Material Design & Processing Communications最新文献

Lattice structures allow achieving high stiffness and strength, maintaining the part weight low. There exist different technologies for the manufacturing of such structures, but the one having high flexibility and offering the possibility of producing parts with complex geometries is the additive manufacturing process. In this paper, titanium specimens with different lengths, presenting a lattice structure as a core, were manufactured by electron beam melting (EBM) process. Then, the bending properties, like stiffness and failure energy, were experimentally determined by subjecting the specimens to the three-point bending test. The analysis of the fracture surface was carried out too. The three-point bending test evidenced that the longer the span was, the higher the elastic contribution over the plastic one was; moreover, the fracture morphology evidenced a ductile behaviour of the material.

This paper investigates the effects of layers orientation on impact energy absorbed by acrylonitrile butadiene styrene (ABS) test specimens, obtained by additive manufacturing (AM), having three in-plane deposition directions (0°, 45°, and 90°). The specimens were tested with instrumented Charpy hammer, CEAST 9050 Pendulum Impact System, according to standard ISO179-1. Unnotched specimens were tested in edgewise direction based on measured velocity and impact force; absorbed energy was computed. The average energy obtained during impact tests for specimens with the orientation of the layers at 45° was about 0.39 J. For those with layer orientation at 0° and 90°, respectively, it was 0.63 and 0.81 J. A hinge break failure mode was observed for 0° and 90° specimens, and brittle fracture for 45° specimens.

In this research article, a hybrid multiple-criteria decision-making approach was implemented to select the optimal brake friction formulation according to several conflicting performance-defining criteria. Friction material formulations based on different abrasives (magnesium oxide, iron oxide, zinc oxide, aluminum oxide, titanium dioxide, zirconium dioxide, and silicon dioxide) were designed, fabricated, and tested for various tribological properties. The inclusions of aluminum oxide proved best from performance and fade coefficient of friction, friction stability, friction fluctuations, and friction variability point of view but confirmed worst in terms of wear and disc temperature rise. The lowest wear and lowest rise in disc temperature were exhibited by zinc oxide added composite. The highest recovery coefficient of friction was displayed by silicon dioxide added composite. Since no single composite alternative could merely satisfy all the desired attributes. To find the optimum composite option for automotive braking application, hybrid analytic hierarchy process (AHP)–criteria importance through intercriteria correlation (CRITIC)–technique for order of preference by similarity to ideal solution (TOPSIS) was used to make the final decision. The results show that the formulation with titanium dioxide as abrasive exhibits the optimal properties.

The Impulse Drum Charger® (IDC) represents a valid and innovative alternative in the field of the superchargers, in particular when the available space is limited, such as in motorcycles. In fact, with respect to the traditional one, which uses turbine-compressor system for engine supercharging, the IDC exploit the deflection of an elastic membrane-spring system to generate overpressure at the intake from the pressure waves generated by the exhaust gases. In this way, the aim of this work is the development of a mathematical model of the membrane-spring system, both realized in 102-RGUD600 glass fiber composite (PA matrix), of a Drum Charger® using Von Karman theory with Berger's approximation. Focusing on the central deflection of the membrane in time and frequency domain, the derived models reproduces with good accuracy the results of the complete finite-element simulations computed with Ansys™, especially in the higher frequencies. Moreover, in order the system work properly, the spring behavior must maintain in linear-elastic range. Hence, a three-point bending test of the spring was carried out, following the specifications in ASTM (D790-03), in order to verify the force-displacement linear relation. The numerical simulations shown excellent agreement with the force-displacement curve observed in the experimental tests.

