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New possibilities of low cycle fatigue material properties testing with the use of micro-specimens are presented in this publication. The discussed solution is of great significance for analysis of local properties of a material, e. g. in welded structures. Properties of a material determined in the manner presented in this publication find application both in fatigue life assessment (fatigue life curves) and in material modeling (cyclic stress-strain curves), e. g. in numerical analysis of local strain and stress that occur in structural components.

Digital image correlation (DIC) is a non-contact optical method that allows measuring displacements on a plane used to determine the strains caused by external loads of a structural element (mechanical or thermal). Currently, digital image correlation is a widely used experimental technique to assess the mechanical behavior of materials, in particular cracking characteristics and destruction methods of various structural elements. In this paper, the DIC method is applied to determine local strains of titanium alloy Ti6Al4V specimen. The samples used in the tests were made with two different technologies: (a) from a drawn bar by machining process; and (b) by the additive manufacturing method Direct Metal Laser Sintering (DMLS). The aim of the paper is to present the mechanical properties test results of the Ti6Al4V titanium alloy produced by the DMLS additive manufacturing under static loads using the digital image correlation method. As a result of the tests carried out on the drawn bar specimens, it was concluded that the change in the measurement base affects the difference in the Young’s E modulus value in the range from 89.2 to 103.8 GPa. However, for samples formed using the DMLS method, the change in the Young’s modulus value was from 112.9 to 115.3 GPa for the same measurement base.

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Description of fatigue crack growth in steel structural components using energy approachInfluence of the microstructure on the FCGR AIP Conference Proceedings 1780, 050003 (2016) Abstract When determining the characteristics of the fatigue crack growth rate, it is necessary, inter alia, to measure the crack length growth which must be combined with the number of accumulated load cycles. The length of the crack is determined using different testing methods. Recently, there is an increased interest in optical systems based on digital image correlation methods. These methods have however some limitations as regards, inter alia, the sharpness of pictures taken during tests e.g. at cryogenic temperatures. This paper presents a comparative analysis of the crack length "a" as a function of a crack-opening-displacement "δ" obtained by experimental and numerical method. The tests were performed under ambient temperature for CT type specimens made of Ti6Al4V titanium alloy. Numerical research was carried out by finite element method using ABAQUS software. Satisfactory results were obtained which gave the reasons for establishing a hybrid methods for the crack length determination.