Preparation of medical Mg–Zn alloys and the effect of different zinc contents on the alloy

In recent years, along with the development and application of magnesium alloys, magnesium alloys have been widely used in automotive, aerospace, medicine, sports, and other fields. In the field of medical materials, magnesium not only has the advantage of light weight, high strength, and a density similar to that of human bone, but also has good biocompatibility and promotes the growth of human bone. However, the mechanical properties and corrosion resistance of magnesium alloys need to be further improved to meet the requirements for human biodegradable implants. In this study, three alloys (mass fractions: Mg–10Zn, Mg–20Zn, and Mg–30Zn (wt.%)) were prepared using powder metallurgy by homogeneously mixing powders of the above materials in a certain amount with magnesium as the substrate through the addition of zinc elements, which also have good biocompatibility. The effect of zinc on the microstructure, mechanical properties, wear performance, and corrosion resistance of magnesium–zinc alloys was studied when the zinc content was different. The results show that compared with the traditional magnesium alloy using powder metallurgy, prepared magnesium alloy has good resistance to compression and bending, its maximum compressive stress can reach up to 318.96 MPa, the maximum bending strength reached 189.41 MPa, and can meet the mechanical properties of the alloy as a human bone-plate requirements. On the polarization curve, the maximum positive shift of corrosion potential of the specimens was 73 mv and the maximum decrease of corrosion-current density was 53.2%. From the comparison of the above properties, it was concluded that the three prepared alloys of which Mg–20% Zn had the best overall performance. Its maximum compressive stress, maximum bending strength, and corrosion-current density reached 318.96 MPa, 189.41 MPa and 2.08 × 10−5 A·cm−2 respectively, which are more suitable for use as human implant bone splints in human-body fluid environment.

Analysis on accumulated deformation and stress of the steel roof of Beijing Opera House during construction

This paper aims to study the stress and deformation of large steel structure buildings in the actual construction process. Midas Gen finite element software is used to simulate and analyze the whole construction process of the curved reticulated shell roof, the peripheral steel columns and the permanent support. The stress and deformation results of the structure in the final construction state are compared with those in the design state under one-time loading. The results show that, in the final construction state, the maximum tensile stress and the maximum compressive stress are 1.9 times and 2.0 times of that in the design state under one-time loading respectively, which is very significant. When the design model is loaded with weight at one time, the maximum tensile stress and the maximum compressive stress of the structure both appear near the opening of the steel roof, while in the final construction state, the maximum tensile stress of the structure appears near the boundary frame beam, and the maximum compressive stress appears on the main ridge beam. The maximum vertical displacement of the structure in the final construction state is 2.0 times of that when the design model is loaded at one time. The maximum vertical displacement of the design state appears near the opening of the steel roof, while the maximum vertical displacement of the structure in the final construction state appears on the main ridge beam. In view of the above, the effective guidance for the construction of steel roof structure is provided in this paper to ensure the safety of the structure.

Development of Low-Cost Wireless Sensing System for Smart Ultra-High Performance Concrete

This study proposes the development of a wireless sensor system integrated with smart ultra-high performance concrete (UHPC) for sensing and transmitting changes in stress and damage occurrence in real-time. The smart UHPC, which has the self-sensing ability, comprises steel fibers, fine steel slag aggregates (FSSAs), and multiwall carbon nanotubes (MWCNTs) as functional fillers. The proposed wireless sensing system used a low-cost microcontroller unit (MCU) and two-probe resistance sensing circuit to capture change in electrical resistance of self-sensing UHPC due to external stress. For wireless transmission, the developed wireless sensing system used Bluetooth low energy (BLE) beacon for low-power and multi-channel data transmission. For experimental validation of the proposed smart UHPC, two types of specimens for tensile and compression tests were fabricated. In the laboratory test, using a universal testing machine, the change in electrical resistivity was measured and compared with a reference DC resistance meter. The proposed wireless sensing system showed decreased electrical resistance under compressive and tensile load. The fractional change in resistivity (FCR) was monitored at 39.2% under the maximum compressive stress and 12.35% per crack under the maximum compressive stress tension. The electrical resistance changes in both compression and tension showed similar behavior, measured by a DC meter and validated the developed integration of wireless sensing system and smart UHPC.

