Small Stress Research Articles

Research on the deformation characteristics of small module tooth during current-assisted splitting spinning of small module tooth-shaped part

Aiming at the problems such as low material utilization, poor strength and toughness of workpiece during manufacturing of small module tooth-shaped parts (SMTSPs) by traditional gear hobbing and shaping method, a current-assisted splitting spinning forming (CASSF) method was proposed to form SMTSPs with high performance requirements. A coupled electrical-thermal-mechanical finite element (FE) model was established based on the ABAQUS software, and the distribution of equivalent stress and equivalent strain, and deformation characteristics of small module tooth were investigated. The results show that the equivalent stress and equivalent strain decrease from tooth groove arc to the tooth crest arc and centre of the tooth groove at tooth profile surface. The distribution of equivalent stress and equivalent strain in the internal deformation region follows the same trend as the tooth profile surface from the centre of the tooth groove to the tooth groove arc, but increases from the tooth groove arc to the tooth crest. The material of small module tooth experiences three-directional stress state. The material in the gear tooth undergoes radial and axial elongation, and tangential compression, while in the tooth groove it undergoes radial compression, tangential and axial elongation.

Static Structural Analysis of Checking Fixture Frame of Car Interior Using Finite Element Method

An inspection is the most important step for the manufacturers producing their cars. This ensures the seamless compatibility of each car part, as even minor errors can lead to user discomfort during operation. To achieve that goal, the utilization of inspection tools, such as a checking fixture is essential. In this research, we will study the structure analysis of a checking fixture with Ansys software. This study aims to examine the structural strength by analyzing the impact of various design variations on the overall strength outcomes. The requirement for checking fixture is that it must meet the datum tolerance of the car with value of ± 2mm. Due to that factor, a rigid checking fixture is needed for inspecting the part without experiencing significant deformation. In static loading, the result of the first variation frame has a stress of 5.71 MPa and deformation of 0.051 mm, the second variation frame has a stress of 6.16 MPa and deformation of 0.049 mm and the third variation frame has a stress of 5.63 MPa and deformation 0.042 mm. In terms of weight, the first variation structure has 2470.48 kg, the second variation structure has 2179.93 kg and the third variation structure has 2210 kg. The second variation frame has the highest stress but it has the lightest weight, and the third variation frame has lower stress and deformation but it has a heavier weight than the second variation model. The study results that the second variation model is superior because it has the lightest weight while the three designs have small stress and deformation that still satisfy the requirement of the fixture.

