Tensile Conditions Research Articles

Experimental analysis of high-temperature shape memory polymers for deployable structures

Shape memory polymers (SMPs) continue to capture interest in the aerospace industry due to their unique properties. In general, the focus has been on SMPs with low transformation temperatures below 100 °C. However, certain aerospace applications require shape memory polymers with higher transformation temperatures to prevent undesirable actuation upon heat exposure. Moreover, and despite significant work on characterizing mechanical and recovery properties of shape memory polymers, the literature lacks full-field characterization of recovery properties, in particular at elevated temperatures. In this work, a high-temperature thermoset epoxy SMP (Tg ≈ 130 °C), named EPON SMP, is thoroughly investigated. This study provides a comprehensive experimental analysis of the mechanical and shape memory properties of the aforementioned high-temperature epoxy SMP. In addition, this study uses a full-field characterization technique, Digital Image Correlation (DIC), to provide further insight on localization, heterogeneity, and local recovery of shape memory strains. Furthermore, the study evaluates the recovery properties of the EPON SMP at different loading conditions (i.e., bending and tensile) and proposes shape-recovery evaluation methods that can be later implemented on other SMPs. • An epoxy-based shape memory polymer with high switching temperature (Tg ≈ 130 °C) was considered in this work. • The temperature dependant mechanical properties were evaluated across a wide temperature range around Tg. • The shape recovery properties were studied under simple tensile and complex bending conditions. • The heterogeneities in the accumulated and recovery strains were evaluated using full-field deformation measurements. • A deep insight into the local accumulation of programmed, thermal, mechanical, and recovery strains is provided.

Seismic Stability of 3D Tunnel Face considering Tensile Strength Cut-Off

Earthquakes can have a very adverse effect on tunnel excavation. The Mohr-Coulomb failure criterion is modified by introducing tensile strength cut-off, which allows nonlinear strength reduction of soil under tensile conditions, and kinematic analysis of tunnel face subjected to the earthquake is carried out. The pseudo-dynamic method is adopted to simulate the earthquake with the acceleration varying with time and space, improving the accuracy of the simulation. The external power and internal energy dissipation rate are equal to obtain the expression of tunnel face support pressure under the limit analysis framework. And the most unfavorable tunnel face support pressure is optimized by using the method of exhaustion. Compared with other research results, the validity of this method is proved. The influence of soil parameters and pseudo-dynamic parameters on the critical support pressure is revealed by further parameter analysis. Finally, this study provides an effective reference for seismic design of tunnel engineering construction.

Static and Fatigue Behaviour of Double-Lap Adhesive Joints and Notched Metal Samples Reinforced by Composite Overlays.

The use of composite overlays to increase the fatigue life of notched steel samples is discussed in this paper. For such purposes, in the first set of studies, static and fatigue tests as well as the detailed analytical and numerical analyses for samples with double-lap joints were performed. Based on such studies, the shapes of the composite overlays were set. For a better understanding of the failure forms of the investigated adhesive joints, the experimental studies were monitored with the use of digital image correlation. In the second set of experimental studies, the static and fatigue tensile tests were performed for steel samples with a rectangular opening with rounded corners reinforced by composite overlays. The different shapes (square 45 × 45 mm and long stripes 180 × 15 mm) and composite materials (GFRP and CFRP) were used as overlays. The obtained improvement of fatigue life was in the range of 180–270% in the case of the rectangular overlays and 710% in the case of application of the overlays in the form of the long stripes. This was also confirmed by numerical analyses in which a reduction in the stress concentration factor from 2.508 (bare sample) through 2.014–2.183 (square 45 × 45 mm overlays) to 1.366 (overlays in the form of long stripes 180 × 15 mm) was observed.