Synthesis and Properties of Mg-Mn-Zn Alloys for Medical Applications

The magnesium alloys Mg-0.5Mn-2Zn, Mg-1.0Mn-2Zn, and Mg-1.5Mn-2Zn (wt.%) with potential biomedical applications, synthesized by powder metallurgy, were investigated to evaluate the influence of manganese content on their microstructure, mechanical properties, and corrosion resistance. The results show that Mg-Mn-Zn alloys prepared by powder metallurgy reached the maximum compressive stress of 316 MPa and the maximum bending strength of 186 MPa, showing their good resistance to compression and bending, and meeting the mechanical properties required for the human bone plate. With an increase in manganese content, the corrosion resistance improved. In the polarization curve, the maximum positive shift of corrosion potential was 92 mV and the maximum decrease of corrosion current density was 10.2%. It was concluded that, of the alloys tested, Mg-1.0Mn-2.0Zn (wt.%) had the best overall performance, and its maximum compressive stress force and corrosion current density reached 232.42 MPa and 1.32 × 10−5 A·cm−2, respectively, being more suitable for service in human body fluids.

Field Tests on the Stress Characteristics of Enriched Water Tunnel Invert

To monitor the changes in the force of the tunnel invert steel bars after the groundwater level changes, field tests were performed to accurately and comprehensively characterize the stress acting on the rebar of a tunnel invert. Changes in stress and temperature were monitored for two layers of rebar (upper and lower) in an actual tunnel invert during its repair. The results showed that the changes in stress followed different paths for the upper and lower layers. After the groundwater is replenished, the maximum tensile stress of the rebar was 17.3 MPa, and the maximum compressive stress was 120 MPa. Major changes in stress were observed 2–6 days after rain. Based on this, the seepage path of groundwater is analyzed. During this period, the compressive stress increased threefold, and the tensile stress increased 9.5-fold. The rebar stress in the tunnel invert followed a Gaussian distribution after stabilizing. Four phases of stress progression are identified and discussed. The results can provide data support and theoretical basis for the treatment of invert floor heave in enriched water tunnel.

Effects of aluminum and copper on the graphite morphology, microstructure, and compressive properties of ductile iron

The effect of aluminum (0, 2, 4, and 6 wt. %) and copper (0, 2, 4, and 6 wt. %) on graphite morphology, microstructure and compressive behavior of ductile iron specimens manufactured by sand casting technique were investigated. The graphite morphology and microstructure were evaluated using optical microscopy (OM) and scanning electron microscopy (SEM) equipped image processing software. To study the mechanical properties, the compression test was conducted on the ductile iron specimens. The results indicated that the surface fraction and nodule count of graphite decreased when the amount of aluminum increased from 0 to 2 wt. % and after that from 2 to 6 wt. %. In addition, the nodularity of graphite increased with the increment of the aluminum amounts. By adding the amount of copper, the surface fraction and nodule count of graphite increased and nodularity of graphite decreased. The addition of aluminum and copper decreased the surface fraction of ferrite and increased the surface fraction of pearlite in the microstructure. By increasing the amounts of aluminum and copper, compressive stress vs. strain curves were shifted upwards, and modulus of elasticity, yield strength, maximum compressive stress, and fracture strain improved. In comparison with copper, aluminum had a greater influence on the mechanical properties of ductile iron.