(Invited) Mechanical Stress Simulations for Advanced Logic Devices

Novel transistor concepts are continuously being investigated to scale beyond FinFETs and nanosheets. One such architecture is the Complementary FET (CFET), consisting of an NFET and a PFET fabricated on top of each other [1-4], offering increased device density thanks to its stacking. However, additional challenges arise, such as significantly complicated processing and higher complexity of the connections between devices. Another concern lies in the optimization of the device performance by incorporating mechanical channel strain: in particular for the top-channel device it is challenging to employ traditional stressors efficiently, as it is largely disconnected from the substrate underneath. The purpose of this study is to study whether a CFET technology, and especially its top-channel device can be properly stressed. To this end, a TCAD process simulation flow that mimics the relevant steps for stress modeling has been built using Sentaurus-Process [5].An example of a quarter-structure of the simulated CFET at the end of the simulation (after channel release) is shown in Fig. 1. The device has a gate length of 14nm, a fin-like silicon channel both for the top and bottom device (5nm width, 30nm height), and fully strained source/drain (S/D) epitaxial layers in the bottom and top devices. For the top (NFET) device, the source/drain epi does not fill up all available space but consists rather of a thin layer grown against the sidewalls of the device, as observed experimentally. Tungsten contacts are added to connect the devices, and a thin oxide layer is present in the source/drain regions to isolate the top from the bottom device.Fig. 2 shows the longitudinal channel stress in the channels for a varying composition of the top-channel S/D epi. A large compressive (i.e. negative) stress is generated in the bottom PFET channels, thanks to the strained Si0.5Ge0.5 bottom S/D epi. On the other hand, the channel stress in the top channel is much smaller and becomes more tensile (positive) for higher Ge% in the top S/D. This opposite trend from traditional S/D’s was reported for nanowires in [6] and can be explained by the fact that the top S/D does not fill up the available space, which leads also to a large reduction in absolute channel stress. Another observation from Fig. 2 is that the stress in the bottom channel is independent of the composition in the top S/D, indicating that the devices are mechanically decoupled. Fig. 3 plots the channel stress in the structure after various steps of the simulation, showing that a small channel stress is generated after S/D etch by the presence of the sacrificial layer (Si0.75Ge0.25) between the channels. Furthermore, dummy gate removal tends to increase the absolute channel stress. Finally, the bottom S/D epi growth does not affect the top-channel stress, again confirming the mechanical decoupling of both channels to first order. Fig. 4 shows how the channel stress is affected for an intrinsic tensile stress of 2GPa in the tungsten or oxide isolation between the devices. Tungsten is a rather ineffective stressor due to its high stiffness: less than 200MPa tensile top-channel stress is generated by a stressed tungsten in its S/D’s. For the bottom device, the effect is even smaller due to the increased distance between the bottom-tungsten and the channel. The oxide isolation proves to be a more efficient stressor for the top channel, leading to about 1GPa additional tensile stress which is concentrated at the bottom of the channel.The presentation will highlight the importance of other stress components besides longitudinal stress. Furthermore, whereas the results in Figs. 1-4 were obtained for fin-like (vertically elongated) devices, a CFET technology can also be built using nanosheet (horizontally elongated) channels. It will be shown that changing towards this type of channels leads to a significant change of the stressor effectiveness in CFET technologies. These insights will help us to continue improving the device performance in advanced transistor architectures like CFETs.

Thermo-Mechanical Stability of Hydrocarbon-Based Pemion® Proton Exchange Membranes

Considering the environmental concerns about the disposal of perfluorosulfonic acid (PFSA) membranes as well as the growing interest in higher temperature operability of polymer electrolyte membrane fuel cells (PEMFCs), non-fluorinated hydrocarbon-based proton exchange membranes (PEMs) with aromatic backbones have become an increasingly active area of research. Low reactant cross-over, tunable electrochemical properties, and differentiated chemistries and potentially safer and cost-reducing synthesis procedures, are additional favourable features of hydrocarbon-based PEMs for prospective use in PEMFCs [1]. Vulnerable linking units, however, are known to be the main disadvantages of these polymers in the oxidative environment of fuel cells. During PEMFC operation, destructive radical species such as hydroxyl (HO•) are produced, causing polymer degradation and thinning in the membrane [2]. Recently, sulfo-phenylated polyphenylenes (sPPPs) have shown outstanding oxidative stability due to a polymer backbone comprising only aryl-aryl bonds, with mitigated chemical degradation in ex-situ and in-situ durability studies [3, 4]. Another concern is regarding the thermo-mechanical stability of PEMs. Thus, a systematic thermo-mechanical stability study is required to confirm the potential of sPPP-based PEMs to replace conventional PFSAs, especially for high temperature PEMFC, i.e., 110-120 °C.The present research objective is to assess the thermo-mechanical stability of a commercial reinforced hydrocarbon-based PEM, Pemion® (PF1-HLF8-15-X, 15 µm thick, reinforced), as well as a mechanically-reinforced PFSA-based reference membrane, across a wide range of temperature (30-120 °C) and relative humidity (RH) (10-90%) conditions that includes the crucial high temperature window of interest for future PEMFCs [6]. To this end, a comprehensive design of experiment yielded 19 tensile tests at various hygrothermal conditions with dynamic mechanical analyzer (DMA 850; TA Instruments) equipped with an external environmental chamber accessory (TA Instruments, RH Accessory). Important mechanical properties such as Young’s modulus, ultimate tensile stress, yield stress, maximum elongation at break, strain hardening, and modulus of resilience were extracted and discussed as well. Datapoints were fitted for empirical model development and mechanical properties were estimated for high temperature and RH conditions beyond the capability of the instrument. This method can be employed to assess if the mechanical properties of membrane materials can be retained at higher temperatures, regardless of polymer chemistry and type. Storage modulus and loss modulus were separately measured in a dynamic mode to observe the impact of temperature on the mechanical response of the hydrophobic backbone and hydrophilic ionic clusters, respectively.Overall, Pemion® demonstrates tough tensile properties in the stress-strain tests due to its sterically encumbered polyphenylene backbone (Figure 1a), whereas the reference PFSA (Figure 1b) shows elastomer-like behavior with much lower Young’s modulus, yield stress, and strain hardening (slope of the curve in the plastic deformation region). Figure 1c-f show the main viscoelastic properties extracted from the tensile tests at room (30 °C, 50% RH) and high temperature fuel cell conditions (110 °C, 50% RH). The modulus of elasticity and strain hardening of Pemion® membrane are almost temperature-independent, whereas these properties for the reinforced PFSA material undergo a significant decay at high-temperature ambience. Pemion® maintains good yielding strength even at high temperature and RH conditions (110-120 °C and 80% RH). Nevertheless, small mechanical stress values as low as 1 MPa can cause spontaneous yielding in the PFSA reference material above 110 °C. The modulus of resilience for the reinforced PFSA is also predicted to be zero at elevated hygrothermal conditions (i.e., 90 °C and 70% RH). This is interpreted as an approach to the material’s glass transition condition, where it loses its mechanical integrity and therefore, is potentially unsuitable for higher temperature PEMFC operation. Moreover, the dynamic mechanical thermal analysis revealed that Pemion® retains its robustness at hygrothermal ambience close to high-temperature PEMFCs, i.e., 110-120 °C and 40-50% RH, whereas the backbone of the PFSA material gradually loses its strength. Acknowledgements This project was financially supported by Natural Sciences and Engineering Research Council of Canada (NSERC), Ionomr Innovations Inc, Canada Foundation for Innovation (CFI), British Columbia Knowledge Development Fund (BCKDF), Western Economic Diversification Canada (WD), and Canada Research Chairs (CRC).

