Internal Strain Distribution Research Articles

MRI based 3D finite element modelling to investigate deep tissue injury

Pressure ulcers occur due to sustained mechanical loading. Deep tissue injury is a severe type of pressure ulcer, which is believed to originate in subcutaneous tissues adjacent to bony prominences. In previous experimental-numerical studies the relationship between internal tissue state and damage development was investigated using a 2D analysis. However, recent studies suggest that a local analysis is not sufficient. In the present study we developed a method to create animal-specific 3D finite element models of an indentation test on the tibialis anterior muscle of rats based on MRI data. A detailed description on how the animal specific models are created is given. Furthermore, two indenter geometries are compared and the influence of errors in determining the indenter orientation on the resulting internal strain distribution in a defined volume of tissue was investigated. We conclude that with a spherically-shaped indenter errors in estimating the indenter orientation do not unduly influence the results of the simulation.

Nanoscale Strain Imaging using Coherent X-ray Light Sources

Coherence properties available from the advanced X-ray synchrotrons and X-ray Free Electron Laser sources bring the opportunities to get new information of the dynamics and local structures non-destructively. Here we review recent progress of the coherent X-ray diffraction imaging technique for measuring internal strain distribution of the nanomaterial systems. We introduce the general coherence properties of the sources and show the fundamental principle and technical aspects of the technique. Some examples of the applications are shown for various nanostructures, grains in polycrystalline films, and semiconducting devices even with in situ and operando conditions. We discuss the future development of the technique in terms of the understanding and control of the strains, which are very crucial in nanomaterial design and applications.

Transient behaviour of grouted connections of offshore wind turbines subject to ship impact

Grouted connections are a critical structural element of monopile-supported offshore wind turbines (OWTs), connecting turbine towers with foundation piles. Due to engineering requirements, they are normally installed at the mean water level (MWL), leading to high risk of ship collisions. In this study, transient response and damage analysis were performed on the grouted connections of monopile OWT when subjected to ship impacts. Taking into account the sandwich construction of the grouted connection of the OWT and the non-linear behaviour of the structure materials, a finite element model of a vessel of 2000-ton displacement collision with a 5 MW monopile OWT was developed using explicit finite element code LS-DYNA. The ship was assumed to strike head-on and at the middle of the grouted connection. Characteristics of the collision system in terms of energy, velocity, impact force and the response of the ship and the grouted connection were analysed. Internal contact forces, stress and effective plastic strain distribution of the grouted connection were discussed. Four phases of the collision process were identified: initial collision, motion towards maximum OWT deflection, towards vessel-OWT separation, and after separation. The ship collision response and damage of the grouted connection were considerably influenced by the strain rate effect of the structure materials. Collided by a ship, even at a low velocity of 2 m/s, the grouted connection for monopile OWT could suffer heavy or major damage. The current analysis sheds light on the dynamic response of grouted connections of monopile OWTs to ship impact. It lays a solid foundation for future analysis on the design of grouted connections of OWTs.

A MESHLESS DEFORMATION SIMULATION METHOD FOR VIRTUAL SURGERY

An accurate and computation-effective model of soft tissues is very important for surgery simulation. When soft tissues are interacted by a surgical instrument, their external deformation and internal stress and strain distribution are closely related. These stress and strain data can not only be used to describe the soft tissue deformation but also can be used to calculate interaction force rendered to the force feedback device, making the user to have a realistic sense of touch during the surgical procedure. It is difficult, however, to solve partial differential equations (PDE) in conventional soft tissue models, and stress and strain data cannot be easily extracted. This paper presents a meshless local radial point interpolation method for soft tissue modelling and demonstrates its feasibility by numerical tests.

