Effect of Strain Rate Sensitivity on Fracture of Laminated Rings under Dynamic Compressive Loading

The effects of cladding layers of rate-sensitive materials on the ductility and fracture strain of compressed rings are numerically investigated by using the finite element method (FEM) and employing the Johnson–Cook (J–C) model. The results show that ductility is governed by the behavior of the material that is located at the ring outer wall regardless of the volume fraction of the core and clad materials. However, as the number of layers increases, this influence becomes less noticeable. Moreover, as barreling increases at the outer wall and decreases at the inner wall, fracture strain increases. Furthermore, the effects of ring shape factor and bonding type of clad and core materials are numerically evaluated. The numerical results show that less force per unit volume is required to fracture narrower rings and that using a noise diffusion pattern at the interface of the materials is more suitable to simulate crack propagation in the compressed rings and functionally graded materials (FGMs). Additionally, delamination has a direct relation to layer thickness and can occur even in the presence of perfect bonding conditions owing to differences among the material and fracture parameters of laminated layers.

Behavior of thermo-mechanically treated rebar exposed to elevated temperatures

PurposeThe purpose of the paper is to mathematically model and predict the characteristics of thermo-mechanically treated (TMT) rebar when subjected to elevated temperatures.Design/methodology/approachData were collected from a few selected studies for developing the constitutive relations. Using the exposed temperature and the duration of heating as independent variables, the empirical relations were developed for determining the changes in mechanical properties of TMT rebars at elevated temperatures.FindingsRecrystallization of TMT rebar crystals took place around 500 °C, which led to a decrease in the dislocation density along with the increase of large-sized grains, resulting in the degradation of strength. Up to a temperature range of 500 °C, the normalized fracture strength was higher, while the normalized fracture strain is not so high. This indicated a failure of brittle nature.Originality/valueThis is an original work done by others as a study to theoretically predict the mechanical behavior of TMT rebars when exposed to elevated temperature.HighlightsThe TMT bars showed brittleness characteristics up to 500 °C and showed ductility characteristics after that on account of its recrystallization and extensive tempering of the outer martensitic rim around that temperature.The comparison between the super ductile (SD) TMT and the regular TMT exhibit shows that the SD-TMT bars were about 1.5 times more ductile than the normal ones.

Definition of catheter jamming: A mechanical analysis of catheter fracture tension and fracture strain

BACKGROUND: Catheter jamming is an emerging and possibly underrated complication. OBJECTIVE: To find the criteria for determining if the catheter cannot be removed through the mechanical analysis of fracture tension and fracture strain (εf) of Peripheral Inserted Central Catheters (PICC). METHOD: We removed 30 pieces of PICC catheters from patients and recorded the indwelling time. Those with an indwelling time shorter than 12 weeks belonged to the short-term group. Those with an indwelling time longer than 12 weeks belonged to the long-term group. The first half of the same catheter is section A, and the second half is section B. The fraction tension and fracture strain of the catheter were measured, and statistical analysis was conducted. RESULTS: The fracture tension of catheter in sections A and B were 5.8917 ± 1.0095 and 6.0670 ± 0.8066 Newtons respectively (p= 0.393) and the fracture strain of catheter in sections A and B were 6.0611 ± 1.0810 and 6.2543 ± 0.7187 Newtons respectively (p= 0.343). The fracture tension of catheter in short-term and long-term group were 6.0696 ± 0.9414 and 5.9192 ± 0.8972 Newtons respectively (p= 0.535) and the fracture strain of catheter in short-term and long-term group were 6.0067 ± 0.7227 and 6.2584 ± 1.0212 respectively (p= 0.301). CONCLUSION: It is objective and consistent to take the catheter fracture tension as the standard. This standard would be able to accurately define the concept of catheter failure and reduce the risk of catheter fracture and the misdiagnosis of catheter failure. The catheter fracture tension and fracture strain was not affected by the catheter indwelling time. It is recommended to set the tensile force as 5 Newtons and carry it out at a speed of 100 mm/min for the catheter drawing of the PICC single-lumen silicone catheter (4.0F) from Budd Company.

Assessing the effect of FDM processing parameters on mechanical properties of PLA parts using Taguchi method

Fused deposition modeling (FDM) is a fast-expanding additive manufacturing technique for fabricating various polymer components in engineering and medical applications. The mechanical properties of components printed with the FDM method are influenced by several process parameters. In the current work, the influence of nozzle temperature, infill density, and printing speed on the tensile properties of specimens printed using polylactic acid (PLA) filament was investigated. With an objective to achieve better tensile properties including elastic modulus, tensile strength, and fracture strain; Taguchi L8 array has been used for framing experimental runs, and eight experiments were conducted. The results demonstrate that the nozzle temperature significantly influences the tensile properties of the FDM printed PLA products followed by infill density. The optimum processing parameters were determined for the FDM printed PLA material at a nozzle temperature of 220°C, infill density of 100%, and printing speed of 20 mm/s.

