Recovery Stress in a Ni-Ti-Nb Shape Memory Alloy with Wide Transformation Hysteresis

The effect of deformation on recovery stress of Ni144.7Ti46.3Nb9 alloy has been studjed using tensile test at various temperatures and TEM observation. It ls shown that the recovery stress increases with jncreasing total strain ET and reaches a maximum value (max) as ET= 9% but the maximum recov erV strain of the alloy is only about 4.6%. This is different from that of Ti-Ni binary alloy in which is obtained usually at maximum recovery strain and the reason of the difference is dis Cussed. Deformation temperature Td has a little effect on recovery stress when Td is less than Ms However, recovery stress decreases sharply when Td is higher than M, and lowers approximately down to zero near Msσ

Conditional Generative Adversarial Network Enabled Localized Stress Recovery of Periodic Composites

Structural damage in heterogeneousmaterials typically originates frommicrostructures where stress concentration occurs.Therefore,evaluating the magnitude and location of localized stress distributions within microstructures under external loading is crucial.Repeating unit cells(RUCs)are commonly used to represent microstructural details and homogenize the effective response of composites.This work develops a machine learning-based micromechanics tool to accurately predict the stress distributions of extracted RUCs.The locally exact homogenization theory efficiently generates the microstructural stresses of RUCs with a wide range of parameters,including volume fraction,fiber/matrix property ratio,fiber shapes,and loading direction.Subsequently,the conditional generative adversarial network(cGAN)is employed and constructed as a surrogate model to establish the statistical correlation between these parameters and the corresponding localized stresses.The stresses predicted by cGAN are validated against the remaining true data not used for training,showing good agreement.This work demonstrates that the cGAN-based micromechanics tool effectively captures the local responses of composite RUCs.It can be used for predicting potential crack initiations starting from microstructures and evaluating the effective behavior of periodic composites.

Characteristics of Deformation and Recovery in Shape Memory Alloy

The mechanical behavior and the effect of pre-strain on recovery behavior of Ti50Ni47Fe3 (at. pct) alloy were investigated systematically by tensile and recovered tests accompanied by electrical resistance measurement. Ti50Ni47Fe3 alloy has different deformation behaviors at different temperature ranges, the deformation curves in different temperature range can be classified into four kinds. The start temperature of recovery increases with the increase of pre-strain. There exists an optimal deformation condition, at which the specimen exhibits maximum free recovery strain. With increasing pre-strain the recovery stress increases and reaches the maximum at 8% pre-strain. R-phase to parent transition offered about 0.2% recovery strain. With pre-strain increasing the recovery stress increases and reaches to the maximum at 8% pre-strain. The recovery stress is corresponding with the critical stress of stress-induced martensitic transformation.

Preliminary data on effects of different street vegetation on stress recovery

Streets are important public spaces in daily life,and their stress-relieving abilities help to improve people’s physical and mental health.To investigate the effects of different types of street vegetation on people’s stress recovery,this study used virtual reality technology to establish five street scenes with different vegetation types,including a non-vegetated street,a street with trees,a street with trees and grass,a street with trees and hedges,and a street with trees,grass,and flowers.Twenty-four participants completed the Trier Social Stress Test and then watched the five street scenes for stress recovery.Participants rated the vegetated streets as significantly better at reducing stress than the non-vegetated street.Compared with the non-vegetated street,the participants’POMS scores decreased by 2.59-12.09 and ROS scores increased by 0.83-3.67 after watching the vegetated streets,indicating significant improvement in mood(P<0.001).HRV data showed that the combination of trees,grass,and flowers was the most effective for stress recovery(LF/HF=0.67±0.42;pNN50=27.41%±16.32%).EEG data showed that participants’alpha power was 0.05-0.66µV2 higher and mental stress scores based on brainwave power were 0.23-0.37 points lower in the vegetated streets than in the non-vegetated street.The occipital and frontal regions showed the most positive responses to changes in vegetation elements,and alpha brainwaves in the O2 channel were the most active.Therefore,the streets with vegetation were more conducive to stress recovery than the non-vegetated street.It is thus suggested to integrate trees,grass,flowers,and other vegetation types along streets.

