Influence of the Self-Heating Temperature on the Cyclic Durability of Composite Materials

Постановка задачи. Для определения выносливости полимерных композиционных материалов используют различные методы ускоренных испытаний. Одним из таких методов является температурный, который имеет свои ограничения применения. Это подразумевает необходимость установления возможности его применения для эпоксидных полимерных материалов. Результаты. Предложена формула для определения величины усталостной долговечности эпоксидного композиционного материала, опытным путем установлена достоверность величин, рассчитываемых по данной формуле. Доказано, что интенсивность роста температуры зависит от скорости загружения. Выводы. Достоверность расчетов по предложенной формуле для расчета показателей усталостной долговечности подтверждена сравнением результатов с опытными данными, значения достаточно близко коррелируют, что позволяет применять эту формулу при расчете выносливости для образцов из эпоксидного композита. Statement of the problem. Various methods of accelerated testing are used to determine the endurance of polymer composite materials. One of these methods is the temperature method which has its own limitations of application. Thus the possibility of its application for epoxy polymer materials should be established. Results. The article proposes a formula for identifying the value of the fatigue life of an epoxy composite material. The reliability of the values calculated using this formula is experimentally established. It is proved that the intensity of the temperature increase depends on the loading speed. Conclusions. The reliability of the calculations according to the proposed formula for calculating the fatigue life indicators is confirmed by comparing the results with experimental data, the values are quite closely correlated, which allows us to use this formula when calculating the endurance for samples made of epoxy composite.

A load spectra design method for multi-stress accelerated testing

Accelerated testing (AT) is an effective testing method for evaluating the reliability of highly reliable products. In many applications, such products are often subject to multiple stresses in actual working environments. Then, how to design the load spectra for multi-stress AT becomes a critical issue. In this paper, a new load spectra design method is proposed to overcome this challenge. Considering the properties of multiple stresses, a novel multi-stress loading matrix (MSLM) is modified to fully describe the load spectra in actual working environments and to generate the corresponding load spectra for AT. For illustration purposes, an inverse Gaussian (IG) process incorporating life-stress relationships is adopted to model product degradation under multiple stresses. A case study on a type of hydraulic piston pump is provided to demonstrate the use of the proposed method in guiding the load spectra design for multi-stress AT.

ENSURING TIGHTNESS IN PRESSURE COUPLING PARTS

Work objective is to solve the urgent problem of increasing the tightness and reliability of pressure couplings during their operation under dynamic loads. Theoretical and experimental studies assessing the impact on the tightness due to roughness nature of mating surfaces and three types of coatings: soft, double-layer and hard have been undertaken. The joints were tested under the influence of axial cyclic load and torque on a bench for accelerated testing. It is established that tightness of pressure couplings during operation under dynamic loads significantly depends on the parameters of microgeometry and physical and mechanical properties of the mating surface material that determine their actual contact area. Recommendations for preparing the surfaces of parts before pressure coupling assembling have been developed. It is proved that the use of regular microrelief and soft galvanic coatings of mating surfaces have a significant effect on the tightness of pressure couplings.

LIFE-TIME PREDICTION FOR POLYMER MATERIALS

Polymer testing including natural, accelerated testing or creep and fatigue testing, etc. is very important to evaluate the changes in properties, structure, morphology and durability of polymer materials. This is also the basis for experts to predict life-time or service working life or safe working life of polymer materials. This review presents an overview of the life-time prediction for polymer materials owing to natural tests or accelerated ageing tests and the methods for extrapolation of data from induced thermal degradation.

Accelerated Testing: A Practitioner's Guide to Accelerated and Reliability Testing

The application of accelerated testing theory is a difficult proposition, yet one that can result in considerable time and cost savings, as well as increasing a product's useful life. In Accelerated Testing: A Practitioner's Guide to Accelerated and Reliability Testing, readers are exposed to the latest, most practical knowledge available in this dynamic and important discipline. Authors Bryan Dodson and Harry Schwab draw on their considerable experience in the field to present comprehensive, insightful views in this book. Development and quality assurance tests are defined in detail and are presented from a practical viewpoint. Included are testing fundamentals, plans and models, and equipment and methods most commonly used in accelerated testing. Individuals seeking to evaluate and improve the design lives of components and systems will find this book a valuable reference, with special attention being paid to testing in the mobility industries.