Numerical Analysis for Basalt Fiber Reinforced High-viscosity Asphalt Concrete Bridge Deck Pavement

Basalt fiber reinforced asphalt concrete has better durability, crack resistance and temperature stability than traditional untreated asphalt concrete, being gradually used in pavement engineering in China over recent years. In 2014, basalt fiber reinforced asphalt concrete with high-viscosity asphalt modifier was utilized as the top layer of the deck pavement on Shangci Bridge, which was a 240m prestressed concrete continuous T-beam bridge, located in Quzhou, Zhejiang Province, China. In this paper, a three-dimensional model was established to analyze the distribution law of internal stress and strain of the deck pavement when it was under traffic load. The results indicate that thickness, elastic modulus and interface bonding conditions of the deck overlays have different effects on its internal stress and strain distribution. In another two-dimensional model, the high-temperature viscoelasticity response induced by cycle load was obtained on the basis of laboratory creep tests. Under the effect of the cycle load, the largest horizontal creep strain at 60 is calculated to be 379 , accounting for 85% of the total strain.

Toward cyclic durable core/shell nanostructure of Sn-C composite anodes for stable lithium storage by simulating its lithiation-induced internal strain

Abstract To explore the capacity fading mechanism during long-term cycling of the milled Sn-C lithium storage anodes, the structural stability of the cycled Sn-C electrodes has been investigated using internal strain distribution as indicator by simulation with different two-dimensional core/shell nanostructure models solved by Lagrangian description, combining with experimental results. It is revealed that the Sn-C composite of a double-coating structure with the smaller Sn coated by a stiff layer Li2O and embedding in graphite sustains less deformation, and has higher structural stability than the single-coating one. Due to the lithiation-induced stress and strain effect, Sn particles aggregate and the Sn whiskers grow in the cycled Sn-C electrodes that observed by SEM and TEM, which is closely related to the Sn transportation. This strain induced structural damage causes the capacity fading of Sn anodes. Based on the simulation of strain distribution induced by lithiation, the nanostructure has been designed for Sn-C electrodes of smaller Sn particles embedded in matrix with large elastic modulus and proper thickness to obtain optimized combination of capacity and cycleability. It would provide a guideline for designing material and microstructure of anodes for lithium ion batteries.

Intragranular twinning, detwinning, and twinning-like lattice reorientation in magnesium alloys

Deformation twinning plays a critical role on improving metals or alloys ductility, especially for hexagonal close-packed materials with low symmetry crystal structure. A rolled Mg alloy was selected as a model system to investigate the extension twinning behaviors and characteristics of parent-twin interactions by nondestructive in situ 3D synchrotron X-ray microbeam diffraction. Besides twinning-detwinning process, the “twinning-like” lattice reorientation process was captured within an individual grain inside a bulk material during the strain reversal. The distributions of parent, twin, and reorientated grains and sub-micron level strain variation across the twin boundary are revealed. A theoretical calculation of the lattice strain confirms that the internal strain distribution in parent and twinned grains correlates with the experimental setup, grain orientation of parent, twin, and surrounding grains, as well as the strain path changes. The study suggests a novel deformation mechanism within the hexagonal close-packed structure that cannot be determined from surface-based characterization methods.

Elastic Full‐Field Strain Analysis and Microdamage Progression in the Vertebral Body from Digital Volume Correlation

AbstractThe strain distribution in vertebral body has been measured in vitro in the elastic regime but only on the bone surface by means of strain gauges and digital image correlation. Digital volume correlation (DVC) based on micro‐computed tomography (micro‐CT) images allowed measurements of the internal strain distribution in bone at both tissue (trabecular and cortical bone) and organ (vertebra) levels. However, DVC has been mainly used to investigate failure of the vertebral body but has not yet been deployed to investigate the internal strain distribution in the elastic regime. The aim of this study was to investigate strain in the elastic regime and up to failure inside the vertebral body, including analysis of strain in all directions. Three porcine thoracic vertebrae were loaded in a step‐wise fashion at increasing steps of compression (5, 10 and 15%). Micro‐CT images were acquired at each step of compression. DVC successfully provided the internal strain distribution both in the elastic regime and up to failure. Micro‐CT images successfully identified regions of failure initiation and progression, which were well quantified by DVC‐computed strains. Interestingly, the same regions where failure eventually occurred experienced the largest strain magnitude also for the lowest degrees of compression (yet in the elastic regime).

