Mechanical properties elastic modulus

As carbon nanotubes present exceptional mechanical, superior thermal and electrical properties in general, by using them as reinforcing elements there are high expectations for improvement of quality of nano- and microcomposites [14-18]. As shown from earlier measurements, through carbon nanotube addition a 15-37% improvement of mechanical properties (elastic modulus and strength) can be achieved in comparison to other carbon-filled samples [19]. 

Table 19.6 Mechanical properties (elastic modulus ( ), shear modulus (G), Poisson s ratio (v), hardness Hz), and fracture toughness Klc) of composites sintered by SPS...

Upper working temperature, °C Mechanical properties Elastic modulus, GPa D638 527... 

It is concluded that the thermal properties (melting temperature, melting enthalpy, and degree of crystallinity), thermal stability, and mechanical properties (elastic modulus tensile strength and extension at break) of highly crystalline polypropylene showed change after irradiation. 

Experimental data issued from tensile tests on samples with varying amyl acetate concentration and ageing temperature have evidenced a decrease of mechanical properties (elastic modulus, peak load, cristalUnity) over time. These experimental results match the amyl acetate molecules penetration effect in the polymeric material, inducing a decrease of the intermolecular interactions in the polymer, like a plasticizer should do. 

The use of the electric field has been proposed and demonstrated to perform very well in defining various other properties. For example, electrical measurements have been used to monitor the foaming process and polymerization of polymeric foams [74], while dielectric measurements have been used for measuring the density of polymer foams [75]. Brady et al. [76] developed electrically conductive polypyrrole-coated PUR foam. The conductance of the foam was found to change linearly with the compressive load applied single and repeated. For aluminum foams, Kim et al. [77] developed a set of mathematical relationships based on experimental data to obtain mechanical properties (elastic modulus, compressive strength, and densification strain), using electrical conductivity as a non-destructive inspection method. 

There is an increase in the polymer strength when the polymers are formed within a gradient of shear stresses, known to result in the alteration of the macromolecular conformation. For example, polyethylene produced by melt extrusion through capillaries rmder high pressure possesses unique physical-mechanical properties—its modulus of elasticity is of the same order as that of glass fiber (7 x 10 ° Pa) [116],... 

Many properties of spider silks have been studied including the physicochem-istry, mechanical stress, elastic modulus and strain energy.The present author has investigated the thermal, optical, molecular, aging and mechanical properties of spider silks. 

Influence of the amount of PEDOT-PSS on mechanical properties was studied using d3mamic mechanical anatysis in tension mode. Uniaxial tensile tests were carried out at 30 1°C with TA Q800 Dynamic Mechanic Analyzer. Elastic modulus and breaking points were measured by increasing ramp force 0.1 N/min to 18.0 N/min. Composite nanofibers were electrospun for three hours to measure mechanical properties. At least four specimens were tested for each measurement and the average values are presented. 

In general, the addition of one layer with better mechanical properties, higher modulus of elasticity, than the subgrade results in reduction of stresses exerted at the subgrade. This can clearly be seen in Figure 11.11. 

Hardness H defines the resistance to local deformation of a material when indented, drilled, sawed, or abraded. It involves a complex combination of properties (elastic modulus, yield strength, strain-hardening capacity). The prevailing deformation mechanism depends upon the material and the type of tester. Hardness is either measured by (1) static penetration of the specimen with a standard inden-ter at a known force, (2) dynamic reboimd of a standard indenter of known mass dropped from a standard height, or (3) scratching with a standard pointed tool under a load. The hardness tester, indenter shape, and force employed strongly influence the hardness numbers (1). 

Lightly crossUnked acrylic networks Bulk rheological properties, elastic modulus, resistance to interfacial crack propagation Dynamic mechanical spectroscopy 129... 

Mechanical properties - elastic (Young s) modulus, yield stress, fracture toughness, hardness, wear resistance... 

Much more information can be obtained by examining the mechanical properties of a viscoelastic material over an extensive temperature range. A convenient nondestmctive method is the measurement of torsional modulus. A number of instmments are available (13—18). More details on use and interpretation of these measurements may be found in references 8 and 19—25. An increase in modulus value means an increase in polymer hardness or stiffness. The various regions of elastic behavior are shown in Figure 1. Curve A of Figure 1 is that of a soft polymer, curve B of a hard polymer. To a close approximation both are transpositions of each other on the temperature scale. A copolymer curve would fall between those of the homopolymers, with the displacement depending on the amount of hard monomer in the copolymer (26—28). 

---