Different Modes Of Deformation Research Articles

Joining sheets to tubes by annular sheet squeezing

This paper proposes a new joining by forming process to secure a sheet to a tube away from the tube end. The process is an alternative to welding, adhesive bonding, mechanical fastening or riveting and consists of squeezing the sheet adjacent to the outer tube radius, instead of applying direct loading on the tube itself as is customary in existing joining by forming processes. This process is cost effective, can be easily used on site and prevents cracking of the plastically deformed beads in tubular materials with low fracture toughness.The presentation combines experimentation and finite element modelling to identity the major process parameters, understand their influence in plastic flow and characterize the different modes of deformation that lead to acceptable and unacceptable joints. Utilization of a deformation-zone geometry parameter Δ, defined as the ratio of the sheet thickness to the cross-section recess length of the punch, is successfully utilized to characterize plastic flow inside the sheet thickness and to establish fundamental design rules. Appropriate values of the deformation-zone parameter in the range Δ=2−3 and placed in-between the limiting values corresponding to inhomogeneous and homogeneous deformation, revealed adequate to obtain sound sheet-tube connections. The maximum pull-out forces are sensitive to the direction of applied loading due to the non-symmetric shape of the joints but no detachments were observed for forces up to 2 kN.

Conceptual consideration and outcrop interpretation on early stage deformation of sand and mud in accretionary prisms for chaotic deposit formation

This paper dealt with the summary of the outcrop observation of chaotic deposits (mélanges) in the present and past accretionary prisms and complexes with comparative consideration from the conceptual results of deformation under un- and semi-lithified (weakly lithified) conditions. I stressed the significance of pore-fluid pressure, mud pressure (both are treated as head), and frequency of stress period in order to interpret chaotic deposits and related structures on outcrops. Most important results were to point out that the vice versa relationships in sandstone and mudstone, as in one case sandstone is a clast within mudstone matrix, but in another case of early stages of deformation, mudstone is a clast within sandstone matrix. This is interpreted due to sudden shake of high frequency of period like earthquake shake. In addition, new ideas of explanation were adoptable using different stress – effective stress diagrams as well as the conventional stress – strain diagrams as applied by the experimental results of solid mechanics, e.g. critical state deformation in uniform flow for slump and convolution, and scaly clays that are commonly developed in accretionary prisms. The different modes of deformation in sandstone and mudstone in case of hydraulic fracturing, liquefaction and fluidization, and also unique structures like vein structure and scaly clay formation are implied. These concepts are available to interpret various chaotic deposits occurrences, and to discuss their origin from on land and under the sea.

Joining sheets to rods by boss forming

This paper proposes a new joining by plastic deformation process to connect sheets to rods that extends a previous idea of the authors to connect sheets to thin-walled tubes. The process makes use of boss forming for compressing the outer radius of the rods and pile-up material into annular flanges with controlled cross-section geometry and size. Special emphasis is put on the identification of the major operating parameters and on understanding their influence on material flow. Two different modes of deformation are identified and a distinction is made between unacceptable chip formation and successfully material pile-up to form the annular flanges that are needed to connect the sheets to the rods. Special design of the upper die to include a pressure ring is introduced as an efficient solution to prevent cracking of the new freshly formed surfaces of the rods during material pile-up. The presentation is supported by experimentation and finite element modelling and the overall performance of the new proposed joint is evaluated by means of a destructive pull-out test.

Ambient Noise Tomography Images Accreted Terranes and Igneous Provinces in Hispaniola and Puerto Rico

AbstractThe North American‐Caribbean plate boundary near the islands of Hispaniola and Puerto Rico is a complex region in which strain is accommodated by different modes of deformation. In 2013, 16 broadband stations were deployed in the Dominican Republic to densify the local permanent network. One goal is to combine their data with those from permanent networks in the Caribbean to develop a better understanding of the crust and upper mantle structure in the Greater Antilles. Here we use the records of 204 stations spanning almost 7 years of data to obtain group velocity maps. We observe at short periods the contacts between accreted terranes and the igneous provinces of Hispaniola and Puerto Rico, at longer periods the collisional boundary between the buoyant Bahamas Carbonate Platform and Hispaniola, and the transition from Hispaniola's accreted terranes to the faster lithosphere of the Venezuelan Basin and Cayman Trough.

