Internal Strain Energy Research Articles

Development of a new generation of quench and partitioning steels: Influence of processing parameters on texture, nanoindentation, and mechanical properties

A novel quenching and partitioning process (Q&P) including the hot stamping (HS) process was studied, using two stamping temperatures (750 °C and 800 °C) and two quenching temperatures (318 °C and 328 °C). This combination is here called Hot Stamping and Quenching and Partitioning process (HSQ&P). The partitioning step was performed at 400 °C for 100 s in all cycles. Microstructural features were comprehensively studied using electron backscattered diffraction and nanoindentation techniques. HSQ&P samples showed a good combination of ductility and high-strength due to the presence of: retained austenite, inter-critical ferrite with low stored internal strain energy, grain refinement via DIFT-effect (deformation induced ferrite transformation), martensite, and bainite. Significant internal stress relief was caused by carbon partitioning, which was induced by the DIFT-effect and the partitioning stage. This also led to a considerable stored energy, which was characterized by the Kernel average dislocation and geometrically necessary dislocation analysis. In addition, predominant {110}//strain direction crystallographic texture was identified, which promotes slip deformation and enhances the mechanical properties. Moreover, remarkable amounts of fine film-like retained austenite oriented along compact crystallographic directions (i.e., 〈111〉 and 〈112〉) were observed. Finally, subsize tensile test verified the optimum mechanical behavior of HSQ&P specimens.

Role of omega phase evolution in plastic deformation of twinning-induced plasticity β Ti–12V–2Fe–1Al alloy

The evolution of the ω phase and its role in plastic deformation in a twinning-induced plasticity β Ti–12 V–2Fe–1Al alloy aged at 373–573 K have been studied in this work. The results show that isothermal ω forms at about 398 K and above, and the growth of isothermal ω is accompanied by a rejection of solute atoms from ω into β. The composition partitioning increases internal elastic strain energy and hydrostatic pressure resulting from the coherency of isothermal ω phase in β. Moreover, the isothermal ω phase becomes hard and even undeformable due to composition partitioning based on first-principles calculations. It is suggested that the internal elastic strain stabilizes the β phase, which suppresses {332} deformation twinning and leads to dislocation glide and stress-induced ω phase transformation in the alloy aged at low temperature. And the embrittlement of the alloy aged at high temperature is thought to arise from undeformability of isothermal ω phase.

Effect of Rolling Temperature on the Microstructural Characteristics of High-Speed-Rolled Mg Alloy with Initial Non-Basal Texture

In this study, the effects of rolling temperature on the microstructural characteristics of a highspeed-rolled Mg alloy with a non-basal texture were investigated. To this end, commercial AZ31 alloy samples in which the basal poles of most grains were tilted at an angle of 45° from the normal direction (ND) to the transverse direction were hot-rolled with a rolling reduction of 80% at a rolling speed of 470 m/min at various temperatures (300 °C, 350 °C, and 400 °C). With increasing rolling temperature, the area fraction of dynamically recrystallized (DRXed) grains increased and the internal strain energy accumulated in the rolled material decreased. This is attributed to the occurrence of homogeneous nucleation throughout the material at higher temperatures. When the rolling temperature increased from 300 °C to 350 °C, the area fraction of coarse unDRXed grains decreased, but the size of the relatively fine DRXed grains increased. Consequently, the average grain size of the rolled material remained nearly unchanged. However, when the rolling temperature increased from 350 °C to 400 °C, the size of the DRXed grains increased considerably owing to enhanced grain growth behavior. This increase led to an increase in the average grain size of the rolled material. The basal poles of the high-speed-rolled materials were mainly tilted 25° - 29° from the ND. This indicates that application of single-pass high-speed rolling causes the non-basal texture of the initial material to transform into a basal texture similar to the typical texture of rolled Mg alloys. Key words: Mg alloy, high-speed rolling, rolling temperature, texture, dynamic recrystallization, microstructure