Force-balance modelling of the impact of glacial erosion, trench sedimentation, megathrust weakening and glacial loading on the stress state of the crust at active continental margins

Force-balance analyses showed that the stress state at active continental margins is largely controlled by the gravitational force and the megathrust shear force and remains unchanged as long as subduction proceeds undisturbed. Glacially induced topographic changes and mass redistribution by glacial erosion, sediment transport and deposition may affect the force balance but the impact on the stress state and the style of deformation in the upper plate has not been investigated so far. Here, we use numerical force-balance models to investigate the stress changes in the upper plate resulting from (i) a reduction in mountain height in the arc by glacial erosion, (ii) a steepening of the arc front, (iii) a decrease in the megathrust shear force due to increased sediment subduction and fault weakening, (iv) an increase in sediment thickness in the trench, and (v) the load by an ice cap. Our model results show that each process causes distinct stress changes that affect different parts of the upper plate. The largest stress changes result from a reduction in mountain height, which increases compression in the arc interior, and fault weakening by increased sediment subduction, which decreases the megathrust shear force and hence deviatoric compression in the forearc and backarc. Smaller stress changes occur for a steepening of the arc front, increased sediment deposition in the trench and the load of the ice cap. The different stress changes may promote or suppress faulting in different parts of the upper plate. Application of our model to the North Patagonian Andes indicates that glacial erosion during late Cenozoic cold periods may explain the localization of deformation in the arc interior, whereas the reduced activity of thrust faults in the forearc and backarc may reflect a decrease in deviatoric compression caused by a decrease in the megathrust shear force.

