Joining sheets made from dissimilar materials by hole hemming

This research work presents a new joining process based on the hemming process for attaching sheets made from dissimilar materials with very different mechanical properties. The process is termed ‘hole hemming’ and consists in producing a mechanical interlock between pre-drilled holes which can be made anywhere on the sheets. The process is carried out in a two-stage operation including flanging the hole of an outer sheet and bending the flange over the hole of an inner sheet. First, the joining stages and the required tools are designed. Then, the joining of DP780 steel and AA6061-T6 aluminium alloy sheets, which are applied to manufacture lightweight structures in the automotive industries, is investigated using finite element analysis. Results show that the hole hemming process is able to successfully join these materials without fracture. The hole-hemmed joint withstood the maximum forces of 2.5 and 0.5 kN in single-lap shear and peel tests, respectively, and failed with hole bearing mode which is known as a gradual failure mode. The results demonstrate the applicability of the hole hemming process for joining dissimilar materials.

Failure mechanism of TRSS mode in landslides induced by earthquake

Investigation of the slopes in the Wenchuan earthquake shows that tension failures appear in the upper part in many landslides. The typical failure mode can be generalized as “tensile-rupture and sheared-sliding” (TRSS). In this paper, the distinct element method (DEM) is employed to simulate the gradual failure process of the Tangjiashan landslide under the excitation of the Wenchuan earthquake. It is found that the first failure is the appearance of deep tension cracks on the top, and then shearing slip along the bottom. The posterior fracture is deep, steep, and rough, and the bottom shear slip surface has a relatively gently dip. The simulation shows the failure mode of TRSS in the slope can be well reproduced, and the geological and mechanical mechanisms can be revealed in the DEM model.

Individual forecasting of reliability of bipolar transistors by using electrical voltage as a simulation factor

Individual forecasting of the reliability of semiconductor devices, taking into account gradual failures, is an urgent task, as it allows you to choose highly reliable instances for critical electronic devices of long-term functioning. In relation to bipolar transistors, an approach is proposed that allows us to solve this problem by using the voltage applied to the collector-emitter junction as a simulated effect. Using the example of highpower bipolar transistors of the KT872A type, it is shown how the problem is solved. For the sample of transistors of this type using the results of a training experiment, two equations were obtained to describe the electrical parameter under consideration (a static base current transfer coefficient in a circuit with a common emitter), the value of which judges the absence or presence of a gradual failure for a specific instance. The first equation shows how the electrical parameter changes on average depending on the voltage applied to the collector – emitter junction. The second equation describes the average degradation of the electrical parameter during long-term operating time of transistors. Based on these two equations, a simulation model of the reliability of bipolar transistors of the type in question is obtained in the form of a communication function that shows what level of simulation voltage corresponds to a given operating time. As applied to the transistors of the type under consideration, the obtained simulation model allows us to individually predict reliability by the gradual failures of the same type of samples that did not participate in the training experiment. To do this, first determine the value of the simulation voltage corresponding to a given operating time. This is achieved by substituting a given operating time into the model. The individual forecasting of the reliability of a new onetype instance consists in measuring the electrical parameter of this instance at a voltage on the transistor collector corresponding to the calculated simulation value, and comparing the measurement result with the norm set on the electrical parameter.

Investigating the effect of different bonding areas on the lateral resistance of polyurethane-mixed ballast using the discrete element method

In order to investigate the characteristics of the lateral resistance of the polyurethane-mixed ballast with different bonding areas, a sleeper–ballast model was established using the discrete element method. The lateral resistance of the polyurethane-mixed ballast with single and combined bonding modes was analyzed. The results show that the lateral resistance increases with the increase of the bonding depth of the shoulder ballast. After the bonding depth of the crib ballast and the base ballast reaches 5 cm and 15 cm below the bottom of the sleeper, respectively, there is no significant development of the lateral resistance. The lateral resistance cannot be improved efficiently by bonding the slope ballast. The combined bonding of the crib ballast and the base ballast is an effective method to improve the lateral resistance. With the gradual failure of the bonding contact points between the sleeper and the ballast, the average value of the lateral resistance decreases linearly and the lateral resistance presents a greater randomness under the more complex bonding mode.

