The present study examines the effect of shot peening on the wear behavior of austenitic high- manganese steels in both low and high silicon. For this purpose, austenitic steel with 17 wt % of ...manganese was cast with 0.6 and 6 wt % of Si. Surface work hardening was performed by using a shot peening device for 15 and 30 min on the samples followed by hardness, impact and wear tests by the dry sand-rubber wheel method. The results showed an intensive reduction of the impact energy from 120 to 7 J and an increase in hardness from 290 to 380 HV in the un-shot peened samples due to the presence of carbide with an increment of silicon percentage. On the other hand, hardness had an enhancing trend owing to the surface work hardening of the samples as a result of shot peening operation. The highest hardness of steel was related to high- silicon–high manganese sample shot peened for 30 min. Accordingly, the highest wear resistance was observed in the same sample. This can be attributed to the presence of carbides precipitation and their sufficient distribution in the matrix of the high-silicon sample, work hardening due to the austenite to martensitic transformation as well as nanocrystallization of the grains on the surface because of the shot-peening process. Studying the wear surfaces showed scratches as a result of the abrasive wear mechanism. Also, the number and depth of the grooves decreased by increasing the hardness.
Extreme C teaches you to use C's power. You will master preprocessor directives, macros, conditional compilation, pointers, and much more, and gain new insight into algorithm design, functions, and ...structures. Amini's book captures his experience as a programmer and scientist, encouraging you to think, question, apply, and experiment for yourself.
•Models for compressive strength prediction solely based on NDT results were developed.•Concrete strength classification using combined NDT results was proposed.
Accurate prediction of concrete ...compressive strength is imperative for investigating the in-situ concrete quality. To avoid destructive testing, developing reliable predictive models for concrete compressive strength using nondestructive tests (NDTs) is an active area of research. However, many of the developed models are dependent on calibration and/or concrete past history (e.g. mixture proportion, curing history, concrete mechanical properties, etc.), which reduces their utility for in-situ predictions.
This paper develops predictive models for concrete compressive strength that are independent of concrete past history. To this end, ultrasonic pulse velocity (UPV) and rebound hammer (RH) tests were performed on 84 concrete cylindrical samples. Next, compressive strengths were determined using destructive testing on these cylinders, and predictive models were developed using NDT results. Furthermore, to ensure generalizability to new data, all models were tested on independent data collected from six different research papers. The results support combined usage of UPV and RH in a quadratic polynomial model structure. Therefore, the final model was proposed based on combining models from a threefold cross-validation of the experimental data. This model predicted the independent data with very good accuracy. Finally, a concrete quality classification table using combined RH and UPV is proposed based on a variant of machine learning k-means clustering algorithm.
The plates of AA5086 aluminium alloy were joined together by friction stir welding at a fixed rotation speed of 1000 r/min various welding speeds ranging from 63 to 100 mm/min. Corrosion behavior of ...the parent alloy (PA), the heat affected zone (HAZ), and the weld nugget zone (WNZ) of the joints were studied in 3.5% (mass fraction) aerated aqueous NaCl solution by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The corrosion susceptibility of the weldments increases when the welding speed increases to 63 and 100 mm/min. However, the value of corrosion rate in the weldments is lower than that in the PA. Additionally, the corrosion current density increases with increasing the welding speed in the HAZ and the WNZ. On the contrary, the corrosion potential in the WNZ appears more positive than in the HAZ with decreasing the welding speed. The WNZ exhibits higher resistance compared to the HAZ and the PA as the welding speed decreases. The results obtained from the EIS measurements suggest that the weld regions have higher corrosion resistance than the parent alloy. With increasing the welding speed, the distribution and extent of the corroded areas in the WNZ region are lower than those of the HAZ region. In the HAZ region, in addition to the pits in the corroded area, some cracks can be seen around the corroded areas, which confirms that intergranular corrosion is formed in this area. The alkaline localized corrosion and the pitting corrosion are the main corrosion mechanisms in the corroded areas within the weld regions. Crystallographic pits are observed within the weld regions.
Three-dimensional porous poly-lactic acid (PLA) scaffold was fabricated using fused deposition modeling (FDM) method including 30%, 50% and 70% nominal porosity. Study of phases in initial polymeric ...material and printed scaffolds was done by X-ray diffraction (XRD), and no significant phase difference was observed due to the manufacturing process, and the poly-lactic acid retains its crystalline properties. The results of the mechanical properties evaluation by the compression test show that the mechanical properties of the scaffold have decreased signifcantly with increasing the porosity of scaffold. The microstructure of scaffolds were studied by scanning electron microscope (SEM), showing that the pores had a regular arrangement and their morphology changed with porosity change. The mechanical properties of the poly-lactic acid scaffolds printed using fused deposition modeling, can be adapted to the surrounding tissue, by porosity change.
