Test methods long-term performance data

The designer is allowed to choose this method provided that he has access to long-term performance data. ISO has proposed three different methods for carrying out performance-based testing. These methods are described in Annex E of ISO/TS 24817 as... 

Free Voiume as the Prediction Tooi. For obvious reasons, prediction of long-term performance from short-term tests is needed. Such prediction methods exist and are in fact quite powerful. Unfortunately, numerous papers and reports are still based on a false assumption that nothing can he predicted and therefore everything has to be measured. Much information can be obtained from a limited amount of experimental data—and also from computer simulations discussed at various locations in this article. 

Long-term performance of bonded joints cannot be predicted from the properties of the adhesive and adherent surfaces. Complex interfacial and interface chemistry requires the testing of bonded structures. There are close to 50 bond-strength test methods accepted by ASTM International for development of data on adhesive joint properties. Typically tensile, lap-shear, and peel are the main adhesive bond configurations that are used for testing. 

Method 3 Elaborate design based on long-term performance testing data. 

Insufficient testing is one of the major causes of method failure. The amount of data needed to publish a new procedure in a peer-reviewed journal and the procedural detail supplied therein are often insufficient to allow a different user to validate a method rapidly. The developer should evaluate if the method will work using chemicals, reagents, solid-phase extraction columns, analytical columns, and equipment from various vendors. Separate lots of specific supplies within a vendor should be evaluated to determine if lot-to-lot variation significantly impacts method performance. Sufficient numbers of samples should be assayed to estimate the lifetime of the analytical column and to determine the effects of long-term use on the equipment. 

Time to rupture can be predicted by using the accelerated times generated by the creep data, and the creep-rupture characteristic generated by performing twelve of these tests over a range of loads. Conventional long-term creep strain and creep-rupture tests have so far confirmed the validity of the predictions for polyester fibres. Comments on the method have been published by Greenwood and Voskamp [10]. 

Evaluation techniques and equipment are as varied as the individual catalytic processes themselves. The long term goal of catalyst evaluation is to reduce the size of the testing equipment consistent with reliable and accurate data as it relates to the commercial process. Invariably, the farther removed in physical size the process simulation attains, the more likely that errors will be introduced which can affect data accuracy, accuracy being defined as commercial observations. In addition, smaller equipment size also places less demand on the physical integrity of a catalyst particle therefore, additional test methods have been developed to simulate these performance characteristics. Despite these very important limitations, laboratory reactors fully eight orders of magnitude (100 million times) smaller are routinely used in research laboratories by both catalyst manufacturers and petroleum refiners. 

Requirements specified in this way are deemed-to-satisfy rules. Such rules cannot be used to quantify the performance of the structure in general, specific effects of additional measures (for instance increasing the cover to the steel), or the consequences of sub-standard practice (for example using a higher w/c). In this respect it is important to note that EN 206 also allows the use of alternative performance-related design methods with respect to durability that consider in a quantitative way each relevant deterioration mechanism, the service life of the element or structure, and the criteria that define the end of the service life. Such methods should draw a picture of the characteristics that the concrete must possess to protect the reinforcement for the service life requested from a predictive model of the corrosion attack. These refined methods (as opposed to standard methods) may be based on long-term experience with local practices in local environments, on data from an established performance test method for the relevant mechanism, or on the use of proven predictive models. 

Nevertheless, more research work is needed to develop appropriate test methods for the accrual of accurate property performance data that consider realistic loading and environmental conditions to overcome the lack of information about extreme service temperature and fire resistance of bonded connections to develop realistic predictive tools for the long-term behaviour of bonded timber joints and connections. These are required in order to promote their wider use through the increased confidence of architects, designers and owners alike. 

The accepted method of nondestructive testing used to control the underfill process is SAM. The thin layer allows this technique to detect voids in the underfill material, which when located near the solder interconnections can be responsible for a significant loss of thermal mechanical fatigue reliability. X-ray techniques can be used to monitor the density of the underfill material, specifically, the distribution of filler material within the layer under the die. Density variations can indicate a larger distribution of underfill mechanical and physical properties, which may affect long-term reliability performance of the solder joints. Quantitative image analysis can be coupled into SAM and x-ray analysis data to provide valuable process control tools for the factory floor. 

The proposed method has some limitations, which open room for future improvements. The main limitation is related to the estimation of the severity factor (D). For the sake of simplicity, a single point severity value has been used for all the at-risk behaviours. However, a more robust estimation should consider different severities for different causes. Again, this estimation could be done by combining historical data, when available, with experts judgments. A further limitation is related to the effectiveness of the model it should be tested by means of a long term pilot implementation to check for any positive correlation between safety performance trends and the implementation maturity of the proposed method. This means that after the implementation of the method, a test should verify that the number of non-conforming behaviours as well as the related risk level reduced over time. 

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