Permanent Plastic Deformation Research Articles

RUTTING IN ASPHALT MIXTURES – A REVIEW

Vehicles that pass over a pavement structure induce load and unload cycles that generate recoverable (resilient) and permanent (plastic) deformations within layers. Pavement has been developing studies since the decade of the 60´s with the purpose of attempting to understand the visco-elasto-plastic behavior of asphalt mixtures. This has the purpose of evaluating and understanding how the main damage mechanisms that are sought to be controlled in flexible pavement design methods are generated. One of the main damage mechanisms for these types of pavements is rutting. Based on the reviewed literature in relation to the phenomenon of rutting in asphalt mixtures, this article depicts and describes in summary, the main variables that influence the generation of said phenomenon in pavement. The end of the article presents the evolution of equations developed through theoretical and experimental studies in order to attempt to predict the phenomenon of rutting.

RUTTING IN ASPHALT MIXTURES – A REVIEW

Vehicles that pass over a pavement structure induce load and unload cycles that generate recoverable (resilient) and permanent (plastic) deformations within layers. Pavement has been developing studies since the decade of the 60´s with the purpose of attempting to understand the visco-elasto-plastic behavior of asphalt mixtures. This has the purpose of evaluating and understanding how the main damage mechanisms that are sought to be controlled in flexible pavement design methods are generated. One of the main damage mechanisms for these types of pavements is rutting. Based on the reviewed literature in relation to the phenomenon of rutting in asphalt mixtures, this article depicts and describes in summary, the main variables that influence the generation of said phenomenon in pavement. The end of the article presents the evolution of equations developed through theoretical and experimental studies in order to attempt to predict the phenomenon of rutting.

Estimation of fatigue life of TiN coatings using cyclic micro-impact testing

We studied the behaviour of a thin titanium nitride (TiN) coating (1.5 µm thick) on a tool steel substrate under dynamic and cyclic impacts through an approach combining experimental testing and computational modelling. Dynamic impact testing was used to investigate the load-dependent dynamic hardness and assess the energy-dissipation capabilities of the coating system. In cyclic impact tests, the coating-substrate system experienced permanent plastic deformation in each cycle, ultimately leading to coating failure. Chemical analysis identified an interlayer between the coating and the substrate that influenced the coating response, while cross-sectional analysis revealed the extent of coating damage due to cycling and impact load. A three-dimensional map was constructed, connecting the acceleration load, sensed depth, and cycles to the coating failure, and an empirical equation was used to characterise the relationship between the depth and cycles to failure. The computational model examined the traction component distribution during loading and unloading, focusing on normal and shear tractions. These findings suggested the potential significance of normal traction in the interfacial fatigue failure due to impact.

Improved deep neural network for predicting structural response of stiffened cylindrical shells to far-field underwater explosion

This paper is focused on the application of the machine learning for predicting structural response of ring stiffened cylindrical shells subjected to far-field underwater explosion. Three deep neural network (DNN) models are combined to predict the progressive plastic deformation behaviour of stiffened cylindrical shells subjected to the shock wave produced by a TNT charge. In the DNN regression models, the input variables include the charge mass, stand-off distance, detonation depth, cylindrical shell thickness, stiffener web and flange. These three DNN models composed of multi hidden layers are trained based on the data collection originated from a series of simulations performed by the ABAQUS finite element solver. Grid search is introduced to the hyperparameter tuning for deep learning, improving the prediction performance of machine learning methods. The DNN models are compared to the models trained using another three methods: multiple linear regression, decision tree and k-nearest neighbour. An improved Adam optimisation algorithm is used to increase the accuracy of prediction. The challenges encountered during the predictions are discussed to provide a more comprehensive insight into the advantage of the proposed DNN models. The DNN regression models can well predict the permanent plastic deformation and strain of stiffened cylindrical shells.

Indentation Depth-Dependent Hardness of Metal-Organic Framework Crystals: The Effect of Local Amorphization Induced by Indentation.

