Review: The need for a fiber with the heat resistance of asbestos and the stiffness of glass led to the development of Kevlar which has a molecular orientation parallel to the fiber axis (see figure). Brian Phillips et al. trace the many faceted course of the development of Kevlar from the initial scientific discovery to the opening of a 45 million lb/yr production plant.

No abstract

Light‐scattering, osmotic pressure, and viscometric studies on fractions of cellulose acetate (degree of substitution 2.45) in three solvents are described. The data yield the dependence of the mean‐square radius of gyration 〈s2〉, the second virial coefficient Γ2, and the intrinsic viscosity [η] on molecular weight M and temperature. The results are interpreted to show that excluded volume effects on 〈s2〉 are negligible, even though Γ2 is large and dΓ2/dT is positive. The large experimental value of d In [η]/d In M is interpreted in terms of partial draining effects. Data on 〈s2〉 and [η] for other cellulose esters in the literature are similarly interpreted. Significant aggregation found in solutions of cellulose acetate in many solvents is discussed.

Limited space permits description of only two examples of Kevlar applications research. There are numerous others. In the early product development there were some indications that Kevlar would go mainly into tire reinforcement. This has turned out not to be true. In the mid‐seventies Kevlar was participating in only ten market segments and less than fifty specific applications, but today, it is in more than twenty market segments, serving more than two hundred applications, and continued growth is anticipated. Kevlar is produced in a 45 million pound plant in Richmond, VA, USA. In 1988, a second plant was started up in Northern Ireland and plans for a third plant in Japan were announced. The Kevlar innovation story exemplifies the kind of obstacles, interdisciplinary skills and systems approach involved in bringing a laboratory discovery to commercial reality. The story is still unfolding and applications currently not envisioned will undoubtedly become important in the future. .

This paper deals with the determination of material constitutive model for P91 and P92 steels at high temperatures. An isothermal, strain-controlled test programme was conducted for both steels for a temperatre range between 400 and 675˚C. The experimental data from these tests were used to obtain the material constants in a viscoplasticity model. The model includes the effects of isotropic and kinematic hardening, as well as time-dependent effects, has been used to model the cyclic material behaviour of each material. Material constants were initially determined from initial cycle stress-strain data, maximum stress evolution data and stress relaxation data. The material constants were improved by use of a least-squares optimisation algorithm. The constitutive models have been implemented into the ABAQUS finite element (FE) code by using the Z-mat software. The performances of the material models for both steels have been assessed by comparing predictions with experimental data obtained from the tests.