EFFECT OF SLAB PULLING RATE ON FRACTURE CHARACTERISTICS AND NOTCH IMPACT TOUGHNESS OF SLAB SURFACE ZONE IN Ti-Nb MICROALLOYED STEEL
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The paper analyzes the marginal cut-outs from two slabs of Ti-Nb microalloyed steel. The first slab was transitional with initial pulling rate 0.5 m.min -1 and final pulling rate 0.8 m.min -1 . The second slab was cast at real pulling rate 1.03 m.min -1 . The V-notch Charpy impact test showed that at low pulling rate 0.5 m.min -1 , the values of impact toughness (KCV) were higher than those at high slab pulling rates. When the pulling rate was 0.5 m.min -1 , mixed fractures were obtained, occasionally ductile, but mostly brittle. On the other hand pulling at rates 0.8 m.min -1 and 1.03 m.min -1 resulted only in brittle fractures with low KCV. Comparison of the mean ferrite grain size d ST , showed that the most fine-grained structure was achieved at a low pulling rate 0.5 m.min -1 , and the coarsest structure at pulling rate 0.8 m.min -1 . Furthermore, it was shown that, at high slab-pulling rates 0.8 m.min -1 and 1.03 m.min -1 , a greater amount of tertiary cementite was found on the boundaries of ferritic grains, compared with the lowest rate of slab pulling 0.5 m.min -1 . At the highest rate of slab pulling 1.03 m.min -1 , in addition to tertiary cementite, presence particles were observed here and there on the boundaries of ferritic grains, mostly oval shaped. On the fracture surfaces of brittle samples transcrystalline cleavage facets (TCF) dominated. In small amounts smooth facet intercrystalline decohesion (FID) was also identified with max. 0.2% , and also ductile transcrystalline failure with dimples (DDTF), usually present only in the form of narrow dimple bridges between cleavage facets. Observation of failures using scanning electron microscope (SEM) revealed the presence of either clusters of inclusions or individual particles, and EDX analysis confirmed the presence of Al, S, O, Mn, i.e. most probably oxides of aluminum and manganese sulphides. Aluminum can come from poorly-cleaned melt contaminated by fumes from deoxidation or from mould powders. There were also complex particles based on (C, Ti, Mn, O, Al, S, Nb, Zr, Ca) observed mainly on the TCF. Moreover, the impact of heterogeneous distribution of particles on embrittlement cannot be excluded - carbides, nitrides, and complex carbonitrides based on (Ti, Nb) (C, N).Keywords:
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The effects of B_4C transformation on the strength and toughness of Si_3N_4 ceramics were studied based on the mechanical properties and microstructure of Si_3N_4 ceramics containing 0-30wt% of B_4C.The strengthening and toughening mechanisms were also discussed by means of several strengthening and toughening models,and toughness of energy-balance theory.Results show that the bending strength and toughness of Si_3N_4 ceramics can be effectively increased by the aid of B_4C transformation.
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According to the present theories of plastic toughening, it is impossible to enhance the toughness, stiffness and/orheat resistance of plastics simultaneously by using rubber. A series of novel nano-rubber particles (UFPR) were introduced,which were prepared through irradiating common rubber lattices and spray drying them. Epoxies toughened with UFPRshowed a much better toughening effect than those with CTBN, and the heat resistance of epoxy was unexpectedly elevated.For polypropylene toughening, UFPR can improve the toughness, stiffness and heat resistance of PP simultaneously. Thesespecial toughening effects overcome the deficiencies in rubber toughening technology and are worth further investigating.
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This review focuses on the modification of the inherent brittleness of biodegradable poly(lactic acid) (PLA) to increase its toughness, as well as recent advances in this field. The most often utilized toughening methods are melt blending, plasticization, and rubber toughening. The process of selecting a toughening scheme is still difficult, although it directly affects the blend's mechanical properties. There has been a lot of development, but there is still a long way to go before we get easily processable, totally bio-based, 100% biodegradable PLA. The blends of PLA with other polymers, such as plasticizers or rubber, are often incompatible with one another, which causes the blend's individual components to behave in a manner consistent with phase separation. Polymer blending has been shown to be particularly effective in attaining high-impact strength. This review addresses the recent progress in improving the toughened PLA to gain properties necessary for the material's future engineering applications. As 3D and 4D printing becomes more accessible, PLA characteristics may be modified and treated utilizing more sophisticated production techniques.
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Summary The relationship between cold‐shortening and toughness has been determined for the sternomandibularis muscles of young ox cooked at both 60 and 80°C, and therefore taken through the recently established first and second stages of cooking toughness development respectively. At both cooking temperatures, toughness increases approximately three‐fold on shortening to 35‐40%, and declines steeply at higher shortenings. At a given shortening, the toughness of meat taken through the first cooking stage is only half that of meat taken through both stages. The pronounced cooking shortening accompanying the second stage contributes to toughness to virtually the same degree as cold‐shortening in pre‐rigor muscle. On the basis of this observation toughness has been related in general terms to muscle structure and function. The mechanics of cleaving cooked meat across the grain and of how shearing force increases with shortening are also discussed.
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This chapter elaborates on the modification of epoxies by different approaches to improve their performance. Toughening is an important means of improving the impact energies of conventional pristine epoxy thermosets. Various approaches for toughening epoxy thermosets are available, and the mechanism by which toughness is improved is crucial. Modifications can also improve the tensile strength, impact resistance, elongation at break, toughness, and resistance to crack propagation of such thermosets, in addition to altering their morphologies. Ultimately, the goal of modifying epoxy thermosets is to broaden their applications and improve their commercial viability.
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Polylactide is a commercially‐produced thermoplastic that is derived from renewable resources and is environmentally degradable. Due to these attributes, polylactide holds tremendous promise as an alternative to the ubiquitous petroleum‐based materials. However, in situations that require a high level of impact strength, the toughness of polylactide in its pristine state is often insufficient. As such, there has been tremendous effort in developing ways to improve this material property deficiency. In this review we summarize these approaches for increasing the toughness of polylactide with an eye toward how the toughening protocols influence the overall mechanical properties of the resultant materials.
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Low molecular weight PC/PP blend was prepared by means of melt blending, and the toughening mechanism of the blend system was studied by means of mechanical test, IR and SEM, so on. Results indicated that the matrix yield and the interface adhesion failure were the main ways to dissipate impact energy. Interfacial tension had strong influence on the morphology and toughness of the blend, and to increase the interface adhesion was of benefit to the increase of the toughness of the blend. A simulating model was proposed, which could be used to explain the toughening mechanism well. PP could be used as toughening agent for PC, which could greatly increase the toughness of low molecular weight PC, without the decrease of the flowability of PC.
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