The hardness of metal-organic frameworks (MOFs) is an important mechanical property metric measuring their resistance to the permanent plastic deformation. The hardness of most MOFs measured from nanoindentation experiments usually exhibits the similar unique indentation depth dependence feature, the mechanism of which still remains unclear. In order to explain the effect of the indentation depth on the hardness of MOFs, we conducted nanoindentation simulations on HKUST-1 by using reactive molecular dynamics simulations. Our simulations reveal that the HKUST-1 material near the indenter can transform from the parent crystalline phase to a new amorphous phase due to the high pressure generated, while its counterpart far from the indenter remains in the crystalline phase. By considering the crystalline-amorphous interface in the energy analysis of MOFs, we derived an analytical expression of the hardness at different indentation depths. It is found that the interface effect can greatly increase the hardness of MOFs, as observed in nanoindentation simulations. Moreover, the proposed analytical expression can well explain the indentation depth-dependent hardness of many MOF crystals measured in nanoindentation experiments. Overall, this work can provide a better understanding of the indentation depth dependence of the hardness of MOFs.

On black holes as topological defects

In this paper, the gravitational field is revisited as a manifestation of defects in continuum media. The Schwarzschild solution is then interpreted as a permanent plastic deformation of space-time and we conjecture that a discrete dislocation leads to a discrete mass spectrum. The dislocation of this black hole is considered as a quasi-local defect, once it vanishes at the spatial infinity. The C-metric is also considered under this viewpoint. The dislocations in such a space-time reveal how the quasi-local defect interacts with a global defect due to the semi-infinite cosmic string. The disclinations are obtained in agreement at certain limits with the literature.

Localized Plastic Deformation and Microstructure Properties of Al/Si Alloy Improved with Al3Ni Compound

The microstructure of AS10/xNi hypoeutectic alloys with (x = 0.01% and 0.05%) was investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Localized permanent plastic deformation (Vickers hardness (HV)) was conducted on the samples before and after sintering. After sintering, the results showed a significant improvement in hardness with the addition of Ni atoms. From the XRD map, it was found that there was a shift in the peak positions as the Ni atoms were added. This shift is a result of the incoincidence of dhkl levels in the Al-phase before and after the addition of Ni. This mismatch in dhkl levels is associated with the lattice defects and lattice parameters. From the SEM images, the silicon powder particles in the binary composition are large and elongated plates, whereas those in the ternary composition are small and semi-spherical particles. This reduction in the particle size of the modified alloy is attributed to the presence of Ni atoms in the alloys.

Correlation between structure and mechanical properties in α-quartz single crystal by nanoindentation, AFM and confocal Raman microscopy

Quartz constitutes a very useful material due to its variety of applications, highlighting solid-state physics for material science with applications for devices and sensors, as piezoelectric for microbalances or oscillators for watches, computers, etc. These applications are very sensible to local pressures and stresses, however, there is not much information in the literature about the effect of high local pressures on the structure and their correlation with mechanical properties. In order to provide more information and clarity on this type of stress-structure-mechanical properties correlation, in this work, nanoindentation combined with Raman Confocal microscopy was carried out since it offers a powerful method to obtain information about the structural deformation and mechanical properties produced by high local pressures in α-quartz single crystal. The information obtained by nanoindentation (pile-up, pop-out, hardness and Υoung modulus) has been correlated with the structural data extracted from Raman spectroscopy, concluding that a permanent plastic deformation occurs under the indentation footprint, sharply appearing a new denser phase, which contribution increases with the applied load.