SUBSEA PIPELINE PROTECTION DESIGN SUBJECTED TO DROPPED ANCHOR USING CONCRETE MATTRESS

Out of the many potential hazards, certain critical possible hazards need to be assessed, and actions need to be taken to improve the probabilities and consequences to an acceptable degree. One of the major hazards commonly found in subsea pipeline operations is a dropped anchor, especially for pipelines located near jetties, where many ships are expected to move across the pipeline. One of the possible protection methods is the use of a concrete mattress. The dropped anchor hazard to a pipeline is characterized by the impact of energy, which will mostly be absorbed by the internal strain energy of the pipeline. The safety criteria for a pipeline subjected to a dropped anchor are given by DNV RP-F107 for the maximum dent depth and DNV OS-F101 for the maximum stress. A finite element analysis using ANSYS software was performed to obtain the maximum equivalent stress and dent depth for a pipeline. The effects of the length and height of a concrete mattress in redistributing the impact energy were obtained.

Factors Stabilizing β-Sheets in Protein Structures from a Quantum-Chemical Perspective.

Protein folds are determined by the interplay between various (de)stabilizing forces, which can be broadly divided into a local strain of the protein chain and intramolecular interactions. In contrast to the α-helix, the β-sheet secondary protein structure is significantly stabilized by long-range interactions between the individual β-strands. It has been observed that quite diverse amino acid sequences can form a very similar small β-sheet fold, such as in the three-β-strand WW domain. Employing "calibrated" quantum-chemical methods, we show herein on two sequentially diverse examples of the WW domain that the internal strain energy is higher in the β-strands and lower in the loops, while the interaction energy has an opposite trend. Low strain energy computed for peptide sequences in the loop 1 correlates with its postulated early formation in the folding process. The relatively high strain energy within the β-strands (up to 8 kcal mol-1 per amino acid residue) is compensated by even higher intramolecular interaction energy (up to 15 kcal mol-1 per residue). It is shown in a quantitative way that the most conserved residues across the structural family of WW domains have the highest contributions to the intramolecular interaction energy. On the other hand, the residues in the regions with the lowest strain are not conserved. We conclude that the internal interaction energy is the physical quantity tuned by evolution to define the β-sheet protein fold.

Effect of beam joinery on bridge structural stability

In this paper, we analyze the load deflection behavior of the superstructure elements of beam bridges under two different beam–beam connection designs. We present a mathematical model for beam–bridge structural analysis and apply the finite element method to solve the problem. We investigate the effects of beam–beam connection design on the response and behavior of the bridge system. We also present the effect of live-loads and dead-loads on structural deformation, stress, and internal strain energy. We perform computer modeling of the beam bridge using ANSYS 19.2.

Grain size effect on twinning and annealing behaviors of rolled magnesium alloy with bimodal structure

Many wrought Mg alloys, which are manufactured by hot forming processes, have an inhomogeneous grain structure with locally different grain sizes. In the present study, variations in twinning and annealing behaviors caused by the difference in grain size within a material were investigated by subjecting a rolled Mg alloy with a bimodal grain structure to precompression and subsequent annealing. Activation of {10-12} twinning during precompression was found to be more pronounced in the coarse-grain region (CGR) than in the fine-grain region (FGR) owing to a lower twinning stress in the former. As a result, the twin structure formed in the FGR was distinctly different from that in the CGR; the CGR had a larger twinned area, stronger twin texture, fewer twin boundaries, and weaker grain refinement effect than the FGR. During the subsequent annealing, the microstructure of the FGR was greatly altered through grain growth driven by strain-induced boundary migration on account of its high internal strain energy, whereas that of the CGR remained nearly unchanged owing to its relatively lower internal strain energy. Consequently, the microstructural differences between the FGR and CGR induced by the precompression almost disappeared due to the subsequent annealing treatment, which resulted in a homogeneous microstructure.

Multi-objective topology optimization using the Boundary Element Method

This article aims to explore the application of an evolutionary optimization technique for multi-objective optimization problems using as criteria the minimization of von Mises maximum stress and minimization of the maximum growth of internal structural strain energy. To evaluate the overall effect on the optimal design configuration, due to the removal of inefficient material from the structure by using these two optimization criteria, a goal weighting scheme is adopted, whereby the weight factors emphasize and balance the stress and strain energy criteria. Also considered in this study was the method of the exponentially weighted criterion for multi-objective optimization and the Pareto optimal concept. Thus, a contribution is made to the study of these two methods in the structural optimization procedure using a linear analysis by the Boundary Element Method. Four examples are presented to demonstrate the ability of the proposed method to solve structural design problems using multi-objective optimization.

