Exponential Stress Research Articles

Alternative Energy Options for a Thai Durian Farm: Feasibility Study and Experiments for the Combination of Solar Photovoltaics and Repurposed Lithium-Ion Batteries

This research examines the viability of incorporating a second-life lithium-ion battery energy storage system with a solar photovoltaic power source to facilitate energy acquisition in two irrigation scenarios at a durian farm located in Thailand. The first option entails selecting the battery with suitable dimensions to effectively harness solar energy following morning irrigation, while the second option involves sizing the battery specifically for storing solar energy solely for the purpose of powering the motor pump. This study conducts an analysis on the degradation of the battery, focusing on the influence of specific environmental conditions and its specification. The degradation analysis employs polynomial functions as an alternative to exponential semi-empirical stress models for fitting stress models. This approach demonstrates a robust fit, as evidenced by a high R-squared value of approximately 1. The economic analysis considers various factors, including solar irradiance derating factors, battery deterioration rate, and photovoltaic power ratings for all scenarios. The sensitivity analysis evaluates the variations in irradiance and costs associated with the battery. When solar radiation levels surpass 500 W/m2 and the cost of the battery remains below $100/kWh, the estimated payback period is approximately 5 years over the duration of the 10-year project lifespan.

Experimental investigation and modeling of the mechanical properties of construction PMMA at different temperatures

Poly-methyl-methacrylate (PMMA) is a polymer material with increasing applications in buildings as an alternative to glass. Compared with glass, PMMA is lightweight, has high light transmittance, and has no risk of self-explosion. PMMA can be bonded to form large components without visible connections through bulk polymerization. PMMA used in construction (construction PMMA) is not toughened by the directional stretching process, which makes it different from the directional PMMA used in aerospace. This study aimed to explore the mechanical properties of construction PMMA. First, uniaxial tensile tests of the base coupons (without bonding areas) and bonding coupons (with bonding areas) at different temperatures (-40 to 60 °C) were conducted, and uniaxial compressive tests were conducted at the same temperatures. Thereafter, predictive formulae were proposed to describe the effect of temperature on the mechanical properties of construction PMMA under tension and compression, and a reduction factor for the ultimate strength of the bonding coupon was proposed. Subsequently, an exponential stress–strain relationship was proposed to describe the mechanical behavior of construction PMMA at different temperatures, which exhibited better accuracy. Finally, the capacity tests of the two PMMA beams were conducted. Finite element models of the test beams were established using the proposed stress–strain relationship. The accuracy of the proposed stress–strain relationship was verified by comparing the results of the finite element analyses and the test.

Stress–Strength Inference on the Multicomponent Model Based on Generalized Exponential Distributions under Type-I Hybrid Censoring

The stress–strength analysis is investigated for a multicomponent system, where all strength variables of components follow a generalized exponential distribution and are subject to the generalized exponential distributed stress. The estimation methods of the maximum likelihood and Bayesian are utilized to infer the system reliability. For the Bayesian estimation method, informative and non-informative priors combined with three loss functions are considered. Because the computational difficulty on working posteriors, the Markov chain Monte Carlo method is adopted to obtain the approximation of the reliability estimator posterior. In addition, the bootstrap method and highest probability density interval are used to obtain the reliability confidence intervals. The simulation study shows that the Bayes estimator with informative prior is superior to other competitors. Finally, two real examples are given to illustrate the proposed estimation methods.

Interval estimation of the two-parameter exponential constant stress accelerated life test model under Type-II censoring

ABSTRACT In this paper, interval estimation of the two-parameter exponential distribution based on constant-stress accelerated life test data under Type-II censoring is studied. The life-stress models of the scale and location parameters are assumed to be log-linear. The maximum likelihood estimators of the model parameters are obtained. The exact and approximate confidence intervals for the parameters in the life-stress model of the scale parameter are developed. The generalized confidence intervals for the parameters in the life-stress model of the location parameter, and mean and reliability function at the designed stress level are derived. The performance of the proposed generalized confidence intervals is assessed by the Monte Carlo simulation. Finally, a real example is used to illustrate our methods.

