Local Plastic Research Articles

Geography and developmental plasticity shape post-larval thermal tolerance in the golden star tunicate, Botryllus schlosseri

Local adaptation and phenotypic plasticity play key roles in mediating organisms’ ability to respond to spatiotemporal variation in temperature. These two processes often act together to generate latitudinal or elevational clines in acute temperature tolerance. Phenotypic plasticity is also subject to local adaptation, with the expectation that populations inhabiting more variable environments should exhibit greater phenotypic plasticity of thermal tolerance. Here we examine the potential for local adaptation and developmental plasticity of thermal tolerance in the widespread invasive tunicate Botryllus schlosseri. By comparing five populations across a thermal gradient spanning 4.4° of latitude in the northwest Atlantic, we demonstrate that warmer populations south of the Gulf of Maine exhibit significantly increased (∼0.2 °C) post-larval temperature tolerance relative to the colder populations within it. We also show that B. schlosseri post-larvae possess a high degree of developmental plasticity for this trait, shifting their median temperature of survival (LT50) upwards by as much as 0.18 °C per 1 °C increase in environmental temperature. Lastly, we found that populations vary in their degrees of developmental plasticity, with populations that experience more pronounced short-term temperature variability exhibiting greater developmental plasticity, suggesting the local adaptation of developmental plasticity. By comparing the thermal tolerance of populations across space and through time, we demonstrate how geography and developmental plasticity have shaped thermal tolerance in B. schlosseri. These results help inform our understanding of how species are able to adjust their thermal physiology in new environments, including those encountered during invasion and under increasingly novel climate conditions.

Atomistic simulations of dislocation activity in Si nanofibers in Al-Si eutectics

Atomistic simulations were used to elucidate the mechanisms of localized plasticity and fracture in Si nanofibers embedded in Al matrix, with uniaxial tensile straining along the fiber axis. The Si nanofibers within the Al matrix exhibited large non-linear elastic strains followed by localized plasticity with the latter accounting for approximately 5 % permanent length increase in the fibers. On the other hand, simulations with aligned Si nanofibers in vacuum (no Al matrix) exhibited elastic deformation only followed by cleavage fracture. Localized plasticity in Si nanofibers is accomplished by gliding of “zonal” partial dislocations with Burgers vector b=aSi3〈112〉, which leads to synchronous shear of two shuffle-sets. Local stress concentration in Si nanofibers due to non-screw segments of dislocation loops around fibers triggers yielding in the nanofibers through the activation of dislocation sources at or near the interfaces but only below some critical fiber diameter, highlighting the role of nanoscale refinement in activating plasticity in embedded Si nanofibers in Al matrix. In addition, the kinetic barriers associated with the glide of edge/screw zonal dislocation in the perfect crystal and twinned crystal are computed using climbing-image nudge elastic band method. A higher mobility of the zonal dislocation in the twinned crystal suggests that twin boundaries can assist in dislocation glide parallel to the boundary. On the other hand, a nano-crack is nucleated at the interaction position of a glide partial dislocation with an intersecting growth twin boundary suggesting that intersecting twins serve to block glide and provide sites for crack nucleation.

Ultra-low cycle fatigue evaluation method for unstiffened steel piers using fiber model

The safety of steel bridge piers is threatened by ultra-low cycle fatigue (ULCF) damage, which dominates the failure mode in those with relatively compact section under strong seismic action. Existing methods for calculating such ULCF damage face the dilemma between accuracy and efficiency. To this end, this paper proposes a simplified evaluation method based on fiber model to expediently evaluate the ULCF damage of unstiffened steel piers, evenly with sound precision. Specifically, the average stress triaxiality is assumed as 0.63 for steel piers, and it is validated by cyclic loading experiments with the modified Coffin-Masson formula and solid element sub-model. The disparity between local plastic strain range in fiber and solid models is compensated by introducing a magnified coefficient. The analyzed results indicate the slenderness ratio, axial compressive ratio, especially the flange thickness and the width-to-thickness ratio, strongly influence the strain concentration effect occurring in the pier bottom. In addition, the proposed close equation for the magnified coefficient fits well with the discrete calculated points. The 3.05% mean absolute error is realized on the predicting half cycles when applying this method in random cyclic loading. Its favorable applicability in practical engineering is also verified with considering different ground motion types.