Simulation of Delamination Growth at CFRP-Tungsten Aerospace Laminates Using VCCT and CZM Modelling Techniques

Delamination analysis in advanced composites is required for the laminate design phase and also during the operation of composite aerospace structures to estimate the criticality of flaws and damage. The virtual crack closure technique (VCCT) and cohesive zone modelling (CZM) have been applied to delamination simulation as numerical tools of crack modelling. VCCT and CZM have their unique advantages and disadvantages per application. This study focuses on the application of VCCT to a brittle delamination in a hybrid tungsten–carbon-fibre reinforced composite (CFRP-W) and pursues to identify the challenges due to very high internal residual stresses and strain energy as well as unstable crack propagation. The CFRP-W composites have application areas in high-performance, light-weight radiation protection enclosures of satellite electronics and ultra-high frequency (e.g. 5G) systems. In our work, we present the effects of free-edge stress concentrations and interfacial separation prior to nodal release on a combined VCCT-CZM model and compare the results to pure VCCT and CZM models of the interfacial crack. Parameter notes are given based on the results to apply the combined method for delamination analyses with interfaces heavily loaded by internal residual strains.

Dynamic deformation behavior and microstructural evolution during high-speed rolling of Mg alloy having non-basal texture

The dynamic deformation behaviors and resultant microstructural variations during high-speed rolling (HSR) of a Mg alloy with a non-basal texture are investigated. To this end, AZ31 alloy samples in which the basal poles of most grains are predominantly aligned parallel to the transverse direction (TD) are subjected to hot rolling with different reductions at a rolling speed of 470 m/min. The initial grains with a TD texture are favorable for {10–12} twinning under compression along the normal direction (ND); as a result, {10–12} twins are extensively formed in the material during HSR, and this consequently results in a drastic evolution of texture from the TD texture to the ND texture and a reduction in the grain size. After the initial grains are completely twinned by the {10–12} twinning mechanism, {10–11} contraction twins and {10–11}-{10–12} double twins are formed in the {10–12} twinned grains by further deformation. Since the contraction twins and double twins have crystallographic orientations that are favorable for basal slip during HSR, dislocations easily accumulate in these twins and fine recrystallized grains nucleate in the twins to reduce the increased internal strain energy. Until a rolling reduction of 20%, {10–12} twinning is the main mechanism governing the microstructural change during HSR, and subsequently, the microstructural evolution is dominated by the formation of contraction twins and double twins and the dynamic recrystallization in these twins. With an increase in the rolling reduction, the average grain size and internal strain energy of the high-speed-rolled (HSRed) samples decrease and the basal texture evolves from the TD texture to the ND texture more effectively. As a result, the 80% HSRed sample, which is subjected to a large strain at a high strain rate in a single rolling pass, exhibits a fully recrystallized microstructure consisting of equiaxed fine grains and has an ND basal texture without a TD texture component.

Rheological model incorporating gap element

Viscoelastic materials undergo creep due to elasticity and viscosity, two intrinsic material characteristics, and a representative rheological model can be constructed for creep behavior analysis. Based on the viscoelasticity theory, this model simulates creep by formalizing elastic and viscous deformations in spring and dash-pot elements, respectively. However, most materials have internal gaps caused by the generation process, changes in the internal or external stress, etc. In this paper, a rheological model is proposed in which a gap is introduced; hence, the phenomenological behaviors are formalized using spring, dash-pot, and gap elements. The gap element has strain, but no material property. The opening or closing of the gap according to time history influences the structural changes in the model. Owing to the gap element, the energy due to external forces is dissipated before the gap is closed. After the gap is closed, it is converted and stored as internal strain energy in the spring element, which causes creep recovery. The proposed rheological model has two types, which depend on the element combination. Further, a generalized model is obtained by constructing n models on the basis of the element material properties. To validate the proposed rheological model for various stress conditions, the results predicted by three creep models (the proposed model, Burgers model, and the step-by-step method) are compared with the previously experimental results of concrete specimens because there is a large difference between the evaluations of internally stored strain energy by the creep prediction models. Analysis of a stepwise loading case and an unloading case reveal the following characteristics and mechanism of the model. When additional stress is applied, the principle of superposition is not applied to the proposed model. Instead, the model predicts creep by considering the linearity and structural change of each element. In addition, the proposed model simulates creep recovery and permanent strain more precisely compared to other creep models, which occur due to stress removal, by considering the structural change caused by the gap.

