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Analysis of the static and dynamic properties of wear-resistant Hardox 600 steel in the context of its application in working elements

Konat Ł., Jasiński R., Białobrzeska B., Szczepański Ł.

Materials Science Poland

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2021

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Vol. 39, No. 1

86--102

EN

The article discusses the static and dynamic properties of high-strength, boron-containing Hardox 600 steel that is resistant to abrasive wear, both in its delivery state and after normalization. Since the available published material in the literature does not have any real mechanical indicators of the abovementioned steel, a static tension test was carried out at an ambient temperature. The steel’s tensile strength, yield strength, Young’s modulus, elongation and reduction of area were determined from the test. The Charpy impact test at temperatures of −40 °C, −20 °C, 0 °C, and +20 °C and fractographic analysis were performed to determine the transition temperature of ductility to brittleness. In dynamic load conditions, the assigned values of impact energy do not always truly determine the material behavior. Thus, the aim of the fractography was to provide precision when determining the behavior. A significant difference in the impact energy of the tested steel with respect to its heat treatment and ductile-brittle transition temperature was observed and determined based on the impact test result, as well as the nature of the fracture. On the basis of the determined structural and strength characteristics, an analysis of the possibility of application of Hardox 600 steel on selected elements of working machines was performed.

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ROP mathematical model of rotary-ultrasonic core drilling of brittle material

Horne M. F.

Advances in Science and Technology. Research Journal

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2017

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Vol. 11, no 1

1--28

EN

The results from the Phoenix mission led scientists to believe it is possible that primitive life exists below the Martian surface. Therefore, drilling in Martian soil in search for organisms is the next logical step. Drilling on Mars is a major engineering challenge due to the drilling depth requirement and extreme environment condition. Mars lacks a thick atmosphere and a continuous magnetic field that shield the planet’s surface from solar radiation and solar flares. As a result, the Martian surface is sterile and if life ever existed, it must be found below the surface. In 2001, NASA’s Mars Exploration Payload Advisory Group proposed that drilling should be considered as a priority investigation on Mars in an effort of finding evidence of extinct or extant life. The results from the Curiosity mission suggested drilling six meters deep in the red planet in search for life. Excavation tools deployed to Mars so far have been able to drill to a maximum depth of 6.5 cm. Thus, the drilling capabilities need to be increased by a factor of approximately 100 to achieve the goal of drilling six meters deep. This requirement puts a demand on developing new and more effective technologies to reach this goal. Previous research shows evidence of a promising drilling mechanism in rotary-ultrasonic for what it offers in terms of high surface quality, faster rate of penetration and higher material removal rate. This research addresses the need to understand the mechanics of the drill bit tip and rock interface in rotary-ultrasonic drilling performance of one drill bit at a time drilling in three types of rocks that vary in strength. A mathematical model identifying all contributing independent parameters, such as drill bit design parameters, drilling process parameters, ultrasonic wave amplitude and rocks’ material properties, that have effect on rate of penetration is developed. Analytical and experimental results under ambient condition are presented to show the effect of the variation of different parameters on rate of penetration performance as a first step of the investigation. It was found that the speed and WOB have significant effect on ROP while the rest of the parameter have very little or no effect.

3

Local and global instabilities in ductile failure

Wnuk M. P.

Eksploatacja i Niezawodność

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2004

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nr 3

40-51

EN

Catastrophic fracture in ductile solids is usually preceded by a certain amount of quasistatic crack growth that occurs as a result of void expansion and coalescence process associated with large deformations localized in the narrow zone adjacent to the crack leading edge. This zone is subject to a tri-axial state of stress, and its local properties may vary from those of the bulk material. To describe this condition a modified cohesive crack model is suggested based on the mesomechanical law of the S-stress distribution and equipped with the "fine structure" feature that is lacking in the standard model. Subcritical crack growth may be likened to the phenomenon of "preliminary displacements" known in the studies encountered in the physics of tribology. Microscopic sliding of a solid block placed on an elastic-plastic substrate located on the inclined plane is observed to begin at angles somewhat smaller than the critical angle q = tan-1(m), where m denotes the coefficient of friction. With careful observational techniques these displacements can indeed be measured. Likewise, in the course of the early stages of ductile fracture, quasistatic crack growth is detected between the lower bound KI = Kini' , tantamount to the onset of stable growth, and the upper bound KI = Kf. equivalent to occurrence of the catastrophic failure. While Kini' is believed to be a material constant, the other quantity, Kf is determined not only by the material properties, but it also depends on specimen geometry, crack configuration and type of the external loading. The exact shape of the terminal instability locus represented in the plane (load, crack length) must be established by employment of the R-curve technique, in which the second variations of the energy terms are involved. When the Liapunov criterion is invoked, then it appears that the propagation of a stable crack should be viewed as a sequence of local instability states, while transition to an unstable propagation becomes equivalent to the loss of global stability, as then the entire component breaks up. A moving quasistatic crack is described on the basis of the Wnuk criterion of final stretch, which leads to the nonlinear differential equations governing the resistance curves for various materials. Both the ductile and brittle limits of material response are discussed. One of the essential results of this study is the partition of energy available for fracture within the end zone, accomplished by means of considerations of the pre-fracture states developed at the mesa-level. This, in turn, leads to a discovery of the energy screening effect, which manifests itself by a significant enhancement of material fracture toughness prior to the catastrophic failure state. Such phenomena are being confirmed by the brilliant experimental work of the Panin group in Tomsk, and Popov's team in Berlin.