Effect of post-heat treatments on the microstructure, martensitic transformation and functional performance of EBF3-fabricated NiTi shape memory alloy

In the present work, a single solution treatment as well as solution/aging treatments were employed to regulate the precipitation behavior, martensitic transformation, mechanical and functional properties of EBF3-fabricated NiTi shape memory alloys. Under the optimized post-process heat treatment conditions, i.e., solution treatment at 1000 oC for 10 h followed by subsequent aging treatment at 500 oC for 4 h, the previously existing elongated Ti4Ni2Ox oxides were partially dissolved and interrupted into granular form and relatively uniformly distributed in the NiTi matrix. Meanwhile, the preexisting nanoscale Ni4Ti3 precipitates gradually transformed from clustered or segregated granular to a lenticular shape with the increase of the aging time. The martensite transformation routes also underwent an accompanying alteration, which changed from a one-step (B2-A ↔ B19’-M) to two-step (B2-A → R → B19’-M) transformation. Moreover, Ni4Ti3 precipitated with a coherent relationship of {123} <111>B2-A //{11–20} <0001>Ni4Ti3 which increase the material strength by hindering dislocation movement and improve plasticity by providing a transition domain for accommodating deformation at the interface. The superelastic stability and narrow response hysteresis promoted by the presence of the R-phase are affected by residual (100) compound twins martensite in the NiTi matrix and the permanent plastic deformation activated in (011) [001] slip system of the B2-A phase. This deteriorates the superelastic recovery ratio from 83.6 to 57.4%, as observed after 10 loading-unloading cycles. The post-heat treatment regime presented in the current investigation can be used to modulate the material precipitation, phase transformation, as well as the mechanical and functional properties of EBF3-fabricated NiTi alloys. These results allow to extrapolate the potential for carefully selected post-heat treatment scheduled for additively manufacturing NiTi shape memory alloys.

Application of sequential cyclic compression on cancer cells in a flexible microdevice.

Mechanical forces shape physiological structure and function within cell and tissue microenvironments, during which cells strive to restore their shape or develop an adaptive mechanism to maintain cell integrity depending on strength and type of the mechanical loading. While some cells are shown to experience permanent plastic deformation after a repetitive mechanical tensile loading and unloading, the impact of such repetitive compression on deformation of cells is yet to be understood. As such, the ability to apply cyclic compression is crucial for any experimental setup aimed at the study of mechanical compression taking place in cell and tissue microenvironments. Here, we demonstrate such cyclic compression using a microfluidic compression platform on live cell actin in SKOV-3 ovarian cancer cells. Live imaging of the actin cytoskeleton dynamics of the compressed cells was performed for varying pressures applied sequentially in ascending order during cell compression. Additionally, recovery of the compressed cells was investigated by capturing actin cytoskeleton and nuclei profiles of the cells at zero time and 24 h-recovery after compression in end point assays. This was performed for a range of mild pressures within the physiological range. Results showed that the phenotypical response of compressed cells during recovery after compression with 20.8 kPa differed observably from that for 15.6 kPa. This demonstrated the ability of the platform to aid in the capture of differences in cell behaviour as a result of being compressed at various pressures in physiologically relevant manner. Differences observed between compressed cells fixed at zero time or after 24 h-recovery suggest that SKOV-3 cells exhibit deformations at the time of the compression, a proposed mechanism cells use to prevent mechanical damage. Thus, biomechanical responses of SKOV-3 ovarian cancer cells to sequential cyclic compression and during recovery after compression could be revealed in a flexible microdevice. As demonstrated in this work, the observation of morphological, cytoskeletal and nuclear differences in compressed and non-compressed cells, with controlled micro-scale mechanical cell compression and recovery and using live-cell imaging, fluorescent tagging and end point assays, can give insights into the mechanics of cancer cells.