Plant leaf-mimetic smart wind turbine blades by 4D printing

Scientists have reported that plant leaf veins grow into an optimized architecture not only to accomplish their biological and physiological functions but also to sustain the environmental loads. Researchers showed that the wind blade mimicking the leaf architecture could always have relatively lower internal strain energy, better static strength and stiffness, smaller stress intensity, and higher fatigue life compared with the conventional blade structures. However, the plant leaf-mimetic wind blade has so far remained at the level of simulations. Here, a new paradigm for design and fabrication of wind blades is demonstrated by 4D printing process, which combines several beneficial attributes in one blade. The proposed blade having the plant leaf structure can show reversible bend-twist coupling (BTC). It does not rely on conventional electromechanical systems such as sensors and actuators to determine proper deflection and change its shape. Additionally, the existing blades capable of BTC through passive methods have inherent flutter instability since they need to be flexible. The proposed blade may solve the flutter challenge. Lastly, this multi-functional blade can lead to eco-friendly wind turbines. Wind-tunnel tests, CFD, and performance analysis are performed on the proposed blade to demonstrate its applicability. • This study demonstrates the plant leaf-mimetic wind blade structure “in practice”. • We organized various shape-shifting behaviors in wind blades and their advantages. • This blade may solve flutter issue seen in existing passive blades capable of BTC. • Wind tunnel tests, CFD, and performance analysis are done on the proposed blade. • This multi-functional 4D printed blade can lead to eco-friendly wind turbines.

Impact Damage of Aero Engine after UAV Ingestion

With the popularization of UAV in the dramatic domain, the accidents and incidents of UAV threatening civil aircraft has often occurred. The study of the UAV impacting on the critical parts of aircraft has become a new issue in aviation safety. In the paper, a numerical model of a high-speed UAV impact on the blade are established based on the classical Lagrange method in the non-linear dynamic program. Under different impact velocities and blade rotating speeds, impacting the root, central and tip of the fan blade respectively are analyzed in detail, together with the impact point displacement and the system internal energy, strain energy and kinetic energy time history of 18 kinds of working conditions. The dynamic response of UAV casings and the lithium battery impact on fan blades were analyzed respectively in same conditions. The results show that the influence of rotating speed of UAV impact on blade is greater than the impact velocity. The deformation of the blade tip is the largest, followed by the blade center and then the blade root.

Weakly strained highly mismatched BxIn1-xBVyAs1-y (BV = Sb, Bi) alloys

Thermodynamically favorable 4B10BV (BV = Sb, Bi) clustering, reducing the internal strain energy, is presented in highly mismatched InAs-rich BxIn1-xBVyAs1-y alloys. The cluster formation decreases the sum of the internal energies of the constituent compounds and internal strain energy. The cohesive energies, enthalpies of formation, bond stretching, and bond bending elastic constants of zinc blende BBi and InBi are calculated. The clustering conditions are estimated up to 800 °C within the compositions 5 × 10−5 ≤ x ≤ 0.01 and x ≤ y ≤ 100x. The internal strain energies of BxIn1-xSbyAs1-y and BxIn1-xBiyAs1-y (y ≥ 2.5x) in which 99.99% boron atoms are in the clusters are more than three and seven times, respectively, less than in alloys without clusters. The formation conditions for such weakly strained highly mismatched alloys have been obtained. Almost all boron atoms should be in 4B10Sb and 4B10Bi clusters at 800 °C in BxIn1-xSbyAs1-y with x ≥ 4.2 × 10−4 and y ≥ 10x and in BxIn1-xBiyAs1-y with x ≥ 6.6 × 10−5 and y ≥ 10x.

