Maximum Strain Values Research Articles

Electrical performance and ferroelectric phase transition characteristic in different oriented 0.73PMN‐0.27PT single crystals

AbstractThe electrical and optical properties of (001)‐ and (110)‐oriented 0.73 Pb(Mg1/3Nb2/3)O3‐0.27PbTiO3 single crystals are systematically investigated at various temperatures, both of which present a series of ferroelectric phase transition processes. Dielectric performance measurements reveal that the ferroelectric phase transition occurs over a temperature range, rather than at one temperature point. By testing the ferroelectric hysteresis P–E curves as well as bipolar and unipolar electric field‐induced strain S–E curves, the values of remnant polarization, coercive field, maximum strain, and converse piezoelectric constant d33* change considerably near the phase transition temperatures. Simultaneously, the 0.73PMN‐0.27PT single crystals with (001)‐ and (110)‐orientations under a low electric field show ultrahigh d33* values of 3540 and 2817 pm/V, respectively, which can be attributed to the electric field‐induced monoclinic and orthorhombic phases, respectively. The series of ferroelectric phase transitions upon heating, that is, from rhombohedral ferroelectric to monoclinic/orthorhombic, followed by from monoclinic/orthorhombic to tetragonal, and finally from tetragonal to cubic paraelectric, are further investigated via polarized light microscopy and Raman spectroscopy.

Moving Load Identification with Long Gauge Fiber Optic Strain Sensing

Moving load identification has been researched with regard to the analysis of structural responses, taking into consideration that the structural responses would be affected by the axle parameters, which in its turn would complicate obtaining the values of moving vehicle loads. In this research, a method that identifies the loads of moving vehicles using the modified maximum strain value considering the long-gauge fiber optic strain responses is proposed. The method is based on the assumption that the modified maximum strain value caused only by the axle loads may be easily used to identify the load of moving vehicles by eliminating the influence of these axle parameters from the peak value, which is not limited to a specific type of bridges and can be applied in conditions, where there are multiple moving vehicles on the bridge. Numerical simulations demonstrate that the gross vehicle weights (GVWs) and axle weights are estimated with high accuracy under complex vehicle loads. The effectiveness of the proposed method was verified through field testing of a continuous girder bridge. The identified axle weights and gross vehicle weights are comparable with the static measurements obtained by the static weighing.

Skin Strain Analysis of the Scapular Region and Wearables Design.

Monitoring scapular movements is of relevance in the contexts of rehabilitation and clinical research. Among many technologies, wearable systems instrumented by strain sensors are emerging in these applications. An open challenge for the design of these systems is the optimal positioning of the sensing elements, since their response is related to the strain of the underlying substrates. This study aimed to provide a method to analyze the human skin strain of the scapular region. Experiments were conducted on five healthy volunteers to assess the skin strain during upper limb movements in the frontal, sagittal, and scapular planes at different degrees of elevation. A 6 × 5 grid of passive markers was placed posteriorly to cover the entire anatomic region of interest. Results showed that the maximum strain values, in percentage, were 28.26%, and 52.95%, 60.12% and 60.87%, 40.89%, and 48.20%, for elevation up to 90° and maximum elevation in the frontal, sagittal, and scapular planes, respectively. In all cases, the maximum extension is referred to the pair of markers placed horizontally near the axillary fold. Accordingly, this study suggests interesting insights for designing and positioning textile-based strain sensors in wearable systems for scapular movements monitoring.

