Deformation mechanisms of NiAl cyclicly deformed near the brittle-to-ductile transformation temperature

One of the ongoing challenges of the aerospace industry is to develop more efficient turbine engines. Greater efficiency entails reduced specific strength and larger temperature gradients, the latter of which means higher operating temperatures and increased thermal conductivity. Continued development of nickel-based superalloys has provided steady increases in engine efficiency and the limits of superalloys have probably not been realized. However, other material systems are under intense investigation for possible use in high temperature engines. Ceramic, intermetallic, and various composite systems are being explored in an effort to exploit the much higher melting temperatures of these systems. NiAl is considered a potential alternative to conventional superalloys due to its excellent oxidation resistance, low density, and high melting temperature. The fact that NiAl is the most common coating for current superalloy turbine blades is a tribute to its oxidation resistance. Its density is one-third that of typical superalloys and in most temperature ranges its thermal conductivity is twice that of common superalloys. Despite these many advantages, NiAl requires more investigation before it is ready to be used in engines. Binary NiAl in general has poor high-temperature strength and low-temperature ductility. On-going research in alloy design continues to make improvements in the high-temperature strength of NiAl. The factors controlling low temperature ductility have been identified in the last few years. Small, but reproducible ductility can now be achieved at room temperature through careful control of chemical purity and processing. But the mechanisms controlling the transition from brittle to ductile behavior are not fully understood. Research in the area of fatigue deformation can aid the development of the NiAl system in two ways. Fatigue properties must be documented and optimized before NiAl can be applied to engineering systems. More importantly though, probing the deformation mechanisms operating in fatigue will lead to a better understanding of NiAl's unique characteristics. Low cycle fatigue properties have been reported on binary NiAl in the past year, yet those studies were limited to two temperature ranges: room temperature and near 1000 K. Eventually, fatigue property data will be needed for a wide range of temperatures and compositions. The intermediate temperature range near the brittle-to-ductile transition was chosen for this study to ascertain whether the sharp change occurring in monotonic behavior also occurs under cyclic conditions. An effort was made to characterize the dislocation structures which evolved during fatigue testing and comment on their role in the deformation process

Deformation mechanisms of NiAl cyclicly deformed near the brittle-to-ductile transition temperature

The intermetallic compound NiAl is one of many advanced materials which is being scrutinized for possible use in high temperature, structural applications. Stoichiometric NiAl has a high melting temperature, excellent oxidation resistance, and good thermal conductivity. Past research has concentrated on improving monotonic properties. The encouraging results obtained on binary and micro-alloyed NiAl over the past ten years have led to the broadening of NiAl experimental programs. The purpose of this research project was to determine the low cycle fatigue properties and dislocation mechanisms of stoichiometric NiAl at temperatures near the monotonic brittle-to-ductile transition. The fatigue properties were found to change only slightly in the temperature range of 600 to 700 K; a temperature range over which monotonic ductility and fracture strength increase markedly. The shape of the cyclic hardening curves coincided with the changes observed in the dislocation structures. The evolution of dislocation structures did not appear to change with temperature

キー溝を有する高周波焼入れ鋼(S45C)の回転曲げ疲労強度

applicationThis study has investigated out the fatigue strength of induction hardening steel materials. Some kinds of specimen possessed key grooves and some did not. Paticularly, the materials with key grooves used in this experiment possessed the various depths of induction hardening. The fracture surfaces were investigated by means of an electron microscope. The conculusions obtained are as follows: (1) Fatigue limits (1×10＾7cycle) increased about 13.6% at the material A(deep induction hardening steel), about 21.6% at the material B(shallow induction hardening steel), and about 8.16% at the material C(steel with no induction hardening). Fatigue limits mentioned above were caluculated using fatigue limits of the materials of key grooves as standard of calculation. (2) The crack propagation patterns of fatigue was observed in the key groove. In particular, the meterial A was observed to have crack propagation to the direction of 45 degrees from the root of the key groove.departmental bulletin pape

Design of power-transmitting shifts

Power transmission shafting which is a vital element of all rotating machinery is discussed. Design methods, based on strength considerations for sizing shafts and axles to withstand both steady and fluctuating loads are summarized. The effects of combined bending, torsional, and axial loads are considered along with many application factors that are known to influence the fatigue strength of shafting materials. Methods are presented to account for variable amplitude loading histories and their influence on limited life designs. The influences of shaft rigidity, materials, and vibration on the design are discussed