A Displacement Based Analytical Model to Determine Residual Stress Components in a Finite Elastic Thin Plate with Hole-Drilling Method

In order to measure the residual stress components in an elastic thin plate, the hole-drilling strain-gage method has been used. This method enables to determine the relation between the magnitudes and directions of the principal stresses and the strain relaxation about the hole. In the existing analytical models based on stress field, the formulations associated with the hole-drilling method are based on the assumption of an infinite plate, this may cause some errors for a finite plate and it’s difficult to validate these solutions by FE methods. Furthermore, in the composite, the displacement field is continuous but the stress field is not necessarily continuous, the displacement field based method has to be used. In the present paper an analyt-ical model based on a displacement field described by a function with coefficients to determine for a finite round thin plate is presented. The coefficients used in the displacement field are independent on the three residual stress components, and they are determined by minimization of the internal strain energy during the hole-drilling process. Once the coefficients in the dis-placement field are determined, three strains measured in three radial directions are utilized to determine the three residual stress components. The proposed analytical model can be also adapted to infinite plate by assuming that the diameter of the round plate tends to infinite.

Unravelling the development of a spheroidally weathered diorite-gabbro, Santa Margarita Ecological Reserve, Peninsular Ranges, southern California, USA

Within Santa Margarita Ecological Reserve (SMER), southern California, an ~108Ma diorite-gabbro pluton has weathered spheroidally resulting in the formation of concentric rindlets, i.e., a rindlet zone, around an unaltered ellipsoidal core of the parent rock. To our knowledge little is known about how spheroidal weathering is produced in Mediterranean climates like that characteristic of portions of the Peninsular Ranges. Hence, we undertook a detailed study aimed at determining the textural and chemical changes associated with the spheroidal weathering of the diorite-gabbro pluton.The parental spheroidally weathered corestone is characterized by a hypidomorphic-granular texture, and consists primarily of plagioclase, amphibole, and biotite, along with minor amounts of pyroxene and quartz. Within the corestone, sericite, and uncommonly, calcite and chlorite, replace plagioclase. The latter mineral also infrequently replaces portions of amphibole and biotite. Such alteration products are derived from sub-solidus deuteric alteration of the pluton.XRD clay mineral analysis of the 13 rindlets indicates the presence of mostly kaolinite and vermiculite, and a far lesser volume of green smectite. Thin section study of rindlet samples suggests that vermiculite is derived from the weathering of biotite, the most extensively altered mineral in the rindlet zone. Such alteration is paralleled by statistically significant losses of K mass across the rindlet zone. In addition, statistically significant losses of Ca and Na mass across the rindlet zone, likely reflect conversion of sericite to kaolinite. In contrast, the absence of statistically significant losses of Mg, Fe, and Mn over most of the rindlet zone, implies that fluids were mostly oxidizing, and that any Mg leached from amphibole was likely fixed within smectite, while leached Fe and Mn precipitated out as oxides or oxyhydroxides. Though calcite was present in the corestone, its absence in the rindlets indicates that fluids were sufficiently acidic to dissolve and remove it.Previous studies have shown that spheroidal weathering occurs when volume expansion produced by a positive ΔV of reaction builds up internal elastic strain energy in the rock. For example, this type of reaction occurs when iron oxidizes within biotite resulting in an expansion of d(001) from 10Å to 10.5Å, or when biotite is transformed into vermiculite leading to an expansion of d(001) from 10Å to 14Å. Data presented here suggest that the conversion of biotite to vermiculite, and the resulting positive ΔV produced the spheroidal fracturing of the corestone at SMER. Hence, these and other data discussed in this paper suggest that the weathering of biotite is the primary driving force in the formation of spheroidally weathered corestone in the Mediterranean climate of the Peninsular Ranges.

Effect of Nitrogen on Deformation-Induced Martensitic Transformation in an Austenitic 301 Stainless Steels

The effect of nitrogen on deformation-induced martensitic transformation (DIMT) in metastable 301 austenitic stainless steel has been studied based on the inelastic deformation theory. DIMT is regarded here as continuous relaxation process of internal strain energy accumulated during inelastic deformation. Using the kinetics equation based on the inelastic deformation theory the relationship between the volume fraction of transformed martensite and inelastic strain for DIMT has been successfully verified with the parameter representing the stability of austenite. The addition of nitrogen is experimentally found to increase austenite stability and the critical inelastic strain below which any DIMT is not observed to occur and to decrease the saturation volume fraction of α’ martensite. On the other hand, DIMT has been analyzed with its effect on stress-strain curve shape and mechanical properties in relation to the addition of nitrogen. The characteristic transition from sigmoidal to parabolic curve shape in stress-strain response has disappeared with the addition of nitrogen.