Simultaneous improvement of mechanical strength and corrosion resistance in aluminum alloy 5083 via severe plastic deformation

In this study, the Repeated Upsetting (RU) process as a severe plastic deformation method was performed on the aluminum alloy 5083 (AA5083) to refine the microstructure. The microstructure, mechanical properties, and corrosion behavior of AA5083 before and after applying 1, 3, and 5-pass through the RU process were investigated. Based on the EBSD analysis, the average grain size of AA5083 decreased from 21.9 μm for the base metal (BM) to less than 5 μm for RUed samples. The potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) results have shown that the corrosion resistance of the AA5083 increased after applying the RU process due to the grain refinement and homogenous distribution of the second phase. By increasing the RU passes from 1 to 5, the corrosion rate of AA5083 was enhanced because of rising localized plastic deformation. Scanning electron microscopy and optical microscopy images confirmed the electrochemical results, in which the BM showed a severe corrosion surface compared with the RUed samples. On the other hand, tensile tests confirmed that the maximum improvement in mechanical properties occurred after the first pass. Accordingly, the 1-pass RU product can be an ideal candidate for application under severe corrosive environments and high-loading conditions.

Mechanical Properties of Titanium Grade 1 After Laser Shock Wave Treatment

Abstract In the presented work the impact of a laser shock wave on the mechanical properties of a Titanium Grade 1 was investigated. Based on a series of experimental studies related to the impact of the laser shock wave on the tested material, the impact of the given treatment on the structure and mechanical properties was assessed. The influence of the environment on the distribution of plasma temperature and pressure in the material during the implementation of the laser shock wave was analyzed. The effect of the laser treatment on the structure and micromechanical properties was initially estimated on the basis of the analysis of experimental results in the form of static strength test of samples after laser treatment. A slight increase in material strength was detected with a minimal decrease in ductility. In order to comprehensively understand the observed phenomenon, a number of fractographic tests were performed, especially the analysis of the porosity of the fracture surfaces. A decrease in the porosity of the material after impact laser treatment was observed as a result of local plastic deformation.

Thawed matrix method for computing local mechanical properties of amorphous solids.

We present a method for computing locally varying nonlinear mechanical properties in particle simulations of amorphous solids. Plastic rearrangements outside a probed region are suppressed by introducing an external field that directly penalizes large nonaffine displacements. With increasing strength of the field, plastic deformation can be localized. We characterize the distribution of local plastic yield stresses (residual local stresses to instability) with our approach and assess the correlation of their spatial maps with plastic activity in a model two-dimensional amorphous solid. Our approach reduces artifacts inherent in a previous method known as the "frozen matrix" approach that enforces fully affine deformation and improves the prediction of plastic rearrangements from structural information.

Dislocation Arrangements and Cyclic Microplasticity Surrounding Stress Concentration in a Ni‐Based Single‐Crystal Superalloy

Local cyclic plasticity near stress concentrations governs the fatigue crack initiation in cyclicly loaded Ni‐based single‐crystal superalloys, but has not been well studied and understood. The first of its kind transmission electron microscopy (TEM)‐based site‐specific study of plasticity in the crack initiation region in a notched single‐crystal superalloy subjected to fatigue testing at 800 °C, coupling it with microstructure‐based crystal plasticity modeling, is presented. Detailed TEM examinations show that local plasticity near the notch significantly differs from bulk plasticity, featuring high dislocation densities and distinctive arrangements of dislocation pairs within γ’ precipitates. It further shows that the increased local stresses alone are responsible for the increase in dislocation density and extensive γ’ shearing, but not solely for the distinctive arrangement of dislocation pairs seen in the notch vicinity, thus highlighting the considerable role played by the local variations in loading rates and stress state surrounding the notch. The results of this work provide new fundamental insights into the deformation micromechanisms leading to fatigue crack initiation in single‐crystal superalloys.