Fatigue performance of geosynthetic-reinforced asphalt layers

This study aims at understanding the influence of different geosynthetic reinforcements on the fatigue performance of asphalt layers and the corresponding mechanisms involved. Three different types of geosynthetic reinforcement, namely a biaxial polypropylene geogrid (PP), a polyester geogrid coated with a polymer-modified binder (PET) and a glass geogrid composite (GGC), were employed to understand the fatigue behaviour of asphalt layers via an asphalt beam fatigue test (ABFT) along with the use of digital image correlation (DIC) techniques. The ABFT results suggest that incorporating geosynthetic reinforcement in the asphalt layers improved the fatigue performance by factors of 11, 27, and 38 for the PP, PET, and GGC specimens, respectively. With the aid of DIC, the mechanisms involved in enhancing the fatigue performance of asphalt layers were effectively evaluated. At failure, a maximum tensile strain of 11.2% was obtained using DIC in control specimens against maximum strain values ranging from 2.7 to 3.8% in geosynthetic-reinforced asphalt specimens. Reductions in layer thickness for the geosynthetic-reinforced asphalt layers on the order of 5.9% (PP), 17.6% (PET), and 23.5% (GGC) were established for the geosynthetics evaluated in this study, based on test results adopted in a design example.

Biomechanics of Different Types of PEEK as Implant Materials for Implant-Retained Mandibular Overdentures.

To evaluate the biomechanical behavior of different types of PEEK as implant materials for mandibular implant-retained overdentures. Virtual models of mandibular overdentures retained by two interforaminal implants were simulated. In each model, one implant material was assumed resulting in four models; titanium, carbon-reinforced PEEK, ceramic-filled PEEK and unfilled PEEK models. Unilateral vertical and oblique loads were applied separately. Von-Mises stresses and maximum equivalent strain values were computed. All PEEK implant models induced higher stresses in the cervical portion of peri-implant bone compared to the titanium model. A more homogenous stress distribution pattern along the whole length of the titanium implants was observed compared to PEEK implants. The highest amount of strain values was recorded in the unfilled PEEK implants. Titanium remains to be the most optimum material for dental implants. Unfilled and ceramic filled PEEK might not be recommended as a dental implant material due to the high stresses generated within the implant bodies and cervical part of peri-implant bone under oblique load which might contribute to an increased probability of implant body fracture and marginal bone loss.

Numerical Simulation of Mechanical Characteristics of a Gas Generator Grain under Temperature Load

In view of the crack phenomenon in the low temperature storage process of a certain type of gas generator, the viscoelastic finite element method is used to study a certain type of adherent cast solid gas generator grain, and the numerical simulation study is completed. The simulation results show that the stress concentration on the inner surface of the star shaped grain is located at the B point of the arc of the star root during the process of cooling and low temperature. At the initial moment of curing stage the rising trend of stress and strain of B point is not obvious, before the end of cooling stage the linear increases with the increase of time. During the low temperature storage, the stress relaxation and creep behavior are not obvious. The maximum stress of the B point is 0.289MPa, and the maximum strain value is 16.881%. The simulation process assumes that more simplification is made, and the actual maximum strain value may have more than 20%, which may lead to the crack phenomenon. It lays a foundation for the optimization of the propellant formula and the structure of the grain.

Stress-strain Test of Exoskeleton Legs Based on Different Postures

Aiming at the design requirements of high-strength and lightweight of exoskeleton leg materials, this paper designs a kind of exoskeleton leg mechanism made of T700 carbon fiber and TC4 titanium alloy. The mechanical properties of exoskeleton leg mechanism under three different postures of standing, stranding and squatting were tested by DH5921 dynamic strain gauge. The results showed that the maximum stress and strain were located at the ankle auricular part under three typical postures, and the maximum stress was 150.7MPa. The maximum strain value of the T700 composite material in the middle of the thigh is 848.05με, which meets the requirements of use. In the three different postures, the stress value of each place in the squatting posture increases obviously, but it is still far less than the required strength of the design material, and meets the requirements of use.