Software for processing of long-term strength data of materials by use of edwards curves

A description of the developed software for saving and analyzing data on high-temperature deformation and long-term strength of metallic materials is provided. The open source Laravel web framework was chosen to implement in the application. The Voyager solution is used together with it as a graphical interface for interacting with the database. A JavaScript programming language solution using Canvas technology is used to build plots. Basic classes and components are described. With the help of diagrams of use cases, the possibility of using the web application in the engineering practice of data processing of experimental high-temperature creep and fracture studies is shown. An approach and an algorithm for approximating long-term strength curves of general appearance, including different types of failure, using Edwards curves are proposed. With their use, an analytical nonlinear expression for the functional dependence between the time to failure and the failure stress was obtained. Approximations of various types of the long-term strength curve corresponding to the processes of accumulation of damage in the material by various types of physical mechanisms are discussed. The undesirable possibility of obtaining an overestimated value of the time to failure in the case of small and medium stress values without using information on the areas of intergranular failure, failure due to oxidation or corrosion, and overaging on the long-term strength curve is demonstrated. The use of the developed software, approach and method of analytical representation of the functional dependence of the values of failure stress on time in the evolution equation for the damage parameter allows you to carry out refined calculations of structural elements operating under high-temperature load conditions

Flexible Fiber Sensors for Monitoring Multi‐point and Distributed Stress and Strain

AbstractIntelligent sensor devices are widely used in the fields of aerospace, automobile, biomedicine, and electronics. However, using traditional bulk sensors, it is challenging to meet the needs of health monitoring, human‐computer interaction, environmental monitoring, and wearable portable electronic devices because of the limitations of flexibility and wearability. Novel flexible sensors should be characterized with stretchable, bendable, breathability, and distributed sensing properties. Herein, a flexible multi‐functional fiber sensor for stress and strain monitoring is prepared using thermal drawing technology. The as‐developed sensor is used for real‐time monitoring of small stress and strain with an accuracy of 1 g (1.7 kPa), positioning spatial resolution of 2 cm, and a strain range of 30 000 µɛ with an accuracy of 86 µɛ. It can sense single‐ and multi‐points weak pressure at the same time during keyboard testing. Furthermore, pulse and breath monitoring are also demonstrated. These results reveal the high sensitivity, lightweight, and good flexibility of this multi‐functional fiber sensor, promoting its applications in fields such as biosensing, aircrafts, and intelligent robot.

Enhanced interfacial structure of (HfZrTiTaNb)C high-entropy ceramic joint brazed using FeCoCrNiTi0.2 alloy filler

To fabricate large-sized and complex-shaped ceramic components for service at elevated temperatures, (HfZrTiTaNb)C high-entropy ceramic (HEC) joints with the improved joint strength of 292 MPa were successfully realized by using a FeCoCrNiTi0.2 high-entropy alloy (HEA) filler at 1430 °C. The reliable joint relied on a direct metallurgical bonding with semi-coherent interfaces between HEC' carbides and HEA' alloy, independent of compounds. The high-entropy interface was confirmed by the habit planes of (020)HEC' // (020)HEA' and the calculated lattice misfit of 1.58%, which represented small internal stresses at bonding interfaces in the joints. The formation of HEC and HEA phases originated from the direct phase transition of HEC induced by active Ti and the residual of liquid HEA, respectively, and they maintained their original lattice structures, nanohardness, and elastic modulus. The joints possessed undiminished strength values when tested at 1000 °C, benefiting from high-entropy microstructures throughout the interfacial region. The failure location migrated from the HEC near the HEC' to the HEA'. In addition, the interfacial formation strategy was investigated by altering HEA thicknesses and bonding times. The HEC' was invariably present in the joint, while preventing phase separation of liquid HEA upon cooling to form HEC'/HEA'/HEC' structure required the HEA thickness of at least 300 µm and the resulting abundant liquid filling. With extended bonding times of up to 60 min, the depletion of the HEA' layer would decrease joint strength by 140 MPa. This work provides a new perspective on joint design toward ∼1000 °C high-temperature applications.

Finite Elements Method Investigation of Plates with Varied Support and Opening for Design Optimization

Plates have an important function in supporting the structural load above them. One important aspect of plate design is the design of the openings or holes. These openings can be needed for various purposes, such as pipe installation, ventilation, and ducts. If the plate openings are not designed carefully, it will cause serious problems such as excessive deflection. This increases the risk of structural accidents and ultimately threatens the safety of building users. This study aims to determine the effect of plates with different types of supports and opening models with 3D modeling. Quantitative descriptive research using the finite element method was used. There are 16 models with different support types (simply and fixed) and opening models (rectangular, square and circular). From the modeling, the deformation and stress values that occur will be obtained. Comparative analysis is carried out to obtain the best support and opening types. The research results show that the increase in stress concentration tends to be higher in rectangular openings, while in square and circular openings, it is smaller than in plates without openings. Circular shapes tend to have high deformation values. Meanwhile, the square shape has the smallest value compared to all models. Simply support has greater stress in rectangular and circular openings. 4-sided fixed support is the best choice because it has the smallest stress and deformation values. Through these results, it is possible to optimize the design of appropriate types of supports and openings to reduce excess stress and improve overall structural performance.