Effect of Ti on the Structure and Mechanical Properties of TixZr2.5-xTa Alloys

To determine the effects of Ti and mixing entropy (ΔSmix) on the structure and mechanical proper-ties of Zr-Ta alloys and then find a new potential energetic structural material with good me-chanical properties and more reactive elements, TixZr2.5−xTa (x = 0, 0.5, 1.0, 1.5, 2.0) alloys were investigated. The XRD experimental results showed that the phase transformation of TixZr2.5−xTa nonequal-ratio ternary alloys depended not on the value of ΔSmix, but on the amount of Ti atoms. With the addition of Ti, the content of the HCP phase decreased gradually. SEM analyses revealed that dendrite morphology and component segregation increasingly developed and then weakened gradually. When x increases to 2.0, TixZr2.5−xTa with the best mechanical properties can be ob-tained. The yield strength, compressive strength and fracture strain of Ti2.0Zr0.5Ta reached 883 MPa, 1568 MPa and 34.58%, respectively. The dependence of the phase transformation and me-chanical properties confirms that improving the properties of Zr-Ta alloys by doping Ti is feasible.

Effects of Heat Treatment on High Temperature Mechanical Property and Corrosion Resistance of Hastelloy X Manufactured by Selective Laser Melting

In previous studies, the microstructure, mechanical properties and corrosion resistance of Hastelloy X fabricated by selective laser melting (SLM) have been investigated; however, it is hoped that heat treatment will effect on its properties. Therefore, this study is to discuss heat treatment effect on Hastelloy X fabricated by SLM. It is interestingly found that fracture strain greatly increases with heat treatment, and the yield ratio decreases, which demonstrates the material is more reliable. High temperature tensile behavior is discussed; it is worth mentioning that not only fracture strain of the HT sample increases greatly at 550∘C in comparison with SLM sample, but also ultimate tensile strength increases from 632 MPa to 639 MPa; the results show that the mechanical property can be improved at medium and high temperature by heat treatment. The corrosion resistance of HT sample deteriorates slightly, which can be explained by Cr-rich precipitates. In conclusion, the material after heat treatment is suitable for applications requiring high mechanical reliability and medium and high temperature occasions, but it is not befitting for corrosive environments.

Trace Scandium addition on the strength and thermal stability of TiB2 particles reinforced Al-4.5 Cu composites

Strategies employed for developing ultrahigh strength and scalable ductile particles reinforced aluminium-copper matrix composites (AMCs) are highly desirable and grandly challenging. In the present paper, the Scandium (Sc) micro-alloying TiB2 particles reinforced Al-4.5 Cu composites were successfully fabricated by the optimized salt-metal reaction method. The observed microstructures displayed that Sc addition could remarkably ameliorate the dispersion of TiB2 particles, enlarge equiaxed α-Al grain zone and refine the grains on the basis of TiB2 heterogeneous nucleation. In particular, for the 0.4 wt.% Sc microalloyed 5%TiB2/Al-4.5Cu composites, more than a 20 %, 87 %, and 118 % increase in the ultimate tensile strength (UTS), fracture strain elongation (%) and microhardness (HV), respectively were found with respect to the 3 %TiB2/Al-4.5Cu composites at room temperature (298K). The improved mechanical properties of strength-ductility synergy were mainly thanks to the homogeneous distribution of TiB2 particles and modification of Al2Cu phase. Moreover, proper Sc also enhanced the elevated-temperature mechanical properties of the composites with the aid of the accelerated precipitation of θ′ phase and much lower coarsens rate.

Comparison of Different Additive Manufacturing Methods for 316L Stainless Steel

In additive manufacturing (AM), the technology and processing parameters are key elements that determine the characteristics of samples for a given material. To distinguish the effects of these variables, we used the same AISI 316L stainless steel powder with different AM techniques. The techniques used are the most relevant ones in the AM of metals, i.e., direct laser deposition (DLD) with a high-power diode laser and selective laser melting (SLM) using a fiber laser and a novel CO2 laser, a novel technique that has not yet been reported with this material. The microstructure of all samples showed austenitic and ferritic phases, which were coarser with the DLD technique than for the two SLM ones. The hardness of the fiber laser SLM samples was the greatest, but its bending strength was lower. In SLM with CO2 laser pieces, the porosity and lack of melting reduced the fracture strain, but the strength was greater than in the fiber laser SLM samples under certain build-up strategies. Specimens manufactured using DLD showed a higher fracture strain than the rest, while maintaining high strength values. In all the cases, crack surfaces were observed and the fracture mechanisms were determined. The processing conditions were compared using a normalized parameters methodology, which has also been used to explain the observed microstructures.