Mechanical properties and field application of constant resistance energy-absorbing anchor cable

During the construction of underground engineering projects, it is often confronted with complex conditions such as high stress, extremely soft rock, and strong disturbance, resulting in stress concentration and energy accumulation in the surrounding rock. Due to insufficient elongation and low safety margin, it is difficult for common anchor cables to effectively absorb the energy released from the rock deformation, which often results in the failure of the supporting structure. To this end, a new material constant resistance energy-absorbing anchor cable (CREAC) is developed with high elongation and high energy absorption properties. To study the mechanical and energy absorption properties of the new anchor cable, the static tensile and dynamic impact tests are conducted. The results between CREAC and structural constant resistance and large deformation anchor cable (CRLDC) are compared. In terms of static mechanical properties, the maximum elongation of CREAC is 16.2%. Based on the commonly used cable length of 10 m in the field, the maximum elongation and the energy absorbed by CREAC are 2.21 times and 2.76 times that of CRLDC, with good static deformation and energy absorption capabilities. In terms of dynamics properties, the average single impact deformation of CREAC is reduced by 88.7% compared to CRLDC, and the energy it can absorb is 7.43 times that of CRLDC, showing advantages in impact deformation resistance and energy absorption. The design method of the constant resistance energy-absorbing support is proposed and the field application of CREAC is carried out. The monitoring results confirm that this new material anchor cable can effectively control the deformation of the surrounding rock.

Investigation on mechanical behavior of clinched joints produced with dissimilar dies

The advantages of well-distributed material flow, easy demolding, and good mechanical interlock structure of the extensible die provide the possibility to be widely used in joining lightweight components. In order to explore the differences in the mechanical properties of the joints produced by different dies, the mechanical behavior of the clinched joints made by the fixed die and extensible dies of 2, 3, and 4 movable segments was investigated in the present study. The process of forming evolution, geometric characterization, failure mode, static strength, joint stiffness, and energy absorption of the dissimilar joints were studied by experimental method. In the clinching process, the neck thickness of joints made by extensible dies can be enlarged by the sliding outward of the movable segments compared with those produced by fixed dies. The failure mode of all clinched joints in this paper is neck fracture. The clinched joints produced by extensible dies of 3 movable segments have the highest static strength in both static tensile and shear tests among the dissimilar joints, which values are 1239.41 and 1259.80 N, respectively. Shearing strength of the joints performed by the extensible dies with 2, 3, and 4 movable segments was increased by 9.84%, 10.09%, and 9.40%, and the tensile strength of those clinched joints was increased by 16.27%, 20.31%, and 14.34% than that of the joints produced by the fixed dies. Experimental have proved that the number of movable segments on the extensible dies has a limited effect on the joint stiffness, tensile strength, and energy absorption of the clinched joints in the cross-lap-tensile test, while it has great effect on the stiffness and energy absorption of the clinched joints in the single-lap-shear test.

Constitutive modelling of a self-healing composite matrix polymer material

In this work, a constitutive model of an intrinsically self-healing composite matrix material is presented. The developed model comprises a micro-damage initiation and evolution model, and a healing evolution model, which are combined with the von Mises linear isotropic hardening plasticity. It is implemented into the Abaqus/Standard user material subroutine UMAT and validated using experimental results of static tensile and two-cycle tensile tests performed on partially neutralised poly(ethylene-co-methacrylic acid) (EMAA) ionomer copolymer, Surlyn® 8940. In the development of the model, Continuum Damage Healing Mechanics (CDHM) concepts of nominal and healing configurations are used. In addition, these concepts are used along with the strain equivalence hypothesis to streamline the numerical implementation. The strain equivalence hypothesis relates strain and stress tensors in the nominal and the healing configuration. Finally, successful validation has shown that the developed model is able to accurately predict behaviour of Surlyn® 8940 coupons during tensile tests and it can precisely predict the accumulation of plastic strain.