Low velocity and compression after impact behaviors of fiber‐reinforced MA‐g‐PP and MA‐g‐ABS matrix composites

AbstractThis study mainly focused on how one layer of fiber fabric can increase the energy absorption and post‐damage behaviors of composite structures. For this purpose, the low velocity and compression after impact behaviors of thermoplastic matrix composite materials were experimentally investigated. A total of 0.1%–0.3% maleic anhydride grafted polypropylene and 0.3%–0.5% maleic anhydride grafted acrylonitrile butadiene styrene polymers were used as the matrix materials, whereas only single‐layer plain weave aramid fiber, carbon fiber, and glass fiber fabric were used as the reinforcement materials. The impact tests were conducted at the energy values of 20, 50, and 80 J. The results showed that the aramid fiber increased energy absorption on every level of impact energy for both matrix materials, while the carbon and glass fiber fabrics only increased the energy absorption of the MA‐g‐ABS matrix. They negatively affected the energy absorption of the MA‐g‐PP polymer. No reinforcement materials had any contribution to the maximum CAI strength value of the two matrix materials, especially in the MA‐g‐ABS composites, while all reinforcement materials increased the maximum strain values of MA‐g‐ABS up to 75%. They did not increase the CAI strain values of MA‐g‐PP due to the flexible structure of polypropylene.

The effect of nanoclay on the nonlinear viscoelastic behavior of high‐density polyethylene

AbstractThe study's main motivation is to determine the creep behavior of high‐density polyethylene (HDPE)‐based nanocomposites in unexpected situations where short‐term constant loading may occur. On this basis, the short‐term creep behavior of 1 wt.%, 3 wt.%, and 5 wt.% nanoclay reinforced HDPE nanocomposites were investigated at room temperature (23 ± 1°C) and strain rate of 1E‐4 1/s under 8, 12, and 16 MPa stress levels. As the nanoclay reinforcement ratio by weight increased, the creep resistance and modulus of neat HDPE increased at 8 MPa stress level, but they decreased at 12 and 16 MPa stress levels. The absorbed energy that corresponds to the area under the stress–strain curve increase as the stress level increase from 8 to 16 MPa. However, absorbed energy decreases as nanoclay reinforcement increases for 8 MPa. The curves produced from the four‐element Burger's model and Findley's power law models were compared with the creep curves obtained from the experiments. The four‐element Burger model was found to fit the creep curves better than Findley's power‐law model. Also, some regression curves were given for interpolations to give intermediate values of the maximum creep strain values at different stress levels. The presented models can be used to evaluate creep strain, considering the usage fields of parts or semi‐products produced from nanoclay/HDPE nanocomposites.

Mechanical analysis of square shaped PMMA using reflection photoelasticity

This research involves an application of reflection photoelasticity used to analyze stressed samples. The poly(methyl methacrylate) (PMMA) had a rectangular shape 2.5 × 2.5 × 0.6 cm and was compressed by hydraulic press system. The observation of a stressed sample using reflection photoelasticity showed isochromatic and isoclinic fringe patterns. We adjusted the polariscope to determine the photoelastic parameters, namely fringe order, angle principal stress and strain value, which were used to calculate the stress-strain based on calibration, shear difference method and stress-strain optic law. It was found that maximum normal stress (y-direction) and strain values were at contact area and decreased to the edge and center along horizontal and vertical direction of sample. Shear stress depended on multiple of fringe order and sin2θ. It was zero along center of vertical and horizontal direction of sample.