The surface treatment is important for titanium and its alloys as promising candidates for dental implantation due to their bioinert surface. Titanium surface samples were modified using H
2
O
2
...solution at different times up to 72 h to boost their bioactivity. According to the results of the field emission scanning electron microscopy test, some nanostructures are formed on the surface of treated titanium samples and increased in size by increasing the time of treatment up to 24 h. After 24 h of application, the sharpness of nanostructures decreased and the micro-cracks and discontinuity in the coating surface increased. The results of the X-ray diffraction study and Raman spectroscopy revealed that anatase (TiO
2
) was formed on the surface of treated titanium samples. The peak intensity of Raman spectroscopy increased with an improvement in treatment time of up to 24 h and then decreased due to the discontinuity of the coating. Full wettability and ability to form apatite were reached at 6 h of treatment. It is clear that the treatment time has a significant effect on the surface treatment of titanium using the H
2
O
2
solution.
► Deep cryogenic increases the carbide percentage, makes a more homogenous distribution and eliminates the retained austenite. ► Quench environment affects carbide distribution and microstructure due ...to the severity of quench media and temperature. ► Virgin martensite does not show any significant potency in carbide formation during the deep cryogenic heat treatment. ► Wear behavior improves with increasing the thermal conductivity of quench media or decreasing its temperature.
Deep cryogenic heat treatment is an add-on heat treatment which has been added to the conventional heat treatment to improve the wear behavior of cold worked tool steels in recent years. In this study, the effect of the different quench environments with different quench severities, including water, oil, air, −30°C ethanol and −195°C liquid nitrogen upon the final microstructure and wear behavior of the 1.2080 tool steel was investigated. Results showed that increasing the quench severity decreases the retained austenite before the deep cryogenic heat treatment, and the final microstructure shows a more homogenous carbide distribution with higher carbide percentages. Despite the low quench severity of liquid nitrogen, the samples quenched in this environment show the highest wear resistance and hardness after the ethanol-quenched samples. This behavior is a function of a very low quenching temperature and a long incubation time for the nucleation of other phases except the martensite. The wear rate and hardness of the ethanol-quenched samples shows the highest values due to the low temperature, higher thermal conductivity (as compared with the liquid nitrogen) and a less stable martensite structure. The formation of nano-sized carbide also shows an important role in the improving mechanical properties. The predominant wear mechanism is adhesive wear.
In recent years, surface mechanical attrition treatment (SMAT) operations have drawn the researchers attention in terms of the impact of this operation on wear resistance, hardness and creation of ...residual stresses. In this study, the effect of SMAT operation time on microstructure, residual stress, hardness and wear resistance was investigated. For this purpose, the specimens were subjected to SMAT at three times of 10, 15 and 20 min and compared with the As-received specimen (specimen without SMAT). XRD has been used to measure grain size and residual stress, SEM to check the microstructure, the hardness, wear resistance and roughness of the specimens were also measured. The results showed that the grain size decreases due to SMAT operation, so that the grain size decreasees from 139.2 nm in the As-received specimen to 93.2, 72.6 and 34.9 nm in the SMAT specimens with times of 10, 15 and 20 minutes, respectively. Also, residual stress is created due to compressive force and microstrain as a result of SMAT operation, which is 158, 170 and 234 MPa for 10, 15 and 20 min SMAT specimens, respectively. As a result of SMAT operation, the hardness and wear resistance of the specimens increase, which is due to the fact that the fine grains, nanocrystalline of their grains and many microstrains created. Studies have shown that hardness and wear resistance increase by 36, 45, 62% and 16, 27, 36% at SMAT times of 10, 15 and 20 min, respectively, compared to the As-received specimen. Examination of the wear mechanism indicates that the wear mechanism in the As-received specimen is strong adhesive and tribochemical wear, which in SMAT specimens decreases due to the increase in hardness of the adhesive wear. Also, by performing SMAT operation, the specimen roughness increases.
Introduction: The use of porous nanobiocomposite scaffolds for maxillofacial fractures and internal surface optimization of artificial grafts utilizing nanotechnology can improve cell adhesion, ...mechanical properties, and adsorption rate. Porous scaffolds have been the subject of numerous investigations, especially for broken and damaged parts of the facial bone. The goal of this study was to look into the biological, experimental, and numerical study of the mechanical properties of porous scaffolds under static loading conditions.Materials & Methods: In this study, a bone scaffold of polycaprolactone- Fluorapatite (PCL / nFA) nanocomposite materials containing (0, 10, 20, 30 %wt.) Fluorapatite nanoparticles was designed and manufactured using a 3D printer with Fused Deposition Modelling (FDM) process. The scaffolds were designed in SolidWorks software with 70% porosity and then transferred to Abaqus software for simulation.Results: In addition, following 28 days of immersion in the simulated body fluid, the bioactivity test of pure and composite scaffolds showed that the PCL /20nFA composite sample produced the most apatite on the surface. DAPI staining and fluorescent microscopy observation, confirm cell viability on the 3D printed scaffold.Conclusion: The Von Mises stress and compressive test simulations revealed that the porous scaffold model may be used for maxillofacial bone replacement and has good mechanical strength and stability.
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