Static and fatigue tensile properties of carbon/glass hybrid fiber-reinforced epoxy composites

The static and fatigue tensile properties of high-strength polyacrylonitrile (PAN)-based carbon (IMS60) and electronic (E)-class glass (E-glass) hybrid fiber-reinforced epoxy matrix composites (HFRPs) were investigated. The fiber orientations of the HFRP specimens were set to unidirectional with [(0(IMS60))/(0(E-glass))]S (subscript S means symmetry and [(0(IMS60))/(0(E-glass))/(0(E-glass))/(0(IMS60))]), [(0(E-glass))/(0(IMS60))]S, [(0(E-glass))/(0(IMS60))2]S, [(0(E-glass))/(0(IMS60))3]S, [(0(E-glass))/(0(IMS60))5]S, [(0(E-glass))2/(0(IMS60))]S, [(0(E-glass))3/(0(IMS60))]S, and [(0(E-glass))5/(0(IMS60))]S. Under static loading for the [(0(IMS60))/(0(E-glass))]S, [(0(E-glass))/(0(IMS60))]S, [(0(E-glass))/(0(IMS60))2]S, [(0(E-glass))/(0(IMS60))3]S, and [(0(E-glass))/(0(IMS60))5]S HFRP specimens, the stress applied to the specimen was almost linearly proportional to the strain until failure. However, the tensile stress–strain curves of the [(0(E-glass))2/(0(IMS60))]S, [(0(E-glass))3/(0(IMS60))]S, and [(0(E-glass))5/(0(IMS60))]S HFRP specimens had a complicated shape (jagged trace). The Weibull statistical distributions of the tensile strength values were also examined. The Weibull moduli for the [(0(E-glass))/(0(IMS60))]S, [(0(E-glass))/(0(IMS60))2]S, [(0(E-glass))/(0(IMS60))3]S, [(0(E-glass))/(0(IMS60))5]S, [(0(E-glass))2/(0(IMS60))]S, [(0(E-glass))3/(0(IMS60))]S, and [(0(E-glass))5/(0(IMS60))]S HFRP specimens were higher than those for the mono carbon fiber-reinforced epoxy (CFRP) and glass fiber-reinforced epoxy (GFRP) specimens. Under fatigue loading, the fatigue properties of the HFRP specimens showed CFRP-dominant behaviour at high stress levels and GFRP-dominant behaviour at low stress levels. The fatigue properties of the HFRP specimens increased with increasing volume fraction of CFRP in the following order: ([(0(E-glass))/(0(IMS60))5]S > [(0(E-glass))/(0(IMS60))3]S > [(0(E-glass))/(0(IMS60))2]S > [(0(IMS60))/(0(E-glass))]S > [(0(E-glass))/(0(IMS60))]S > [(0(E-glass))2/(0(IMS60))]S > [(0(E-glass))3/(0(IMS60))]S > [(0(E-glass))5/(0(IMS60))]S).

Deformation and fracture behavior in TRIP steels under static and dynamic tensile conditions

The present study sought to explore the deformation and fracture behavior of Quenching and Partitioning (Q&P) steel at five different strain rates (10−4 s−1, 1 s−1, 10 s−1, 100 s−1 and 1400 s−1). Tensile tests were carried out on Q&P steel at different strain rates, and the deformation and fracture behaviors were explored through digital image correlation (DIC) and scanning electron microscope (SEM). The results indicated that the strength and plasticity of Q&P steel had significant strain rate sensitivity. The yield strength and ultimate strength increases continuously, whereas the elongation first decreased and then increased with increase in strain rate. The dimples gradually became smaller and flatter with increase in strain rate. The dislocation density increased when strain rate was above 100 s−1, indicating that resistance to dislocation slip increases and the slip distance becomes shorter at high strain rates, which inhibits generation of large deformation. The local plastic strain at the fracture significantly decreased from 0.7 to 0.3, resulting in partial brittle fracture characteristics in fracture morphology. These findings provide a basis for further elucidating the deformability and fracture behavior of Q&P steel at different strain rates.

