High shear moduli

Hardness measures the resistance of a material to a permanent change of shape. That is, the resistance to shear deformation (not the resistance to a volume change). The precursor to a permanent shape change is a temporary elastic shape change, and a shear modulus determines this. Therefore, the first necessity for high hardness is a high shear modulus. 

P.-Y. Lin. High shear modulus aramid honeycomb. US Patent 5 137 768, assigned to E. I. Du Pont de Nemours and Company (Wilmington, DE), August 11, 1992. 

Carbon Fibres (provide dimensional stability and retention, performance at high temperatures, very low GTE, tailorable thermal conductivity, high shear modulus) ... 

Aniline-formaldehyde condensation products, when treated with MA may be used to prepare polyfunctional maleimldes. " After curing, under heat and pressure, these materials exhibit high flexural strength, high shear modulus, and excellent solvent and heat resistance. 

Figure 9.1 The crystal structure of M5-HT seen along the chain axis. Note the bidirectional hydrogen-bonded network between the chains resembling a honeycomb and reinforcing the lateral chain - chain interaction. This leads to a high shear modulus and shear strength and thus to good compressive properties of the M5 fiber. We speculate that this honeycomb-like structure may be involved in the explanation of the impact and damage tolerance properties of M5 products (reprinted from ref. 38 with permission from Elsevier).

Manuf urers Comments Low viscosity with good wetting. Cures at 95 C. Good hoVwet strength. High shear modulus. 6MS 8-301 quaiHied. 

The elastic moduli are considered to be related to the interatomic forces in intermetallic compounds. Thus, the elastic moduli at room temperature have been related to melting temperatures for various intermetallic compounds (Fleischer, 1991 Skinner and Zedalis, 1988). Figure 19 shows the shear modulus G at room temperature versus melting temperature for polycrystalline intermetallics (Fleischer, 1991). This indicates that the probability of a high shear modulus increases remarkably with melting temperature. The correlation presented in Figure 19 may indicate that... 

Superabsorbents. Water-sweUable polymers are used extensively in consumer articles and for industrial appUcations. Most of these polymers are cross-linked acryUc copolymers of metal salts of acryUc acid and acrylamide or other monomers such as 2-acrylamido-2-methylpropanesulfonic acid. These hydrogel forming systems can have high gel strength as measured by the shear modulus (134). Sometimes inorganic water-insoluble powder is blended with the polymer to increase gel strength (135). Patents describe processes for making cross-linked polyurethane foams which contain superabsorbent polymers (136,137). 

With appropriate caUbration the complex characteristic impedance at each resonance frequency can be calculated and related to the complex shear modulus, G, of the solution. Extrapolations to 2ero concentration yield the intrinsic storage and loss moduH [G ] and [G"], respectively, which are molecular properties. In the viscosity range of 0.5-50 mPa-s, the instmment provides valuable experimental data on dilute solutions of random coil (291), branched (292), and rod-like (293) polymers. The upper limit for shearing frequency for the MLR is 800 H2. High frequency (20 to 500 K H2) viscoelastic properties can be measured with another instmment, the high frequency torsional rod apparatus (HFTRA) (294). 

The solidity of gel electrolytes results from chain entanglements. At high temperatures they flow like liquids, but on cooling they show a small increase in the shear modulus at temperatures well above T. This is the liquid-to-rubber transition. The values of shear modulus and viscosity for rubbery solids are considerably lower than those for glass forming liquids at an equivalent structural relaxation time. The local or microscopic viscosity relaxation time of the rubbery material, which is reflected in the 7], obeys a VTF equation with a pre-exponential factor equivalent to that for small-molecule liquids. Above the liquid-to-rubber transition, the VTF equation is also obeyed but the pre-exponential term for viscosity is much larger than is typical for small-molecule liquids and is dependent on the polymer molecular weight. 

In many isotropic materials the shear modulus G is high compared to the elastic modulus E, and the shear distortion of a transversely loaded beam is so small that it can be neglected in calculating deflection. In a structural sandwich the core shear modulus G, is usually so much smaller than Ef of the facings that the shear distortion of the core may be large and therefore contribute significantly to the deflection of a transversely loaded beam. The total deflection of a beam is thus composed of two factors the deflection caused by the bending moment alone, and the deflection caused by shear, that is, S = m + Ss, where S = total deflection, Sm = moment deflection, and Ss = shear deflection. 

The simply supported beam has a load applied centrally. The upper skin go into compression while the lower one goes into tension, and a uniform bending curve will develop. However, this happens only if the shear rigidity or shear modulus of the cellular core is sufficiently high. If this is not the case, both skins will deflect as independent members, thus eliminating the load-bearing capability of the plastic composite structure. 

TDI isomers, 210 Tear strength tests, 242-243 TEDA. See Triethylene diamine (TEDA) Telechelic oligomers, 456, 457 copolymerization of, 453-454 Telechelics, from polybutadiene, 456-459 TEM technique, 163-164 Temperature, polyamide shear modulus and, 138. See also /3-transition temperature (7)>) Brill temperature Deblocking temperatures //-transition temperature (Ty) Glass transition temperature (7) ) Heat deflection temperature (HDT) Heat distortion temperature (HDT) High-temperature entries Low-temperature entries Melting temperature (Fm) Modulu s - temperature relationship Thermal entries Tensile strength, 3, 242 TEOS. See Tetraethoxysilane (TEOS)... 

We conclude that high internal stresses are generated by simple shear of a long incompressible rectangular rubber block, if the end surfaces are stress-free. These internal stresses are due to restraints at the bonded plates. One consequence is that a high hydrostatic tension may be set up in the interior of the sheared block. For example, at an imposed shear strain of 3, the negative pressure in the interior is predicted to be about three times the shear modulus p. This is sufficiently high to cause internal fracture in a soft rubbery solid [5]. 

The latter can be estimated from the side force coefficients obtained during the abrasion experiments for a small shp angle and a high speed. They reflect directly the compound stiffness and since the dimensions are the same also the shear modulus. 

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