Materials Science Forum Vol. 726

Abstract: The paper assessed the impact of the laser welding speed on the strength and fatigue properties of the aluminum layer found in multilayer pipes. The conducted experiment has shown that during the adjustment of the welding speed one has to take into account not only the results of static tests, but also the results of fatigue tests. The impact of the welding speed on fatigue life depends on the level of stress max. This level is slight in the area of the biggest stresses and increases along with the decrease in stresses.

Abstract: The paper focuses on the development of a mathematical representation of deformation characteristics under the conditions of an elevated changeable temperature and mechanical loads. The method proposed in the paper is based on the use of characteristics determined in low-cycle fatigue tests at constant temperatures. Hysteresis loops reflecting the behaviour of a material under the conditions of low-cycle loads at an elevated temperature were primarily used. The effect of relaxation on the course of the hysteresis loop was taken into account. The steady state of the material is referred to in the proposed representation. A calculation algorithm was developed to enable the determination of the stress value for subsequent increases of strain over time. The results obtained were compared with experimentally determined characteristics.

Abstract: This paper attempts to describe changes of the cyclic properties of martensitic cast steel in the function of the number of loading cycles under temperature of 25 and 600oC was made. The cyclic properties were described by means of three hysteresis loop parameters: stress amplitude, plastic strain amplitude, plastic strain energy. It was stated martensitic cast steel always undergoes clear softening which is independent of the temperature and level of total strain.

Abstract: This paper presents sample applications of passive infrared thermography for research on temperature changes of mini-specimens resulting from monotonously increasing or cyclically variable mechanical load. The MFS system developed in the Department of Machine Design at the University of Technology and Life Sciences in Bydgoszcz (Poland) and designed for testing mechanical properties of microelements were used for tests. The MFS system ensures nanometric measurement accuracy of many static and fatigue-related material properties, including, i.a., static tension curves, cyclic strain curves, fatigue life curves as a function of force, stress and strain. Measurements of the mini-specimens temperature were performed using thermographic camera equipped with microscope lens. The tests have shown that research on the passive infrared thermography may be successfully applied for determining strength properties of materials in micro scale. The used research instrumentation is characterized by sufficient sensitivity and resolution (camera with the microscope lens), while the MFS system ensures accurate load and position control.

Abstract: This paper provides the results of research on temperature changes of cylindrical specimens depending on the pattern of the multiaxial load. The research were made by using passive infrared thermography. It was found out that the average temperature value is significantly dependent on the plastic strain energy and that the temperature change amplitude depends on the nominal normal stress (except for torsion).

Abstract: The article presents the results of fatigue life and fractographic testing of steel X2CrNiMo17-12-2 exposed to proportional and non-proportional fatigue loads. The following load types were applied: tension-compressive strength, torsion, proportional combined/complex loads produced by tension-compressive strength and torsion as well as non-proportional combined load – by tension-compressive strength and torsion by the phase shift angle φ=90°. The paper analyses the effect of the load method on the fatigue life and fractography of fatigue fractures recorded, and especially the effect of non-proportional load.

Abstract: The paper presents the algorithm of fatigue life estimation for materials with out-of-parallel fatigue characteristics under block loading. Brass CuZn40Pb2, medium-alloy steel 30CrNiMo8 and high-alloy steel 35NCD16 belong to such materials. Brass CuZn40Pb2 was used for analysis. The experimental results were compared with those calculated according to the assumed model, and satisfactory results were obtained.

Abstract: The paper presents the fatigue criteria, representing the integral criteria, most frequently reported in literature. They were verified for uniaxial loadings and for combined: tension-compression with torsion both proportional and non-proportional. The verification involved a comparison of the fatigue life reported based on the criterion with the experimental fatigue life.

Abstract: Abstract. In the paper several formulae to compute the fracture toughness are presented. The formulae include either parameter characterizing the in-plane constraint or out-of-plane constraint or both. The formulae are based on different assumptions and approaches to fracture mechanics. Namely, small or finite strains were assumed, global or local approach was adopted. In all cases the standard, plain strain fracture toughness was used as a reference state.

Abstract: Abstract. In the study, there were investigated the effects of friction stir processing (FSP) which was applied in order to improve the surfaces of notched specimens made of S235JR and S355J2 carbon steels, on their fatigue crack growth rates in the air. There were presented the results of comparative fatigue tests conducted at asymmetric tension (R= -0.2) for these steels treated by means of FSP and for the ones in the delivery state. The method of successive etched material layers used revealed the presence of internal tensile stresses in the surface layers of treated specimens. Crack growth rates were described on the basis of non-linear fracture mechanics, taking the effects of internal stresses into account.