Experimental investigation on the effect of open fire on the tensile properties and damage evolution behavior of granite

The stability of rock mass after fire is a concern of many engineering projects. In this paper, the effects of open fire and different cooling methods on granites were investigated. The static Brazilian test, dynamic Brazilian test, and P-wave velocity test were carried out to evaluate the mechanical properties and damage evolution behavior. A high-speed camera is employed to monitor the failure process of rock. The microstructures of the treated granites were observed by scanning electron microscope (SEM). The results showed that the fire duration and cooling treatment have a significant effect on the P-wave velocity, static nominal tensile strength, and dynamic nominal tensile strength of granite. These characteristics decrease rapidly during 0 to 10 min, and slowly decrease after 20 min. Compared to the air-cooling treatment, the water-cooling treatment has greater damage to the heated granite. To better understand the results, the rapid heating process of open fire heating was simulated using Abaqus software. The results reveal that there is a thinner compressive stress zone at the bottom of the specimen, and there is a large zone in the middle of the sample with higher tensile stress. The crack extension would be expanded due to high tensile stress, leading to the reduction of the tensile strength of the rock. This paper aims to better predict the degree of damage of rock materials after actual fire, as well as preliminarily explore the effect of the fire exposure duration and fire extinguishing method on the tensile properties of rock.

Cold resistance of new casting Cr – Mn – Ni – Mo – N steel. Part 2. Investigation of the factor of non-metallic inclusions particles under static and impact loading at low temperatures

The new casting austenitic Cr – Ni – Mn steel with 0.5 % N (grade 05Kh21AG15N8MFL) surpasses the casting steel of the 18Cr – 10 Ni type used for comparison in the entire range of climatic temperatures. In this part of the article, attention is paid to the particles of non-metallic inclusions (NMI) in the cast metal of nitrous steel as a factor that can affect the mechanical properties under static and impact loading at low temperatures. NMI in laboratory metal are globular oxysulfides, with SiO2 oxides in the central part and an outer layer formed by manganese sulfide MnS, with an average particle size of ~75 % up to 4 μm. It has been established that when testing casting steel for impact bending at –160 °C, these NMI do not serve as a source of crack initiation, do not contribute to their propagation and are in a fracture surface in isolated pits. Under tensile conditions at –110 °C, the yield strength of nitrogen containing steel increases by more than 1.7 times in comparison with the properties at +20 °C; ductility does not decrease when cooled to –110 °C. In this case, NMI particles are strongly deformed due to the development of cracks in their oxide part, and even when NMI reaches the surface of the sample in working part in the neck zone, they do not serve as a source of crack initiation. Cracks at the boundary “NMI/ deforming metal” are not formed. Even with a random arrangement of particles in the form of chains along the axis of application of the tensile load, at a distance of 5 – 20 μm from each other, pores do not form around the particles and merge into a crack nucleus. The results obtained correlate with the literature data that NMI can act as stress relaxers in ductile steels.

Experimental study on the durability of polymer‐impregnated basalt textile applied as concrete reinforcement

AbstractThis paper presents an experimental study on the durability of polymer‐impregnated basalt textile considering the effects of impregnation material, corrosion temperature, and corrosion solution. The variations in tensile strength, elastic modulus, surface condition, and failure mode were examined. Furthermore, a prediction model for the tensile strength degradation of basalt textiles was proposed. The experimental results showed that the tensile strength degradation of the textile was significantly influenced by the impregnation materials. The epoxy resin/acrylic emulsion‐impregnated textiles had superior durability to the styrene‐butadiene latex/vinyl resin‐impregnated textiles. As the temperature increased, the tensile strength decreased, whereas the variation in the elastic modulus was insignificant. In addition, the tensile strength of the weft textile degraded slightly faster than that of the warp textile owing to the larger contact area with the corrosion solution for the former. The saline–alkaline solution was more aggressive than the alkaline solution for the impregnated textiles owing to the corrosion caused by the combination of alkaline hydroxide ions and salt chloride ions in the former. The proposed model to predict the strength degradation considering both the aging time and temperature effect is in good agreement with the experimental results, which can be used to predict the long‐term strength of basalt textiles used as concrete reinforcement in real engineering applications.

