Hardness, Youngs Modulus, and Strength

Hardness of polyurethane pads can vary from shore D values of less than 15 (very soft and flexible pads) to greater than 65 (very stiff and rigid pads), and Young s (elastic) modulus of polyurethane pads can vary from a low of 1 MPa (very soft, flexible, and elastomeric pads) to greater than 1 GPa (very stiff and rigid pads). Usually, hardness increases with the increase in Young s modulus. 

Urethane stoichiometry also plays a key role in influencing the polyurethane pad properties. Stoichiometry refers to the ratio of reactive groups (usually diol or diamine moieties) to isocyanate groups. The presence of excess isocyanates 

2 Pad Porosity/Density Type I, II, and III pads all have pores although their microstructures are different. Type IV pads (noncell, nonporous, solid) do not have native porous microstructure except those generated by the conditioning process. Typical physical properties of ICIOOO pad (type III, porous) and IC2000 pad (type IV, noncell, nonporous, solid) are listed in Table 5.2. 

Pad porosity is inversely related to its density. Many physical properties of the polyurethan pad are strongly dependent upon its porosity (or density). The hardness and Young s modulus (elastic or storage modulus) of porous pads have a clear linear correlation with the density (or porosity) of the pads [1]. It is obvious that nonporous (noncell) pads have much smaller variability in density and other physical properties compared to porous pads. Nonporous pads have much higher strength, modulus, hardness, and elongation than porous pads. 

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