Modification of Surface and Subsurface Properties of AA1050 Alloy by Shot Peening

AA1050 Al alloy samples were shot-peened using stainless-steel shots at shot peening (SP) pressures of 0.1 and 0.5 MPa and surface cover rates of 100% and 1000% using a custom-designed SP system. The hardness of shot-peened samples was around twice that of unpeened samples. Hardness increased with peening pressure, whereas the higher cover rate did not lead to hardness improvement. Micro-crack formation and embedment of shots occurred by SP, while average surface roughness increased up to 9 µm at the higher peening pressure and cover rate, indicating surface deterioration. The areal coverage of the embedded shots ranged from 1% to 5% depending on the peening parameters, and the number and the mean size of the embedded shots increased at the higher SP pressure and cover rate. As evidenced and discussed through the surface and cross-sectional SEM images, the main deformation mechanisms during SP were schematically described as crater formation, folding, micro-crack formation, and material removal. Overall, shot-peened samples demonstrated improved mechanical properties, whereas sample surface integrity only deteriorated notably during SP at the higher pressure, suggesting that selecting optimal peening parameters is key to the safe use of SP. The implemented methodology can be used to modify similar soft alloys within confined compromises in surface features.

Effect of Pre-Strain on Microstructure and Tensile Properties of Ti-6Al-4V at Elevated Temperature

Research on pre-deformation influences on material properties in multistep hot forming is of important scientific interest. In this paper, hot tensile tests at 850 °C and a strain rate of 0.001 s−1 were performed to study the microstructural evolution and mechanical properties of Ti-6Al-4V with pre-strains at 0.05, 0.1 and 0.15. The tensile test results showed that the specimen with 0.05 pre-strain exhibited higher flow stress and larger elongation. Additionally, increasing the pre-strain resulted in a decrease in ultimate tensile strength (UTS) and elongation (EL). The EBSD results showed that the main deformation mechanism of Ti-6Al-4V was high-angle grain boundary sliding. Pre-strain promoted dynamic recrystallization (DRX) by increasing the deformation substructure. The refinement of grains and the eradication of dislocations enhanced the deformability, resulting in an increase in flow stress.

Comparison Between the Facial Flow Lines of Androids and Humans

The behavior of an android robot face is difficult to predict because of the complicated interactions between many and various attributes (size, weight, and shape) of system components. Therefore, the system behavior should be analyzed after these components are assembled to improve their performance. In this study, the three-dimensional displacement distributions for the facial surfaces of two android robots were measured for the analysis. The faces of three adult males were also analyzed for comparison. The visualized displacement distributions indicated that the androids lacked two main deformation features observed in the human upper face: curved flow lines and surface undulation, where the upstream areas of the flow lines elevate. These features potentially characterize the human-likeness. These findings suggest that innovative composite motion mechanisms to control both the flow lines and surface undulations are required to develop advanced androids capable of exhibiting more realistic facial expressions. Our comparative approach between androids and humans will improve androids’ impressions in future real-life application scenes, e.g., receptionists in hotels and banks, and clerks in shops.

A comprehensive experiment-based approach to generate stress field and slip lines in cutting process

This study proposes a comprehensive experiment-based method to determine stress field and slip lines in metal cutting process. The chip geometry and workpiece's strain and strain rate fields are determined using an in-situ imaging technique. The two-dimensional (2D) heat transfer problem for the steady-state cutting process is solved to derive the cutting temperature, and the flow stresses of work material in the main deformation zone are calculated based on the plasticity theory. Furthermore, the stress field is comprehensively determined to satisfy the stress equilibrium, friction law along the tool-chip interface, and traction-free boundary condition along the uncut chip surface. In addition, slip lines in the main deformation zone are derived according to the direction of maximum shear stress without the assumption of perfect rigid-plastic material. The proposed method is validated by comparing the cutting forces calculated based on the obtained stress field with the experimentally measurements.

FE Simulation Investigation of Magnesium Alloy by Equal Channel Angular Processing

Magnesium alloy is one of the structure metals of great potential. The hcp structure makes its plasticity is poor at room temperature, which severely limits the development of magnesium alloy. Magnesium alloy plastic problem can be resolved through grain refinement method, and equal channel angular processing is one of the more effective methods of grain refinement. In this paper, two-dimensional dynamic simulation of equal channel angular processing for magnesium alloy were done with the finite element software. The deformation of magnesium alloy was analyzed when die angle and die corner angle were different. The results show that: in the main deformation zone, when die angles were different, the sample deformation in the horizontal direction is very uniform. But in the sample longitudinally direction, the greater the die angle, the more uniform the sample deformation. Die corner angle has no significant effect on the uniformity of the longitudinally deformation of the sample, but its affects the size of the dead zone and sample warpage.