Quest for Bioactive Compounds in Our Diet with Anti-Ageing and Anti-Aggregation Properties

Ageing is a complex process affected by both genetic and environmental factors, characterized by a gradual failure of functionality, reduced stress response and resistance, leading to enhanced probability for age-related diseases and mortality. During the last decades, natural compounds have attracted the attention of researchers in the quest of bioactive phytochemicals with anti-ageing properties. For a few of these compounds an extra advantage appears; many of them have been shown to decelerate the progression of age-related diseases with emphasis on aggregation-related diseases. Using the nematode Caenorhabditis elegans along with the replicative senescence model of human primary fibroblasts, we have identified compounds that are part of our diet with anti-oxidation, anti-ageing and anti-aggregation activities. Some of the identified compounds promote their anti-ageing activity through activation of the proteasome, others through the activation of Nrf2 transcription factor, while others through inhibition of glucose transporters (GLUTs). Our work identifies new bioactive compounds with anti-ageing and/or anti-aggregation properties or reveals additional beneficial properties on already known bioactive compounds.

Age and size dependencies of firm failure processes: an analysis of bankrupted Estonian firms

Purpose This study aims to find out whether firm failure processes are age- and size-dependent. Design/methodology/approach The sample consists of 333 bankrupted Estonian firms. Failure processes are detected with consecutive factor and cluster analyses of six financial variables calculated for three pre-failure years. Multinomial logistic regression is applied to study the interconnections between failure processes (dependent variable) and firm size and age (independent variables). In addition, the contingency between detected failure processes and failure causes obtained from court judgements are studied. Findings Three failure processes are detected, of which the predominant one accounting for 55 per cent of cases is a gradual failure process, indicating a step-by-step decline in the values of financial variables. The two minority processes are mixed, meaning that some financial variables are poor for many years before the bankruptcy and others decrease only shortly before bankruptcy declaration. With an increase in firm size, the gradual failure process becomes more common, but in turn, the presence of the gradual failure process is not age-dependent. Failure causes detected by trustees are not associated with failure processes. Originality/value This paper is the first one to specifically outline the age and size dependencies of firm failure processes. In addition, the interconnection of failure causes and firm failure processes detected with financial variables are rarely studied topics.

Failure processes of exporting firms: evidence from France

Purpose This paper aims to detect failure processes of French exporting firms and study their contingency with export processes. Design/methodology/approach The sample consisted of 131 bankrupted exporting firms from Bureau van Dijk’s Amadeus database. Factor and cluster analyses of six financial variables from Laitinen’s (1991) model were used to detect failure processes. Export processes were detected with cluster analysis of export share in total turnover. Contingency between failure and export processes was studied with a statistical test. Findings Three different failure processes existed for exporting firms. Two of these processes, which accounted for 79 per cent of firms, were classified as gradual failure: a step-by-step worsening of financial performance before the bankruptcy was declared. One was a symbiotic process reflecting varying pre-bankruptcy behaviours of different financial variables. Two different types of exporters existed. Most firms (77 per cent) were occasional exporters, while 23 per cent were constantly and more strongly involved in international markets before their bankruptcy was declared. There was no contingency between failure and export processes. Originality/value This study is the first one to detect failure processes specifically for exporting firms based on financial variables. In line with previous literature about non-exporting firms, gradual failure processes were most characteristic to exporting firms. The study shows that different types of exporters were not characterized by any unique behaviour of financial variables before their bankruptcy was declared.

Production Hollow Ferrocement Beams Through Solid Waste Recycling

Present research includes the study of theoretical and experimental behavior of hollow ferrocement beams, by using solid waste of empty plastic bottles and empty metal can. Solid reinforced concrete and reinforced cement mortar for the purposes of comparison between behavior of hollow ferrocement beams and solid beams were casted. The results showed the possibility and efficiently of producing lightweight hollow beams using solid waste. The hollow ferrocement beam have a good flexural strength resistance, toughness, and high ductility as use wired mesh converts a sudden failure to a gradual failure and distributes cracks along the beam. The results also show the possibility of the production of hollow ferrocement beams without rebar, where using of wire mesh only increasing the economic and easily produce these lightweight beams. The study proved that the ferrocement hollow beam fail under the load higher than the design load.