PSI - Issue 20

Yakovleva S. P. et al. / Procedia Structural Integrity 20 (2019) 154–160

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Yakovleva S. P. et al. / Structural Integrity Procedia 00 (2019) 000 – 000

1. Introduction Recently, safety of the vehicles and technical systems in the North and Arctic, the working capacity of which is influenced by intensity and conditions of the operation, significantly changing during the calendar year, have become particularly relevant as shown by Makhutov et al. (2013). For the vehicles, a variation of the operation intensity is mainly associated with the changes in the air temperature and road conditions. These factors affect loading of parts and systems, which determines a rate of destructive physical processes in the material, leading eventually to the failure. This implies two important tasks, solutions of which are necessary to ensure the working capacity and reliability of the vehicles in the climatic conditions of the cryolithozone. The first is identification of the systems and parts that limit the reliability of the vehicles operating in the North, which requires the analysis of malfunction data taking into account the seasonal changes in the temperature and road profile. The second is the study of local structural damages of the material, the accumulation and fusion of which leads to initiation and development of micro- and macrocracks as pointed by Murakami (2002), Romanov (2006), Sakai et al. (2011). The research of the structural damage in the various metals and alloys has been and remains the urgent problem of materials science and engineering. In this regard evaluation of an effect of the various factors (including road and temperature ones) on the working capacity of technical facilities and assessment of the current state of their material have important scientific and applied significance as shown by Botvina (2008), Matvienko (2014), Sangid (2013). Since the vehicle parts experience mostly repeated and alternate loads, one of the main requirements to be met by the metal for the purpose of preventing the fatigue cracks from spontaneous propagation by a brittle fracture mechanism is an ability to remain cold-resistant throughout the entire useful life. It should be noted that the processes such as cyclic hardening (softening), the fatigue failure accumulation, and their influence on brittle fracture strength of the part materials of the vehicles operated in northern territories remain understudied. The work purpose is to study the effect of the operation in the conditions of the northern roads on the fatigue damage, the brittle fracture resistance and working capacity of the metal of the KAMAZ truck leaf spring (the trucks of this make are one of the widely demanded types of the trucks in Yakutia). This problem formulation is new and allows us to compare a degree of the influence of the seasonal changes in the air temperature and road profile † on the working capacity of the vehicle elements with appropriate justification from a standpoint of strength physics and materials science. Nomenclature n i quantity of the results per specific interval of a microhardness histogram of the conditionally initial state of the material N i total number of microhardness measurements upon controlling the microhardness in the conditionally initial state n i * quantity of the results per specific interval of the microhardness histogram for all three groups N i * total quantity of the microhardness measurements upon controlling the microhardness for all three groups i number of the current interval of the microhardness histogram m, m * quantities of the intervals of the microhardness histogram compiled for the conditionally initial state and for three groups of specimens, respectively а i , а i * weight coefficients found for each interval of the microhardness within the limits of m , m* of each histogram

† The analysis of the failures and impact of the seasonal changes in the road profile on the working capacity of the elements and systems of the KAMAZ truck was a subject of the separate studies, and therefore only their main results are presented and used in this paper .