Accelerated and Sequential Life Testing Applied to Steel Components Used in Highway Overpasses in Brazil

摘要

Sequential life testing approach with a truncation mechanism is an attractive alternative to that of predetermined, fixed sample size hypothesis testing because of the fewer observations required for its use, especially when the underlying sampling distribution is the three-parameter Weibull model. But it happens that sometimes the amount of time available for testing could be considerably less than the expected lifetime of the component. To overcome such a problem, there is the accelerated life-testing alternative aimed at forcing components to fail by testing them at much higher-than-intended application conditions. To go from the failure rate obtained at high stress to what a product or service is likely to experience at much lower stress, under use conditions, we will need additional modeling. These models are known as acceleration models. One possible way to translate test results obtained under accelerated conditions to normal using conditions could be through the application of the application of the Eyring's model. In a previous paper by De Souza (2008) we applied a sequential life testing approach to a low alloy-high strength steel part used in highway overpasses in Brazil. The underlying distribution was the three-parameter Inverted Weibull model. The data was collected over a period of a few years with the steel parts working under normal use conditions. In this paper we decided to use a combined approach of an accelerated life testing with a sequential life testing to verify if the test results obtained under accelerated conditions could be translated to the results verified under normal use conditions with a certain degree of accuracy. We elected as sampling distribution the three-parameter Weibull model. To estimate the three parameters of the Weibull underlying sampling distribution we will use a maximum likelihood approach for censored failure data. We will be assuming a linear acceleration condition. To evaluate the accuracy (significance) of the parameter values obtained under normal conditions for the underlying three-parameter Inverse Weibull model we will apply to the expected normal failure times a sequential life testing using a truncation mechanism developed previously by De Souza (2005). An example will illustrate the application of this procedure.