A principal stress cap model for stresses in square silos, with some examples of exponential stress

The principal stress cap approach has been used to model stresses in square hoppers, based upon an orthogonal grid upon a spherical surface sector, bounded by “great circles”. The model agrees with Rotter's correlation for lateral variation of wall normal stress for concave, active systems at uniform state of stress. However, systems of convex, passive stress do not conform to Rotter. The data of Jarrett{Geotechnique, 1995, 45, 95–104} and Brown{Chemical Engineering Science, 2000, 55, 4399–4413} have been modelled successfully, both qualitatively and quantitatively. Regions of the exponential stress regime have been found in the corner regions of the silo, alongside conventional Janssenian stress at the wall mid-points. Equivalent data of Jarrett and Brown are in reasonable agreement when plotted in dimensionless form. • Stresses in square hoppers have been modelled. • Principal stress cap approach is easy-to-use and visual model. • The model has been fitted to 2 sources of experimental data. • The data and the model show regions of exponential stress. • Horizontal variations in wall normal stress are seen.

Bayesian and Non-Bayesian Analysis of Exponentiated Exponential Stress–Strength Model Based on Generalized Progressive Hybrid Censoring Process

In many real-life scenarios, systems frequently perform badly in difficult operating situations. The multiple failures that take place when systems reach their lower, higher, or extreme functioning states typically receive little attention from researchers. This study uses generalized progressive hybrid censoring to discuss the inference of R=P(X<Y<Z) for a component when it is exposed to two stresses, Y,Z, and it has one strength X that is regarded. We assume that both the stresses and strength variables follow an exponentiated exponential distribution with a common scale parameter. We obtain R’s maximum likelihood estimator and approximate confidence intervals. In addition, the Bayesian estimators for symmetric, such as squared error, and asymmetric loss functions, such as linear exponential, are developed. Credible intervals with the highest posterior densities are established. Monte Carlo simulations are used to evaluate and compare the effectiveness of the many proposed estimators. The process is then precisely described using an analysis of real data.

Thixotropic spectra and Ashby-style charts for thixotropy

There is no universal model for thixotropy, and comparing thixotropic effects between different fluids is a subtle yet challenging problem. We introduce a generalized (model-insensitive) framework for comparing thixotropic properties based on thixotropic spectra. A superposition of exponential stress modes distributed over thixotropic time scales is used to quantify buildup and breakdown times and mode strengths in response to step-change input. This mathematical framework is tested with several experimental step-shear rate data on colloidal suspensions. Low-dimensional metrics based on moments of the distribution reveal characteristic average thixotropic properties, which are visualized on Ashby-style diagrams. This method outlines a framework for describing thixotropy across a diverse range of microstructures, supporting scientific studies as well as material selection for engineering design applications.

Multi-Scale Modelling of Plastic Deformation, Damage and Relaxation in Epoxy Resins.

Epoxy resin plasticity and damage was studied from molecular dynamic simulations and interpreted by the help of constitutive modelling. For the latter, we suggested a physically motivated approach that aims at interpolating two well-defined limiting cases; namely, pulling at the vanishing strain rate and very rapid deformation; here, taken as 50% of the speed of sound of the material. In turn, to consider 0.1–10-m/s-scale deformation rates, we employed a simple relaxation model featuring exponential stress decay with a relaxation time of 1.5 ns. As benchmarks, deformation and strain reversal runs were performed by molecular dynamic simulations using two different strain rates. Our analyses show the importance of molecular rearrangements within the epoxy network loops for rationalizing the strain-rate dependence of plasticity and residual stress upon strain reversal. To this end, our constitutive model reasonably reproduced experimental data of elastic and visco-elastic epoxy deformation, along with the maximum stress experienced before fracturing. Moreover, we show the importance of introducing damage elements for mimicking the mechanical behavior of epoxy resins.

English

Two isothermal motions of incompressible Maxwell fluids with power-law dependence of viscosity on the pressure are investigated when gravity effects are taken into account. The fluid motion, between two infinite horizontal parallel plates, is generated by the lower plate that applies a time-dependent shear stress to the fluid. Exact expressions are established for the steady-state components of the dimensionless start-up velocity, shear stress, and normal stress. They are used to find the needed time to touch the steady-state and to provide corresponding solutions for the motion of the same fluids induced by an exponential shear stress on the boundary. This time is useful for experimentalists who want to eliminate transients from their experiments. It is higher for motions of ordinary fluids as compared to fluids with pressure-dependent viscosity. The variation of starting solutions (numerical solutions) in time and space is graphically represented and some characteristics of the fluid motion are brought to light.

