An open fireside is estimated to produce smoke equivalent to that of burning 400 cigarettes per hour. To reduce indoor air pollution from improved cookstoves, manufacturers should demonstrate the reliability of various aspects of their product, including thermal efficiency, cooking power, emissions, safety, and durability. This study investigated the optimal design of a reliability demonstration test (RDT) plan for accepting or rejecting a batch of cookstoves based on a target of no more than 5% failures at the end of the warranty period. The planning parameters for the RDT plan included the number of units to be tested (3, 5, 7), the reliability target of 95%, the confidence level of 95%, the maximum number of allowed failures (0, 1, 2, 3), the statistical power of the reliability test, and the values of the Weibull shape parameter (β_1=2.5; β_2=3.0; and β_3=3.5). The required number of samples and testing time for a successful reliability demonstration were determined using Minitab statistical software. The study results show that larger sample sizes or Weibull shape parameters lead to shorter required test times. The statistical power results for eleven scenarios demonstrate that the probability of passing the demonstration test increases as the improvement ratio or shape parameter increases. When the improvement ratio was 1.5 and the shape parameter was 2.5, the probability of passing the test increased from 34% to 54% for a fixed number of maximum allowable failures. Moreover, if the stove’s actual performance exceeds the standard that the test was designed to measure, the demonstration test’s power for one maximum allowable failure would be equivalent to that for three maximum allowable failures.

Reed valves in a compressor are critical parts that have a high fatigue failure potential due to cyclic bending and impact caused by the cyclic nature of the compression process. A sudden failure of a valve renders the compressor useless. Although the refining process of methods of fatigue design has already taken more than 50 years, older criteria such as Gerber and Goodman models are still attractive for engineering design of high cycle fatigue components. This paper presents an investigation on the effect of nonzero mean stress on the design of valve reeds that are widely used in compressors. The investigation relates the choice of a mean stress compensation models, with the predicted fluctuating bending fatigue strength and estimated safety coefficient values. The calculations have been performed using Gerber, Goodman, Soderberg, ASME, Crossland, and Tsapi-Soh models. The most relevant goal of this paper is to verify the efficiency of classical and advanced stress based multiaxial fatigue criteria to estimated value of fluctuating bending fatigue strength. The criterion proposed by Tsapi-Soh was found to gives estimated value of the fluctuating bending fatigue strength very close to the typical value from technical data and satisfying results in predicting the survival of the reed valves under bending fatigue failure.

Newer fatigue prediction models for estimating the multiaxial fatigue limit often lack a simple analytical solution and the complexity of multiaxial solutions during programming makes testing an unattractive task. This paper summarizes an attempt to propose a novel equivalent stress approach suitable for estimating fatigue damage in the presence of complex multiaxial fatigue loadings. According to the devised method, fatigue limit under multiaxial loading is evaluated by proposing an equivalent loading with zero out-of-phase angles. The accuracy of the proposed approach was systematically checked by means of 87 experimental data taken from the literature and generated by testing different metallic materials under both in-phase and out-of-phase biaxial fatigue loading. Results show that the equivalent stress approach is an elaboration of non-conservative stress invariant based multiaxial fatigue criteria like the well-known Sines method. This exercise allowed us to prove that the systematic application of the equivalent stress resulted in highly accurate predictions and it held true independently of the cause of the mobility of principal stress directions of the stress field damaging the fatigue process zone. Simulations also emphasize a general quite better precision of the proposed equivalent stress approach when compared to another method, namely the minimum circumscribed ellipse approach.

This article is a comparative study of metallurgical characteristics of the different aluminium alloys gotten through recycling of recovered aluminium in Cameroon. A simple experimental device for the foundry of secondary aluminium blend, of very good quality built around a movable charcoal furnace is presented. It enables better energy efficiency, a better distribution of the heat around the crucible and indirectly assures good quality of the products obtained, while respecting the economic constraints and users' safety. Six refining methods are proposed by the addition of polyvinyl chloride (method A), coke rich in carbon CH_S (method C), ammonium chloride NH₄Cl (method E), manganese dioxide MnO (method T), acrylic nitrite (C₂H₃Cl)_n (method P) and sodium chloride NaCl (method S). A critical analysis of the different recycling techniques is presented as well as a proposed process of melting and refining that enables the obtaining products with high degrees of purity. The results are then compared to the results obtained from the industrial methods of aluminium refining such as fractional crystallization (FC), granular filtration (GF) and dissolution in a metal solvent (DS). The later (DS) gives the rate of 6.540% of accumulated alloy elements and enables the best purification (93.460%), while the NaCl gives the lowest global rate of additive elements (9.478%), with the best purity index (90.522%) amount the proposed methods. Results obtained show that this method of refining improves the metallurgical properties of secondary aluminium alloy blends and guarantees better safety, as well as reducing the risks of environmental pollution.