Calculation of sub-surface-initiated fatigue fractures in gears

Power-transmitting gears are typically heat-treated, most often case-hardened, to improve the fatigue strength and therefore to ensure higher fatigue life. The heat treatment causes higher hardness in the surface area as well as compressive residual stresses in the hardened layer. The near-surface compressive residual stresses are compensated by tensile stresses in higher depths of the gear volume. Pitting and tooth root breakage are the most common failure modes of gears, which are well researched and are also addressed in ISO 6336 [14]. The assessment of these failure modes provides the basis for the dimensioning of gears in the design phase. However, subsurfaceinitiated failures, like tooth flank fracture (TFF), can also appear at loads below the allowable level of loading for pitting and tooth root bending. TFF is a fatigue damage with crack initiation in the region of the transition between compressive and tensile residual stresses and usually leads to a total loss of drive. The existing calculation models for fatigue strength of gears with regard to TFF consider residual stresses differently. The base of the investigated calculation models is a local comparison of the occurring stresses and the strength value in the gear volume. The outcome of the calculation model from Oster [26] is highly influenced by the residual stress state. However, the material-physical model by Hertter [10] is more tolerant to slightly varying residual stresses. Further approaches such as Weber [34] and Konowalcyk [18] are based on the ideas of Oster and Hertter. The verification of the models is complicated due to the lack of residual stress measurements in larger depths under the gear flank surface. For example, residual stress measurement by Xray diffraction is only possible up to depths of approximately one millimeter. Therefore, tensile residual stresses in the inner tooth volume are considered zero in the common residual stresses calculation of Lang [19] and are not considered in the current calculation approach of ISO/DTS 6336-4 [15]. The paper describes local calculation approaches for the fatigue strength of gears with different consideration of residual stresses. Furthermore, the crack initiation point, which is mandatory for the validation of an approach, is examined. The failure mode TFF is hereby the key

Social emotional skills (SES) among lecturers in relation students performance

Social emotional skills (SES) of a lecturer are considered to play a vital role towards student performance. Despite of the fact, when it comes to Technical Vocational Education and Training (TVET), very little research is found on the importance and implementation of these skills. This research therefore determined the level of TVET lecturers’ SES based on lecturers’ and students’ perspective, their relationship with student performance and difference in the level of SES between lecturers in education faculty and in engineering faculty. A case study method with quantitative approach was employed at Universiti Tun Hussein Onn Malaysia (UTHM). A total of 99 lecturers and 373 of final year bachelor degree students from an education and an engineering faculties were involved in this study. They were selected using purposive sampling and total population sampling techniques. Data were collected using two sets of questionnaire, Empathy Quotient (EQ) to measure empathy and Teacher Interpersonal Self-efficacy Scale to measure self-efficacy. Findings showed that lecturers have high level of SES from lecturers’ and students’ perspective. Furthermore, the results of Mann Whitney U Test indicated statistically significant difference the perspective of lecturers and students. However, there was no significant correlation between lecturers’ SES with students’ performance. Nonetheless, lecturers’ self-efficacy for classroom management had statistically significant relationship with students’ performance. Meanwhile, there was also significant difference found in the level of lecturers’ social emotional skills between both faculties. It is concluded that external related reliable feedback is important for lecturers to get to know about their level of SES. SES have a vital role towards students’ performance and that lecturers with professional education background are more effective than lecturers with engineering background. It is hoped that this study could enhance the awareness of TVET institutions in SES as such could help the development of better skill workers in future

Application of Alloy 718 in M-1 engine components

Alloy 718 applied to components of M-1 rocket engin

An Experimental Investigation of Hot Machining with Induction to Improve Ti-5553 Machinability

The manufacturing of aeronautic parts with high mechanical properties requires the use of high performance materials. That’s why; new materials are used for landing gears such as the titanium alloy Ti-5553. The machining of this material leads to high cutting forces and temperatures, and poor machinability which requires the use of low cutting conditions. In order to increase the productivity rate, one solution could be to raise the workpiece initial temperature. Assisted hot machining consists in heating the workpiece material before the material removal takes place, in order to weaken the material mechanical properties, and thus reducing at least the cutting forces. First, a bibliography review has been done in order to determine all heating instruments used and the thermal alleviation that exists on conventional materials. An induction assisted hot machining was chosen and a system capable to maintain a constant temperature into the workpiece during machining (turning) was designed. Trails permit to identify the variation of cutting forces according to the initial temperature of the workpiece, with fixed cutting conditions according to the TMP (Tool-Material-Pair) methodology at ambient temperature. Tool life and deterioration mode are identified notably. The results analysis shows a low reduction of specific cutting forces for a temperature area compatible with industrial process. The reduction is more important at elevated temperature. However, it has consequences on quality of the workpiece surface and tool wear

Analysis of thermomechanical fatigue of unidirectional titanium metal matrix composites

Thermomechanical fatigue (TMF) data was generated for a Ti-15V-3Cr-3Al-3Sn (Ti-15-3) material reinforced with SCS-6 silicon carbide fibers for both in-phase and out-of-phase thermomechanical cycling. Significant differences in failure mechanisms and fatigue life were noted for in-phase and out-of-phase testing. The purpose of the research is to apply a micromechanical model to the analysis of the data. The analysis predicts the stresses in the fiber and the matrix during the thermal and mechanical cycling by calculating both the thermal and mechanical stresses and their rate-dependent behavior. The rate-dependent behavior of the matrix was characterized and was used to calculate the constituent stresses in the composite. The predicted 0 degree fiber stress range was used to explain the composite failure. It was found that for a given condition, temperature, loading frequency, and time at temperature, the 0 degree fiber stress range may control the fatigue life of the unidirectional composite