The contribution of a directional preference of stiffness to the efficacy of prophylactic sacral dressings in protecting healthy and diabetic tissues from pressure injury: computational modelling studies.

The sacral region is the most common site for pressure injuries (PIs) associated with lying in bed, and such sacral PIs often commence as deep tissue injuries (DTIs) that later present as open wounds. In complex patients, diabetes is common. Because, among other factors, diabetes affects connective tissue stiffness properties, making these tissues less able to dissipate mechanical loads through physiological deformations, diabetes is an additional biomechanical risk factor for PIs and DTIs. A preventive measure with established successful clinical outcomes is the use of sacral prophylactic dressings. The objective of this study has been to expand our previous work regarding the modes of action and biomechanical efficacy of prophylactic dressings in protecting the soft tissues adjacent to the sacrum by specifically examining the role of a directional stiffness preference (anisotropy) of the dressing while further accounting for diabetic tissue conditions. Multiple three-dimensional anatomically detailed finite element (FE) model variants representing diabetic tissue conditions were used, and tissue loading state data were compared with healthy tissue simulations. We specifically compared soft tissue exposures to elevated internal shear stresses and strain energy densities (SED) near the sacrum during supine weight bearing on a standard (foam) hospital mattress without a dressing, with a prophylactic dressing lacking directional stiffness preferences and with an anisotropic dressing. Our results have clearly shown that an anisotropic dressing design reduces the peak tissue stresses and exposure to sustained tissue deformations in both healthy and diabetic cases. The present study provides additional important insights regarding the optimal structural and material design of prophylactic dressings, which in turn, informs clinicians and decision makers regarding beneficial features.

Application of energy dissipation approach for notched behavior in fiber metal laminates

Characterization of the complicated failure behavior in fiber metal laminate (FML) depends on well understanding of the contributions from metal and composite layers. It seems to be very cumbersome to deal with this by conventionally collecting the stress, strain and damage patterns through experiments or numerical simulations, especially when complicated load (e.g., off-axis load) or a more hybrid degree is adopted. Since all mechanical responses in nature are governed by energy principles, in the present study an energy dissipation approach was introduced in FML. Analyses were carried out with employing the available history outputs in Abaqus, where four kinds of energy variables in terms of internal or total strain energy (Eint), elastic or recoverable strain energy (Eelast), energy dissipated by plastic deformation (Eplast) and damage (Edam) were requested for both the constituents and the laminates. Two issues were clarified by this energy approach: off-axis dependence of mechanical response and damage behavior in notched glass fiber reinforced aluminum laminate (Glare), and the reinforced effect of titanium on notched Glare (a more hybrid case). Results have shown the potentiality of energy approach in straightforwardly and effectively characterizing the failure behavior of FMLs.

Affine and non-affine deformations quantified in cytoskeletal networks through three-dimensional form-finding model

Actin filaments and cross-linkers are main components of cytoskeletal networks in eukaryotic cells, and they support bending moments and axial forces respectively. A three-dimensional form-finding model is proposed in this work to investigate affine and non-affine deformations in cytoskeletal networks. In recent studies, modeling of cytoskeletal networks turns out to be a key piece in the cell mechanics puzzle. We used form-finding analysis to compute and analyze cytoskeletal models. A three-dimensional model is much more flexible and contains more elements than a two-dimensional model, and non-linear finite element analysis is difficult to converge. Thus, vector form intrinsic finite element analysis is employed here for valid results. The three-dimensional model reveals new behaviors beyond earlier two-dimensional models and better aligns with available data. Relative density of actin filaments and height of the form-finding model both play important roles in determining cytoskeletal stiffness, positively and negatively, respectively. Real cytoskeletal networks are quite mixed in terms of affine and non-affine deformations, which are quantified by internal strain energy in actin filaments and cross-linkers. Results are also influenced by actin filament relative density and height of the model. The three-dimensional form-finding model does provide much more room for intensive studies on cytoskeletal networks. In our future study, microtubules, fluidics, viscoelastic-plastic cross-linkers and even the whole cell model may be taken into account gradually to improve the cytoskeletal form-finding model.