Habitat fragmentation affects climate adaptation in a forest herb

Abstract Climate change and the resulting increased drought frequencies pose considerable threats to forest herb populations, particularly where additional environmental challenges jeopardize responses to selection. Specifically, habitat fragmentation may hamper climate adaptation by altering the distribution of adaptive genetic variation and may also induce evolutionary changes in mating systems. To assess how habitat fragmentation disrupts climate adaptation, we conducted a common garden experiment with Primula elatior offspring originating from 24 populations sampled along a latitudinal gradient with varying climate and landscape characteristics. We then quantified a range of vegetative, regulatory and reproductive traits under distinct soil moisture regimes to evaluate imprints of local adaptation and phenotypic plasticity. Additionally, we conducted a more extensive field campaign in 60 populations along the same latitudinal gradient to evaluate the potential evolutionary breakdown of reciprocal herkogamy. For large, connected populations, our results demonstrated an evolutionary shift from a strategy in southern populations that seems aligned with drought avoidance—where plants minimize their exposure to dry conditions and optimize photosynthesis—to a drought tolerance strategy in northern populations, where plants are adapted to function despite water scarcity. However, habitat fragmentation disrupted climate clines and the adaptive responses to drought stress in key traits related to growth, biomass allocation and water regulation. Additionally, our findings indicate the onset of evolutionary breakdown in reciprocal herkogamy and divergence in other key flower traits. The disruption of climate clines, drought responses and adaptations in mating systems contributed to a substantially diminished flowering investment across the distribution range, with the most pronounced effects observed in southern fragmented populations. Synthesis. We present novel empirical evidence of how habitat fragmentation disrupts climate adaptation and drought tolerance in a wide range of traits along the range of the forest herb Primula elatior. These findings emphasize the need to account for habitat fragmentation while designing effective conservation strategies in order to preserve and restore resilient meta‐populations of forest herbs amidst ongoing global changes.

State-of-the-art on microstructural, mechanical and tribological properties of friction stir processed aluminium 2xxx series alloy

As a noble surface modification technique, friction stir processing (FSP) has been established based on the principle of friction stir welding that refines the microstructure and localized plastic deformation of the material. Nevertheless, despite notable technological progress, challenges persist in utilizing FSP to improve material characteristics. This review paper offers a concise overview, summarizing the influence of process parameters on the microstructure mechanical and tribological properties of aluminium alloy subjected to FSP. In particular, the performance of aluminium alloy is discussed about FSP factors such as tool travel speed, rotating speed, reinforcement particles, multiple passes and tool tilt angle. This paper also reviewed the effect of different process parameters on the wear properties, corrosion and tribological characteristics of the processed alloy, which will facilitate researchers and business organizations in creating the needed upgraded composite.

Tailoring of residual stress by ultrasonic vibration-assisted abrasive peening in liquid cavitation of metallic alloys

The present study proposes a novel method of ultrasonic vibration assisted-abrasive peening for the enhancement of residual stress on the surface of metals and their alloys. The system employs a vibrating sonotrode that drives the formation and collapse of bubbles within a fluid medium. The imploding bubbles produce pressure waves which transfer momentum to the abrasives which are uniformly distributed in the fluid medium. The abrasives bombard a targeted surface along with intense pressure waves. This induces compressive residual stress through local plastic deformation in a short period. The capability of the ultrasonic-assisted abrasive peening setup is analysed in terms of residual stress by altering the abrasive concentration, peening time, and stand-of-distance between the bottom of the sonotrode and the exposed surface to be treated. The process is able to induce significant residual stress at around 67 % of yield strength for hard material Ti–6Al–4V and more than 80 % of yield strength for ductile materials, Al-6061 and OFHC-Cu. A numerical method coupled with a finite element model is employed to predict the dynamics of the process from cavitation of the bubble to the plastic deformation of the work material. At first, the model estimates the magnitudes of high-pressure waves at the bubble implosion near the solid surface, micro-jet velocity, and abrasive velocity. This information is then fed to Abaqus for numerical modelling of the deformation of work material. The impact of high-speed abrasives in the range of 100 m/s, pressure waves and microjets at the material surface are simulated through the FE model. The simulated results are verified with experimental findings in terms of surface residual stress for different materials, deviating within 10 %.

