Mechanical load-displacement responses

For the noncooled specimen NC, during the pre-fire mechanical loading, a linear-elastic load-axial displacement response was observed until the maximum load of 145 kN was achieved. The lateral deflection at this load at midheight remained small 1.4 mm toward the fire side. When fire exposure started (attime t = 0), lateral deflection toward the fire side started to increase owing to the thermal expansion of the inner fire-exposed face sheet and reached a maximum of 8.1 mm after 20 min, see Figure 7.8. From this point on, lateral deflections started to decrease owing to... 

To study the interactions of yarns, a large number of analytical models have been developed. Most of these analytical models use mathematical relations to predict the mechanical response of yarns and fabrics in specific modes of deformation, such as the load-displacement relationship of the fabric under uniaxial and biaxial extension along the warp or weft directions. 

It may have already been noticed that all the described experiments correspond to a common basic scheme There is a force or field, represented here by the stress or the electric field, which leads to a displacement , as given by the strain or the polarization. In all the cases considered, the force and the resulting displacement are related by a linear equation. Hence, we dealt throughout with linear responses Clearly, many other effects exist which represent linear responses too. There are the reactions on still other kinds of mechanical loading but also on the applications of other fields, as for example, a magnetic field B which induces a magnetization M. 

Perhaps the most significant complication in the interpretation of nanoscale adhesion and mechanical properties measurements is the fact that the contact sizes are below the optical limit ( 1 t,im). Macroscopic adhesion studies and mechanical property measurements often rely on optical observations of the contact, and many of the contact mechanics models are formulated around direct measurement of the contact area or radius as a function of experimentally controlled parameters, such as load or displacement. In studies of colloids, scanning electron microscopy (SEM) has been used to view particle/surface contact sizes from the side to measure contact radius [3]. However, such a configuration is not easily employed in AFM and nanoindentation studies, and undesirable surface interactions from charging or contamination may arise. For adhesion studies (e.g. Johnson-Kendall-Roberts (JKR) [4] and probe-tack tests [5,6]), the probe/sample contact area is monitored as a function of load or displacement. This allows evaluation of load/area or even stress/strain response [7] as well as comparison to and development of contact mechanics theories. Area measurements are also important in traditional indentation experiments, where hardness is determined by measuring the residual contact area of the deformation optically [8J. For micro- and nanoscale studies, the dimensions of both the contact and residual deformation (if any) are below the optical limit. 

In a recent study, Saintier et al. ° investigated the multiaxial effects on fatigue crack nucleation and growth in natural mbber. They found that the same mechanisms of decohesion and cavitation of inclusions that cause crack nucleation and crack growth in uniaxial experiments were responsible for the crack behavior in multiaxial experiments. They studied crack orientations for nonproportional multiaxial fatigue loadings and found them to be related to the direction of the maximum first principal stress of a cycle when material plane rotations are taken into account. This method accounts for material rotations in the analysis due to the displacement of planes associated with large strain conditions. 

The mechanical and electrical displacements for metalized and free surfaces at liquid-36 YX LiTa03 interface are shown in Figure 4.4a and 4.4b [22]. Most of the acoustic energy is conhned to within one wavelength from the surface of the substrate. When the surface is metalized and electrically shorted, the potential on the surface is zero. In this case, only the normalized displacement (U2) interacts with the liquid loading, and the phenomenon is called mechanical perturbation. If the surface is free and electrically open, then both U2 and normalized electric potential (d>) interact with the adjacent liquid medium (Figure 4.4b). Interactions of d> and the electrical properties of the liquid constitute the acoustoelectric interaction. The influence of both the mechanical and acoustoelectrical interactions on sensor response and material characterization is discussed in the subsequent sections. 

Structural mechanics analyses are used to determined design variables such as displacements, forces, vibrations, buckling loads, and dynamic responses, including application of corresponding special areas of structural mechanics for simple structural elements. General purpose finite element programs such as NASTRAN are used for the structural analysis of complex structural shapes, large structures made from simple structural elements. And structural parts made from combinations of simple elements such as bars, rods and plates. 

Residual strength and displacement/gage length to failure of specimens with holes was presented in this work. It was observed that although the effect of the existence of the hole has an impact on the material response when compared to specimens without holes, the effect of the change in the hole size between 2.286 and 4.572 mm did not show a difference in response. A possible damage mechanism due to repeated loading evident in the reduction in the area of hysteresis loops was discussed. 

The material requirements for these classes of devices are somewhat different, and certain compounds will be better suited to particular applications. The ultrasonic motor, for instance, requires a very hard piezoelectric with a high mechanical quality factor Qm, to suppress heat generation. Driving the motor at the antiresonance frequency, rather than at resonance, is also an intriguing technique to reduce the load on the piezoceramic and the power supply [42]. The servo displacement transducer suffers most from strain hysteresis and, therefore, a PMN electrostrictor is used for this purpose. The pulse drive motor requires a low permittivity material aimed at quick response with a certain power supply rather than a small hysteresis, so soft PZT piezoelectrics are preferred rather than the high-permittivity PMN for this application. 

Recently, Boland et al utilized AFM to evaluate the mechanical properties of individual SWNT/PVA electrospun composite fibers prepared on a silicon surface pre-patterned with trenches [133]. These nanofibers were prepared with different loadings of SWNTs and had radii between 20 and 40 nm. Individual fiber sections were pinned across the trenches and laterally loaded by an AFM tip to yield mechanical response curves. A simple model was exploited to extract the tensile mechanical properties from the lateral force-displacement data. Depending on the fiber composition, the optimum tensile properties were reached when the nanotubes concentration was around 0.05 vol%, with the observed maximal strength and moduli of 2.6 and 85 GPa, respectively. Such optimized fibers break at strains of -4% and exhibit fracture toughness of up to 27 MJ/m, ... 

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