Internal deformation monitoring for centrifuge slope model with embedded FBG arrays

The fiber Bragg grating (FBG) sensing technology was utilized for internal deformation monitoring in a centrifuge test of soil slope. An array of FBG sensors were encapsulated into a sensing fiber with a diameter of 0.9 mm. A pullout test was designed to investigate the frictional behavior between the sensing fiber and soil. It was concluded that, for a certain value of overburden pressure, the fiber strain is equal to the strain of soil as long as the fiber strain is less than its peak value in the pullout test. The sensing fibers were embedded directly into a slope centrifuge model to monitor the internal strain distribution and its variation. It can be found that the horizontal sensors were stretched extremely and the vertical sensors were compressed distinctly near a potential slip surface. Thus, it is possible to evaluate the soil internal deformation as well as the failure of the slope model by using FBG sensing technology. This is verified by a comparison between the results of FBGs and that of a numerical simulation. According to these preliminary results, discussions and recommendations for further research are presented.

Application of digital volume correlation to study the efficacy of prophylactic vertebral augmentation

BackgroundProphylactic augmentation is meant to reinforce the vertebral body, but in some cases it is suspected to actually weaken it. Past studies only investigated structural failure and the surface strain distribution. To elucidate the failure mechanism of the augmented vertebra, more information is needed about the internal strain distribution. This study aims to measure, for the first time, the full-field three-dimensional strain distribution inside augmented vertebrae in the elastic regime and to failure. MethodsEight porcine vertebrae were prophylactically-augmented using two augmentation materials. They were scanned with a micro-computed tomography scanner (38.8μm voxel resolution) while undeformed, and loaded at 5%, 10%, and 15% compressions. Internal strains (axial, antero-posterior and lateral-lateral components) were computed using digital volume correlation. FindingsFor both augmentation materials, the highest strains were measured in the regions adjacent to the injected cement mass, whereas the cement-interdigitated-bone was less strained. While this was already visible in the elastic regime (5%), it was a predictor of the localization of failure, which became visible at higher degrees of compression (10% and 15%), when failure propagated across the trabecular bone. Localization of high strains and failure was consistent between specimens, but different between the cement types. InterpretationThis study indicated the potential of digital volume correlation in measuring the internal strain (elastic regime) and failure in augmented vertebrae. While the cement-interdigitated region becomes stiffer (less strained), the adjacent non-augmented trabecular bone is affected by the stress concentration induced by the cement mass. This approach can help establish better criteria to improve vertebroplasty.