A high performance piezoelectric hetero-junction based on the configuration reform on interfacial potential barrier

In this paper, the barrier region of a mixed hetero-junction consisting of a p-type Si and an n-type ZnO was fully opened by abandoning the depletion layer approximation in advance. The barrier configuration was reconstructed by the artificial potential barrier based on a new fully coupled model in which the interaction between physical fields and charge carriers was taken into account. Then, we put forward an interesting design idea of elevating the mechanical regulation performance of a PN junction by manufacturing it with a third-generation piezoelectric semiconductor and a narrow bandgap semiconductor. It is through the deformation of the third-generation piezoelectric semiconductor on one side under mechanical loadings to excite polarization charges at the PN interface such that the movement of charge carriers in the narrow bandgap semiconductor on the other side is able to be tuned by the interface polarization charges. Besides, it is found a specific current-stress characteristic for such a mixed hetero-junction, which will present three stages, i.e., rising stage, platform stage and falling stage. The rising stage is caused by the improving recombination rate, which can be used as a high sensitivity stress sensor (output current improved by more than 10 times in a small stress). Oppositely, the falling stage is caused by the weakened recombination rate due to carrier type-inversion, which can be used to determine overload (output current reduced dramatically when the stress increased to a specific value). Finally, the platform stage is caused by the competition of the above two cases. At this stage, the device operates very stable and can resist the external perturbation. Obviously, the study possesses referential significance to the design and mechanical tuning on performance of piezotronic devices.

Comparison of electrical sensing and image analysis for in situ transmission electron microscopy nanomechanical testing of thin films

An in situ transmission electron microscopy (TEM) microelectromechanical system (MEMS) device has been designed to utilize TEM imaging for measuring stress and strain of thin film micro-specimens while simultaneously recording the microstructure evolution. Digital image correlation is also used to measure local normal strain values by tracking edge features of the specimens. The device performance is compared to that of a similar MEMS device that utilizes capacitive sensors for stress and strain measurements, using 100-nm thick Au thin film specimens. It is shown that there is a significant improvement in the noise levels from ∼1–2 MPa to ∼0.2 MPa and increased sensitivity with the capability of measuring small stress changes. The device can be used to perform both in situ TEM monotonic and transient tests (for activation volume measurements) to investigate the active plastic deformation mechanisms.

Clustering of vascular aging manifestations and incident cardiovascular events. The Paris Prospective Study III