The prediction intervals of remaining useful life based on constant stress accelerated life test data

In practice, the prediction of the remaining useful life (RUL) of the product is a very important issue. This paper considers the prediction intervals of the RUL of the product at the normal operating stress level based on the exponential or Weibull constant stress accelerated life test (CSALT) data. For the exponential CSALT with type II censoring, we derive the exact and approximate prediction intervals for the RUL of the product. Using the asymptotic normality of the maximum likelihood estimation and the bootstrap method, we provide the two prediction intervals for the RUL of the product based on the exponential CSALT type I censored data. Under the Weibull CSALT with type II censoring, we use the generalized inferential procedure to obtain the generalized prediction interval of the RUL of the product. We also get the bootstrap prediction interval of the RUL of the product based on the Weibull CSALT type I censored data. The performance of the proposed prediction intervals is assessed by Monte Carlo simulation. The simulation results show that the coverage probabilities of the proposed prediction intervals are very close to the nominal confidence level. Finally, two examples are used to illustrate the proposed methods.

A Data-Driven Memory-Dependent Modeling Framework for Anomalous Rheology: Application to Urinary Bladder Tissue

We introduce a data-driven fractional modeling framework for complex materials, and particularly bio-tissues. From multi-step relaxation experiments of distinct anatomical locations of porcine urinary bladder, we identify an anomalous relaxation character, with two power-law-like behaviors for short/long long times, and nonlinearity for strains greater than 25%. The first component of our framework is an existence study, to determine admissible fractional viscoelastic models that qualitatively describe linear relaxation. After the linear viscoelastic model is selected, the second stage adds large-strain effects to the framework through a fractional quasi-linear viscoelastic approach for the nonlinear elastic response of the bio-tissue of interest. From single-step relaxation data of the urinary bladder, a fractional Maxwell model captures both short/long-term behaviors with two fractional orders, being the most suitable model for small strains at the first stage. For the second stage, multi-step relaxation data under large strains were employed to calibrate a four-parameter fractional quasi-linear viscoelastic model, that combines a Scott-Blair relaxation function and an exponential instantaneous stress response, to describe the elastin/collagen phases of bladder rheology. Our obtained results demonstrate that the employed fractional quasi-linear model, with a single fractional order in the range α = 0.25–0.30, is suitable for the porcine urinary bladder, producing errors below 2% without need for recalibration over subsequent applied strains. We conclude that fractional models are attractive tools to capture the bladder tissue behavior under small-to-large strains and multiple time scales, therefore being potential alternatives to describe multiple stages of bladder functionality.

Colloidal hydrogels made of gelatin nanoparticles exhibit fast stress relaxation at strains relevant for cell activity

Viscoelastic properties of hydrogels such as stress relaxation or plasticity have been recognized as important mechanical cues that dictate the migration, proliferation, and differentiation of embedded cells. Stress relaxation rates in conventional hydrogels are usually much slower than cellular processes, which impedes rapid cellularization of these elastic networks. Colloidal hydrogels assembled from nanoscale building blocks may provide increased degrees of freedom in the design of viscoelastic hydrogels with accelerated stress relaxation rates due to their strain-sensitive rheology which can be tuned via interparticle interactions. Here, we investigate the stress relaxation of colloidal hydrogels from gelatin nanoparticles in comparison to physical gelatin hydrogels and explore the particle interactions that govern stress relaxation. Colloidal and physical gelatin hydrogels exhibit comparable rheology at small deformations, but colloidal hydrogels fluidize beyond a critical strain while physical gels remain primarily elastic independent of strain. This fluidization facilitates fast exponential stress relaxation in colloidal gels at strain levels that correspond to strains exerted by cells embedded in physiological extracellular matrices (10-50%). Increased attractive particle interactions result in a higher critical strain and slower stress relaxation in colloidal gels. In physical gels, stress relaxation is slower and mostly independent of strain. Hence, colloidal hydrogels offer the possibility to modulate viscoelasticity via interparticle interactions and obtain fast stress relaxation rates at strains relevant for cell activity. These beneficial features render colloidal hydrogels promising alternatives to conventional monolithic hydrogels for tissue engineering and regenerative medicine. Statement of significanceIn the endeavor to design biomaterials that favor cell activity, research has long focused on biochemical cues. Recently, the time-, stress-, and strain-dependent mechanical properties, i.e. viscoelasticity, of biomaterials has been recognized as important factor that dictates cell fate. We herein present the viscoelastic stress relaxation of colloidal hydrogels assembled from gelatin nanoparticles, which show a strain-dependent fluidization at strains relevant for cell activity, in contrast to many commonly used monolithic hydrogels with primarily elastic behavior.