Study on Mechanical Performance of Prestressed UHPFRC U-Beam Bridges

The forms of U-shaped UHPFRC beams have not been investigated for the highway footbridge. Compared with the traditional section forms, the U-shaped UHPFRC beams can reduce the material consumption under the condition of providing the same bearing capacity. Furthermore, prestressed U-shaped UHPFRC beams are rarely reported in the existing research. This paper explores the flexural behavior of prestressed ultrahigh-performance fiber-reinforced concrete (UHPFRC) beam bridge having unique design and the material properties of prestressed reinforcement combined with UHPFRC. Based on the unique shape of the U beam, the flexural performance test of the full-scale model of the prestressed UHPFRC U beam is conducted. Then, the finite element model considering material nonlinearity and structural ductility is established using Midas FEA software. Finally, the failure mode, failure process, cracking moment, ultimate moment, and strain of the full-scale model are studied. The calculation formulas of the flexural capacity of UHPFRC U beam considering ductile failure are derived. The comparative analysis results show that the prestressed UHPFRC U beam has an excellent flexural performance. The bending failure of a U-shaped beam belongs to the group of ductile failures, which is characterized by the main crack along the central rib and the loading center, which is accompanied by multiple microcracks. The failure process can be divided into four stages: linear deformation, microcracks development, main cracks development, and bearing capacity decline. The incorporation of steel fiber and the interaction between UHPFRC and reinforcement can effectively reduce the development of cracks. The U-beam bending moment is 50–55% of the ultimate bending moment. In the UHPFRC bridge design, the deformation can be used as a control index, and material advantages of the UHPFRC can be used to a certain extent. The strain-hardening characteristics of the UHPFRC are obvious in the loading process. The finite element analysis results show that the maximum strain value appears at the central rib, followed by the transverse strain value of the bottom plate, while the minimum strain is the longitudinal strain value of the bottom plate. The deformation of the rib plate is the largest, and the strain of the other measuring points changes slowly. The farther away from the center the measurement point is, the slower its strain changes. Therefore, the load is mainly caused by the central rib and the loading center plate. With the increase in the deformation, the load on both sides continuously moves to the central rib along the plate surface. This study can provide a useful reference for theoretical analysis and design of prestressed U-UHPFRC bridges.

Force Characteristic Analysis of Different Steel Deck Pavement under Temperature Load Coupling Situation

In order to investigate the force characteristic of different steel deck pavement under extreme temperature and load coupling situation, we established the three dimensional extreme high temperature and extreme low temperature field of simple supported beam bridge, the paving structure were double layered SMA, double layered epoxy concrete, SMA+GA, using material elastic modulus changing with temperature. Analysis indicated that the maximum value of high temperature normal stress occurred in the epoxy upper layer pavement, the maximum value of shear stress occurred in the epoxy lower layer pavement, the maximum value of high temperature strain occurred in the upper layer of double layered SMA pavement. The maximum value of low temperature stress occurred in the SMA+GA lower layer pavement, the maximum value of low temperature strain occurred in the SMA+GA upper layer pavement, the maximum value of shear strain occurred in the SMA lower layer pavement. The maximum value of high temperature stress usually occurred in the bottom of pavement layer, maximum strain usually occurred on top of pavement layer. The maximum value of low temperature shear stress and shear strain usually occurred in the bottom of pavement layer, normal strain occurred on top of pavement layer. The stress difference between the upper and lower layers in SMA+GA pavement structure is very large which adversely affected the structural force.

Design and Simulation of Sandwich Structure of Exoskeleton Backplate Based on Biological Inspiration

The backplate is the main skeleton of the exoskeleton robot, and its structural strength and lightweight design are very important to the body structure of exoskeleton. In this paper, a design scheme of grille reinforced foam sandwich structure based on biological inspiration is presented. By analyzing the influence of core thickness on the mechanical properties of the sandwich structure, a new sandwich structure of exoskeleton backplate with a surface thickness of 2mm and a core thickness of 15mm was designed. Based on finite element software ABAQUS, the simulation calculation was carried out. The results show that the maximum stress of the sandwich structure is 298.5Mpa and the maximum strain value is 2730με, which is less than the allowable value. This meets the structural strength design and lightweight design requirements.