Abstract Background Vascular aging is a key contributor to cardiovascular disease (CVD). Manifestations of vascular aging are heterogeneous and include atherosclerosis, arterial stiffening, increased arterial wall stress and arterial diameter enlargement. These manifestations have different pathophysiological mechanisms and likely require different prevention strategies. How the different vascular aging manifestations co-exist, or cluster, at the individual level and the association of any such clusters with incident CVD is unknown. Purpose To examine how vascular aging manifestations cluster and whether any such clusters are associated with incident CVD. Methods In the Paris Prospective Study III, a French community-based prospective study on novel determinants of CVD, 10,157 participants underwent a high-resolution carotid echotracking (Artlab, Esaote) between 2008 and 2012, and were thereafter monitored every two years for CVD events up to end 2020 . Hospitalized stroke and coronary heart disease (CHD) events were validated after the review of all medical records. Hierarchical clustering analysis was employed to identify patterns of vascular aging. Hazard ratios (HRs) were quantified in Cox models. Results The study sample included 8,360 participants (39% women, mean age 59.6 years) without prevalent CVD. Three clusters of vascular aging manifestations were identified: - Cluster 1 included 3,995 (47.8%) participants and was characterized by low prevalence of carotid plaques, low carotid intima-media thickness (IMT), low carotid artery stiffness, small carotid diameter and low carotid circumferential wall stress (healthy vascular aging cluster). - Cluster 2 included 2,109 (25.2%) participants and was characterized by high carotid artery stiffness and high carotid circumferential wall stress (arterial stiffness vascular aging cluster). - Cluster 3 included 2,256 (27.0%) participants, and was characterized by high prevalence of carotid plaques and high carotid IMT(atherosclerosis vascular aging cluster). After a median follow-up of 8.5 years, 108 incident stroke events, 218 CHD events and 192 deaths occurred. Compared with cluster 1, cluster 2 (HR 1.76, [95%CI, 1.06-2.94]), but not cluster 3 (HR 1.57, [0.94-2.62]), was associated with a higher risk of stroke. In addition, compared to cluster 1, cluster 3 (HR 1.53, [1.08-2.16]), but not cluster 2 (HR 1.38, [95% CI, 0.96-1.98]), was associated with higher risk of CHD. Both cluster 2 and 3 were associated with higher all-cause mortality (HR for cluster 2: 1.50, [1.02-2.21]; HR for cluster 3: 1.48, [1.01-2.17]). Internal validation using bootstrapping methods (n=1000 samples) provided consistent findings. Conclusion The simultaneous analysis of carotid-echotracking vascular aging parameters identified three patterns of vascular aging that are differentially associated with CHD and stroke in the community.Carotid properties by clustersKM survival curves by clusters

Wave Velocities and Poisson Ratio in a Loose Sandy Martian Regolith Simulant Under Low Stresses: 2. Theoretical Analysis

AbstractThis paper presents a theoretical analysis of the data on wave velocity measurements at small stresses presented in a companion paper describing the experimental results on a Martian regolith loose sandy simulant (Fontainebleau sand) of the soil at the InSight landing site on Mars (Elysium Planitia). Experimental data of wave velocities and Poisson's ratio are interpreted in the light of a granular contact mechanics theory and completed accounting for rugosity effects that are suspected to have stronger effects in sands under low stresses. The asperities of a grain of Fontainebleau sand were investigated through Atomic Force Microscopy, but larger asperities had to be adopted so as to better fit the model prediction with experimental data. A good agreement between the experimental data and the model predictions is obtained for stress above 10 kPa. Below 5 kPa, an area in which asperities are suspected to have a stronger influence, the model is not fully satisfactory, showing that further experimental and theoretical investigation is necessary in a stress zone particularly relevant to surface soils in planets, with probably enhanced effects of asperities on the intergrain contact mechanics.

The influence of inelastic materials on freeform kerf structures

Kerfing or relief cutting is a fabrication approach to create moldable surfaces out of wood and metal panels. The kerf panels with pre-defined microstructural topology enable the creation of freeform kerf structures of complex geometries, which found many applications in building constructions. This study investigates the influence of inelastic materials, i.e., plastic deformation of stainless steel and viscoelastic wood, and microstructural topology on the overall moldability of kerf panels. Kerf unit cells fabricated from stainless steel (SS) and medium-density fiber (MDF) with different cut patterns, cut densities, and cell sizes are first studied. Experimental tests and mathematical models are used to examine the deformations of the kerf unit cells. Kerf panels of various microstructural topology, which depends on the cut patterns, cut densities, cell sizes, and cell arrangements, are then modeled to create freeform shapes. The effect of inelastic deformations, i.e., shape reconfiguration due to creep of MDF and utilizing inelastic deformations of SS to form the freeform shapes, are studied. When only an elastic deformation is considered, increasing the flexibility in kerf panels by increasing cut densities enables easy shape configurations. However, when a plastic deformation is utilized to form the shape, flexible kerf structures are less effective due to the relatively small stresses in the flexible SS kerf structures to induce plastic deformations. Flexible MDF kerf structures can experience significant creep deformations, inducing nonnegligible shape reconfigurations. To avoid shape reconfigurations due to the creep effect when using viscoelastic wood, one approach is to consider developable surfaces.