Mixed initial-boundary value problems describing motions of Maxwell fluids with linear dependence of viscosity on the pressure

Abstract Some mixed initial-boundary value problems are analytically studied. They correspond to unsteady motions of the incompressible upper-convected Maxwell (IUCM) fluids with linear dependence of viscosity on the pressure between infinite horizontal parallel plates. The fluid motion is generated by the upper plate that applies time-dependent shear stresses to the fluid. Exact solutions are established for the dimensionless velocity and nontrivial shear stress fields using a suitable change of the spatial variable and the Laplace transform technique. They are presented as sum of the steady-state and transient components and are used to determine the required time to reach the permanent state. Comparisons between exact and numerical solutions indicate an excellent agreement. Analytical solutions for the unsteady motion of the same fluids induced by an exponential shear stress on the boundary are obtained as limiting cases of the general solutions. Moreover, the steady-state solutions corresponding to the ordinary IUCM fluids performing the initial motions are provided by means of asymptotic approximations of standard Bessel functions. Finally, spatial variation of starting solutions and the influence of physical parameters on the fluid motion are graphically underlined and discussed.

Kinetics and mechanisms of stress relaxation in sputtered silver thin films

The post-growth stress relaxation in thin polycrystalline Ag films, deposited by direct-current magnetron sputtering under different growth conditions, was explored through wafer curvature measurements. It exhibits exponential behaviour with three distinct characteristic time components τ. The slowest one, namely τth≃200 s, is ascribed to thermal stress inherent to the deposition method. In fact, the performed temperature measurements match perfectly with an exponential stress variation with heating or cooling, as predicted by a thermal exchange model detailed in this work. Based on a comparison between different deposition conditions (continuous/interrupted sputter deposition and evaporation), the case of Mo deposition and stress relaxation modelling, the remaining components are assigned to the out-diffusion of atoms from grain boundaries (τgb≃3 s) and to changes in the grain surface shape induced by grain boundary grooving (τsurf≃20 s). The relaxation amplitude of the first mechanism varies linearly with the steady-state stress at the end of growth in agreement with theoretical expectations. Yet, that of the second one does not. However, clues point to a kinetic limitation of atomic diffusion mechanism along grain boundaries. This study provides proofs of the simultaneous occurrence of several mechanisms of stress relaxation in thin metallic films.

Design-oriented uniaxial material model for predicting longitudinal compressive behaviour of D36 steel plates with multiple mechanically induced pits

ABSTRACT An experiment was conducted on D36 steel plates under various corrosion scenarios. This was realised to determine the interactive effect of multiple corrosion pits on the compressive behaviour of stiffened plates and to establish a generalised design-oriented uniaxial material model for application in fibre element models to assess the strength and stability of ship structures. The performance parameters were observed to be highly sensitive to corrosion through the test. To obtain a better understanding of the transition between the two typical failure modes, i.e. strength failure and buckling failure, a parametric sensitivity analysis was performed on corroded specimens to identify the effects of some factors on the length coefficient. Using the test data, a design-oriented linear–exponential stress vs. strain material model was proposed, and it was observed that the corrosion-based exponent in this model could switch it smoothly from a bilinear form for lower corrosion cases to an exponential form for higher corrosion cases.

Objective Bayesian analysis for generalized exponential stress–strength model

In reliability studies, a stress–strength model is often used to analyze a system that fails whenever the applied stress is greater than the strength. Statistical inference of reliability is widely used in a number of areas, such as engineering, clinical trials, and quality control. In addition to the common stress–strength model with one stress and one strength, the reliability of more complex systems has also been studied. In this study, we consider the reliability of a generalized stress–strength model that consists of a serial system with one stress and multiple strengths. We then develop the probability matching priors and reference priors for a generalized exponential stress–strength model. We demonstrate that the two-group reference prior and Jeffreys prior are not a matching prior. Through a simulation study and real data example, we also demonstrate that the proposed probability matching priors match the target coverage probabilities in a frequentist sense even for a small sample size.

