Probability justification for a minimum margin of safety when calculating ship machine parts and endurance mechanisms

Расчеты прочности при проектировании и создании современной техники являются одним из главных критериев качества и конкурентоспособности изделий машиностроения. Неотъемлемой частью расчета прочности на выносливость является оценка минимально допустимого запаса прочности. Существующая оценка этого запаса на основе данных по отказам деталей несет в себе большую долю субъективизма. Предлагается методика определения минимально допустимого коэффициента запаса прочности. Ее принципиальное отличие от существующих заключается в том, что здесь этот коэффициент запаса прочности подсчитывается с учетом рассеяния характеристик прочности детали и действующих в ней напряжений при заданной вероятности отсутствия усталостного разрушения. Это позволяет исключить многие условности при прогнозировании прочностной надежности деталей и создает предпосылки для получения проектных решений, оптимальных по прочности и массе. Strength calculations in the design and creation of modern technology are one of the main criteria for the quality and competitiveness of engineering products. An integral part of the endurance strength calculation is the assessment of the minimum allowable margin of strength. The existing assessment of this stock, based on data on the failure of parts, carries a large share of subjectivism. It is proposed a method of determining the minimum allowable safety factor. Its fundamental difference from the existing one is that here this strength factor is calculated taking into account the scattering of the characteristics of the strength of the part and the stresses in it at a given probability of absence of fatigue destruction. This eliminates many conventions when predicting the strength of the reliability of parts and creates the prerequisites for obtaining design solutions that are optimal in strength and mass.

RESOURCE–SAVING RESERVE OF STRENGTH CHARACTERISTICS OF LONGITUDINAL BEAM OF THE METRO WAGON TRUCK

In this paper, an analysis of methods for calculating structures from allowable stresses and from limiting states is made. It is shown that when the transition from the longitudinal beam calculation to the allowable stresses to the calculation of the limiting state, the strength limit increases by 1.5 times. A mathematical model of the stress–strain state of a longitudinal beam of metro wagon truck without taking into account the transverse force is developed. The mathematical modeling with the given margin of strength of the power calculation of the longitudinal beam metro wagon track, which is a simple beam of a constant hollow rectangular section, pinched at its ends and loaded along the middle of the span by a concentrated stationary force, is carried out. Thus, the application of the method of calculation for the limiting state makes it possible to identify the resource–saving reserve of the strength characteristics of the longitudinal beam of the metro wagon truck – a 3-fold increase in the maximum permissible load.

A Study of the metabolism of fowls: I. A calorimeter for the direct determination of the metabolism of fowls

Some years ago my colleague, Mr E. T. Halnan, suggested the construction of the present instrument for the purpose of determining figures for domestic fowls corresponding to those of Kellner for ruminants.Owing to the activity of the fowl, it is essential that an instrument for this purpose should be capable of recording accurately a heat output which may be varying with some rapidity.From this point of view the advantages of the indirect method were considered but were eventually rejected for the following reasons: (a) the advantage accruing from our greater experience of the direct method in this laboratory, (b) the work of Adams & Poulton (1933, 1934, 1935) calling in question the fundamental bases of the indirect method, and (c) the very variable R.Q.'S obtained in earlier work by numerous investigators working with birds.That the decision was wise soon became apparent when work on birds was begun. It is certain that no ordinary apparatus of that kind could possibly take account of the variations caused by the constant changes in activity.The principle of a “compensatory” or “balanced” calorimeter more or less as developed by Noyons (1927), Benedict (1927) and Heyster (1933), was selected as the most likely to give promptness in registration, and this choice has been amply justified in the result. Such instruments can be very lightly constructed, although where living animals are concerned, since their movements cannot be controlled, as can those of a human being, a greater margin of strength has to be provided, which naturally increases the heat capacity and lag and reduces sensitivity to small changes in heat evolution.

Experiments to determine the effects of impact, vibratory action, and a long-continued change of load on wrought-iron girders

The author observes that the experiments which were undertaken, nearly twenty years ago, to determine the strength and form of the Tubular Bridges which now span the Conway and Menai Straits, led to the adoption of certain forms of girder, such as the tubular, the plate, and the lattice girder, and other forms founded on the principle developed in the construction of these bridges. It was at first designed that the ultimate strength of these structures should be six times the heaviest load that could ever be laid upon them, after deducting half the weight of the tubes. This was considered a fair margin of strength ; but subsequent considerations, such as generally attend a new principle of construction with an untried material, showed the expediency of increasing i t ; and instead of the ultimate strength being six times, it was in some instances increased to eight times the weight of the greatest load.