This paper presents an experimental testing of two short-fiber reinforced composites (SFRC). The two materials are a polyphthalamide with 33% glass fiber inclusion (PPA-GF33) and a polyphenylene sulfide with 40% glass fiber inclusion. Rectangular plates were obtained from these two materials by injection molding. Specimens, type 1BA, according to ISO 527-2, were cut out with orientations of 0°, 15°, 30°, 45°, 60°, and 90°, with respect to the longitudinal direction of the plate. The cutting was conducted using a CNC water jet machine. Tension tests were performed at room temperature, in order to determine the mechanical behavior. Results are presented in the form of stress–strain curves, considering different orientations of the specimens. The experimental results were processed in order to assess the differences that appear due to fiber orientation. A comparison between the two materials was performed in terms of Young's modulus, tensile strength, and tensile strain. The experimental data were used to calibrate the Tsai–Hill fracture criterion.

Spray forming technology has been adopted to prepare essential castings in various industry fields. Understanding what happen during the impaction of droplet on deposited layer is critical to optimize spray forming processes and so improve the final casting quality. The present work investigated the morphology evolution of droplet and deposited layer during impaction, with particularly emphasis on the nonrigid feature of deposited layer in practical spray forming. The results demonstrate that the deposited layer would suffer obvious deformation under the impaction of flighting droplet, which produce puddle-like structure on the deposited layer. The droplet spreading process would be suppressed by this puddle-like structure when the droplet temperature is not high enough, which might introduce gap between the droplet and the deposited layer, so might cause tiny holes in the final casting. Moreover, the simulation results suggest that multiple droplet impaction might cause column structure on the deposited layer, this would seriously increase the surface roughness of the final casting. The investigations hint that the mechanical properties of deposited layer should be considered when studying the microstructure evolution and mechanism of spray forming casting.

The mechanical behavior of Ti-6Al-4V produced by additive manufacturing processes is assessed as based on a model derived from the Kocks–Mecking relationship. A constitutive parameter c_b is derived from a linear Kocks–Mecking relationship for the microstructure that is characteristic of the work hardening behavior. The formulation for c_b is determined by considering the plastic strain between the strengths at the proportional limit and the plastic instability. In this way, the model accommodates the variation in work hardening behavior observed when evaluating material as produced and tested along different orientations. The modeling approach is presented and evaluated for the case of Ti-6Al-4V additively manufactured materials as tested under quasi-static uniaxial tension. It is found that different test specimen orientations, along with postbuild heat treatments, produce a change in the microstructure and plasticity behavior which can be accounted for in the corresponding change of the c_b values.

The Phase-Field method is an attractive numerical technique to simulate fracture propagation in materials relying on Finite Element Method. Its peculiar diffuse representation of cracks makes it suitable for a myriad of problems, especially those involving multiple physics and complex-shaped crack patterns.

Recent literature provided linear relationships between the width of the diffuse crack and the material intrinsic fracture toughness, through a material characteristic length. However, lately, it was shown how the existence of a residual stress field can affect the represented crack width even for fully homogeneous materials, in terms of toughness.

In this short note, the authors tried to shed some light on the factors influencing the width of the diffuse crack representation. By simulating crack propagation in several residually stressed brittle materials, it was shown how the width of the diffuse crack is affected by the ratio between the driving force - due to the externally applied load - and the driving force required to propagate the crack. In other words, the diffuse crack extent can be linked to the degree of crack propagation stability/instability. Monitoring the evolution of the studied quantity can be of great interest to rapidly assess crack instability circumstances, under displacement control.

The present work investigates the effects of tool size on microstructural evolution, tensile strength, and microhardness on double-sided friction stir welding of 12.7-mm-thick AA6061-T6 plates. Three different tools were designed having pin diameters equal to pin lengths of 6.25, 7.5, and 8.5 mm and corresponding shoulder diameters of 18.75, 22.5, and 24.5 mm, respectively. The welds obtained with these three tools were designated as Welds A, B, and C, respectively. Results showed the highest tensile and yield strength for Weld B. The tensile fracture appearance of Welds A and B indicated reasonable necking with crack initiation and propagation through heat affected zone on the advancing side of the weld. However, in the Weld C, fracture appeared in the stir zone near the confluence of thermo-mechanically affected zone. Electron back scatter diffraction indicates dominance of high angle grain boundaries and major shear textures C and components which corresponds to {001}<110>, <110>, and <> textures in the weld nugget.