Strain Intensity Research Articles

Mechanical properties and influence mechanism of hydroxyl‐terminated polybutadiene propellant under confining pressure

AbstractTo better understand the mechanical properties and influence mechanism of hydroxyl‐terminated polybutadiene (HTPB) propellant under various confining pressures, the uniaxial tension tests with low to medium strain rate and various confining pressures were carried out. The coupling effects of strain rate and confining pressure on mechanical properties were presented. Meanwhile, the confining pressure influence mechanism was analyzed and revealed using the meso numerical simulation method and scanning electron microscopy images of fracture surfaces. The meso damage evolution processes under various confining pressures were presented. The results show that strain rate and confining pressure affect mechanical responses of HTPB propellant significantly. As confining pressure increases, the maximum tension strength and fracture strength increase. The maximum tension strain and failure strain vary slightly with confining pressure under low strain rate, while they increase significantly with confining pressure at medium strain rate. The fracture energy density increases with the increase of strain rate and confining pressure. Meanwhile, the value of saturation pressure depends on strain rate. The confining pressure influence mechanism is to suppress dewetting damage initiation and evolution. Besides, the failure mode of HTPB propellant under different confining pressures is still particles dewetting.

Temporal evolution of mechanical stimuli from vascular remodeling in response to the severity and duration of aortic coarctation in a preclinical model

Coarctation of the aorta (CoA) is one of the most common congenital cardiovascular diseases. CoA patients frequently undergo surgical repair, but hypertension (HTN) is still common. The current treatment guideline has revealed irreversible changes in structure and function, yet revised severity guidelines have not been proposed. Our objective was to quantify temporal alterations in mechanical stimuli and changes in arterial geometry in response to the range of CoA severities and durations (i.e. age of treatment) seen clinically. Rabbits were exposed to CoA resulting in peak-to-peak blood pressure gradient (BPGpp) severities of ≤ 10, 10–20, and ≥ 20 mmHg for a duration of ~ 1, 3, or 20 weeks using permanent, dissolvable, and rapidly dissolvable sutures. Elastic moduli and thickness were estimated from imaging and longitudinal fluid–structure interaction (FSI) simulations were conducted at different ages using geometries and boundary conditions from experimentally measured data. Mechanical stimuli were characterized including blood flow velocity patterns, wall tension, and radial strain. Experimental results show vascular alternations including thickening and stiffening proximal to the coarctation with increasing severity and/or duration of CoA. FSI simulations indicate wall tension in the proximal region increases markedly with coarctation severity. Importantly, even mild CoA induced stimuli for remodeling that exceeds values seen in adulthood if not treated early and using a BPGpp lower than the current clinical threshold. The findings are aligned with observations from other species and provide some guidance for the values of mechanical stimuli that could be used to predict the likelihood of HTN in human patients with CoA.

A gradient regularized model for shape memory alloys

In this work a transformation strain gradient enhancement is introduced into a phenomenological constitutive model for the pseudoelastic behavior of shape memory alloys. The constitutive model is able to capture several unique features of the constitutive response of these materials during the transformation between austenite and martensite during the pseudoelastic response. These features include the asymmetry in the initial transformation stresses in tension versus compression, the asymmetry in the transformation strains in tension and compression, and finally the asymmetry in the hardening behavior in tension and compression. In fact, experiments have shown that untrained NiTi exhibits hardening during its transformation in compression, but softening for tensile loading. It is this softening behavior that motivates the need for the introduction of the transformation strain gradient into the constitutive modeling. Transformation strain gradient effects are introduced via a phase variable that describes the extent of transformation. The free energy of the material then depends on gradients of the phase variable, which introduces a material length scale into the theory. The governing equation for the phase variable is developed from a microforce balance and continuum thermodynamics analysis. The model is implemented in the commercial finite element software Abaqus through user defined subroutines and several numerical simulations are performed to illustrate the model response and lack of numerical mesh-dependency of the results.

Analysis of the Effects of an Unconventional Rolling Process under Cumulative Plastic Deformation Conditions.