Cyclic degradation mechanisms of Al0.3CoCrFeNi high-entropy alloy under different loading rates

The effect of loading rate on the cyclic degradation behavior of Al0.3CoCrFeNi high-entropy alloy (HEA) was investigated through nanoindentation experiments and molecular dynamics simulations. The evolution of mechanical properties and microstructure characteristics under different loading rates, as well as the mechanisms of cyclic degradation, were revealed. It is found that the increase of the loading rate induces higher hardness and smaller nanoindentation depth of the Al0.3CoCrFeNi HEA, which gradually increases with the cyclic loading of nanoindentation, resulting in a larger difference in characteristic nanoindentation depth among different loading rates. What’s more, a larger loading rate is inclined for nanoindentation depth to reach a steady state. Slip lines and pile-ups are formed around the nanoindentation region at higher loading rates indicating the occurrence of a more localized plastic deformation, while an amorphous transformation occurs at different loading rates after cyclic nanoindentation. Cyclic loading results in the gradual accumulation of residual stress, nanoindentation depth and amorphous structures within the material, and a localized plastic deformation. In summary, cyclic degradation of the Al0.3CoCrFeNi HEA is featured by cyclic softening due to dislocation slipping and the accumulation of amorphous phases.

Experimental investigation and micromechanics-based constitutive modeling of the transition from brittle to ductile behavior in saturated low-porosity rocks

This paper presents a unified experimental and numerical investigation on the transition from brittle to ductile behavior in a low-porosity sandstone under drained conditions. The experimental results demonstrate a transition in the mechanical behavior from brittle faulting to dilatant ductile flow at room temperature with an increase in effective confining pressure, suggesting that microcracking-controlled local friction is the underlying plastic deformation mechanism. For constitutive modeling, the sandstone is considered as a heterogeneous medium composed of a pores-weakened elastic solid matrix and distributed microcracks. By following a two-step homogenization procedure and irreversible thermodynamics framework, a micromechanics-based elastoplastic damage model incorporating a non-associated local plastic flow rule is formulated, in which the coupling between plasticity, damage and pore pressure is taken into account. In this context, a non-associated macroscopic effective strength criterion as an inherent part of the corresponding model is derived. Originally, a theoretical linear relation between critical state of damage at peak strength and effective confining pressure is established, which is efficient in describing post-peak softening behavior. Comparisons of numerical simulations with experimental data demonstrate that the proposed model effectively reproduces the main features of the sandstone with a brittle-ductile transition.

Spatial and seasonal variation in thermal sensitivity within North American bird species.

Responses of wildlife to climate change are typically quantified at the species level, but physiological evidence suggests significant intraspecific variation in thermal sensitivity given adaptation to local environments and plasticity required to adjust to seasonal environments. Spatial and temporal variation in thermal responses may carry important implications for climate change vulnerability; for instance, sensitivity to extreme weather may increase in specific regions or seasons. Here, we leverage high-resolution observational data from eBird to understand regional and seasonal variation in thermal sensitivity for 21 bird species. Across their ranges, most birds demonstrated regional and seasonal variation in both thermal peak and range, or the temperature and range of temperatures when observations peaked. Some birds demonstrated constant thermal peaks or ranges across their geographical distributions, while others varied according to local and current environmental conditions. Across species, birds typically demonstrated either geographical or seasonal adaptation to climate. Local adaptation and phenotypic plasticity are likely important but neglected aspects of organismal responses to climate change.

Quantitative analysis of local plasticity accompanying hydrogen-related fracture in low-carbon martensitic steel

In this study, the local plasticity accompanying hydrogen-related fracture in a low-carbon martensitic steel was quantitatively investigated by correlative microscopy analysis combining digital image correlation technique and electron backscatter diffraction. The results revealed that strain localization occurred mainly in the bulk of martensite blocks and at prior austenite grain boundaries, both with and without the presence of hydrogen. Moreover, hydrogen enhanced strain localization during deformation and facilitated crack nucleation and propagation. The quantitative analysis showed that the hydrogen-related quasi-cleavage cracking was closely related to the local plastic deformation, and increasing hydrogen content decreased the local strain level required for quasi-cleavage cracking. It was found that strain localization also occurred around the intergranular cracks, suggesting that hydrogen-induced intergranular cracking was not a classical simple decohesion process and strain localization was involved in the sequence of hydrogen-induced intergranular cracking. These findings shed light on the understanding of the intrinsic nature of hydrogen embrittlement.