Influence of varying water content on permanent deformation of mud-fouled ballast

The contamination of ballast by mud pumping is known to cause considerable reduction in the shear resistance as well as increased settlement of railroad foundations. However, how varying water content (w) of fouled ballast can affect this deterioration has not been properly understood. The current study thus adopts a large-scale cyclic triaxial test to examine permanent (plastic) deformation of mud-fouled ballast collected from a site with a history of mud pumping with a consideration of different water contents. In these tests, fouling content varies from 5 to 30 %, while the water content changes from 0 to 40 %. The results show that while increasing content of fines causes larger permanent settlement of ballast, varying water content of fines can influence this behaviour significantly. A salient finding of this study is the critical threshold of water content near to the liquid limit (LL) of fine soil (finer than 0.425 mm) that can cause a swift increase in ballast settlement. The results show that the peak permanent strain can increase by about 26 % compared to the dry state when w of fines reaches the LL. On the other hand, permanent strain of fouled ballast can decrease at the optimum water content of fines, if a sufficient mass of fines (>20 % by weight) is provided to reinforce the granular assembly. An empirical method is provided to estimate the ultimate settlement of mud-fouled tracks considering the moisture state that would be most beneficial in real-life applications.

A new design of Borax-Cannabinol nanomaterial used to strengthen concrete structures: Non-Scc-GFN1xTB model

The aim of this study is to investigate the effect of cannabinol addition to borax, one of the raw materials of glass, on stress-strain behavior. For this purpose, the tight-binding approach of density functional theory was applied to detect the stress–strain behavior of nanosized a new borax–cannabinol model system with the molecular dynamics (MD) process. This process was investigated by extended density functional based tight-binding without self-consistent charge (NonSCC-GFN1-xTB), which is an effective approach to ensure high-accuracy simulation calculations. The features of the Non-Scc-GFN1xTB model, which has base functions and experimental potential parameters for covalent and non-covalent interactions, and can make molecular models of large systems, are highlighted. The results show that the addition of cannabinol to borax causes an extra resistant against the formation of permanent plastic deformation. This resistance can enable to increase the durability used to design the strengthened of materials including adding borax–cannabinol. The MD results show that the addition of cannabinol to borax crystal cause to formation of borax–cannabinol in a nanorod structure. This nanorod composite structure is considered as material that can be used to strengthen concrete structure because the plastic deformation of structure under stress begins at high strain zone.

Examining solid-state sintering of AlCoCrFeNi multi-principal element alloy by molecular simulations

With the emergence of solid-state sintering techniques for metal additive manufacturing of multicomponent alloys, understanding the fundamental sintering mechanisms is vital for effective process control. Here, we employ molecular dynamics simulations to investigate the mechanisms involved during solid-state sintering of AlCoCrFeNi multi-principal element alloy. Our results reveal that the cross migration of atoms between the surface of powder particles promotes neck growth while minimizing the surface free energy. This phenomenon is mediated by a transition from BCC to amorphous phase resembling a pre-melt and assisting in the densification as a function of temperature. Stress–strain analysis on the alloy single crystal at room temperature suggests that permanent plastic deformation occurs with a gradual phase change to FCC predicting a tensile strength of ∼ 1547 MPa at the onset of yield and a peak stress of 2267 MPa.

Investigating the effects of abrasive water jet machining parameters on surface integrity, chemical state in machining of Ti-6Al-4V

This study examined into the surface roughness and microhardness of titanium (Ti6Al4V) alloy caused by the abrasive waterjet milling (AWJM) process. Waterjet pressure (WJP), stand-off distance (SOD), and abrasive flow rate (AFR) were studied on surface roughness and microhardness in three distinct regions: the initial damage region (IDR), the smooth cutting region (SCR) and the rough cutting region (RCR). X-Ray Diffraction was used to examine the lattice strain, crystallite size, and phase composition of abrasive waterjet machined samples. WJP is discovered to be a useful factor in reducing surface roughness, increasing striations, and decreasing waviness on the AWJM's surface. The higher hardness is caused by the material's permanent plastic deformation during the AWJM process. The FWHM of AWJ machined samples is reduced, and the presence of TiOxCx increases the crystallite size during the AWJM process. In relation to surface deformation, the AWJM causes severe plastic deformation (SPD), resulting in continuous internal oxide formation.

