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Orthotropic yield criterion for Ti-6Al-4V titanium alloy after friction stir processing (FSP)

Farias A., Delijaicov S., Bordinassi E. C., Batalha M. H. F., Batalha G. F.

Archives of Materials Science and Engineering

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2015

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Vol. 72, nr 1

33--45

EN

Purpose: This works aims at applying friction stir processing (FSP) to Ti-6Al-4V titanium alloy. Derived from friction stir welding (FSW), it is a recent process developed in the 1990s for aluminum joining. Its application to other types of materials such as steel and high performance alloys, in particular titanium, has interested industry. Design/methodology/approach: The methodology applied to evaluate FSP in this work consisted in tensile testing Ti-6Al-4V sheets in mixed conditions. The workpieces were processed in a conventional CNC milling machine with special fixture devices. Findings: A contribution to the modeling of anisotropic materials yield stress is proposed based on an orthotropic yield criterion. Additional equations based on the mixed tests for tensile and shear loadings are proposed to modify the former Cazacu orthotropic model. Research limitations/implications: Although the application limit for the model appears to be small, sheet forming process similar to those used in this work, are predominantly in the region of this analysis. Practical implications: The purpose of the model is to indicate the conditions under which the material has reached its yield regime, and may be a basis for practical simulations in similar conditions. Originality/value: The purpose of this model is to indicate the conditions under which the material has reached its yield regime, and may be a basis for practical simulations in similar conditions.

2

Residual stresses modelling in hard turning and its correlation with the cutting forces

Batalha G. F., Delijaicov S., Aguiar J. B., Bordinassi E. C., Stipkovic Filho M.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 24, nr 1

350-356

EN

Purpose: This paper aims to study the cutting parameters influence (cutting speed, feed rate, cutting depth and tool radius nose) on the cutting forces (cutting force, feed rate cutting force and penetration cutting force) as well as on the residual stresses, in conical bearings made of steel DIN 100 CrMn6 hardened (62 HRc), searching correlations between the residual stresses and the cutting forces. Design/methodology/approach: A complete factorial planning was used to establish the correlations. At the same time, the cutting parameters influence in the microstructure of the material and it's correlation with the residual stress was studied. A turning center machine and CBN inserts was employed for the tests. To the cutting force measurements was carried out using a piezoelectric dynamometer. The residual stresses measurements were carried out by X-ray diffractometry. Findings: The penetration cutting force was the most important factor in the residual stress generation, and it was influenced by the feed rate and the cutting depth. A correlation between the cutting depth and the residual stresses was established. The results do not showed any changes in the microstructure of the material, even when the greater cutting parameters were used. Research limitations/implications: The residual stress is one of the major causes of failures in bearings by contact fatigue, keeping this on mind, this work helps the developer to select correct cutting parameters in order to increase the machined workpiece life in service. Originality/value: This work were based on the real components (conical bearings), real cutting conditions and with these results were possible to make greater improvements in the manufacturing and in the quality of the studied parts.

3

Superficial integrity analysis in a super duplex stainless steel after turning

Bordinassi E. C., Stipkovic M. F., Batalha G. F., Delijaicov S., Lima de N. B.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 18, nr 1-2

335--338

EN

Purpose: Purpose of this paper was to study the main effects of the turning in the superficial integrity of the duplex stainless steel ASTM A890-Gr6A. Design/methodology/approach: The focus of the work was the finishing operations and a complete factorial planning was used, with 2 levels and 5 factors. The tests were conducted on a turning center with carbide tools and the main entrances variables were: tool material class, feed rate, cutting depth, cutting speed and cutting fluid utilization. The answers analyzed were: micro structural analysis by optical microscopy and x-ray diffraction, cutting forces measurements by a piezoelectric dynamometer, surface roughness, residual stress by x-ray diffraction technique and the micro-hardness measurements. Findings: The results do not showed any changes in the micro structural of the material, even when the greater cutting parameters were used. All the other answers were correlated with the cutting parameters and its better combination was founded for the best superficial integrity. The smaller feed rate (0.1 mm/v), smaller cutting speed (110 m/min) and the greater cutting depth (0.5 mm) provided the smaller values for the tensile residua stress, the smaller surface roughness and the greater micro-hardness. Research limitations/implications: The correlation between all the answers was very difficult to analyze because there was great interaction between the factors, but for some data group it was possible. Originality/value: The paper contribute for the study of the super duplex stainless steel, considering that no one researches was founded for the studied topics in this material in witch presents different behavior in machining when compared with another stainless steels.