Grey prediction analysis of cutoff wall affected by construction effect

The long-term stability analysis of cutoff wall affected by construction effect is crucial. The longterm stability of the cutoff wall of Daning Reservoir is mainly affected by the combined action of highway vehicle load, extreme highway load and water load under different water storage loads. In this paper, the prediction model and method of grey theory are used to predict the horizontal displacement at the top of the cutoff wall, the settlement at the top, the maximum principal stress of the reinforced concrete wall, and the maximum principal stress of the plastic concrete wall based on grey analysis with each storage and drainage cycle as the time series point combined with the actual situation of the project. The long-term stability of the cutoff wall under load is predicted and evaluated. The results show that the maximum stress of the monitoring 2 – 2 section cutoff wall gradually tend to be stable during the whole storage and drainage cycle. The limit maximum compressive stress of reinforced concrete wall is 4.320 MPa, and the limit maximum compressive stress of plastic concrete wall is 1.758 MPa. Judging from the material strength, the maximum principal stress is within the design strength of the material, and the plastic failure of the wall does not occur, indicating that the combined anti-seepage system of rigid cutoff wall and plastic cutoff wall adopted by the Daning Reservoir is stable and safe in the later normal operation period.

Influence of the Secondary Ion Beam Source on the Laser Damage Mechanism and Stress Evolution of IBS Hafnia Layers

Ion beam sputtered hafnia is a preferred high index coating material for laser applications. It exhibits a mostly amorphous structure and an adequate laser-induced damage (LIDT) threshold. In this work, we investigated the influence of an assisting ion source on the film stress as well as the LIDT of the sputtered hafnia layers. The stress increases with an increasing ion energy of the assisting ion beam. We identified a maximum compressive stress of 3–3.5 GPa before the film cracks, blisters, and delaminates. Different states of stress lead to different laser-induced damage thresholds and damage morphologies.

Comparison of Biomechanical Parameters between Medial and Lateral Compartments of Human Knee Joints

Background: The knowledge of biomechanics helps in predicting stresses in different parts of the knee joint during daily activities. Objective: The objective of this study is to evaluate the biomechanical parameters of the knee joint, such as contact pressure, contact area, and maximum compressive stress, at full extension position during the gait cycle. Methods: The three-dimensional finite element models of human knee joints are developed from magnetic resonance images (MRI) of multiple healthy subjects. The knee joints are subjected to an axial compressive force of 1150 N at full extension position. Results: The maximum compressive stresses on the medial and lateral tibial cartilages were 2.98±0.51 MPa and 2.57±0.53 MPa, respectively. The maximum compressive stresses on the medial and lateral menisci were 2.81±0.92 MPa and 2.52±0.97 MPa, respectively. The contact area estimated on medial and lateral tibial cartilages were 701±89 mm2 and 617±63 mm2, respectively. Conclusion: The results were validated using experimental and numerical results from literature and were found to be in good agreement. The magnitude of maximum compressive stress and the contact pressure was found to be higher at the medial portion of the cartilages as compared to that in the lateral portion of the cartilages. This study shows that the medial meniscus is more prone to tear under severe loading conditions, as the stresses in the medial meniscus are higher than that in the lateral meniscus. The total contact area in the medial tibial cartilage is larger than that in the lateral tibial cartilage.

Molecular dynamics simulation of sI methane hydrate under compression and tension

Molecular dynamics (MD) analysis of methane hydrate is important for the application of methane hydrate technology. This study investigated the microstructure changes of sI methane hydrate and the laws of stress–strain evolution under the condition of compression and tension by using MD simulation. This study further explored the mechanical property and stability of sI methane hydrate under different stress states. Results showed that tensile and compressive failures produced an obvious size effect under a certain condition. At low temperature and high pressure, most of the clathrate hydrate maintained a stable structure in the tensile fracture process, during which only a small amount of unstable methane broke the structure, thereby, presenting a free-motion state. The methane hydrate cracked when the system reached the maximum stress in the loading process, in which the maximum compressive stress is larger than the tensile stress under the same experimental condition. This study provides a basis for understanding the microscopic stress characteristics of methane hydrate.