This article presents the results of research carried out on an experimental rolling mill with axial, cyclic movement of rolls (RCMR). The device was made on the basis of an unconventional technical solution for the movement of shaping tools and equipped with a complete measuring system recording all the parameters of the process. The research was conducted on selected copper alloys CuFe2 and CuCr0.6. Rolling tests in the RCMR process were carried out for rolling speeds vr = 3.1 × 10-3, 6.3 × 10-3 and 9.4 × 10-3 m/s, which correspond to the rotational speed of the rollers at ω = 1, 2 and 3 rpm for an active diameter of the rollers = 60 mm. In testing the thermal effects of the process, the rolling speed ω = 0.7 rpm was also used. A constant value of the frequency of axial movement of the rollers f = 1 Hz and the amplitude of the displacement of the rollers A = 0.8 mm were assumed. The rolling process for the strands was carried out in six culverts using the average relative crush in the passage of Δh = 15%. Conventional rolling tests were carried out to compare rolling processes, and the obtained data formed the basis for assessing the strain intensity and identifying local deformation zones in the RCMR rolling process. The waveforms of rolling pressures, intensity and non-uniformity of deformation, and increase in the temperature of the strip surface in subsequent culverts were compared with the results obtained in the conventional rolling process.

Macro synthetic fiber pullout behavior in short- and long-term tests

The creep phenomenon in fiber-reinforced composites is particularly important when synthetic macro fibers are used. In addition to the low modulus of elasticity, the polymers used in fibers have pronounced viscoelastic behavior even at room temperature, which can lead to changes in the cracking control over time. The long-term fiber pullout response also results from fiber and interface creep contributions. To understand the above phenomena, pullout tests with short- and long-term loads were conducted on three types of polymeric macro fibers subject to different levels of long-term loads (20, 30, 40 and 50%). The results of the pullout tests were strongly dependent on the fiber configuration, surface corrugation and modulus of elasticity. Macro fibers with crimped surfaces and higher modulus of elasticity achieved higher bond stresses and lower creep deformations. The Burgers model was applied and showed a good agreement with the experimental creep curves, therefore consisting of a promising alternative for modeling long-term behavior. Microtomography and scanning electron microscopy images showed that a large portion of the strain in tension, under sustained load, can be attributed to the creep of the fiber itself, thus making it challenging to estimate the creep of this type of composite, given the considerable variability of fiber configurations.

The influence of water vapor on the structural response of asphalt pavement

Abstract A series of water damage phenomena of asphalt pavement during service show that water is very important. To comprehensively analyze the influence of water vapor factors on the response of pavement structure, this article first tests the water vapor diffusion coefficient of asphalt pavement materials at different temperatures establishes the water vapor concentration field model of the pavement structure, and analyzes the actual water vapor distribution of the pavement structure; then, the relationship between viscoelastic parameters of the mixture and water vapor concentration is established. Based on this, the finite element model of the pavement structure considering the water vapor factor is established, and the influence of the water vapor factor on the pavement structure response and fatigue life is quantified. It is found that water vapor has an important influence on the mechanical response. On the hottest days in summer, the attenuation of surface modulus caused by water vapor has the greatest impact on the upper layer of the pavement structure. Under the influence of water vapor, the position just below the wheel of the upper layer at the bottom of the horizontal tension strain increases by 108.26%, and the horizontal tension strain of the other layers increases by about 5%, increasing the risk of upper layer cracking. At the same time, water vapor reduces the stress that can be borne by the surface layer, while the rest of the stress is borne by the base. Compared with the fatigue life calculation method in the specification, the actual non-uniform water vapor concentration field reduces the fatigue life of the surface layer by 12.246%. This shows that the current structural calculation does not consider the water vapor factor, which makes the pavement structure more dangerous, and the influence of the water vapor factor should be fully considered.