Study on the creep permeability of mining-cracked N2 laterite as the key aquifuge for preserving water resources in Northwestern China

This research focused on the impact of mining on the permeability of key aquifuge （N2 laterite） that is widespread in the arid and semi-arid areas of northwestern China and is critical for preserving water resources. The impact of mining stress recovery on the permeability of cracked N2 laterite was assessed for parts of northwestern China that included the Jingle laterite and Baode laterite. The mineral compositions and swelling properties of the laterite at both locations were examined, and analytical results showed that the laterite contained abundant clay minerals. The Baode laterite exhibited higher expansibility than Jingle laterite. The triaxial creep permeability performance of laterite specimens with a prefabricated crack width of 1.0, 1.5, and 2.5 mm were tested. The results indicated that strain of cracked laterite all exhibited transient creep following each level of loading, and then unstable creep and stable creep. With the increase of loading, the transient creep deformation corresponding to each level of loading decreased, the unstable creep deformation produced by identical loading gradually and incrementally increased. The nonlinear power function equation was selected to fit creep grading curves which have high precision. The cracks within the laterite gradually closed with the stress recovery, and permeability gradually recovered. During the stress recovery, the narrower cracks exhibited a smaller change in permeability. However, for narrow cracks in mining soil, permeability recovered after mining stress when permeability was closer to initial permeability, and the Baode laterite showed greater recovery than that of the Jingle laterite.

Elements and Element Components of the Rural Landscape in Linpan of Western Sichuan in Relation to Perception,Preference and Stress Recovery

Natural environments contribute to people’s perception,preference and health restoration.Many researchers have focused either on the positive effects of overall rural environments on stress recovery or concentrated on the perception and preference aspects of the rural landscape,but few have integrated perception,preference and stress recovery simultaneously.This paper developed a framework which includes 11 elements and 38 element components related to Linpan,China,and distributed it online as part of a survey.As a result,a total of 324 valid questionnaires were collected.The questionnaire included demographic details,perception and preference degree for Linpan,as well as self-estimations of stress recovery.Stepwise multiple linear regression was employed,and revealed 16 significant predictors for the perception,preference and stress recovery in rural environments.In terms of elements,atmosphere and imagery were the two elements that could be best perceived,while woodland,farmland,water,residence and road were the five most important elements for the preference.Moreover,seven elements were also identified as significant predictors for stress recovery.Among the element components,tranquility as well as road and water proximity were the two significant predictors for perception,while wide visibility as well as woodland and residence blending contributed significantly to stress recovery.The five element components of woodland interior,vegetable field,stream,courtyard space and branch road each had a significantly predictive ability for preference and stress recovery.These findings extend the understanding of the perception,preference and restorative properties of rural environments through the combination of elements and element components in Linpan of Western Sichuan,helping to improve the quality and characteristics of rural external and internal environments and create health-promoting environments.

Evaluation of rutting performance of stone matrix asphalt mixtures containing warm mix additives

Permanent deformation or rutting, one of the most important distresses in flexible pavements, has long been a problem in asphalt mixtures and thus a great deal of research has been focused on the development of a rheological parameter that would address the rutting susceptibility of both unmodified and modified bituminous binders. In this research, three warm mix additives(Sasobit, Rheofalt and Zycotherm) were used to modify 60-70 penetration grade base binder. The rutting potential of both modified and unmodified binders were evaluated through the multiple stress creep recovery(MSCR)-based parameter, nonrecoverable compliance(Jnr) and recovery parameter(R). Several performance tests carried on stone matrix asphalt(SMA) mixtures comprising different nominal maximum aggregate sizes(NMASs, 9.5, 12.5 and 19 mm), like Marshall stability, dynamic and static creep and Hamburg wheel tracking tests to evaluate their rutting performance. The objective of this work is to correlate MSCR test results to performance. Results indicate that for the range of the gradations investigated in this work, increasing the nominal maximum aggregate size of the gradation would increase the permanent deformation resistance of the SMA mixture. Addition of 3% sasobit to base binder leads an increase in Jnr100 about 82%. Addition of 2% rheofalt to base binder leads an recovery increase of about 9.76 % and 27.44% in stress levels of 100 and 3200 Pa, respectively. The results reveal that rutting resistance of mixtures improves as Jnr decreases. The use of the MSCR test in the rutting characterization of bituminous binders is highly recommended based on the results of this work.