Himalayan leucogranites and migmatites: nature, timing and duration of anatexis

AbstractWidespread anatexis was a regional response to the evolution of the Himalayan‐Tibetan Orogen that occurred some 30 Ma after collision between Asia and India. This paper reviews the nature, timing, duration and conditions of anatexis and leucogranite formation in the Greater Himalayan Sequence (GHS), and compares them to contemporaneous granites in the Karakoram mountains. Himalayan leucogranites and associated migmatites generally share a number of features along the length of the mountain front, such as similar timing and duration of magmatism, common source rocks and clockwise P–T paths. Despite commonalities, most papers emphasize deviations from this general pattern, indicating a fine‐tuned local response to the dominant evolution. There are significant differences in P–T– conditions during anatexis, and timing in relation to regional decompression. Further to that, some regions underwent a second event recording melting at low pressures. Zircon and monazite ages of anatectic rocks range between c. 25 and 15 Ma, suggesting prolonged crustal melting. Typically, a single sample may have ages covering most of this 10 Ma period, suggesting recycling of accessory phases from metamorphic rocks and early‐formed magmas. Recent studies linking monazite and zircon ages with their composition, have determined the timing of prograde melting and retrograde melt crystallization, thus constraining the duration of the anatectic cycle. In some areas, this cycle becomes younger down section, towards the leading front of the Himalayas, whereas the opposite is true in other areas. The relationship between granites and movement on the South Tibetan Detachment (STD) reveals that fault motion took place at different times and over different durations requiring complex internal strain distribution along the Himalayas. The nature and fate of magmas in the GHS contrast with those in the Karakoram mountains. GHS leucogranites have a strong crustal isotopic signature and migration is controlled by low‐angle foliation, leading to diffuse injection complexes concentrated below the STD. In contrast, the steep attitude of the Karakoram shear zone focused magma transfer, feeding the large Karakoram‐Baltoro batholith. Anatexis in the Karakoram involved a Cretaceous calcalkaline batholith that provided leucogranites with more juvenile isotopic signatures. The impact of melting on the evolution of the Himalayas has been widely debated. Melting has been used to explain subsequent decompression, or conversely, decompression has been used to explain melting. Weakening due to melting has also been used to support channel flow models for extrusion of the GHS, or alternatively, to suggest it triggered a change in its critical taper. In view of the variable nature of anatexis and of motion on the STD, it is likely that anatexis had only a second‐order effect in modulating strain distribution, with little effect on the general history of deformation. Thus, despite all kinds of local differences, strain distribution over time was such that it maintained the well‐defined arc that characterizes this orogen. This was likely the result of a self‐organized forward motion of the arc, controlled by the imposed convergence history and energy conservation, balancing accumulation of potential energy and dissipation, independent of the presence or absence of melt.

Kinematic 3-D Retro-Modeling of an Orogenic Bend in the South Limón Fold-and-Thrust Belt, Eastern Costa Rica: Prediction of the Incremental Internal Strain Distribution

The South Limon fold-and-thrust belt, in the back-arc area of southern Costa Rica, is characterized by a 90° curvature of the strike of the thrust planes and is therefore a natural laboratory for the analysis of curved orogens. The analysis of curved fold-and-thrust belts is a challenge because of the varying structural orientations within the belt. Based on seismic reflection lines, we created a 3-D subsurface model containing three major thrust faults and three stratigraphic horizons. 3-D kinematic retro-deformation modeling was carried out to analyze the spatial evolution of the fold-and-thrust belt. The maximum amount of displacement on each of the faults is (from hinterland to foreland); thrust 1: 800 m; thrust 2: 600 m; thrust 3: 250 m. The model was restored sequentially to its pre-deformational state. The strain history of the stratigraphic horizons in the model was calculated at every step. This shows that the internal strain pattern has an abrupt change at the orogenic bend. Contractional strain occurs in the forelimbs of the hanging-wall anticlines, while a zone of dilative strain spreads from the anticline crests to the backlimbs. The modeling shows that a NNE-directed transport direction best explains the structural evolution of the bend. This would require a left-lateral strike-slip zone in the North to compensate for the movement and thereby decoupling the South Limon fold-and-thrust belt from northern Costa Rica. Therefore, our modeling supports the presence of the Trans-Isthmic fault system, at least during the Plio-Pleistocene.

Cartilage Strain Distributions Are Different Under the Same Load in the Central and Peripheral Tibial Plateau Regions

There is increasing evidence that the regional spatial variations in the biological and mechanical properties of articular cartilage are an important consideration in the pathogenesis of knee osteoarthritis (OA) following kinematic changes at the knee due to joint destabilizing events (such as an anterior cruciate ligament (ACL) injury). Thus, given the sensitivity of chondrocytes to the mechanical environment, understanding the internal mechanical strains in knee articular cartilage under macroscopic loads is an important element in understanding knee OA. The purpose of this study was to test the hypothesis that cartilage from the central and peripheral regions of the tibial plateau has different internal strain distributions under the same applied load. The internal matrix strain distribution for each specimen was measured on osteochondral blocks from the tibial plateau of mature ovine stifle joints. Each specimen was loaded cyclically for 20 min, after which the specimen was cryofixed in its deformed position and freeze fractured. The internal matrix was viewed in a scanning electron microscope (SEM) and internal strains were measured by quantifying the deformation of the collagen fiber network. The peak surface tensile strain, maximum principal strain, and maximum shear strain were compared between the regions. The results demonstrated significantly different internal mechanical strain distributions between the central and peripheral regions of tibial plateau articular cartilage under both the same applied load and same applied nominal strain. These differences in the above strain measures were due to differences in the deformation patterns of the collagen network between the central and peripheral regions. Taken together with previous studies demonstrating differences in the biochemical response of chondrocytes from the central and peripheral regions of the tibial plateau to mechanical load, the differences in collagen network deformation observed in this study help to provide a fundamental basis for understanding the association between altered knee joint kinematics and premature knee OA.