Clamping force integrated computer aided tolerancing in composite assembly

Traditional computer aided tolerancing method could not accomplish the tolerancing and variation simulation well in composite assembly. The paper presents a clamping force integrated computer aided tolerancing method for composite assembly. The stochastic variations and the stackup of variations are affected by clamping forces. The clamping force modified probability distribution is used to represent the modification based on the verified FEA model of the composite assembly. The clamping forces are coordinated based on the main deformation mode extracted by the principal component analysis to satisfy the coaxial tolerance requirements of the composite assembly. The assembly of an aircraft composite elevator is considered to illustrate the computational aspects of the proposed methods. The computer aided tolerancing method involving clamping forces outlined in the paper is found to be effective for composite assembly.

Long-wavelength late-Miocene thrusting in the north Alpine foreland: implications for late orogenic processes

In this paper, we present new exhumation ages for the imbricated proximal molasse, i.e. Subalpine Molasse, of the northern Central Alps. Based on apatite (U-Th-Sm)/He thermochronometry, we constrain thrust-driven exhumation in the Subalpine Molasse between 12 and 4 Ma. This occurs synchronously to the main deformation in the adjacent Jura fold-and-thrust belt farther north and to the late stage of thrust-related exhumation of the basement massifs (i.e. external crystalline massifs) in the hinterland. Our results agree with other findings along the north Alpine foreland. While site-specific variations in the mechanical stratigraphy of the molasse deposits influence the pattern of thrusting at the local scale, we observe that late-Miocene thrusting is a long-wavelength feature occurring along the north Alpine foreland roughly between Lake Geneva and Salzburg. The extent of this thrusting signal as well as the timing suggests that late-Miocene thrusting in the north Alpine foreland coincides with the geometries and dynamics of the attached Central Alpine slab at depth. Interestingly, this implies that the slab geometry at depth does not coincide with the boundary between the Eastern and Central Alps as observed in the surface geology. Using this observation, we propose that thrusting in the Subalpine Molasse and consequently also the late stage of thrust-related exhumation of the external crystalline massifs, as well as the main deformation in the Jura fold-and-thrust belt are at least partly linked to changes in slab dynamics.

Microstructure and texture of Ti-6Al-4V alloy deformed by rotary forging at elevated temperatures

Ti-6Al-4V alloy cylinder samples were subjected to rotary forging at temperatures ranging from room temperature to 1 473 K. The microstructure and texture were examined by means of electron back-scatter diffraction and X-ray diffraction. The results indicated that the rotary forging could remarkably promote formability at elevated temperatures but not room temperature. For the 1 073 K and 1173 K samples, dynamic recrystallization led to a notable grain refinement effect and produced a typical basal texture. With the further increase of deforming temperature to 1 473 K, dislocation slip contributed the main deformation and the effect of grain refinement was weakened. The martensitic transformation took place during the cooling process of the 1 473 K sample, forming a strip type microstructure and a special texture different from basal texture.

Influence of the effect of crumpling of clay soils in compression tests on the determination of the subsidence of the base

The effect of "compression error" - the effect of crumpling samples of dusty clay soils in compression tests - has been investigated experimentally. For this purpose, compression tests of sands and loams were carried out on a special compression device with a ring area A = 360 cm2 and a height hk = 7 cm. The second difference of this device is the presence in the upper stamp of holes with a diameter of up to 5 mm for the installation of screw marks, which were placed in clay soil samples at a distance of up to 5 mm from the contact surface between the stamp and the soil. The modulus of deformation is the main deformation mechanical characteristic of the soil. It is known from practice that more reliable values of this characteristic can be obtained by testing soil bases with stamps in the field. However, when designing the foundations of shallow foundation, as a rule, apply odometric tests of soils in the laboratory on standard compression devices with a ring area of 60 cm2 and a height of hk = 25 mm by the method of 2 curves [6]. To obtain the calculated values, the compression modules are corrected using transient coefficients [7, 4]. And most importantly, when determining the values of odometric laboratory modules, using standard compression devices, the result is affected by the "compression error". That is, the initial data for the calculated modules of deformation of the engineering-geological elements of the base can be significantly underestimated, which has been confirmed many times by complex pair (stamp-odometer) studies of soils under compression. Studies of soil compression in compression conditions, conducted in the laboratory of foundations and foundations of KNUBA [2] prove the possibility of improving the results of odometric tests of soils for compression, bringing them closer to the strain.