal analysis is the group of techniques known as thermomechanical analysis (TMA). These techniques are based on the measurement of mechanical properties such as expansion, contraction, extension or penetration of materials as a function of temperature. TMA curves obtained in this way are characteristic of the sample. The technique has obvious practical value in the study and assessment of the mechanical properties of materials. Measurements over the temperature range - 100°C to 1000°C may be made. Figure 11.19 shows a study of a polymeric material based upon linear expansion measurements. 

Other than in polymer matrix composites, the chemical reaction between elements of constituents takes place in different ways. Reaction occurs to form a new compound(s) at the interface region in MMCs, particularly those manufactured by a molten metal infiltration process. Reaction involves transfer of atoms from one or both of the constituents to the reaction site near the interface and these transfer processes are diffusion controlled. Depending on the composite constituents, the atoms of the fiber surface diffuse through the reaction site, (for example, in the boron fiber-titanium matrix system, this causes a significant volume contraction due to void formation in the center of the fiber or at the fiber-compound interface (Blackburn et al., 1966)), or the matrix atoms diffuse through the reaction product. Continued reaction to form a new compound at the interface region is generally harmful to the mechanical properties of composites. 

Another important mechanical property of a coating layer is the coefficient of thermal expansion (CTE). Residual stresses generated due to the differential thermal contraction between the composite constituents are extremely detrimental to the... 

Shao, Z. and Vollrath, F. (1999). The effect of solvents on the contraction and mechanical properties of spider silk. Polymer 40 1799-1806. 

T = 140 °C. Here, during solidification, the H increase from 140 °C down to about 100 °C is the result of a double contribution of (a) the crystallization of the fraction of molten crystals and (b) the thermal contraction of the nonpolar phase crystals. The hysteresis behavior is also found in other mechanical properties (dynamic modulus) derived from micromechanical spectroscopy [66, 67], where it is shown that the hysteresis cycle shifts to lower temperatures if the samples are irradiated with electrons. It has also been pointed out that the samples remain in the paraelectric phase, when cooling, if the irradiation dose is larger than 100 Mrad. 

Thermal and Mechanical Properties of Advanced Heat hield Resinous (CP) and Carbonaceous (CC) Composites, Vol 1. Test Methods, Comparative Data, Recommended Inputs and Analysis , AFML-TR-72-160 Vol-1, Contract F33615-69-C-1796, SRI, Birmingham (1972) 11) J.-P. 

D, Tabor et al, Mechanical Properties of Energetic Materials , Final TR, Cavendish Lab, Cambridge (Engl), Contract DA-ERO-75-G-008... 

Decrease in the ability of the heart to effectively contract is one of the major causes for the increased incidence of morbidity and mortality in diabetic patients (Rubier 1972). Both electrical and mechanical properties of the myocardium from diabetic patients may be significantly impaired, which has been attributed to alterations in intracellular Ca2+ homeostasis (Pierce 1983 Bouchard 1991 Yaras 2005). Weakened contractility of myocytes isolated from streptozotocin (STZ)-induced diabetic rats correlated with a reduced rate of the rise and decline of intracellular Ca2+ transients elicited by electrical stimulation (Choi 2002), which has been attributed to abnormal SR pump activity (Ganguly 1983), decreased SR Ca2+ storage (Bouchard 1991), and reduced Na+/Ca2+ exchanger activity (Yaras 2005). However,... 

Fukushi K, Nagai M. Kamata Y, Kadotani K (1984) Mechanical properties of low thermal contraction GFRP. In Hartwig G, Evans D (eds) Nonmetallic materials and composites at low temperature, vol 3. Plenum, New York, p 187... 

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. 

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