Treatment of Lumbar Degenerative Disease with a Novel Interlaminar Screw Elastic Spacer Technique: A Finite Element Analysis.

A novel interlaminar elastic screw spacer technique was designed to maintain lumbar mobility in treating lumbar degenerative diseases. A validated finite element model of L4/5 was used to establish an ISES-1/2 model and an ISES-1/3 model based on different insertion points, a unilateral fixation model and a bilateral fixed model based on different fixation methods, and a Coflex-F model based on different implants. The elastic rods were used to fix screws. Under the same mechanical conditions, we compared the biomechanical characteristics to investigate the optimal entry point for ISES technology, demonstrate the effectiveness of unilateral fixation, and validate the feasibility of the ISES technique. Compared to ISES-1/3, the ISES-1/2 model had lower intradiscal pressure, facet cartilage stress, and posterior structural stress. Compared to the ISES-BF model, the ISES-UF model had lower intervertebral pressure, larger mobility, and smaller stress on the posterior structures. The ISES model had a similar intervertebral pressure and limitation of extension as the Coflex-F model. The ISES model retained greater mobility and reduced the stress on the facet cartilage and posterior structure compared with the Coflex-F model. Our study suggests that the ISES technique is a promising treatment of lumbar degenerative diseases, especially those with osteoporosis.

Correlation between reliability and safety factor based methods in characterizing uncertainty of creep rupture properties

Reliability and safety factor based methods are usually employed to characterize uncertainty of creep rupture properties, but the correlation between these two methods is rarely reported. In this work, a framework of correlation between reliability and safety factor based methods was proposed, and application of this framework in representation of minimum stress to creep rupture was reported. Effect of standard deviation on correlation results was discussed and comparisons of minimum stress to creep rupture in codes and standards were conducted. Results indicated that for a given reliability, the safety factor included in the minimum stress to creep rupture is higher at a small stress level and a high temperature. Accordingly, the minimum stress to creep rupture by reliability based method in ASME code (i.e. 95 %) is lower than that by safety factor based method in RCC-MRx code (i.e. 1.25), presenting a smaller allowable stress value and more conservative evaluation. Contrarily, a smaller safety factor is gained at a high stress level and a low temperature for a given reliability. The opposite conclusion is drawn when the reliability at a given safety factor is analyzed. In addition, the safety factor of 1.5 is larger than that at the reliability of 99 % for a wide range of stress levels, inducing an over-conservative design and excessive manufacturing costs.

The Settlement Behavior Using Replacement Embankment with Mortar Foam and Geofoam using LISA FEA

The IKN area, especially in the dock and stockyard construction area, is in an area with soft surface soil and requires several options for handling the stockyard area with several materials that are being widely used and easy methods and provide economic value in development. The use of geoform can increase the CBR value of native soil and the use of geofoam as embankment material provides a higher safety factor value with a smaller deformation value besides that the foam mortar material contributes to a small decrease and stress on the surface of the native soil. This study provides a behavioral review of the vertical settlement and stresses that occur in the soil and gives special behavior to the Geofoam material in the presence of hydrostatic forces. The largest settlement that occurred was 0.0961 m on the surface of the foam mortar, while on the existing soil surface a settlement of 0.0288 m occurred, while the largest settlement that occurred was 0.04254 m on the surface of the geofoam, while on the existing soil surface a settlement of 0.0277 m occurred.

Unusual step-like stress flow behavior and mechanisms of a 1.3 GPa grade medium-Mn steel with 51.2 % ductility