Optimization of CrN/CrCN Gradient Coatings

The paper describes the optimization procedure supporting the designing process of geometry of gradient coatings basing on numerical simulation of internal stress and strain distributions in the coating and substrate. In mathematical model the gradient coating is represented by the so-called transition functions describing the change of physico-chemical parameters such as Young's modulus, Poisson's ratio, thermal expansion coefficient and the density as a function of the spatial variables. The object of optimization is system composed of a CrN/CrCN gradient coating and Cr interlayer between the CrN /CrCN coating and the steel substrate deposited on nitrided 4140 steel substrate. Decision variables are: the parameters of the of curvature of transition function , thickness of gradient coating and the thickness of the Cr interlayer. Optimization was carried out under pre-defined fixed continuous external loads and created decision criteria were the functions of the state of stress and strain in the coating and the substrate. Using the optimization procedure the sets of optimal parameters (Pareto sets) of the PVD gradient coating/nitrided substrate systems, due to the adopted decision criteria were determined. The analysis of the obtained optimal solutions (Pareto-optimal sets) was carried out using the "utopian solution method". It was also examined the technological stability of the Pareto-optimal solutions (nondominated) by analyzing the number of direct neighbors of these solutions in the decision variables space.

Full-field mapping of internal strain distribution in red sandstone specimen under compression using digital volumetric speckle photography and X-ray computed tomography

It is always desirable to know the interior deformation pattern when a rock is subjected to mechanical load. Few experimental techniques exist that can represent full-field three-dimensional (3D) strain distribution inside a rock specimen. And yet it is crucial that this information is available for fully understanding the failure mechanism of rocks or other geomaterials. In this study, by using the newly developed digital volumetric speckle photography (DVSP) technique in conjunction with X-ray computed tomography (CT) and taking advantage of natural 3D speckles formed inside the rock due to material impurities and voids, we can probe the interior of a rock to map its deformation pattern under load and shed light on its failure mechanism. We apply this technique to the analysis of a red sandstone specimen under increasing uniaxial compressive load applied incrementally. The full-field 3D displacement fields are obtained in the specimen as a function of the load, from which both the volumetric and the deviatoric strain fields are calculated. Strain localization zones which lead to the eventual failure of the rock are identified. The results indicate that both shear and tension are contributing factors to the failure mechanism.

Micromechanics of plastic deformation and phase transformation in a three-phase TRIP-assisted advanced high strength steel: Experiments and modeling

The micromechanics of plastic deformation and phase transformation in a three-phase advanced high strength steel are analyzed both experimentally and by microstructure-based simulations. The steel examined is a three-phase (ferrite, martensite and retained austenite) quenched and partitioned sheet steel with a tensile strength of ~980MPa. The macroscopic flow behavior and the volume fraction of martensite resulting from the austenite–martensite transformation during deformation were measured. In addition, micropillar compression specimens were extracted from the individual ferrite grains and the martensite particles, and using a flat-punch nanoindenter, stress–strain curves were obtained. Finite element simulations idealize the microstructure as a composite that contains ferrite, martensite and retained austenite. All three phases are discretely modeled using appropriate crystal plasticity based constitutive relations. Material parameters for ferrite and martensite are determined by fitting numerical predictions to the micropillar data. The constitutive relation for retained austenite takes into account contributions to the strain rate from the austenite–martensite transformation, as well as slip in both the untransformed austenite and product martensite. Parameters for the retained austenite are then determined by fitting the predicted flow stress and transformed austenite volume fraction in a 3D microstructure to experimental measurements. Simulations are used to probe the role of the retained austenite in controlling the strain hardening behavior as well as internal stress and strain distributions in the microstructure.