Arl13b promotes the proliferation, migration, osteogenesis, and mechanosensation of osteoblasts

Primary cilia are microtubule-based organelles presenting on the surface of most postmitotic mammalian cells. As being signaling hubs and sensory organelles, primary cilia can respond to mechanical and chemical stimuli from the extracellular environment. Arl13b (ADP-ribosylation factor-like 13B), an atypical Arf/Arl family GTPase, was identified in genetic screening as a protein essential for maintaining the integrity of cilia and neural tubes. Previous studies on Arl13b have mostly focused on its role in the development of neural tubes, polycystic kidneys, and tumors, but no role in bone patterns was described. This study reported the essential roles of Arl13b in bone formation and osteogenic differentiation. Arl13b was highly expressed in bone tissues and osteoblasts, positively correlated with osteogenic activity during bone development. Furthermore, Arl13b was essential for primary cilium maintenance and Hedgehog signaling activation in osteoblasts. Arl13b knockdown in osteoblasts decreased the length of primary cilia and the upregulated levels of Gli1, Smo, and Ptch1 upon Smo agonist treatment. Additionally, Arl13b knockdown inhibited cell proliferation and migration. Moreover, Arl13b mediated osteogenesis and cell mechanosensation. Cyclic tension strain upregulated the Arl13b expression. Arl13b knockdown suppressed osteogenesis and mitigated cyclic tension strain-induced osteogenesis. These results suggest that Arl13b have important roles in bone formation and mechanosensation.

Volume Loss and Recovery in Bovine Knee Meniscus Loaded in Circumferential Tension.

Load-induced volume change is an important aspect of knee meniscus function because volume loss creates fluid pressure, which minimizes friction and helps support compressive loads. The knee meniscus is unusual amongst cartilaginous tissues in that it is loaded not only in axial compression, but also in circumferential tension between its tibial attachments. Despite the physiologic importance of the knee meniscus' tensile properties, its volumetric strain in tension has never been directly measured, and predictions of volume strain in the scientific literature are inconsistent. In this study, we apply uniaxial tension to bovine knee meniscus and use biplanar imaging to directly observe the resulting three-dimensional volume change and unloaded recovery, revealing that tension causes volumetric contraction. Compression is already known to also cause contraction; therefore, all major physiologic loads compress and pressurize the meniscus, inducing fluid outflow. Although passive unloaded recovery is often described as slow relative to loaded loss, here we show that at physiologic strains the volume recovery rate in the meniscus upon unloading is faster than the rate of volume loss. These measurements of volumetric strain are an important step toward a complete theory of knee meniscus fluid flow and load support.

The role of epitaxial strain on photoconductive performance in LaNiO3 epitaxial thin films

In this work, LaNiO3 epitaxial thin films on (001) single-crystal LaAlO3 and SrTiO3 substrates were deposited by polymer assisted deposition method, respectively. Additionally, LaNiO3 polycrystalline film was coated on ceramic substrate using LaNiO3 powder obtained from precursor solution in polymer assisted deposition. Due to the difference of lattice mismatch between LaNiO3 and single-crystal substrates, LaNiO3 thin films suffer different epitaxial strain, resulting in distortion of NiO6 octahedrons which increases with the intensity of strain. Such phenomena lead to the decrease of the field splitting energy of NiO6 octahedron and the band gap value of LaNiO3, further increasing the charge transition and enhancing the visible-light photoconductivity. The existence of epitaxial strain brings more Ni2+ and adsorbed oxygen into perovskite type LaNiO3, introduces more oxygen vacancy defects, reduces the complex rate of photo induced electron-hole pairs, and thereby improves the photoelectric activity of LaNiO3. This work provides a feasible method to control the structure distortion and photoconductivity effect of all-inorganic perovskite.

Highly Sensitive Strain Sensor Fabricated by Direct Laser Writing on Lignin Paper with Strain Engineering

Paper‐based strain sensors (PSS) have broad prospects in disposable products due to their low cost and easy degradation as environmentally friendly materials. Herein, a strain sensor made of a laser‐induced carbonization electrode is created by direct laser writing with filter paper. The conductivity and gauge factor (GF) of this strain sensor are improved by adding lignin and applying strain engineering. This enables the sensor to simultaneously satisfy high sensitivity (GF ≈ 408 and 91) for weak tension and compression strain, respectively, and with long‐term reliability. The tensile strain GF factors of up to 201 are possible, even with a weak tensile strain of 0.00088%. Furthermore, the paper‐based sensor for monitoring physiological activities like finger gestures, pulsing, swallowing, and eye blinking is demonstrated. The facile fabrication and superior performance of PSS fabricated by direct laser writing with strain engineering may pave the way for promising applications of flexible, portable, and wearable electronic devices.

