Effect of stress level on the high temperature deformation and fracture mechanisms of Ti-45Al-2Nb-2Mn-0.8 vol. pct TiB²: an 'In Situ' experimental study

The effect of the applied stress on the deformation and crack nucleation and propagation mechanisms of a gamma-TiAl intermetallic alloy (Ti-45Al-2Nb-2Mn (at. pct)-0.8 vol. pct TiB2) was examined by means of in situ tensile (constant strain rate) and tensile-creep (constant load) experiments performed at 973 K (700 °C) using a scanning electron microscope. Colony boundary cracking developed during the secondary stage in creep tests at 300 and 400 MPa and during the tertiary stage of the creep tests performed at higher stresses. Colony boundary cracking was also observed in the constant strain rate tensile test. Interlamellar ledges were only found during the tensile-creep tests at high stresses (sigma > 400 MPa) and during the constant strain rate tensile test. Quantitative measurements of the nature of the crack propagation path along secondary cracks and along the primary crack indicated that colony boundaries were preferential sites for crack propagation under all the conditions investigated. The frequency of interlamellar cracking increased with stress, but this fracture mechanism was always of secondary importance. Translamellar cracking was only observed along the primary crack.Funding from the Spanish Ministry of Science and Innovation through projects (MAT2009-14547-C02-01 and MAT2009-14547-C02-02) is acknowledged. The Madrid Regional Government partially supported this project through the ESTRUMAT grant (P2009/MAT-1585). CJB acknowledges the support from the Spanish Ministry of Education for his sabbatical stay in Madrid (SAB2009-0045).Publicad

Mobilise-D insights to estimate real-world walking speed in multiple conditions with a wearable device

This study aimed to validate a wearable device’s walking speed estimation pipeline, considering complexity, speed, and walking bout duration. The goal was to provide recommendations on the use of wearable devices for real-world mobility analysis. Participants with Parkinson’s Disease, Multiple Sclerosis, Proximal Femoral Fracture, Chronic Obstructive Pulmonary Disease, Congestive Heart Failure, and healthy older adults (n = 97) were monitored in the laboratory and the real-world (2.5 h), using a lower back wearable device. Two walking speed estimation pipelines were validated across 4408/1298 (2.5 h/laboratory) detected walking bouts, compared to 4620/1365 bouts detected by a multi-sensor reference system. In the laboratory, the mean absolute error (MAE) and mean relative error (MRE) for walking speed estimation ranged from 0.06 to 0.12 m/s and − 2.1 to 14.4%, with ICCs (Intraclass correlation coefficients) between good (0.79) and excellent (0.91). Real-world MAE ranged from 0.09 to 0.13, MARE from 1.3 to 22.7%, with ICCs indicating moderate (0.57) to good (0.88) agreement. Lower errors were observed for cohorts without major gait impairments, less complex tasks, and longer walking bouts. The analytical pipelines demonstrated moderate to good accuracy in estimating walking speed. Accuracy depended on confounding factors, emphasizing the need for robust technical validation before clinical application. Trial registration: ISRCTN – 12246987

Variation of the yield strength and strain-rate sensitivity exponent of type 21-6-9 stainless steel over a wide temperature range

The yield strength of solution-annealed 21-6-9 austenitic stainless steel was determined over a wider temperature range (-195 to 1100/sup 0/C) than has been previously reported. The most noteworthy characteristic of the variation of yield stress with temperature was the dramatic decrease in yield strength from -195/sup 0/C to 300/sup 0/C. The strain-rate sensitivity exponent, N, was determined using strain-rate change tests. A plot of N vs temperature showed that n dramatically increased at about 850/sup 0/C and that N is approximately independent of strain (structure). 3 figures

Power Law Breakdown in the Creep in Single-Phase Metals

New analysis provides insight into the basis of power-law breakdown (PLB) in the steady-state creep of metals and alloys. A variety of theories has been presented in the past but this new examination suggests that there is evidence that a dramatic supersaturation of vacancies leading to very high diffusion rates and enhanced dislocation climb is associated with the rate-controlling process for creep in PLB. The effect of vacancy supersaturation may be enhanced by dislocation short circuit diffusion paths at lower temperatures due to the dramatic increase in dislocation density

Mechanical damage introduced into aluminum monocrystals during TEM thin-foil preparation

The article of record as published may be found at http://dx.doi.org/10.1016/0026-0800(86)90013-3The mechanical damage that is introduced into annealed aluminum by the various steps used in the preparation of thin foils for transmission electron microscopy (TEM) is discussed. These steps are: (1) preparation of 3-mm discs by mechanical punching; (2) preparation of 3-mm discs by spark-cutting; and (3) intermediate thinning by hand-grinding discs to thicknesses of 500, 375, 300, or 200 ..mu..m. Often these steps precede the final electrochemical jet-thinning used to obtain perforated TEM foils. The mechanical damage produced by these steps was evaluated by comparing, in the TEM, thin foils utilizing one of these steps with other thin foils of annealed (undamaged) aluminum. Damage was manifested by an increased dislocation density. The mechanical punching was performed on a device machined at the Lawrence Livermore National Laboratory that was very similar to smaller, commercially available punches. The spark-cutting was performed on a Metal Research LTD Servomet at a setting of 6 using a tubular brass cutting tool. Jet-thinning was done on a Struers Tenupol 2 using an electrolyte of 469 mL methyl alcohol, 25 mL H/sub 2/SO/sub 4/ and 6 mL HF at 265 K. Thinning was performed at 25 V. The aluminum (99.999% pure) was provided by Highways International as plate (1 x 100 x 100 mm). The plate was annealed at 723 K for 20 min in vacuum. The resulting average grain size was about 4 mm. Therefore, the discs that were punched, spark-cut, and ground were smaller than the typical grain or monocrystal

Yield stress of Type 21-6-9 stainless steel over a wide range of strain rate (10/sup -5/ to 10/sup 4/ s/sup -1/) and temperature

Hopkinson split-bar tests were performed on Type 21-6-9 austenitic stainless steel from ambient temperature to 1023 K. These high-strain-rate tests (10/sup 2/ to 10/sup 4/ s/sup -1/) were compared with lower-strain-rate tests (10/sup -4/ s/sup -1/). The results indicate that over this temperature range, the strain-rate sensitivity of 21-6-9 is not strongly dependent on the strain rate. This suggests that the mechanism(s) of plastic flow at the higher rates is similar to that at the lower rates. This contention was corroborated by transmission electron microscopy