Seismic behaviour of recycled aggregate thermal insulation concrete (Ratic) shear walls

This study investigated recycled aggregate thermal insulation concrete (Ratic) containing glazed hollow beads. The study of ten shear walls investigated shear-span ratio, axial compression ratio, reinforcement ratio and concrete material type. Quasi-static tests were carried out to obtain the failure modes, load–displacement curves, skeleton curves, stiffness degradation and energy dissipation capacity of Ratic shear walls. Compared with shear walls made from normal concrete, the Ratic shear walls offered a slight improvement in bearing capacity and significant improvements in deformation and energy dissipation capacities. A finite-element model was developed and non-linear simulations of shear walls with the same parameters as in the quasi-static test were carried out using Ansys software. The internal stress and strain distributions of different concrete shear walls are intuitively shown in stress contour plots and the reliability of test results further verified. The paper proposes the calculation method of the fourfold line restoring force model used for the restoring force calculation of Ratic shear wall, which is validated by comparing with the test results.

OS3-3 In-situ Measurement of Internal Strain Distribution in Laser Welding Materials under High Temperature and Tensile Stress(Stress/strain evaluation,OS3 Stress/strain analyses by diffraction method,MEASUREMENT METHODS)

OS3-3 In-situ Measurement of Internal Strain Distribution in Laser Welding Materials under High Temperature and Tensile Stress(Stress/strain evaluation,OS3 Stress/strain analyses by diffraction method,MEASUREMENT METHODS)

Investigation using digital image correlation of Portevin-Le Chatelier Effect in Hastelloy X under thermo-mechanical loading

The plastic behavior of Hastelloy X subjected to thermo-mechanical loading was investigated in this work, and the phenomenon of dynamic strain aging was studied under isothermal conditions, using digital image correlation (DIC). The material of interest, Hastelloy X a Ni-based superalloy, is widely used in high temperature applications. It was seen that Hastelloy X exhibits serrated plastic flow behavior between temperatures of 300°C and 700°C, as a consequence of the dynamic strain aging effect, which, depending on temperature, manifests as type A/B or A and B oscillations on the uniaxial tension stress–strain curve, and is characterized by strain concentration bands propagating along the length of the specimen. The characteristics of Portevin-Le Chatelier (PLC) band internal strain distribution in uniaxial tension experiments were also investigated. The bands themselves were seen to have internal (sub)bands of two or three smaller strain jumps. An analysis of the strain increments induced by these bands was performed and clearly illustrates the inhomogeneous nature of the deformation – both spatially and temporally. In addition to the uniaxial behavior, biaxial stress states were investigated by studying PLC band formation near a notch in a double notched tensile geometry. Similar macroscopic results to the uniaxial case were seen while the strain bands themselves were seen to initiate in the notch region and travel away from the notches.

Free Shrinkage Strains in Concrete Overlays

Concrete decks are commonly rehabilitated using concrete overlays. Overlay shrinkage is restrained at the interface with the substrate. An analytical method is presented to compute the distribution of internal humidity and free shrinkage strains in the overlay and substrate for bridge decks with solid rectangular cross sections and therefore overcomes the shortcomings of generic shrinkage models. Drying humidity is modeled using Fick's Second Law and the concrete diffusivity as a function of the internal humidity. The prediction of internal humidity is validated using experimental data obtained by others. The distribution of free shrinkage strains through the overlay thickness is strongly nonlinear with localized maxima at the top of the overlay and at the interface with the substrate. Large swelling strains also occur in the upper fibers of the substrate. Thin overlays develop large free shrinkage strains rapidly, whereas thick overlays produce large swelling strains in the substrate.