VERTICAL DISPLACEMENT OF BORED PILES GROUP FOR PROJECT OF LRT USING NUMERICAL ANALYSIS

This article discusses the problem of the bearing capacity of piles with defects in the pile body. Field trials were performed using the non-destructive Sonic Logging (CSL) method. The object of the study is bored piles with a diameter of 1.0 - 1.5 m and a length of 8 - 55 m. This article solves the problem of bearing capacity of piles with defects of 10%, 20% and 30%, respectively, in the body of the pile. For modeling, we used load test data from bored piles at the LRT construction site. In this study, only the maximum strain value is needed to compile several cases with various defects using two-dimensional finite element analysis (FEMA) based on the Midas-GTS NX program. According to the results of field tests and modeling of piles, it was found that more than 20% of piles have defects. Field data and numerical simulations have also been confirmed on the recommendation of Bjerrum

Improving the biomechanical performance of screws fixation in a customized mandibular reconstruction prosthesis based on reliability measure

Background: The customized prosthesis is a new method for the reconstruction of large mandibular defects. The ability of dental rehabilitation to improve masticatory functions while maintaining the aesthetics of the main anatomy of the patient's jaw. But the most important problem with all custom prosthesis is the poor performance of screw fixation strength the connections at the bone-plate interface. Materials and Methods: This study was performed to investigate the effect of the number and layout of screws to improve the strength of the bone–prosthesis interface. Due to the inherent variability of input parameters, Analysis of the biomechanical performance of screw fixation strength, a probabilistic finite element method approach has been used. Random input parameters include mechanical properties of the cortical bone, cancellous bone, titanium alloy (Ti6Al4V), and bite force. The layout of the screws was designed in 6 models. Criteria for evaluating the biomechanical performance of screw fixation strength include maximum stress and strain of von Mises cortical bone around the screws. The Monte-Carlo method was used for finite element simulation. Results: The most critical screw in all models is screw No.1, which by increasing the number of screws and correcting the layout shape, the values of maximum stress and strain in the bone around screw No.1 has decreased by 26.7% and 46.3%, respectively, and increased the reliability of the screw connection performance by 25% and 28%, respectively. Conclusion: Finally, in the reconstruction of a large lateral mandibular defect by the customized prosthesis, the strength of the prosthesis to connect to the remaining mandible bone can be improved by increasing the number and modifying the layout of the screws.

Flexural and flammability evaluation of a new bio-based polyurethane foam with alumina trihydrate

Flexural and flammability evaluation of a new bio-based polyurethane foam (PUF) with alumina trihydrate (ATH) added as flame retardant were carried out. The PUF was obtained from a blend of vegetable oils. Flexural behavior of the polyurethane with different mass fractions of flame retardant (ATH) was investigated according to ASTM D790-17. Flammability tests were performed according to ASTM D3801-20 and ASTM D635-14 for the vertical and horizontal positions, respectively. The ATH addition influenced the flexural strength of the tested specimens, showing mean values for pure PUF and PUF with 50% of ATH were very close, but the highest value was obtained for PUF with 20% of ATH. Besides, the maximum strain value under flexural load was substantially reduced as the ATH mass increased, which was 11.4% for pure PUF and 3.38% for PUF with 50% of ATH. The flexural modulus increased with ATH incorporation up to 40% mass fraction. The obtained values for pure PUF, PUF with 40% of ATH and PUF with 50% of ATH specimens were 30.63 ± 1.95 MPa, 73.01 ± 2.82 MPa, and 62.16 ± 2.30 MPa, respectively. In addition, flammability test results presented better responses as the amount of ATH increased. PUF with 40% of ATH received V-2 classification, and PUF with 50% of ATH obtained HB classification. Therefore, the results for PUF with the addition of ATH show that the new bio-based material can be designed by using different mass fractions. Thus, this material becomes very useful for many types of applications, such as furniture and automobile industries, as well as sandwich structures and building constructions.

Modeling Uniaxial Bond Stress-Slip Behavior of Reinforcing Bars Embedded in Concrete with Different Strengths.