Elastoplastic Indentation Response of Sigmoid/Power Functionally Graded Ceramics Structures

Due to the applicability of new advanced functionally graded materials (FGMs) in numerous tribological systems, this manuscript aims to present computational and empirical indentation models to investigate the elastoplastic response of FG substrate under an indention process with spherical rigid punch. The spatial variation of the ceramic volume fraction through the specimen thickness is portrayed using the power law and sigmoid functions. The effective properties of two-constituent FGM are evaluated by employing a modified Tamura–Tomota–Ozawa (TTO) model. Bilinear hardening behavior is considered in the analysis. The finite element procedure is developed to predict the contact pressure, horizontal displacement, vertical deformation, and permanent deformation of FG structure under the rigid cylindrical indentation. The empirical forms for permanent deformation were evaluated and assigned. Model validation with experimental works was considered. The convergence of the mesh and solution procedure was checked. Numerical studies were performed to illustrate the influence of gradation function, gradation index, and indentation parameters on the contact pressure, von Mises stresses, horizontal/vertical displacements, and permanent plastic deformation. The present model can help engineers and designers in the selection of an optimum gradation function and gradation index based on their applications.

Method for identifying the impact load condition of thin-walled structure damage based on PSO-BP neural network.

Thin-walled structures (TWS) were widely used in engineering equipment, and may be subjected to impact loads to produce different degrees of structural damage during application. However, it is a difficult problem to determine the impact load conditions for these structural damages. In this study, we developed a novel method of identifying the impact load condition of the thin-walled structure damage, which is based on particle swarm optimization-backpropagation (PSO-BP) neural network. First, the known impact position and velocity are applied to the finite element model (FEM) of the TWS to produce permanent plastic deformation, and to fit the characteristic shape of the deformation is needed by invoking the multivariate polynomial function. Then, the method is devoted to build a basic data set. With impact position and velocity as input and function coefficients as output, a model of extended PSO-BP neural network is established. Besides, the basic sample set is expanded to solve the lack of samples. Ultimately, utilizing the expanded total sample set as training data, function coefficients, impact position and velocity will be outputted. On the basis of the known functional coefficients of deformed surfaces, a model of predictive PSO-BP neural network is established and predicted. Furthermore, we predicted the collision position and velocity using a conventional BP neural network in the same way. Finally, the predicted impact position and velocity is compared with the analysis results of the FEM, which verifies that the PSO-BP neural network algorithm has high accuracy.

Analysis of Wedge Lock Washer using the Finite Element Method

Washers with a so-called wedge-locking effect are available for the engineering industry. The manufacturer assures, as confirmed by the Junker vibration test, that the tension in the thread increases when the screw is unscrewed. This is due to the appropriate geometry of the washers, which always work together in pairs. On the outside, the washers have serrations which, when tightening the screw, cut into the material of the clamped part, leaving a permanent plastic deformation. On the inside they have wedges, the angle of which is greater than the angle of the helix of the thread. The subject of this work is a study of creating a simulation model that takes into account the discussed effect of wedge lock of the washers. This model will be used in the future for simulation tests of washers with a different geometry than the one proposed by the manufacturer.

On Modelling Approaches to the Influence of Mechanical Deformation on the Micromagnetic Activity in a Mild Steel

In this study an attempt is made to develop a theoretical modelling by which the influence of certain mechanical deformation factors on the micromagnetic emission behavior of a low-carbon steel can reasonably be described and estimated. This modelling consists of a simple kinetics – kinematics – aided approach of the pinning state – controlled domain wall motion by which appropriate specific parameters are introduced. In this aspect the basic notion of specific micromagnetic activity (s.m.a.) is introduced by which the energetic strength of the activity is reflected. In this way, the synergetic effect of the quantitative (count rate) and qualitative (voltage) the detected micromagnetic Barkhausen emission (MBE) is taken into consideration. Thus it is possible, theoretically, to give a prediction of the general trend of changes in the s.m.a. under the influence of the tensile elastic as well as plastic deformation. For instance, one can demonstrate that tensile elastic deformation cannot influence the s.m.a. whereas plastic one leads to an increase in this. Furthermore, one can also predict that increasing permanent (residual) plastic deformation, obtained after unloading from prior tensile loading, leads to an obvious decrease in the s.m.a. Similar decrease in the s.m.a. can also be predicted for increasing rolling deformation by means of the same modelling approach used for the permanent tensile plastic deformation. Owing to the good agreement with the experimental results and the simplicity of the proposed theoretical approaches that can be seen as a promising valuable tool for further similar studies.

