Considerations concerning fatigue life of metal matrix composites

Since metal matrix composites (MMC) are composed from two very distinct materials each having their own physical and mechanical properties, it is feasible that the fatigue resistance depends on the strength of the weaker constituent. Based on this assumption, isothermal fatigue lives of several MMC's were analyzed utilizing a fatigue life diagram approach. For each MMC, the fatigue life diagram was quantified using the mechanical properties of its constituents. The fatigue life regions controlled by fiber fracture and matrix were also quantitatively defined

Response of a Cracked Cantilever Beam to Free and Forced Vibrations

Cracks present in machine parts affect their vibrational behaviour like the fundamental frequency and the resonance. In this paper, the resonance response of a cracked cantilever rectangular beam has been studied based on fracture mechanics quantities like strain energy release rate, stress intensity factor and compliance. The spring stiffness and the fundamental frequency decrease with increase in crack length. The amplitude of vibration increases and the occurrence of resonance gets shifted with increase in crack length

Equivalent Stress Approach to Life Prediction of Creeping Solids with Initial Defect

High temperature components contain many crack like defects introduced during the fabrication processes. These defects will grow during service under the action of applied stress and elevated temperature. An equivalent stress approach has been developed in this paper which can be effectively used to predict the life of defective materials under creep conditions

The structure of integrated pulse profiles

We offer two possible explanations to account for the characteristics of integrated pulse profiles, in particular their degree of complexity, their variation from pulsar to pulsar, their stability, and the tendency of complex profiles to be associated with older pulsars. It is proposed that the pulse structure could be a reflection of surface irregularities at the polar caps, and it is shown how the surface relief can affect the number of positrons released into the magnetosphere which are subsequently responsible for the observed radio radiation. The electrons produced in the vacuum break-down in the gap carry enough energy to allow creating such a surface relief in ˜ 106 years, and one way in which this could be achieved is discussed. Alternatively, the presence of multipole components in the magnetic fields of older pulsars could lead to significant variations in the curvature of the field lines across the gap, and hence to structure in the integrated pulse profiles. An assessment of the two hypotheses from observed pulse profiles seems to favour the polar cap relief picture

Lobster culture and live transport

Eight species of spiny lobsters, six shallow water and two deep sea species and two slipper or sand lobsters constitute the lobster fishery of Indi

Problems and prospects for lobster farming in India

The potential for increasing the lobster yield from the wild is limited, as most of the stocks have reached optimum levels of production. Hence attempts were made by the CMFR Institute to successfully grow the non-cannibalistic species under captivity in view of the above and demand for live lobster in export market. The paper reviews the previous culture attempts and the present status on the spiny lobster, distribution of culturable species for farming and fattening, brood stock maintenance, larval culture, availability and growth of pueruli, collection and transportation of Juvenile lobsters, fattening of sub adults, growth acceleration by eye stalk ablation, farming in intertidal pits, environmental conditions for Juvenile rearing, stock density, food diease, economics of farming and fattening, and the future prospects in Indian condition

The status of lobster fishery in India and options for sustainable management

Lobsters form one of the most valuable cru stacean resources, which have been exploited commercially for the past four decades. Annual landings increased from 350 t in 1965 to 4100 t in 1985 but have declined since then , Though lobsters are distributed along the entire coast of India major tishery grounds are located in the northwestern, south-western and south eastern coasts. Among the twelve species recorded from Indian waters four species of spiny lobsters (three linoral and one deep-sea) and one species of slipper lobster constitute the commercial fishery

An assessment of the potential of spiny lobster culture in India

Fluctuating catches and increasing demand in both internal and international markets for lobster tails necessitate augmentation of production through proper management strategies and possible aquaculture practices. The technical feasibility of economically viable aquaculture of few species of spiny lobsters Is underway at the Field Laboratory of Central Marine Fisheries Research Institute, Kovalam, Madras. Though captive breeding of various species of spiny lobsters was achieved with ease, rearing of phyllosoma larvae to puerulii under controlled conditions was not successful. So serious attempt to cultivate spiny lobsters should begin with rearing juveniles which are caught in large numbers along with the commercial size lobsters It has been shown that commercial size (300 g) lobsters can grow in less than half the time that Is required in nature, by proper feeding schedules and environment management. A further reduction in this growing period has been achieved through bilateral eyestalk ablation. Enhancement of growth in ablated lobsters up to 20 times of normal rate has been achieved. An objective assessment of the present status of spiny lobster culture and the problems which need further attention for developing commercially feasible lobster culture are discusse

Early larval development of spiny lobster, Panulirus homarus (Linnaeus, 1758) reared in the laboratory

Phyllosoma larvae of the spiny lobster, Panulirus homarus were hatched and reared in the laboratory on a diet of Artemia salina nauplii. The larvae were rcared in individual as well as in mass culture systems. The temperature of the rearing water ranged from 26 to 29°C and salinity from 34 to 35‰. The larvae reared individually moulted nine times and reached the sixth stage in sixty days. Mean total length of the newly hatched larva was 1.48 mm and stage VI larva measured an average of 4.87 mm. The early stages ofphyllosoma larva of P. homarus are morphologically similar to those of other tropical species. Larvae infested with sedentary ectoparasites were effectively treated with 10 ppm malachite green. Change in feeding habits resulted in mortality of the larvae in the sixth stage

On the Excess Dispersion in the Polarization Position Angle of Pulsar Radio Emission

The polarization position angles (PA) of pulsar radio emission occupy a distribution that can be much wider than what is expected from the average linear polarization and the off-pulse instrumental noise. Contrary to our limited understanding of the emission mechanism, the excess dispersion in PA implies that pulsar PAs vary in a random fashion. An eigenvalue analysis of the measured Stokes parameters is developed to determine the origin of the excess PA dispersion. The analysis is applied to sensitive, well-calibrated polarization observations of PSR B1929+10 and PSR B2020+28. The analysis clarifies the origin of polarization fluctuations in the emission and reveals that the excess PA dispersion is caused by the isotropic inflation of the data point cluster formed by the measured Stokes parameters. The inflation of the cluster is not consistent with random fluctuations in PA, as might be expected from random changes in the orientation of the magnetic field lines in the emission region or from stochastic Faraday rotation in either the pulsar magnetosphere or the interstellar medium. The inflation of the cluster, and thus the excess PA dispersion, is attributed to randomly polarized radiation in the received pulsar signal. The analysis also indicates that orthogonal polarization modes (OPM) occur where the radio emission is heavily modulated. In fact, OPM may only occur where the modulation index exceeds a critical value of about 0.3.Comment: Accepted for publication in Ap