Material Design & Processing Communications最新文献

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.

Polycarbonate composites are widely spread in many industries, for product manufacturing. Although these materials are being used with high fidelity, their mechanical properties will highly depend on manufacturing processes, fiber orientations with respect to external loads, type of loading, environmental conditions, and so forth. This paper presents the Charpy impact behavior of three polycarbonate grades, in notched and unnotched conditions, as follows: Makrolon 2405—unreinforced polycarbonate, Makrolon 9415—polycarbonate with 10% glass fiber, and Makrolon 8035—polycarbonate with 30% glass fiber. The experimental measurements clearly demonstrated the effect of the fiber content on the impact strength of the material: as the fiber ratio increases, the impact strength decreases, exhibiting brittle behavior. The impact characterization of the notched specimens can facilitate the material selection for applications with higher geometrical complexities, where stress concentrators cannot be eliminated. In addition, the material models obtained through correlations could help increase simulation accuracy and speed up product development cycles.

Despite the great potential of additively manufactured (AM) metallic lattice materials, a comprehensive understanding of their mechanical behavior, particularly fatigue, has yet to be achieved. The role of the sub-unital lattice elements, that is, the struts and the nodes (or strut junctions), is rarely explored, even though it is well known that fatigue is a local phenomenon, determined by the small features of a structure (defects and local geometrical discontinuities).

In this work, the mechanical behavior of nodes and struts has been investigated by designing laser powder bed fusion (L-PBF) Ti6Al4V single strut specimens, with a node placed in the central part of the gauge length. The specimens were manufactured according to four different building orientations, namely, 90°, 45°, 15°, and 0° to the build plane. The influence of the fillet radius at the node and of the printing direction on the fatigue strength has been examined.

Laser powder bed fusion process is widely used in producing cellular materials for various applications. However, there are limitations in the process to produce high-porosity cellular materials with accuracy. A deviation is observed between the as-built and the as-designed geometrical parameters that lead to variation in the obtained stiffness of the cellular material. This study investigates the behavior of three cell topologies, cubic regular, cubic irregular, and trabecular under as-designed and as-built configurations to study their Young's modulus variation. The obtained results are compared with the ideal predictions of the Gibson–Ashby law to evaluate the deviation. Eventually, a linear correlation was developed between the as-designed and as-built Young's modulus to generate a database to select the as-designed geometry/properties to obtain the required as-built geometry/properties.

This study demonstrates the feasibility of fabricating by additive manufacturing composite objects based on acrylic hybrid photocurable formulations, containing 45% by weight of silica nanoparticles, with an average size of about 30 nm. A commercial stereolithography apparatus was used to selectively cure, layer by layer, the high-loaded acrylic resin. The presence of the filler determines an increase in the physical and mechanical properties of the samples that become significantly stiffer and stronger than the pristine matrix. Dynamic mechanical analysis performed on the printed samples gave promising results for the use of developed formulation in the realization of three-dimensional (3D) polymeric structures with improved mechanical properties.