A Fe-8.9Mn-1.59Si-1.0Al-0.25C medium-Mn steel have achieved a superior combination of strength and ductility, i.e., the product of strength and elongation (PSE) of 66.5 GPa%. Meanwhile, an unusual step-like stress–strain curve due to heterogeneous deformation bands including Lüders band and multiple Portevin–Le Chatelier (PLC) bands was investigated systematacially. The repeated heterogeneous deformation is due to a combination of extrinsic and intrinsic factors. The former refers a small stress concentration near the grip ends of the tensile sample, and the latter is associated with low density of initial mobile dislocations, limited capacity of mobile dislocation multiplication and the presence of meta-stable austenite. As for meta-stable austenite, stress-assisted martensite transformation (SAMT) was confirmed experimentally, which will facilitate strain concentration and the starting of heterogeneous deformation. Moreover, before strain-induced martensite transformation (SIMT), it is the plastic deformation of austenite grains through the slip of partial dislocation and stacking faults (SFs) that contributes to a larger Lüders strain. Finally, we propose that whether it is possible to make the heterogeneous deformation to be a positive side for certain working conditions, which may open new doors for the application of medium-Mn steels. We will continue to do some exploratory studies in this direction next.

Innovative Use of Waste PET-Derived Additive to Enhance Application Potentials of Recycled Concrete Aggregates in Asphalt Rubber.

Polyethylene terephthalate (PET) drinking bottles, rubber tires, and concrete are the very common municipal solid wastes, which are usually disposed of at landfills and stockpiles and cause continuous damage to the environment. Some studies have indicated that waste PET can be chemically converted into an additive for improving the overall properties of asphalt pavement incorporating natural aggregates, especially the moisture-induced damage resistance. However, it is not clear whether this PET additive still works for asphalt rubber containing recycled concrete aggregates (RCA). To well reveal this issue, this study first adopted a similar way to chemically recycle waste PET into the additive for modifying crumb rubber modified asphalt (CRMA) binder and then mixed the binder with the 13 mm maximum aggregate stone matrix asphalt containing 100% coarse RCA for preparing the mixtures. After a series of physicochemical characterizations of the PET additive, the moisture resistance, rutting resistance, low-temperature cracking resistance, and fatigue resistance of the mixture were systematically evaluated. The results showed that the PET additive is capable of improving the resistance to moisture and high-temperature deformation of asphalt rubber and helps greatly reduce the moisture-induced damage to the interfacial bonding layer. To be more detailed, the residual Marshall stability (RMS) value of RCA-CRMAM/1PET after 72 h of immersion is higher than 85% by contrast to that of RCA-CRMAM (77.1%), while the tensile strength ratio (TSR) value of RCA-CRMAM/1PET shows more than 80% compared to that of 65.2%. In addition, only 1% PET additive can enhance the high-temperature resistance of asphalt rubber containing RCA to rut and allow it to maintain higher resistance to rut after moisture-induced damage. 1% PET additive can help improve the bearing capacity of RCA-CRMAM under a low-temperature environment and delay its fatigue life at small stresses. Generally, with the successful introduction of PET additives to asphalt rubber containing RCA, more durable and sustainable highway pavement can be produced and applied in practice to alleviate the negative impacts caused by waste PET, waste tire rubber, and waste concrete.

Numerical Study on the Influence of Fault Structure on the Geostress Field

A geostress field continuously evolves with long-term tectonic activity. A fault, as a general product of tectonic movements, has a great influence on the geostress field in the vicinity. To analyze the geostress field characteristics and influencing factors near the fault fracture zone in high-altitude areas, this study takes the Dianda-Piru fault on the Qinghai–Tibet Plateau as its research object. Based on the geological conditions and in situ stress measurement data in the study area, a refined numerical model was established using numerical simulation to invert the geostress field in the vicinity of the fault fracture zone, and a quantitative analysis of the factors influencing the geostress distribution was carried out. The results show that the overall relationship between large horizontal principal stress σH, vertical stress σv, and small horizontal principal stress σh is σH > σv > σh, and the surrounding rock stress is dominated by horizontal stress. Geostress is released within the fault fracture zone to a certain extent, and there is a certain degree of stress concentration within the intact rock mass on the upper plate of the fault. The elastic modulus has a greater influence on the geostress field near the fracture structure area than Poisson’s ratio, and the range of the stress-weakening zone increases with the decrease in the elastic modulus. The maximum principal stress inside the fault increases with the increase in the angle between the fault strike and regional principal stress, while the deflection angle of the surrounding principal stress direction decreases with the increase in this angle. The study of the distribution law of geostress fields with developed fracture structures can provide theoretical guidance for the sustainable development of engineering construction in tectonically active areas.