Permanent Plastic Deformation Research Articles

Reliability and durability assessment of bridge stay cables

AbstractAn algorithm for the reliability and durability assessment of stay cables in bridges is presented in this study enabling their probability of failure and a safe working period to be determined under various loading scenarios. The algorithm was originally developed based on data collected from an extensive structural monitoring campaign of the biggest single-pylon concrete cable-stayed bridge in Poland and used to assess the durability of its suspension system. It was then modified to be suitable for the evaluation of stay-cables subjected to wind excitation and structural reliability of the suspension system in a real steel bridge where permanent plastic deformations occurred in the anchor zones of the stay cables. The algorithm takes into account analytical models describing the stay cables and their numerical finite element models (FEM). As such, it is a universal tool having a wide range of applications, also beyond stay cables often encountered in medium- and long-span bridges forming a critical part of the civil engineering infrastructure.

Study on the composition and properties of EME-SBS-Nano ZnO high modulus asphalt material

The objective of this research is to address the rut problems in asphalt pavements and to resist the permanent plastic deformation with the increasing heavy traffic loads. In this paper, a new type materials of high modulus asphalt was developed by incorporating styrene–butadiene–styrene (SBS) and zinc oxide nanoparticles (nano ZnO) with an (EME)-type high modulus modifier, guided by the synergistic effects and the preparation methods of High-speed shear. The basic road performance, mechanical response and thermal stability of the new high modulus asphalt materials were analysed through basic physical indicator tests, dynamic shear rheometer tests, thermogravimetric analysis (TGA), the time–temperature superposition principle, the Refutas model, and the Christensen-Andersen-Marasteanu model. The optimal results demonstrate that the optimal blend ratio of the developed asphalt is 12% EME/8% SBS/1.5% ZnO. Under this composition, the road performance indicator values of softening point, penetration and ductility of the modified asphalt met the standard requirements. The dynamic shear rheometer tests demonstrates that the inclusion of SBS and nano ZnO considerably enhanced the shear resistance and recovery deformation capacity of EME, effectively improving the high-temperature deformation resistance of asphalt. Furthermore,the Refutas and the Christensen-Andersen-Marasteanu model fitting results showed that adding SBS and nano ZnO considerably improved the temperature sensitivity of the EME types high modulus modified asphalt and exhibiting low frequency sensitivity. Compared to PR Module-type high modulus modifier(PRM),TGA reveals that the maximum thermal weight loss of EME-SBS-ZnO decreased by 3.5441%, indicating better thermal stability and the major character of SBS,EME and asphalt is physical reaction. Moreover, EME-nano ZnO-SBS high modulus asphalt at 64 °C shows Jnr-diff = 9.5% and passes the "E" extreme traffic grade. Additionally, its cost is 4.67% lower than that of the PRM high modulus modified asphalt, presenting considerable economic benefits.

Experimental and Numerical Insights into the Multi-Impact Response of Cork Agglomerates

Due to their extraordinary qualities, including fire resistance, excellent crashworthiness, low thermal conductivity, permeability, non-toxicity, and reduced density, cellular materials have found extensive use in various engineering applications. This study uses a finite element analysis (FEA) to model the dynamic compressive behaviour of agglomerated cork to ascertain how its material density and stress relaxation behaviour are related. Adding the Mullins effect into the constitutive modelling of impact tests, its rebound phase and subsequent second impact were further examined and simulated. Quasi-static and dynamic compression tests were used to evaluate the mechanical properties of three distinct agglomerated cork composite samples to feed the numerical model. According to the results, agglomerated cork has a significant capacity for elastic rebound, especially under dynamic strain rates, with minimal permanent deformation. For instance, the minimum value of its bounce-back energy is 11.8% of the initial kinetic energy, and its maximum permanent plastic deformation is less than 10%. The material’s model simulation adequately depicts the agglomerated cork’s response to initial and follow-up impacts by accurately reproducing the material’s dynamic compressive behaviour. In terms of innovation, this work stands out since it tackles the rebounding phenomena, which was not previously investigated in this group’s prior publication, either numerically or experimentally. Thus, this group has expanded the research on cork materials’ attributes.

Assessment of various polymeric sulphur as soft bitumen improver for pavement applications

ABSTRACT In this study, five polymeric sulphurs are utilised, including polymeric sulphur based on both aliphatic copolymers and styrene copolymers, namely PS1 to PS5 correlated to amorphous poly alpha olefins (APAO) PS1, olefin residues from MAC carpet company PS2, Ethylene Vinyl Acetate (EVA) copolymer PS3, Styrene Butadiene Styrene (SBS) copolymer PS4 and Dicyclopentadiene monomer (DCPD) PS5. The five polymeric sulphur compounds were mixed by 25wt% with soft bitumen penetration grade (80/100) to produce five sulphur-extended asphalt binders, namely SEA1, SEA2, SEA3, SEA4, and SEA5. The physical properties, including softening point, viscosity, and penetration, are examined to characterise the consistency of SEA binder. The dynamic mechanical behaviour such as complex modulus, temperature sweep, and stress relaxation test was investigated for SEA binder and compared with a reference soft bitumen (Blank) using a dynamic mechanical analyzer (DMA). It is concluded that polymeric sulphur based on styrene compounds SEA2 and SEA4 binders have the highest resistance against cracking of the pavement at low temperatures according to penetration index readings, and have the least permanent (plastic) deformation at high temperatures according to temperature sweep from DMA data. It is noticed that SEA5 binder has a negative effect on the performance of soft bitumen.

