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The mean temperature of the entire plantar area was found to be more stable than the individual subregions, serving as a more practical indicator for thermoregulatory functions. The study also found that the overall mean plantar temperature stabilized after 15 minutes, and, thus, this time was recommended for clinical thermographic measurements. The normalized temperature may have more useful application than the plantar absolute temperature, as exemplified by the better correlation in diabetic feet. The mean plantar temperature, the wait time to start measurement, and the proposed normalization are believed to play important roles in neuropathic foot disorders.

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Fiber reinforced composites have high specific strength, excellent fatigue resistance and variable directional freedom in property control, allowing for optimal structural design. A deficiency in stiff fiber reinforced composites is poor low-speed im pact resistance (i.e., low energy absorption before major failure). This has been ex perimentally shown to be remediable by coating the reinforcing fibers with an elastomeric coating. However, the stiffness of the composites is decreased because of reduced effi ciency in interface load transfer in the soft coating. This can be improved by making the coating very thin. For practical design, it is necessary therefore to provide an analytical relation between the increase in failure work and the corresponding decrease in stiffness with the coating properties. Interface stress concentration is parametrically studied in this paper. A formula for calculating the longitudinal modulus of composites reinforced by aligned coated fibers is proposed. The formula is based on a combination of both compos ite mechanics and finite-element stress analysis. The results provide fundamental guide lines to practical engineering applications of composites of elastomer-coated fibers.

The use of a thin rubber coating on the fiber in a fibrous composite has been shown to increase the composite low-speed impact resistance [1,2]. The coating used was very thin compared to the fiber diameter, in order to preserve the other composite properties. From elastic consideration, the thin rubber coating was understood to have a direct effect upon the reduction of the stress concentration in the region near the fiber/matrix interface, especially at the chopped fiber end or at the matrix crack front reaching the fiber [3,4]. If the possible existence of localized high stress zones is reduced, the material can be subjected to higher loading before global failure occurs. With the rub ber coating the high stress zones inside the material can spread out to a larger volume. There will be less chance for local damage to initiate under the same loading level. The material will therefore exhibit higher resistance to failure, i.e., it will absorb more energy before failure. Three injection-molded glass/nylon composites were tested for tensile fail ing energy. One is reinforced with bare chopped fibers and the other two are with rubber- coated fibers. Tensile experiments showed significant increase of energy absorption in one sample with a rubber coating. Micrograph study was extensively carried out on the failed samples to identify the parameters of this desirable consequence. The rupture of the rub ber interphase and the limited plastic flow of the nylon matrix on the fractured surface of failed specimens were clearly evidenced. Meanwhile, interfacial bonding measured through microdebonding tests [4] revealed reasonable relation of the characteristic inter facial bonding and the energy absorption.