The Effect of Functional Gradient Material Distribution and Patterning on Torsional Properties of Lattice Structures Manufactured Using MultiJet Fusion Technology

Functionally graded lattice structures have attracted much attention in engineering due to their excellent mechanical performance resulting from their optimized and application-specific properties. These structures are inspired by nature and are important for a lightweight yet efficient and optimal functionality. They have enhanced mechanical properties over the uniform density counterparts because of their graded design, making them preferable for many applications. Several studies were carried out to investigate the mechanical properties of graded density lattice structures subjected to different types of loadings mainly related to tensile, compression, and fatigue responses. In applications related to biomedical, automotive, and aerospace sectors, dynamic bending and rotational stresses are critical load components. Therefore, the study of torsional properties of functionally gradient lattice structures will contribute to a better implementation of lattice structures in several sectors. In this study, several functionally gradient triply periodic minimal surfaces structures and strut-based lattice structures were designed in cylindrical shapes having 40% relative density. The HP Multi Jet Fusion 4200 3D printer was used to fabricate all specimens for the experimental study. A torsional experiment until the failure of each structure was conducted to investigate properties of the lattice structures such as torsional stiffness, energy absorption, and failure characteristics. The results showed that the stiffness and energy absorption of structures can be improved by an effective material distribution that corresponds to the stress concentration due to torsional load. The TPMS based functionally gradient design showed a 35% increase in torsional stiffness and 15% increase in the ultimate shear strength compared to their uniform counterparts. In addition, results also revealed that an effective material distribution affects the failure mechanism of the lattice structures and delays the plastic deformation, increasing their resistance to torsional loads.

Carbon nanotube-reduced graphene oxide fiber with high torsional strength from rheological hierarchy control

High torsional strength fibers are of practical interest for applications such as artificial muscles, electric generators, and actuators. Herein, we maximize torsional strength by understanding, measuring, and overcoming rheological thresholds of nanocarbon (nanotube/graphene oxide) dopes. The formed fibers show enhanced structure across multiple length scales, modified hierarchy, and improved mechanical properties. In particular, the torsional properties were examined, with high shear strength (914 MPa) attributed to nanotubes but magnified by their structure, intercalating graphene sheets. This design approach has the potential to realize the hierarchical dimensional hybrids, and may also be useful to build the effective network structure of heterogeneous materials.

Effect of Cutting Flute Offset and Surface Treatment on Self-tapping Bone Screw

Background: Self-tapping bone screws hard to insert will brings many surgical risks such as damage the bone, screw failure. This study investigated the effect of different cutting flute offset and different surface treatment on the insertion torque and pullout strength for self-tapping bone screws.Methods: Titanium alloy screws with five types cutting flute offset and two types surface treatment, were tested for maximum insertion torque and pullout strength in a simulation cortical bone material. One group of each type surface treatment screws were tested for torsional properties. All tests were principally performed according to bone screws test standard. Results: For two types surface treatment, the insertion torque of design with 0.4mm offset was less than others cutting flute offset (p＜0.05), and the pullout strength of design with 0.2mm offset was bigger than others group (p＜0.05). Compared two surface treatment, the insertion torque of dark anodized screws was less than bead blasted, and the former pullout strength was bigger than the latter screws with the offset from 0mm to 0.4mm(p＜0.05).Conclusions: The study results show that different cutting flute offset design and surface treatment effect on the insertion torque, and the bigger cutting flute offset has the lower inserting resistance, and the comprehensive performance of dark anodized screws were better than bead blasted.

Delamination of Pearlitic Steel Wires: Role of Strain Partition on Mechanical Properties of Pearlitic Wires

Cold drawn wires were produced by drawing the pearlitic wire rod (5.5 mm diameter). Cold drawing involved multiple stages to a final drawing strain of ≈ 2.5. The cold drawing alters the pearlite morphology. During the wire drawing, the change in morphology is location dependent. This will create the gradient in stain and strain mode between the surface and the center. This led to have a strain partition among ferrite and cementite phases. The strain partitioning plays a major role in the final tensile and torsional performance of the cod drawn wire. The present work dealt with the experimental and their numerical simulations of stress gradients and the role of pearlite morphology on tensile and torsional properties of the pearlitic steel wire.