Early Detection of Damage of Inconel 718 with the Use of Strain-Hardening Cross-Effect

Indentation tests were used for early detection of deformation-induced damage of Inconel 718. Damage was produced in a controlled manner using specially designed specimens with a variable width of the gage part. Static tension, LCF, and HCF tests were performed to induce material damage. Accumulated plastic strain intensity was used as the reference measure of deformation-induced damage. Detection of damage progress in its early phase was based on the use of strain-hardening cross-effect. Experimentally determined correlation of hardness and indentation work with reference damage parameter was analyzed. The results of our analysis lead to the conclusion that the proposed experimental procedure is useful for the detection of deformation-induced damage in the early stage of the process.

Real-Time Damage Self-Diagnosis and Self-Localization Brillouin Distributed Optical Fiber–Fiber-Reinforced Polymer Composite Smart Cables

Cables are important components of long-span space structures, cable-supported bridges, slopes, and so on. However, they often suffer from damage such as wire breakage, corrosion, and anchor head loosening, which threatens structural safety seriously. Therefore, it is very important to diagnose and localize their damage. To address this problem, a real-time damage self-diagnosis and self-localization smart cable is proposed. It is made of a polyethylene cover pipe and some parallel intelligent steel strands with the Brillouin distributed monitoring capability. Fiber-reinforced polymer (FRP) and optical fiber are put together in the thermosetting molding process to form the intelligent central wire of each intelligent steel strand. When the side wire of the steel strand reaches the ultimate load, the intelligent central wire only reaches about 50% of its ultimate load, so it can be used in the real-time monitoring of side wires. Numerical models of seven-wire steel strands with different lengths were established, and the broken wire damage was simulated by changing coupling conditions in single and multiple damage cases. To further verify the proposed smart cable, experiments were carried out based on two intelligent steel strands with the length of 34.5 m. Experimental damage cases were simulated by cutting side wires at different positions under different loads. Both numerical and experimental results show that the change in the tension strain of the intelligent central wire can indicate the damaged location of the broken side wire. For a healthy steel strand, the tension strain of the central wire is a constant value; for a damaged steel strand, damage can be localized according to the strain waveform of the intelligent central wire and its ratio of peak strain to stable strain. The proposed smart cable has functions of real-time stress self-sensing, damage self-diagnosis, damage self-localization, damage self-warning of any side wire, and its central wire has excellent corrosion resistance; it can be well used in life-cycle real-time structural health monitoring of cable structures/substructures, which dramatically reduces the probability of cable accidents, and lays a good foundation for smart civil structures.

Increased physical workload in home care service is associated with reduced recovery from work

ObjectiveThis study investigated the physical workload of home care service workers and determined whether the different intensities of physical work strain experienced by home care nurses have different impacts on their recovery from work.MethodsPhysical workload and recovery were measured among 95 home care nurses based on heart rate (HR) and heart rate variability (HRV) recordings during one work shift and the following night. Differences in the physical work strain were compared between younger (≤ 44-year-old) and older (≥ 45-year-old) employees and between morning and evening shifts. To determine the effects of occupational physical activity on recovery, HRV at all time points (during the workday, when awake and asleep, and whole measurement) in relation to the amount of occupational physical activity was examined.ResultsThe average physiological strain during the work shift, measured as metabolic equivalent (MET), was 1.8 ± 0.5. Moreover, the occupational physical demands in relation to maximal capacity were higher for the older employees. The results of the study showed that a higher occupational physical workload reduced the HRV of home care workers during the workday, leisure time, and sleep.ConclusionsThese data indicate that increased occupational physical workload is associated with reduced recovery among home care workers. Therefore, decreasing occupational strain and ensuring sufficient recovery is recommended.

Heterogeneous Structure Omnidirectional Strain Sensor Arrays With CognitivelyLearned Neural Networks.

