Fiber orientation of polymer injection weld and its strength evaluation

This paper discusses the microstrure related fracture behavior of short-fiber reinforced thermoplastics. The microstructure of an injection molded weld was studied by microscopic methods for the purpose of describing fiber orientation. Injection welds are the place where two flow fronts come together, leading to fiber orientations having flower and volcano-like patterns. The polymer composite materials used in the experiment were polycarbonate(PC) with amorphous structure containing 30% short glass fiber and polyphenylene sulfide(PPS) with crystalline structure containing 40% short glass fiber. The specimen used was a dumbbell type tensile specimen with a weld line created by double gate injection molding. Microtoming technique was used for slicing ultrathin sections from the molded polymer parts. Microstructural analysis of fiber orientation at injection weld was carried out using light transmission microscopy (LM) and scanning electronic microscopy (SEM).     

A fuzzy controller based on self-tuning rules for the nuclear steam generator water level

It was demonstrated that the fuzzy control method could be applied successfully to control and regulate the nuclear steam generator water level through previous works. However, this method has some limitations from the fact that its performance largely depends on the tuning method and how to settle the rule base. In this work, a fuzzy control algorithm based on self-tuning rules is investigated to find the optimal tuning point and to generate the control rule automatically. It adopts an on-line iterative method and the objective error function which contains the variation errors of all time-steps. The triangular membership functions based on the mass flow rate and water level errors are applied. And also, a forgetting factor is used to account for an exponential decay of the past data in tracking the slow drift in system parameters. Thus it controls the steam generator water level from low power to full power with a little transients. This control algorithm is validated by computer simulations.     

Effects of grain size on the wear of recycled AZ91 Mg

Magnesium alloy AZ91 chips have been recycled using mechanical milling to yield samples with fine grain sizes. Together with cast samples of the same alloy, the wear behavior of these materials was studied through pin-on-disc sliding, with speeds varying from 1 to , under a normal load of 10 N. Despite the differences in grain size (0.6–) and mechanical properties, the various specimens did not differ significantly in their wear performance. Scanning electron microscopy observed abrasive wear to be dominant under low-speed sliding, and a transition to the formation of a protective mechanically mixed layer (MML) as sliding speed increased.     

Experimental study of acoustic characteristics of expansion chamber with mean flows

For the measurement of transmission loss of the silencers which have mean flow, the noise levels of signals depicted by microphone usually prohibit accurate measurements of the transmission loss. To overcome this difficulty, static pressure compensation technique has been developed to increase the dynamic range of the microphones, resulting accurate measurement of transmission loss in the presence of high noise level. Series of experiments to investigate the acoustic characteristics of expansion chamber with mean flow has been performed using the pressure compensated microphones. Results demonstrate: (1) frequency shift due to the presence of mean flow, (2) effect of length, diameter, offset length and twisting angles to the transmission loss of expansion chamber with and without mean flow (up to 50m/sec), (3) relation between the proposed parameter ‘aspect ratio’ and number of peaks of transmission loss in low frequency region.     

An evaluation method of probability of elastic-plastic fracture by 2-parameter criterion

Many researchers have made a lot of progress in studying the evaluation of fracture probability of brittle materials. However, studies of fracture probability for elastic-plasticity have not been made yet. An evaluation method for fracture probability which is grafted onto a 2-parameter criterion and statistical probability analysis is not only introduced in this study, but also applied to the simple 2-dimensional model and carbon steel piping to vealuate the effect of statistical variables.     

The unlubricated wear of sintered steels

The unlubricated wear of 10.3% porosity sintered medium-carbon and 12.8% porosity sintered low-alloy steels was investigated under different sliding conditions. Their wear characteristics were found to be similar to their non-sintered counterparts. Within this range of sliding conditions, both mild-oxidational and delamination wear took place, with the former dominating the wear processes. The oxide debris produced changed with the applied load: switching from a low-temperature oxide to a high-temperature one at higher loads. The wear rates agreed reasonably well with Archard's law and with data from other sources, suggesting that Archard's law can account for the wear rates produced by both mild-oxidational wear and delamination wear. This agreement also suggests that within the range of porosites investigated an overall framework can be established in the unlubricated wear of both sintered and non-sintered steels.