Creep failure experiment

Thus, it has been concluded that the creep process of elastomers is one of the suitable processes for separating the second factor from the canbined state and that the creep failure experiment gives us a good information for estimating the failure mechanism of polymers. 

As shown before, me is a function of stressed state ( > and an important parameter for the failure process, and the functional form cannot be introduced from theoretical considerations in this stage. However, we can determine it by experiment, particularly by creep failure experiment because of a simple relation between and mg as shown in eq(7). 

Figure 3. (a) Creep failure experiment and (b) close up of the creep curve at breaMng. There are no previous signs for failure. 

Based on the theory presented here, eq(9) is applicable not only to creep failure, but also to the other deformations where 0 varies with time. If we substitute n and c which are obtained from creep failure experiments into eq(9), the P(tg) for the constant rate extension process must be described by this equation. To examine this, the constant rate extension experiment has been carried out. In constant rate uniaxial extension, stretch ratio X is given by a function of time t as following. 

It has been shown that the life time in the creep process of rubbery polymers scatters largeley but obeys the specified statistical distribution which are introduced theoretically based on some assumptions. Two assumptions are made here that "one crack leads the body to failure" and "the v th crack leads the body to failure". The former assumption leads the exponential distribution of tg, and the latter the unimodal distribution when v>2. It has been explained from experiments that the distribution of tg for pure rubbers of vulcanized SBR and NR are the exponential, type and for filled systems the unimodal type. Theory introduced here can be applied not only to the creep failiire but also to the failure process varing stress level such as uniaxial extension with constant strain rate. It has been demonstrated that the distribution of Xg, the stretch ratio at breedc in the constant rate of extension, is well estimated by the theory substituting the parameters n and c which are obtained from creep failure experiment to eq(l9). 

Although the creep behavior of a material could be measured in any mode, such experiments are most often run in tension or flexure. In the first, a test specimen is subjected to a constant tensile load and its elongation is measured as a function of time. After a sufficiently long period of time, the specimen will fracture that is a phenomenon called tensile creep failure. In general, the higher the applied tensile stress, the shorter the time and the greater the total strain to specimen failure. Furthermore, as the stress level decreases, the fracture mode changes from ductile to brittle. With flexural, a test specimen... 

The author s first research on creep failure to investigate the failure mechanism the view point was done in 196U with P. J. Blatz (1) and this research was Improved in 1970 (2). In this article, theories and the experiments will he Introduced based on above researches adding new experimental data obtained recently by author. 

Author vlshes to thank Mr. K. Fukumori, Mr. M. Yoneda and Mr. K. Tei, who are graduate students of Department of Polymer Chemistry, Kyoto University, for their assistance in the experiments of creep failure and the preparation of this manuscript, and also thank the Mitsubishi Monsanto Chemicals Co., Nagoya and the Nippon Zeon Co., for their assistance in preparing the samples used. 

Which of the product requirements in this section is most likely to result in a structural failure Of course any of them can or they would not be listed. However, in the author s experience, the most common failures (short of gross design errors) occur due to weakening of the material at elevated temperature, impact failure at low temperature, or creep failure over time. 

Zeitstandverhalten creep deformation Kriechverformung creep elongation Kriechdehnung creep experiment Kriechversuch creep failure Kriechbruch creep fracture Kriechbruch Zeitstandbruch creep limit... 

Miyano et al. propose a method to predict creep strength Oc from the master curve for static strength using the linear cumulative damage law. fs(o) and 4(0) are static and creep failure time, respectively for stress 0. It is supposed that the material experiences a monotonic stress history o(f) for 0 < t < t where t is the failure time for this stress history. The linear cumulative damage law states ... 

If you see the amps on your precipitator creeping up, or spiking up, something is beginning to short-circuit the electric grids, or insulators. Most commonly, corrosion products are falling off the walls of the precipitator vessel. In my experience, this is the most common cause of precipitator failure. 

Fig. 13.84c, known as the Smith failure envelope, is of great importance because of its independence of the time scale. Moreover, investigations of Smith, and Landel and Fedors (1963,1967) proved that the failure envelope is independent of the path, so that the same envelope is generated in stress relaxation, creep and constant-rate experiments. As such it serves a very useful failure criterion. Landel and Fedors (1967) showed that a further generalisation is obtained if the data are reduced to ve, i.e. the number of elastically active network chains (EANCs). The latter is related to the modulus by... 

Preliminary research has indicated that a PBT/PBA co-poly(ester ester) is susceptible to environmental stress cracking in water and in phosphoric acid solution, in both cases at 80°C. Time-to-Failure creep experiments were initiated to obtain quantitative data. These tests were performed in water and phosphoric acid solutions (pH = 1.6) at 80°C with notched tensile specimens under constant load (ranging from 0.6-7 MPa). The results have shown that the phosphoric acid solution decreases the lifetime when compared to tests done in water. Both environments decrease the lifetime tremendously when compared to creep tests in air. 

Comparing the results with the influence of that only hydrolysis on its own has on the degradation of mechanical properties has showed that the results of the Time-to-Failure creep experiments cannot be explained exclusively on the basis of hydrolysis. This confrrms the conclusion drawn in our preliminary experiments that the PBT/PBA co-poly(ester ester) is susceptible to stress cracking in both water and phosphoric solution at 80°C. 

In a subsequent series of experiments, Landes and Wei [2] demonstrated that the phenomenon is real, and modeled the crack growth response in terms of creep deformation rate within the crack-tip process zone. The effort has been further substantiated by the work of Yin et al. [3]. The results and model development from these studies are briefly summarized, and extension to probabihstic considerations is reviewed. It is hoped that this effort will be extended to understand the behavior of other systems, and affirm a mechanistic basis for understanding and design against creep-dominated failures. The author relies principally on the earher works of Li et aL [1], Landes and Wei [2], Yin et al. [3], Krafft [4] and Krafft and Mulherin [5]. The findings rely principally on the laborious experimental measurements by Landes and Wei [2], and the conceptual modeling framework by Kraftt... 

Samples subjected to time dependent testing in creep or dwell fatigue experiments (exposure) were subjected to cyclic tensile loading at room temperature until failure (post exposure). Elastic and creep strains from exposure experiments as well as strain to failure during post-exposure... 

Structural adhesives such as epoxy resins can be treated as any rigid polymer and samples can be machined from cast sheets to produce test-pieces. These can then be used to measure typical tensile properties such as failure stress and strain. Using accurate exten-sometry, it is possible to characterize completely the uniaxial properties of an adhesive. The Creep of adhesive joints is especially important for structural adhesives maintained at high temperature. It is possible to determine the creep resistance of such materials by applying suitable loads at an appropriate temperature to samples of the adhesive, and to record the deformation with time. From such data, it will soon be evident if the adhesive is suitable for use or if it will cause a joint to deform with time. It is important to remember that humidity is likely to affect the properties of the adhesive, and in a long-term creep experiment, the humidity could cause premature failure. 

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