Analytical Solutions of Upper Convected Maxwell Fluid with Exponential Dependence of Viscosity under the Influence of Pressure

Some unsteady motions of incompressible upper-convected Maxwell (UCM) fluids with exponential dependence of viscosity on the pressure are analytically studied. The fluid motion between two infinite horizontal parallel plates is generated by the lower plate, which applies time-dependent shear stresses to the fluid. Exact expressions, in terms of standard Bessel functions, are established both for the dimensionless velocity fields and the corresponding non-trivial shear stresses using the Laplace transform technique and suitable changes of the unknown function and the spatial variable in the transform domain. They represent the first exact solutions for unsteady motions of non-Newtonian fluids with pressure-dependent viscosity. The similar solutions corresponding to the flow of the same fluids due to an exponential shear stress on the boundary as well as the solutions of ordinary UCM fluids performing the same motions are obtained as limiting cases of present results. Furthermore, known solutions for unsteady motions of the incompressible Newtonian fluids with/without pressure-dependent viscosity induced by oscillatory or constant shear stresses on the boundary are also obtained as limiting cases. Finally, the influence of physical parameters on the fluid motion is graphically illustrated and discussed. It is found that fluids with pressure-dependent viscosity flow are slower when compared to ordinary fluids.

Exponential stress in silos — An example from literature

Matchett proposed an exponential stress regime in silos from principal stress cap modelling. It could result in dangerously high stresses in silos. Practical examples of the exponential stress field have been found in the published work of Ramirez et al., for wheat and maize in a steel silo 1.9 m diameter and 5 m tall. The exponential stresses were found during the early stages of the discharge cycle.The data have been modelled by a modified, exponential, Janssen equation with the direction of wall friction reversed, and Matchett’s principal stress cap model for a convex-active configuration.This phenomenon requires further investigation.

Transcriptomic Profiles of Zymomonas mobilis 8b to Furfural Acute and Long-Term Stress in Both Glucose and Xylose Conditions.

Zymomonas mobilis 8b is an ethanologenic bacterium engineered to utilize both glucose and xylose. The impacts of lignocellulosic hydrolyzate inhibitors on the growth of Zymomonas mobilis 8b have been investigated. However, the molecular responses of these inhibitors have not been completely elucidated yet. In this study, molecular responses to furfural were investigated using transcriptomic approaches of both chip-based microarray and a directional mRNA-Seq. Furfural acute shock time-course experiment with 3 g/L furfural supplemented when cells reached exponential phase and stress response experiment in the presence of 2 g/L furfural from the beginning of fermentation were carried out to study the physiological and transcriptional profiles of short-term and long-term effects of furfural on 8b. Furfural negatively affected 8b growth in terms of final biomass and the fermentation time. Transcriptomic studies indicated that the response of 8b to furfural was dynamic and complex, and differences existed between short-term shock and long-term stress responses. However, the gene function categories were similar with most down-regulated genes related to translation and biosynthesis, while the furfural up-regulated genes were mostly related to general stress responses. Several gene candidates have been identified and genetic studies indicated that expression of ZMO0465 and cysteine synthase operon ZMO0003-0006 driven by its native promoter in a shuttle vector enhanced the furfural tolerance of 8b. In addition, the relationship between microarray and mRNA-Seq was compared with good correlations. The directional mRNA-Seq data not only provided the gene expression profiling, but also can be applied for transcriptional architecture improvement to identify and confirm operons, novel transcripts, hypothetical gene functions, transcriptional start sites, and promoters with different strength.

Average austenite grain size evolution simulation during multi-pass shape metal hot rolling process

Constitutive equations describing the flow stress of Q235 steel undergoing hot plastic deformation have been developed by integrating the microstructure models and exponential flow stress models presented in literatures, in which the microstructure models parameters have been re-determined based on the related experiments carried out on cylindrical specimens of the Q235 steel. Therefore, the integrated constitutive equations are capable of calculating the evolution of austenite grain size and investigating the effects of average austenite grain size on the flow stress of Q235 steel during hot deformation. A three-dimensional thermo-mechanically coupled FEM simulation of an 11-pass H-shape metal roughing rolling process with the austenite grain size evolution taken into account have been carried out to verify the rationality of roll pass schedule. The accuracy of the integrated constitutive equations has been preliminary validated by the comparisons between measured and the calculated values of rolling force.