Sequentially combined thermo-mechanical and mechanical simulation of double-pulse MIG welding of 6061-T6 aluminum alloy sheets

Double-pulse MIG (DP-MIG) welding is an efficient aluminum alloy jointing technique, which can form heterogeneous aluminum alloy welded sheets with different microstructure and mechanical properties. In order to accurately analyze and predict mechanical properties of welded structures, the geometrical features, local material properties and residual stresses of different welded zones should be synthetically considered in the numerical simulation. This work proposes a sequentially combined thermal-mechanical and mechanical simulation to accurately characterize the mechanical properties of the welded joint through the finite element analysis (FEA) method. The thermo-mechanical simulation was carried out to analyze the transient temperature field and residual stress distribution, which are conductive to build mechanical simulation model with detailed geometric features, the corresponding local material properties as well as attached residual stress. Subsequently, the mechanical simulation was performed to investigate the stress distribution of the welded joint. The deformation behavior and load-carrying capacity of the welded joint from numerical simulation are all in good agreement with corresponding experimental study, which indicates the feasibility and superiority of the developed sequentially combined thermal-mechanical and mechanical simulation method. Also, the stress distribution of the welded joints analyzed by numerical simulation reveals that the fracture evolution mechanism depends on whether the reinforcement has been removed from the welded specimen. The existence of the weld reinforcement leads to the increase of shear stress under tensile condition; hence, the fracture morphology includes equiaxed dimples and elongated dimples. When the reinforcement is removed, the mechanism is trans-granular and inter-granular mixed fracture in the welded zone; otherwise, trans-granular fracture occurs in the heat-affected zone.

Effects of Compaction Efforts on Tensile Strength Characteristics And Durability of Warm-asphalt Mixture Containing Natural And Synthetic Zeolite

Many studies have been conducted to evaluate the mechanical properties of warm-mix asphalt (WMA) mixtures using Natural Zeolite (NZ) and Synthetic Zeolite (SZ) without considering the impact of compaction efforts. In this study, the influence of compaction cycles on the mechanical characteristics of WMA mixtures including NZ & SZ additives, is studied and compared with hot mix asphalt (HMA) mixtures. The amount of NZ and SZ used to make the WMA mixes was 5% of the whole asphalt mass. For the research, six WMA mixtures with a penetration grade of 40-50 were designed and compared to HMA traditional mixture. HMA &WMA mixtures were designed with 35, 50 and 75 compaction efforts. Mechanical and durability experiments were performed on HMA and WMA mixtures, involving Marshall stability, Marshall quotient, static indirect tensile strength at 25 and 60°C, and tensile stiffness modulus at 25 and 60°C. Calculating the tensile strength ratio (TSR) to study the moisture susceptibility of the mixes was used to assess their durability. The study indicates that compaction efforts had a considerable impact on the performance of the mixtures. The Natural Zeolite of WMA & Synthetic Zeolite of WMA mixtures display lower Marshall stability and Marshall quotient with greater tensile strength and tensile strength ratio than HMA mixture for 35, 50 and 75 compaction efforts. Increased compaction efforts result in a greater reduction in mechanical and durability characteristics of WMA. The flow values of NZWMA and SZWMA mixtures are larger than HMA mixtures indicating higher strain capacities to achieve failure. All NZWMA and SZWMA mixtures achieve the SCRB standard specifications of 8kN stability, 2-4mm flow, 14 percent VMA, and 85 percent TSR when using the same optimum binder content. Furthermore, the NZAC mixtures show higher performance than SZAC mixtures in terms of stability and strength

Tensile Mechanical Properties of Nanowoven Composites Based on Homogenization Theory

The nanocomposite is a multiphase material composed of two or more component materials with different properties and different forms through composite means. New material properties. The stress distribution of nano-braided composites in bending is much more complicated than in tension. Like the tensile condition, the braid angle is still the main factor affecting the bending failure mode. In order to study the tensile strength of nano-braided composites from a microscopic perspective, the nonlinear damage analysis under multiple tensile load steps is carried out in this paper. The damage analysis results show that the microscopic damage modes of different braided angle composites differ. Based on this, this paper determines the transformation of the failure mechanism to characterize the braided composites. An important parameter—critical braiding angle, established different tensile strength failure criteria for small braided angle composites and large braided angle composites and numerically predicted the tensile strength of nano braided composites based on these criteria. The value of each stress component increases with the increase of the braiding angle, and the ratio is about 1:1.25. The strength prediction results are in good agreement with the experimental results.