Mechanically stretchable strain sensors gain tremendous attention for bioinspired skin sensation systems and artificially intelligent tactile sensors. However, high-accuracy detection of both strain intensity and direction with simple device/array structures is still insufficient. To overcome this limitation, an omnidirectional strain perception platform utilizing a stretchable strain sensor array with triangular-sensor-assembly (three sensors tilted by 45°) coupled with machine learning (ML) -based neural network classification algorithm, is proposed. The strain sensor, which is constructed with strain-insensitive electrode regions and strain-sensitive channel region, can minimize the undesirable electrical intrusion from the electrodes by strain, leading to a heterogeneous surface structure for more reliable strain sensing characteristics. The strain sensor exhibits decent sensitivity with gauge factor (GF) of ≈8, a moderate sensing range (≈0-35%), and relatively good reliability (3000 stretching cycles). More importantly, by employing a multiclass-multioutput behavior-learned cognition algorithm, the stretchable sensor array with triangular-sensor-assembly exhibits highly accurate recognition of both direction and intensity of an arbitrary strain by interpretating the correlated signals from the three-unit sensors. The omnidirectional strain perception platform with itsneural network algorithm exhibits overall strain intensity and direction accuracy around 98% ± 2% over a strain range of ≈0-30% in various surface stimuli environments.

STUDY OF THE ADDITIONAL POSSIBILITY EFFECT OF ELASTIC-PLASTIC ALTERNATING DEFORMATION ON THE PROPERTIES OF METAL MATERIALS DURING THEIR PROCESSING ON A ROLLER STRAIGHTENING MACHINE

The only way to increase the impact of elastic-plastic alternating bending on the properties and structure of metal materials is to go beyond the minimum input gap set by the nomogram from the operation manual of the EcoMaster®25 precision roller straightening machine. Analysis of the position of the working rollers when they are in contact and after the setting of a gap between them showed that within the limits of reducing the input gap by 30% from the boundary set by the nomogram, the possibilities of implementing the alteration process remain. Analytical dependences are constructed to determine the input gap for any values of the thickness of strips or sheets in the range from 1 to 3 mm, in which the distribution of the total equivalent intensity of the principal true strains is especially effective. The additivity of this magnitude of the deformation effect on metallic materials (along with the intensity of the principal true strains) is proved, which allows to consider it as a measure of the accumulated strain.

A comparison on isothermal and thermomechanical fatigue behavior of 316LN stainless steel with various tension dwell time

Isothermal and thermomechanical fatigue tests with various tension dwell time (designated as creep-IF and creep-TMF respectively) were conducted. The cyclic stress response and stress relaxation behavior were qualitatively and quantitatively discussed based on TEM and EBSD characterization. The fatigue dominated transgranular crack initiation and propagation led to specimen fracture in all creep-IF tests. The transition of dominant damage mechanism from fatigue to creep-fatigue interaction occurred when dwell time increased to 1800 s in creep-TMF test, which caused the intergranular fracture mode and a much shorter life than creep-IF. Moreover, the life prediction model based on tension strain energy was proposed.

Bond of corroded reinforcement in strain resilient cementitious composites

Abstract In corroded steel anchorages, radial pressures generated by corrosion and bond are balanced by hoop tension provided by the concrete cover. As the concrete has negligible tension strain capacity, in the absence of confinement, anchorage failure occurs by cover splitting and consequent bond deterioration. This paper presents an experimental study of short reinforcement anchorages embedded in a strain resilient cementitious composite matrix, which were preconditioned under simulated corrosion before mechanical loading. The experiment was meant to assess the restraining effect of randomly dispersed plastic fibers on the build-up of expansive rust, by measuring the degree of rebar corrosion that led to cracking of the concrete cover, and the consequent improvements in residual anchorage capacity, by measuring the mechanical response to four-point loading. A total of eighteen short beams were tested with variables being the anchorage length extending into the shear span of the beams as well as the matrix (with and without fibers). Comparisons among artificially corroded and non-corroded coupons demonstrate the favorable effect a strain resilient matrix has in delaying metal consumption as a consequence of the fibers’ restrain against crack initiation/widening; their mechanical testing reveals even increase of local bond strength for corrosion level less than 10%.