Clayey Soil Improvement with Polyethylene Terephthalate (PET) Waste

Population expansion and the development of technology have led to an increase in construction activities. In many cases, foundation grounds do not have a high enough bearing capacity and are not capable of ensuring the safe exploitation of the construction. A soil with poor mechanical characteristics must be improved using various methods, such as adding hydraulic binders (lime and cement), natural fibres, or more recently, plastic waste materials. This work aims to study the behaviour of plastic waste materials made from polyethylene terephthalate (PET) in soil improvement. Thus, the mechanical characteristics of a clay improved with shredded PET were studied. PET was added in relation to the dry mass of the clay, in percentages of 2%, 4% and 6%. The studied clay was collected from a construction site around Cluj-Napoca, Romania, from a depth of 1 ÷ 10 m. PET was provided by a local plastic waste repository. It comes from recycled water, beer and soda bottles and was cleaned using specific methods for cleaning and recycling plastic waste. PET was shredded into irregular shapes with sizes ranging from 3 mm to 12 mm and was randomly distributed in the test specimens. Compression and direct shear tests were carried out to study the compressibility and shear parameters of the improved soil (internal friction angle and cohesion). The experimental results showed an improvement in the mechanical characteristics of the clay even at a low PET addition of 2% and 4%. This method can contribute to solving two current problems of the modern world: reducing pollution by recycling plastic waste materials and using them to improve the mechanical characteristics of soil.

Rolling contact fatigue failure mechanism of bearing steel on different surface roughness levels under heavy load

It is inherent knowledge that rolling contact fatigue (RCF) failure of subsurface-initiated spalls usually occur under optimum surface under heavy load. However, our previous work has revealed surface-initiated RCF failure mechanism under heavy load and initial high roughness surface. The formation of surface crack caused by RCF is a complicated phenomenon that is accompanied by surface morphology and lubrication condition, as well as stress distribution and microstructure evolution. To clarify the main failure mechanism, this study carried out systematic RCF tests with different surface roughness specimens and conducted characterization of superficial microstructure for specimens of pre-service and post-service by Focused Ion Beam (FIB). The results clearly suggest precursor of collapsed morphology and nanocrystalline layer are the main factor that causes the RCF life with high roughness is lower than that with low roughness. While the spalling failure initiating from low roughness surface under heavy load are strongly relied on surface plastic deformation. Two main plastic deformation mechanisms are conductive to formation of surface cracks: the micro-plastic deformation and the local severe plastic flow. A newly failure mechanism that spalling failure initiates from surface has been proposed to link surface roughness and microstructure evolution.

Investigation of Passive Pile Groups’ Responses Induced by Combined Surcharge-Induced and Excavation-Induced Horizontal Soil Loading

Excessive lateral forces and the deformation of pile groups caused by adjacent surcharge loading and excavation can potentially lead to the failure or collapse of nearby pile foundations. This paper presents a simplified analytical method to investigate the lateral displacement of passive pile groups caused by combined surcharge-induced and excavation-induced horizontal soil loading and validates it by utilizing two published centrifuge tests and numerical modeling. Firstly, the passive load resulting from surcharge-induced horizontal soil loading is determined using the improved formula of Boussinesq and the theory of local plastic deformation. The additional horizontal force exerted on the pile axis subjected to excavation-induced horizontal soil loading is also taken into account using the Mindlin solution. Furthermore, the shielding effect between pile groups is also proposed to analyze the response of a laterally loaded pile group due to excavation unloading. Secondly, according to the Pasternak foundation model of soil–pile interaction, the equilibrium differential equations are solved by the finite difference method. Finally, parametric analyses are undertaken to evaluate the behavior of different constraints on the pile head and surcharge procedure. The results demonstrate that the capped-head pile groups can provide greater restraint compared to the free-head groups for the lateral displacement of pile groups. The front pile experiences greater forces than the rear one in passive pile groups as a result of the smaller soil pressure on the rear pile. Additionally, increasing the horizontal stiffness of the capped head with fully fixed ends can significantly decrease the horizontal deformation of the pile groups.