Features of the stress state of porous brittle materials under tensile conditions

The paper discusses the problem of taking into account the influence of the heterogeneous structure of a material on its effective characteristics and mechanical behavior. To evaluate the effective properties and features of the stress and strain analysis of porous materials, it is proposed to use a combined method that includes experimental data (an SEM image of a porous material surface) and numerical methods of solids mechanics. Numerical simulation of the mechanical behavior of porous ceramics is performed on the basis of experimental data on its pore structure. As a result of the performed research, it is shown that this method makes it possible to determine the features of the stress and strain state of porous ceramics. The stress analysis reveals both tensile and compressive local stresses in porous ceramics mesovolumes under uniaxial tension. At the same time, the values of these local stresses exceed the mesovolume-average values by an order of magnitude.

Investigation on the dynamic tensile behaviour of rubberized mortar using the Brazilian disc method

The use of tire rubber particles as a partial substitute for fine aggregate in cement-based materials has been proven to potentially have both environmental and economic benefits. Although the studies on the physical and mechanical properties of rubberized mortar are abundant, those related to the dynamic tensile behaviour are scarce. In this study, rubber powders with three sizes (0.125 mm, 0.180 mm, and 0.425 mm) are used to fabricate the Brazilian disc rubberized mortar specimen, with rubber volume percentages up to 40%. A 50 mm-diameter split Hopkinson pressure bar (SHPB) apparatus is then adopted to conduct the dynamic split tension tests, and the static tensile tests are also conducted for comparison purposes. Experimental results show that the dynamic split tensile strength of the rubberized mortar linearly increases with increasing the loading rate, whereas decreases with the increase of the rubber volume percentage. The mortars with smaller rubber powder at the same percentage exhibit more significant dynamic strength loss. As compared with the static tests, the reduction ratio of the dynamic split tensile strength of mortar with different rubber content is much smaller. The dynamic increase factors of the rubberized mortar are more sensitive to the loading rate, and positively correlated to both the rubber volume and the powder size. Besides, the occurring time of the primary crack initiation gradually decreases with increasing the loading rate and rubber size, whereas increases with increasing the rubber volume percentage. In addition, the dissipated energy density of the rubberized mortar is positively correlated with the rubber volume percentage, and the addition of the smaller rubber powder can enhance the dynamic energy absorption capacity.

Влияние степени деформации в условиях низких температур на превращения и свойства метастабильных аустенитных сталей

Introduction. For reliable operation of low-temperature equipment, it is necessary to use materials capable of ensuring operability in a wide temperature range under conditions of alternating loads, exposure to corrosive media, etc. Most often, in such cases, metastable austenitic steels (MAS) of various alloying systems are used. Despite sufficient experience in the use of such materials, not enough information is collected on the behavior of such materials at low temperatures, including phase-structural transformations, the features of such transformations in different temperature zones, including when a load is applied, both static and dynamic. The subject of the study in this work is selected MAS 10Cr14NMn20 and 10Cr14Mn14Ni4Ti grades. The purpose of the study is to evaluate the performance of industrially used metastable austenitic steels for its possible use instead of steel 12Cr18Ni10Ti. Research methodology. The phase composition of the samples was studied on a DRON-3.0 X-ray diffractometer. Mechanical tests were carried out in the temperature range from +20 to -196 °C. Static uniaxial tensile tests were carried out on a R-20 tensile testing machine; cylindrical specimens with threaded heads were prepared according to GOST 11150–75, as well as samples with a circumferential notches. Dynamic bending tests were carried out on a pendulum impact tester, using samples according to GOST 9454–78. Results and Discussion. Based on the data obtained, it is found that an increase in the strain rate at low temperatures contributes to a decrease in the number of martensitic phases in the steels under study. It is found that the hardenability during elastic-plastic deformation decreases and completely disappears at the temperature of the material transition to a brittle state. It is shown that an increase in the rate of low-temperature deformation of samples prevents the development of phase martensitic transformations in steels. The results obtained can be recommended for use in the selection of materials for the manufacture of equipment operating at temperatures down to -196 °C. Conclusions. It is shown that the obtained values of the characteristics of mechanical properties make it possible to recommend the studied MAS as a substitute for steel 12Cr18Ni10Ti, down to a temperature of -196 °C.