Engineering the Substrate Specificity of Toluene Degrading Enzyme XylM Using Biosensor XylS and Machine Learning.

Enzyme engineering using machine learning has been developed in recent years. However, to obtain a large amount of data on enzyme activities for training data, it is necessary to develop a high-throughput and accurate method for evaluating enzyme activities. Here, we examined whether a biosensor-based enzyme engineering method can be applied to machine learning. As a model experiment, we aimed to modify the substrate specificity of XylM, a rate-determining enzyme in a multistep oxidation reaction catalyzed by XylMABC in Pseudomonas putida. XylMABC naturally converts toluene and xylene to benzoic acid and toluic acid, respectively. We aimed to engineer XylM to improve its conversion efficiency to a non-native substrate, 2,6-xylenol. Wild-type XylMABC slightly converted 2,6-xylenol to 3-methylsalicylic acid, which is the ligand of the transcriptional regulator XylS in P. putida. By locating a fluorescent protein gene under the control of the Pm promoter to which XylS binds, a XylS-producing Escherichia coli strain showed higher fluorescence intensity in a 3-methylsalicylic acid concentration-dependent manner. We evaluated the 3-methylsalicylic acid productivity of XylM variants using the fluorescence intensity of the sensor strain as an indicator. The obtained data provided the training data for machine learning for the directed evolution of XylM. Two cycles of machine learning-assisted directed evolution resulted in the acquisition of XylM-D140E-V144K-F243L-N244S with 15 times higher productivity than wild-type XylM. These results demonstrate that an indirect enzyme activity evaluation method using biosensors is sufficiently quantitative and high-throughput to be used as training data for machine learning. The findings expand the versatility of machine learning in enzyme engineering.

Mg-3Al-1Zn alloy deformed along different strain paths: Role of latent hardening

The mechanical properties of magnesium alloy AZ31 were investigated experimentally with visco-plastic self-consistent modeling. Tension, compression and plane strain compression (PSC) tests were performed along 3 directions of a hot rolled plate, and the material parameters input in the model were fitted with the uniaxial stress-strain curves. The critical resolved shear stress (CRSS) for tension twinning was modeled with a modified Voce hardening law first decreasing, and then increasing with strain, that could reproduce better the flow stress for twin-predominant deformation. Such CRSS evolution may better model twin nucleation, propagation and growth. Firstly simulations were carried out assuming latent hardening coefficients for slip by other slip systems equal to self-hardening. Then different heterogeneous latent hardening were used, whose values were based on dislocation dynamics simulations from the literature. This study shows that equal self and latent hardening can reproduce the stress strain curves and plastic anisotropy as well as heterogeneous mode on mode latent hardening. Discrepancies between simulations and experimental results from PSC are explained by an under-estimation of twinning for some PSC strain paths.

Tensile test of a specimen from different-thickness sheet material

A technique for tensile testing of a sample cut from a sheet blank of different thicknesses is proposed. Gage interference sheet blanks are obtained by rolling or welding sheet materials of different thicknesses and are used in the manufacture of various shells by metal forming in the automotive, electrical, and aerospace industries. Currently existing test methods provide for the tension of samples having the same thickness and width. Therefore, an urgent task is to develop a technique for tensile testing of a sample of different thicknesses. The proposed technique uses a sample cut from a sheet material of different thicknesses joined by welding, having different widths, in which the cross-sectional area along the estimated length is constant, which creates the same conditions for its deformation throughout the volume. In contrast to existing tensile test methods, in which the averaged values of mechanical and plastic properties are determined, the proposed method obtains mechanical and plastic properties in several cross sections of the sample located along the estimated length. The sample is subjected to tension with a uniform rate of deformation until the onset of the neck formation with the recording of the load-displacement diagram. By changing the dimensions of the cross sections when using the load-displacement diagram, at the considered moment of tension, the intensity of stresses and strains, parameters of hardening curves, anisotropy coefficients, and the non-uniformity of plastic deformation in each cross section of the sample are determined. For example, tests of a different thickness sample made of NHX260YD steel with a weld in the transverse direction are given.