Microstructural evolution and strain hardening of Fe–24Mn and Fe–30Mn alloys during tensile deformation

High Mn steels demonstrate an exceptional combination of high strength and ductility owing to their sustained high work hardening rate during deformation. In the present work, the microstructural evolution and work hardening of Fe–30Mn and Fe–24Mn alloys during uniaxial tensile testing at 293 K and 77 K were investigated. The Fe–30Mn alloy did not undergo significant strain-induced phase transformations or twinning during deformation at 293 K, whereas these transformations were observed during deformation at 77 K. A modified Kocks–Mecking model was successfully applied to describe the strain hardening behavior of Fe–30Mn at both temperatures, and quantitatively identified the influence of stacking fault energy and strain-induced phase transformations on dynamic recovery. The Fe–24Mn alloy underwent extensive ε martensite transformation during deformation at both test temperatures. An analytical micromechanical model was successfully used to describe the work hardening of Fe–24Mn and permitted the calculation of the ε martensite stress–strain curve and tensile properties.     

Three-dimensional modelling of manufacturing tolerancing using the ascendant approach

This paper proposes a three-dimensional approach towards manufacturing tolerancing that uses a strategy to strictly consider the definition of a datum system imposed by ISO standards. This approach, called three-dimensional manufacturing tolerancing (TMT), is based on the small displacement torsor, which describes the possible deviations between machined surfaces and nominal surfaces of the part model. Every requirement of the definition drawing is treated separately with its own calculation model. The iterative ascending analysis allows one to establish the influence of the most recent phase and determine the influential parameters from previous phases. The nominal part model is defined on the datum systems of the requirement, and deviations are expressed with respect to both the machining process and the chosen machine adjustment method. The result takes the form of a formula that yields the variation in characteristics specified in the requirement based on quantifiable parameters identified on the machine.     

Effect of Titania Additive on Structural and Mechanical Properties of Alumina–Fluorapatite Composites

Mechanical properties of alumina-fluorapatite composites with different titania additive amounts (0, 0.5, 1, 1.4, 2, 3, 4 and 5 wt%) have been investigated between 1200 and 1600℃. The optimum values of densification and mechanical properties of composites have been reached with 1.4 wt% of titania after the sintering process at 1500℃ for 1 h. Thus, the rupture strength of alumina-26.52 wt% Fap-1.4 wt% TiO2 reaches 75 MPa. At higher temperature and beyond 1.4 wt% TiO2 ,the densification and mechanical properties were hindered by the formation of both intergranular porosity and secondary phase. X-ray diffraction (XRD) analysis of alumina-Fap-TiO2 composites shows the formation of aluminium titanate (Al2O3-TiO2:Al2TiO5 ). The 27Al magic angle scanning nuclear magnetic resonance analysis of Al2O3-Fap-TiO2 composites reveals the presence of octahedral and pentahedral aluminium and novel environment relative to tetrahedral aluminium sites.     

Sintering and mechanical properties of tricalcium phosphate–fluorapatite composites

Tricalcium phosphate and synthesized fluorapatite powder were mixed in order to elaborate biphasic ceramics composites. The effect of fluorapatite addition on the densification and the mechanical properties of tricalcium phosphate were measured with the change in composition and microstructure of the bioceramic. The Brazilian test was used to measure the mechanical resistance of the tricalcium phosphate–26.52 wt% fluorapatite composites. The densification and rupture strength increase versus sintering temperature. The composites have a good sinterability and rupture strength in temperature ranging between 1300 and 1400 °C. Thus, the densification ultimate was obtained at 1350 °C and the mechanical resistance optimum reached 9.6 MPa at 1400 °C. Above 1400 °C, the densification and the mechanical properties were hindered by the allotropic transformation of tricalcium phosphate, grain growth and the formation of both intragranular porosity and many cracks. The ³¹P magic angle spinning nuclear magnetic resonance analysis of composites reveals the presence of tetrahedral P sites.     

Experimental analysis,hybridization and exergetic investigation of an absorption refrigeration unit

In this work, an experimental and theoretical investigation of a frozen and hot water production unit with direct gas absorption is developed. Water/ammonia couple is used.A particular interest is given to the system performances evaluation such as exergetic efficiency and total exergy loss. Parameters analyzed are coefficients of performance, irreversibility and exergetic efficiency.Results show that the machine can reach a COP up to 65% and exergetic efficiency up to 18% for a working temperature and a condensation temperature of 120 °C and 18 °C, respectively. These performances decrease for a condensation temperature of 37 °C and 47 °C. Indeed, the engine is less efficient and presents more irreversibility, which is major in the pre-absorber and the absorber.An improvement of the machine cycle is proposed, in order to adapt it to low grade heat sources, using a compressor upstream of the pre-absorber. Performances of the new hybrid cycle are better than those of the real cycle.