No abstract

Biomass may be converted to energy by enzymatic hydrolysis to monomer components and fermentative conversion of those products to ethanol for use as fuel. Both glucose and xylose in aqueous solution were directly converted to electrical energy using a liquid alkaline fuel cell (AFC) at room temperature. Hydrolysis products derived from the action of cellulase and amylase on cellulose and starch, respectively, were also used as fuels in the AFC system. We suggest that this approach may provide a more direct means of accessing some of the energy available from biomass.

No abstract

No abstract

THE PURPOSE of this note is to draw attention to the apparently little-known fact that stage I1 type fatigue cracks can initiate and grow under compressive applied loads. The effect has been demonstrated in compact tension specimens, 25 mm thick [I], of normalised mild steel and En 8. First, the specimen with a machined notch was compressed for about 10 s by a load of 50.5 kN (corresponding to a stress intensity at the notch tip of 77.4 MN rnP3/'). Next, the specimen was subjected to a 25 Hz sinusoidal compressive load with a mean level of 14.1 kN and an amplitude of 11.7 kN (corresponding to a stress intensity range of 35.9 MN m-3/2). Growth of a crack from the notch tip was seen parallel to the plane of the notch. The length a of this crack on the surface of the specimen is plotted in Fig. 1 as a function of the number of compressive load cycles. It is clear that the crack grows at a decreasing rate until eventually it stops growing altogether. Once it was established that crack growth had stopped, the cyclic loading was ended and the specimen was subjected to a tensile "ramp" load, causing a brittle fracture. The fracture surface of such a specimen is shown in Fig. 2. The fatigue crack front has a marked concave shape in contrast to the slightly conveli shape shown in Fig. 3, which was obtained by subjecting an identical specimen to cyclic loads of the same magnitude in tension but without prior overload. Note too the smoother appearance of the fatigue fracture surface in this specimen.It is tentatively suggested that during the initial compressive overload, a plastic zone is formed near the tip of the notch with a shape that depends on the depth below the surface of