A Small-Deformation Rate-Independent Continuous-Flow Model for Elasto-Plastic Frames Allowing Rapid Fatigue Predictions in Metallic Structures

Fatigue analysis in metallic frame structures can be challenging due to associated computational costs; if localized plasticity is involved, then the approach of three-dimensional (3D) continuum plasticity models for direct computation of stresses will be infeasible for the analysis of cyclic loading that would need to be modeled in medium- to high-cycle fatigue and vibratory fatigue applications. This difficulty is particularly accentuated in architected structures, for which high-resolution 3D finite element analysis (FEA) would be prohibitively expensive. In this work, we propose an alternative approach based on the use of novel elasto-plastic frame model with continuous flow (i.e. no sharp yield function) for modeling 3D frame and lattice structures. Rather than splitting the strains (as is done in classical plasticity) we split the deformation measures, extension, curvature and twist, into elastic and plastic components and postulate a rate type evolution rule for the plastic variables in terms of the stress resultants (axial force, bending moment, and torque). The combination of structural models together with the use of elasto-plastic operator split to solve the resulting boundary value problem allows for much faster determination of localized plasticity than continuum models can provide. The use of a continuous transition from elastic to rate-independent plasticity (as opposed to an abrupt change with classical plasticity models) allows us to capture localized microplasticity and determine resulting fatigue progression using a cycle-count-free, plastic work-based approach, formulated in terms of the curvatures and resultants. We demonstrate that (a) the model is able able to reproduce the response of 3D FEA with very few elements and (b) the model has the ability to rapidly predict the fatigue life under variable amplitude combined loading with relatively few frame elements.

Evaluation of process parameter of friction stir processing of AA2024-T351 Alloy using RSM and GRA

A fundamental method for changing the characteristics of metals through localised severe plastic deformation is friction stir processing (FSP), which is both straightforward and efficient. Because of its high strength-to-mass ratio and resilience to fatigue, aluminium alloy 2024 is commonly utilised. The experiments were designed utilising the Box–Behnken method and the process parameters’ chosen range values. In this research, the impact of FSP process variables on the tensile, surface roughness, and hardness properties of AA2024 will be examined. These parameters include tool rotation speed, welding speed, and axial load. The base sample tensile strength, surface roughness and microhardness values were 325 MPa, 0.5125 μm, and 120 HV. The optimised sample’s maximum tensile strength, minimum surface roughness, and maximum microhardness values were 420 MPa, 0.4 μm, and 144 HV. The grey relational analysis (GRA) determines the ideal combination of process parameter values for the best values in all responses. XRD was used to assess residual stress, dislocation density and micro-strain. The optimal process parameters have been obtained at a rotational speed of 1000 rpm, traverse speed of 45 mm/min, and axial load of 10.25 kN.

Insights into building a digital twin of closed-cell aluminum foam during impact loading: Microstructural, experimental and finite element investigations

The mechanical behavior of metal foams under impact loading depends on multiple and complex parameters like impact velocity, strain-rate, local plastic deformation, oscillating and micro-inertial effects, etc. The prediction of the behavior of metal foams that are subject to impact loads is still challenging and engineering application of these materials typically requires time-consuming experimental tests. Numerical models based on the finite element method (FEM) can contribute to minimizing the experimentation effort. Realistic FEM models were built that account both for the macro- and micro-scopic characteristics of the porous material, explain the acting mechanisms that take place during impact, and study the yield properties as well as the energy absorption during the impact of closed-cell aluminum foams. The simulation results are compared with the ones derived from respective experimental uniaxial tests. Two different modeling approaches were applied thus creating two models. The first model relies on a cell-based method where the initial geometry of the foam was generated based on the Voronoi tessellation algorithm and the second one relies on the isotropic, strain-hardening, and continuum-based model developed by Deshpande-Fleck. The outcome of the investigation sheds light on the metal foam behavior under impact by explaining macro- and micro-structural phenomena that develop during impact.