Wyniki wyszukiwania - BazTech

Ograniczanie wyników

Znaleziono wyników: 2

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: service life prediction

Sortuj według:

Ogranicz wyniki do:

Research, standardization and practice in accelerated ageing tests

Jakubowicz I.

Polimery

2004

T. 49, nr 5

321-326

The increasing use of polymers in various technological environments requires understanding of the degradation phenomena and ultimately controlling them. Questions associated with performance, cost, durability and environmental effects are closely related to each other and must be answered before the industry and the consumers can adopt new materials. Often, the use of accelerated ageing tests constitutes the only possibility to produce measurable degradation and the desired materials assessment. However, prediction of service life, especially for materials expected to perform reliably for many decades, is a continuing challenge, which contains many pitfalls. In this paper, examples of the many years' work with accelerated ageing tests and lifetime predictions carried out at SP Swedish National Testing and Research Institute are used to demonstrate some problems and pitfalls that can be met with in practice. Some examples are also given on insufficient information in international standards for ageing tests. Special attention is given to prediction of service life with one data point only as well as the influence of different previous history, different environments and different evaluation methods on lifetime prediction. Other examples concern the use of high stress levels and physical depletion of stabilizers.

W artykule o charakterze przeglądowym przedstawiono specyfikę badań przyspieszonego starzenia w porównaniu z odpowiednimi badaniami prowadzonymi w warunkach rzeczywistych. Podano matematyczne podstawy tej metody; sprowadzają się one do równań Arrheniusa. Przedyskutowano możliwość prognozowania czasu użytkowania badanego materiału na podstawie jednego pomiaru przyspieszonego starzenia (rys. 1, 2). Praktyczne przykłady zastosowania omawianej metody dotyczą trzech wariantów: (a) różniące się historią próbki tego samego materiału (rys. 3); (b) ten sam materiał, różne otoczenie (rys. 4); (c) ten sam materiał, odmienne metody oceny starzenia (rys. 5). Ponadto omówiono dwa istotne czynniki wpływające na wyniki przyspieszonego starzenia, mianowicie wysoki poziom naprężeń (czynnik ważny w badaniach kauczuków - rys. 6) oraz ubytek stabilizatorów w trakcie próby (rys. 7).

Evaluation of a fatigue cumulative damage in service life prediction

Čačko J.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

2001

Vol. 269, z. 67

27-46

Damage accumulation is evaluated according to a cumulative damage hypothesis, and the residual life is predicted with respect to a fatigue failure criterion. The estimation of cumulative damage under service loading is significantly influenced by a time loading history. The problem of the history effect can be converted to the problem of investigation of equivalent loading with non-zero stress/strain mean value. The conversion method is based in specification of an equivalent amplitude of the harmonic cycle with zero stress and strain mean values. At the same time, a relative damage that is accumulated in the course of equivalent cycle must be the same as the relative damage of actual cycle which has been identified by the rainflow method. The submitted approach enables to utilize the knowledge of cumulative damage process and fatigue behaviour prediction under harmonic loading and to use it for any complex operating loading spectrum. The base of the method and obtained results are presented in the paper.