This paper aims to study the uniaxial bond stress–slip characteristics of reinforcing bars embedded in concrete with different strengths. Tests were conducted on tension–pull specimens that had a cross-sectional dimension with a reinforcing bar embedded in the center section. The experimental variable was the concrete compressive strength (20, 40, and 60 MPa). The test results show that in the specimen subjected to any fixed load, the maximum value of the concrete strain occurred around the central position, and its value increased as the compressive strength of the concrete increased. Depending on the embedded position of the steel bars, the bond stress–slip relationship was also different. In addition, the analytical results indicate that the proposed bond stress–slip constitutive relationship is very accurate in describing the true bond stress–slip relationship.

Laser-induced porous graphene on Polyimide/PDMS composites and its kirigami-inspired strain sensor

The laser-induced porous graphene (LIG) prepared in a straightforward fabrication method is presented, and its applications in stretchable strain sensors to detect the applied strain are also explored. The LIG formed on the polyimide/polydimethylsiloxane (PI/PDMS) composite exhibits a naturally high stretchability (over 30%), bypassing the transfer printing process compared to the one prepared by laser scribing on PI films. The PI/PDMS composite with LIG shows tunable mechanical and electronic performances with different PI particle concentrations in PDMS. The good cyclic stability and almost linear response of the prepared LIG's resistance with respect to tensile strain provide its access to wearable electronics. To improve the PDMS/PI composite stretchability, we designed and optimized a kirigami-inspired strain sensor with LIG on the top surface, dramatically increasing the maximum strain value that in linear response to applied strain from 3% to 79%.

Luminescent Gold Nanocluster-Methylcellulose Composite Optical Fibers with Low Attenuation Coefficient and High Photostability.

Because of their lightweight structure, flexibility, and immunity to electromagnetic interference, polymer optical fibers (POFs) are used in numerous short-distance applications. Notably, the incorporation of luminescent nanomaterials in POFs offers optical amplification and sensing for advanced nanophotonics. However, conventional POFs suffer from nonsustainable components and processes. Furthermore, the traditionally used luminescent nanomaterials undergo photobleaching, oxidation, and they can be cytotoxic. Therefore, biopolymer-based optical fibers containing nontoxic luminescent nanomaterials are needed, with efficient and environmentally acceptable extrusion methods. Here, such an approach for fibers wet-spun from aqueous methylcellulose (MC) dispersions under ambient conditions is demonstrated. Further, the addition of either luminescent gold nanoclusters, rod-like cellulose nanocrystals or gold nanocluster-cellulose nanocrystal hybrids into the MC matrix furnishes strong and ductile composite fibers. Using cutback attenuation measurement, it is shown that the resulting fibers can act as short-distance optical fibers with a propagation loss as low as 1.47dB cm-1 . The optical performance is on par with or even better than some of the previously reported biopolymeric optical fibers. The combination of excellent mechanical properties (Young's modulus and maximum strain values up to 8.4GPa and 52%, respectively), low attenuation coefficient, and high photostability makes the MC-based composite fibers excellent candidates for multifunctional optical fibers and sensors.

Fatigue response of friction stir welded joints of Al 6061 in the absence and presence of inserted copper foils in the butt weld

The present study examines the impact of inserted copper foil on n mechanical characteristics and fatigue strength of aluminum 6061 butt joints welded through the Friction Stir Welding (FSW) process. Thin copper foils were inserted between the faying surfaces of the sheet joints alloying Al 6061 locally with copper foil over FSW operation. Test specimens were then cut off from the welded plates to examine the quasi-static and fatigue behavior of the joints. The load-controlled condition tests were conducted on the specimens with a stress ratio of R = 0.1. Insertion of copper foils of 100 μm and 200 μm in the stirred zones, improved tensile strengths respectively 48 % and 31 %. The fatigue life of alloyed joints was improved as compared to as-welded joints in the absence of foils. A three-dimensional finite element (FE) analysis was employed to simulate the maximum stress and strain values in the weld zones. Weld regions due to their different mechanical properties experienced different stress magnitudes. The simulated stress and strain components were then used to predict uniaxial fatigue lives of FSW joint samples through the Smith-Watson-Topper (SWT) approach.