Contact-Stress-Based Stress Recovery Methods for Discontinuous Deformation Analysis

Discontinuous deformation analysis(DDA)has been widely applied for the simulation of block systems that have many discontinuous surfaces.The penalty method is utilized to ensure that there are no penetrations between blocks.A linear polynomial function for displacement leads to a constant stress for a block,which cannot precisely describe the stress field within the block.Therefore,a high-order polynomial displacement function and a flue mesh are always used to improve the precision of the stress field.However,these means are not practical for simulating block systems that have many contacts.In this paper,the contact-stress-based stress recovery methods are proposed for DDA.High-precision solutions for the contact stresses on the boundaries of the blocks are utilized.The first-order Gaussian point of a block is the block's centroid,where the constant stress obtained via DDA is of higher precision.The high-precision solutions for the stresses are utilized in the least squares method to recover a single block's inner stress field.The proposed methods enhance the resolution of the stress field inside a single block without increasing the computational effort in the main iterative process for displacement in DDA.Numerical examples are simulated using both the finite element method(FEM)with a fine mesh and the proposed DDA program.The recovered DDA results can accurately describe the distribution of the stresses in a single block and,in some areas,have the same precision as the FEM results.Moreover,the precision of the proposed methods improves as the gradient of the contact stress on the boundary decreases.

Superconvergence and recovery type a posteriori error estimation for hybrid stress finite element method

Superconvergence and recovery type a posteriori error estimators are analyzed for Pian and Sumihara's 4-node hybrid stress quadrilateral finite element method for linear elasticity problems. Superconvergence of order O(h^(1+min){α,1}) is established for both the displacement approximation in H^1-norm and the stress approximation in L^2-norm under a mesh assumption, where α > 0 is a parameter characterizing the distortion of meshes from parallelograms to quadrilaterals. Recovery type approximations for the displacement gradients and the stress tensor are constructed, and a posteriori error estimators based on the recovered quantities are shown to be asymptotically exact. Numerical experiments confirm the theoretical results.

Stress Recovery Procedure for the Bonded Particle Model

In the simulation of discontinuous block systems,the discrete element method(DEM)has better computational efficiency and convergence than the finite element method(FEM).When several DEM particles are bonded together with parallel bonds(the bonded particle model,BPM),various shapes and block fractures can be simulated.The main aim of the BPM is to simulate a continuous material in which the stress distribution is continuous.Since the existing stress result for a single particle is an average value over the particle’s area,stress results do not exist in the area between particles.In this paper,the stress value for a single two-dimensional DEM particle is deduced.A stress recovery procedure with a linear stress function for a triangular element generated by the centroids of three bonded particles is proposed.In this way,the recovered stress field for the whole mesh composed of all triangular elements is continuous.A stress gradient exists in the whole mesh.This can also provide more accurate stress values for judging a fracture inside a block.Symmetrical and asymmetrical models are simulated by the BPM and FEM.Similar to the FEM results,the recovered stress results for the BPM can describe the stress distribution in the simulated continuous blocks.For the model with the theoretical stress solution,the recovered result and the theoretical solution coincide well.

Springback behavior of tailor rolled blank in U-shape forming

The springback of tailor rolled blanks with quenching and partitioning steels was investigated.In order to find out the springback behavior and related influence factors for the novel sheets,both experimental and simulation methods have been used to compare and analyze the springback characteristics of equal thickness blanks and tailor rolled blanks in U-channel forming.From the results,the overall springback angles of tailor rolled blanks at thin and thick sides are respectively 106.79° and 99.705°,which are both lower than those of the corresponding equal thickness blanks.Due to the existence of the thickness transition zone,the stress distribution in thin and thick sides of blanks is changed.The location of dangerous region in thin side of tailor rolled blanks is closer to the end of side,and the thick side moved to the middle of straight wall,which are different with the equal thickness blanks.Afterwards,the released quantitles of tangential stress and strain per unit section of blank are adopted to calculate relative springback angles and give novel evaluation criteria for qualitatively analyzing the amount of springback angles.By comparing the results,it shows that the tangential strain method is more suitable for the actual situation.