Dynamic response mechanisms of thin UHMWPE under high-speed impact

This study systematically explores the dynamic response mechanisms and energy dissipation mechanisms of ultra-high-molecular-weight polyethylene (UHMWPE) fiber laminated plates with thicknesses of 1.1 mm, 2.8 mm, and 5.4 mm under high-speed steel ball impacts through experimental, theoretical analysis, and dimensional analysis. By analyzing the damage mechanisms from experimental results, the main modes of energy absorption were identified, and a relatively accurate predictive model for ballistic limit speed was established. The results show that under high-speed steel ball impacts, the primary failure modes of UHMWPE fiber laminated plates are localized permanent bulging plastic deformation and perforation failure caused by compressive shear. The ballistic limit speeds for UHMWPE with thicknesses of 1.1 mm, 2.8 mm, and 5.4 mm are respectively 233.5 m/s, 415.7 m/s, and 602.9 m/s. The theoretical calculations of the energy model align well with the experimental results, indicating that as the speed increases, the proportion of tensile energy absorption gradually decreases, consistent with the observed phenomena. Near the ballistic limit, there are significant turning points in the level of energy absorption and the height of the rear bulge. The ballistic limit increases linearly with target thickness, and the unit area density energy absorption also increases continuously. Finally, this study established a dimensionless ballistic limit model considering the mechanical properties of fibers and the matrix, which through regression analysis, can accurately describe the ballistic limits of various strengths and types of fiber laminated plates, suitable for predicting the ballistic performance of various composite materials.

Penetration resistance of Al2O3 ceramic-ultra-high molecular weight polyethylene (UHMWPE) composite armor: Experimental and numerical investigations

To enhance the protective performance of ceramic composite armor, ballistic penetration experiments were conducted on Al2O3 ceramic-ultra-high molecular weight polyethylene (UHMWPE) composite armor with different thickness configurations. The damage and failure modes of hard projectiles and ceramic-fiber composite targets were analyzed. The recovered projectiles and ceramic fragments were sieved and weighed at multiple stages, revealing a positive correlation between the degree of fragmentation of the projectiles and ceramics and the overall ballistic resistance of the composite targets. Numerical simulations were performed using the LS-DYNA finite element software, and the simulation results showed high consistency with the experimental results, confirming the validity of the material parameters. The results indicate that the projectile heads primarily exhibited crushing and abrasive fragmentation. Larger projectile fragments mainly resulted from tensile and shear stress-induced failure. The failure modes of the composite targets included the formation of ceramic cones and radial cracks under high-velocity impacts. The UHMWPE laminated plates exhibited interlayer separation caused by tensile waves, permanent plastic deformation of the rear surface bulging, and perforation failure primarily due to shear forces.Through extended numerical simulations, while maintaining the same areal density and configuration of 9 mm Al2O3 ceramic + 12 mm UHMWPE laminated composite armor, the thickness configurations of the Al2O3 ceramic and UHMWPE laminated backplates were varied, and various thicknesses of UHMWPE laminates were simulated as the cover layer for the ceramic panels. The simulation results indicated that the composite armor configuration of 10 mm Al2O3 ceramic + 8 mm UHMWPE composite armor increased energy absorption by 13.48 %. When altering the cover layer thickness, a 4 mm UHMWPE + 9 mm Al2O3 + 8 mm UHMWPE composite armor demonstrated a 27.11 % improvement in energy absorption, showing a relatively significant enhancement.

Nanostructured amorphous Al2O3-ZrO2 (La2O3) ceramics with plastic deformation via interface inducing hierarchical shear bands

Ionic-bonded ceramics are featured by their thermal stability, corrosion resistance, hardness and strength, but their applications are limited by the inherent brittleness. Ceramics are composed of strong chemical bonding and intricate crystal structures, making plastic deformation by dislocation slip highly challenging. A nanostructured amorphous Al2O3-ZrO2 ceramic comprising nanoscale amorphous particles and amorphous interfaces between particles was achieved in practice, where the amorphous interface is in scale of approximately 2.34 nm and amorphous particles is in width of approximately 6.75 nm. Based on nano-indentation tests, the shear transformation zone (STZ) volumes of nanostructured amorphous ceramics hot-pressed under various conditions are calculated, suggesting attenuation of free volume with the increase in pressure and temperature. The medium-temperature compression test of the samples exhibits a permanent plastic deformation of 14.6 %, with the presence of hierarchical shear bands in the deformed samples. The main shear bands (MSBs) in width of 0.84–9.15 μm are generated by the stress concentration in crystal-amorphous interface, and the small shear bands (SSBs) of 31–428 nm are related to abundant free volumes in the interface between amorphous particles.

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.