Evaluation of the damping capacity of common CAD/CAM restorative materials

ObjectivesTo evaluate and quantify the damping capacities of common CAD/CAM restorative materials (CRMs) and to assess their energy dissipation abilities by comparing loss tangent and Leeb hardness data. MethodsLeeb hardness (HLD), together with its deduced energy dissipation data (HLDdis), and loss tangent values recorded via dynamic mechanical analysis (DMA) were determined for 4 ceramic, 13 composite, and 2 polymer-based CRMs as well as 1 metal. For Leeb hardness, ten indentations per material were performed on two separate specimens (12.0 × 12.0 × 3.5 mm3) after water storage (24 h; 37.0 ± 1.0 °C). For DMA, ten specimens (16.00 × 4.00 × 1.00 mm3 ± 0.05 mm) per material were investigated in distilled water (37.0 ± 0.5 °C) with a dynamic force of 1 N at 1.5 Hz. Each data set was analyzed using two-way analysis of variance (ANOVA) with material type and material nested in material type as factors. Post-ANOVA contrasts were performed using a Bonferroni adjustment for multiple comparisons (α = 0.05). Correlations between different parameters were tested (Pearson, α = 0.05). ResultsHLDdis data revealed the significantly highest damping capacity for metal and the lowest values for ceramics with composites and polymers in between. However, for loss tangent, the metal together with lithium disilicate glass-ceramics exhibited the lowest damping effects and polymer materials the highest results with composites likewise in between. A strong dependency of the loss tangent results on the filler content of the investigated CRMs was indicated (r = - 0.822, p < 0.001), while a positive and only moderate correlation between loss tangent and HLDdis was observed (r = 0.565, p < 0.001), which conversely revealed a very strong correlation (r = 0.911, p < 0.001) if the metal was excluded from the calculation. ConclusionsAlthough HLDdis and loss tangent values both allowed a distinct differentiation of the damping capabilities of various CRMs and the respective material types, HLDdis data appeared to more accurately describe the damping capacity of CRMs as the energy dissipation mechanism of permanent plastic material deformation, that is commonly observed for metals and some composite-based CRMs, is equally captured. This finding could be particularly interesting for the future development of new CRMs with improved mechanical properties as HLDdis data determination in principle is a very efficient and simple technique to entirely specify unknown damping capacities of materials.

A new constitutive model for permanent deformation of blood clots with application to simulation of aspiration thrombectomy

As a first line option in the treatment of acute ischemic stroke (AIS), direct aspiration is a fast and effective technique with promising outcomes. In silico models are widely used for design and preclinical assessment of new developed devices and therapeutic methods. Accurate modelling of the mechanical behaviour of blood clot is a key factor in the design and simulation of aspiration devices. In this study we develop a new constitutive model which incorporates the unrecoverable plastic deformation of clots. The model is developed based on the deformation-induced microstructural changes in fibrin network, including the formation and dissociation of the cross-links between fibrin fibres. The model is calibrated using previously reported experimentally measured permanent clot deformation following uniaxial stretching. The calibrated plasticity model is then used to simulate aspiration thrombectomy. Results reveal that inclusion of permanent plastic deformation results in ∼ 15 % increase in clot aspiration length at an applied aspiration pressure of 100 mmHg. The constitutive law developed in this study provides a basis for improved design and evaluation of novel aspiration catheters leading to increased first-pass revascularization rate.