Strain-Controlled Fatigue Behavior of a Nodular Cast Iron in Real Off-Highway Axles: Effects of Casting Skin and Strain Ratio

Nodular cast irons are widely adopted in off-highway vehicles, since they allow to obtain components with complex shapes as well as good mechanical properties. However, the fatigue strength of such components is a major issue, which is typically addressed by adopting the strain-life approach, since it considers the local strains at stress concentrators where fatigue cracks are prone to initiate. In the fatigue design of off-highway components, the detrimental effect of casting skin, due to both surface and subsurface features, must be accounted for in all cases where machining is not needed. Moreover, the local strain ratio at stress raisers can be different from the nominal one due to forward plasticity. In this paper, static tensile as well as strain-controlled fatigue tests have been executed on specimens taken from real EN-GJS-450-10 off-highway axles. Static tensile tests have been performed on specimens with machined surfaces, while fatigue tests at a strain ratio equal to −1 have been carried out on specimens with surfaces in both machined and as-cast conditions. In addition, machined specimens have been tested at strain ratios equal to 0.1 and 0.5 to investigate the material sensitivity to the mean strain. Finally, the high-cycle downgrading effect of the casting skin has been evaluated, and experimental data of machined specimens tested at different strain ratios have been summarized by using the Smith–Watson–Topper expression.

Ultrasensitive and highly stretchable sensors for human motion monitoring made of graphene reinforced polydimethylsiloxane: Electromechanical and complex impedance sensing performance

Highly stretchable sensors based on graphene nanoplatelet (GNP) reinforced polydimethylsiloxane (PDMS) are manufactured for human motion monitoring purposes. The strain sensing analysis shows ultra-high gauge factor (GF) values from 40 to 300 at low strain levels up to 106 at high deformations at tensile conditions, and a decreasing sensitivity as GNP content increases. The compressive behavior shows an initial decrease of the electrical resistance, due to the prevalence of in-plane mechanisms, followed by a stable increase, due to the prevalence of out-of-plane mechanisms. In this regard, the Electrical Impedance Spectroscopy (EIS) analysis shows an increase of the complex impedance with increasing compressive strain. The equivalent RC-LRC circuit allows to explain the electrical mechanisms governing the compressive behavior, where the LRC element denotes the contact and intrinsic resistance and the RC element the tunnelling effect. Finally, a proof of concept of human motion monitoring proves the capability of the scalable and easy-manufactured sensors to detect frowning, raising eyebrows, blinking, breathing, blowing and, even, vocal cord motion, where each phoneme follows a unique pattern, with a robust electrical response.

Dislocation microstructures of single crystal ⟨001⟩ CMSX-4 specimens tensile tested at 700 and 1000°C

Abstract Two principal methods are used to derive constitutive equations for single crystal Ni-base superalloys: development of a creep potential according the Hill’s theory and the summarization of all activated slip systems: theoretically, the octahedral and the cubic slip system must be considered. An overview of dislocation structure evolution has been performed using transmission electron microscopy (TEM) techniques on 〈001〉-orientated CMSX-4 specimens after tensile tests. The aim of the applied conventional TEM methods was to provide with more details about the influence of temperature and deformation rate on the deformation behaviour of CMSX-4 nickel-base single crystal. A correlation of the γ' phase deformation mechanisms and associated mechanical responses for different tensile testing conditions has been done. With TEM methods the dislocation dipole identification as well as the stacking fault nature has been demonstrated.