Design of Engineered Elastomeric Substrate for Stretchable Active Devices and Sensors

AbstractIn the field of flexible electronics, emerging applications require biocompatible and unobtrusive devices, which can withstand different modes of mechanical deformation and achieve low complexity in the fabrication process. Here, the fabrication of a mesa‐shaped elastomeric substrate, supporting thin‐film transistors (TFTs) and logic circuits (inverters), is reported. High‐relief structures are designed to minimize the strain experienced by the electronics, which are fabricated directly on the pillars' surface. In this design configuration, devices based on amorphous indium‐gallium‐zinc‐oxide can withstand different modes of deformation. Bending, stretching, and twisting experiments up to 6 mm radius, 20% uniaxial strain, and 180° global twisting, respectively, are performed to show stable electrical performance of the TFTs. Similarly, a fully integrated digital inverter is tested while stretched up to 20% elongation. As a proof of the versatility of mesa‐shaped geometry, a biocompatible and stretchable sensor for temperature mapping is also realized. Using pectin, which is a temperature‐sensitive material present in plant cells, the response of the sensor shows current modulation from 13 to 28 °C and functionality up to 15% strain. These results demonstrate the performance of highly flexible electronics for a broad variety of applications, including smart skin and health monitoring.

Pressure Response of Photoluminescence in Cesium Lead Iodide Perovskite Nanocrystals

In this paper, we address the phase stability and the relationship between optical gap and structural perturbations in cesium lead halide nanocrystals. We report photoluminescence (PL) spectra for cesium lead iodide (CsPbI3) perovskite nanocrystals under hydrostatic pressures up to 2.5 GPa. The peak position of the CsPbI3 PL shifts as a function of pressure. Initially, the PL shifts to lower energies, until a reversal occurs near 0.33 GPa. At higher pressures, the PL peak position shifts to the blue until PL vanishes above 2.5 GPa. We explain the pressure response with different modes of deformation of the perovskite crystal structure.

Elastic strain and twist analysis of protein structural data and allostery of the transmembrane channel KcsA

The abundance of available static protein structural data makes the more effective analysis and interpretation of this data a valuable tool to supplement the experimental study of protein mechanics. Structural displacements can be difficult to analyze and interpret. Previously, we showed that strains provide a more natural and interpretable representation of protein deformations, revealing mechanical coupling between spatially distinct sites of allosteric proteins. Here, we demonstrate that other transformations of displacements yield additional insights. We calculate the divergence and curl of deformations of the transmembrane channel KcsA. Additionally, we introduce quantities analogous to bend, splay, and twist deformation energies of nematic liquid crystals. These transformations enable the decomposition of displacements into different modes of deformation, helping to characterize the type of deformation a protein undergoes. We apply these calculations to study the filter and gating regions of KcsA. We observe a continuous path of rotational deformations physically coupling these two regions, and, we propose, underlying the allosteric interaction between these regions. Bend, splay, and twist distinguish KcsA gate opening, filter opening, and filter–gate coupling, respectively. In general, physically meaningful representations of deformations (like strain, curl, bend, splay, and twist) can make testable predictions and yield insights into protein mechanics, augmenting experimental methods and more fully exploiting available structural data.

Twinning to slip transition in ultrathin BCC Fe nanowires

We report twinning to slip transition with decreasing size and increasing temperature in ultrathin <100> BCC Fe nanowires. Molecular dynamics simulations have been performed on different nanowire size in the range 0.404–3.634 nm at temperatures ranging from 10 to 900 K. The results indicate that slip mode dominates at low sizes and high temperatures, while deformation twinning is promoted at high sizes and low temperatures. The temperature, at which the nanowires show twinning to slip transition, increases with increasing size. The different modes of deformation are also reflected appropriately in the respective stress–strain behaviour of the nanowires.

Effect of temperature and punch speed on forming limit strains of AA5182 alloy in warm forming and improvement in failure prediction in finite element analysis

Formability of AA5182-O aluminum alloy sheets in the warm working temperature range has been studied. Forming limit strains of sheets of two different thicknesses have been determined experimentally in different modes of deformation (biaxial tension, plane strain and tension–compression) by varying temperature and punch speed. A correlation has been established for plane strain intercept of the forming limit diagram (FLD0) with temperature, punch speed and thickness from the experimental results. This correlation has been used to plot the forming limit diagrams for failure prediction in the finite element analysis of warm deep drawing of cylindrical cups. The effect of strain and strain rate on material flow behavior has been incorporated using a strain rate–sensitive power hardening law in which the strain hardening exponent and strain rate sensitivity index have been experimentally determined. The predictions from simulations have been validated by warm deep drawing experiments. Large improvement in accuracy of failure prediction has been observed using the FLDs plotted based on the developed correlation when compared to the existing method of calculating FLD0 using only strain hardening coefficient and thickness. The results clearly indicate the importance of incorporating temperature and punch speed in failure prediction of Al alloys using FLDs in the warm working temperature range.

Architected cellular ceramics with tailored stiffness via direct foam writing

Hierarchical cellular structures are ubiquitous in nature because of their low-density, high-specific properties, and multifunctionality. Inspired by these systems, we created lightweight ceramic architectures composed of closed-cell porous struts patterned in the form of hexagonal and triangular honeycombs by direct foam writing. The foam ink contains bubbles stabilized by attractive colloidal particles suspended in an aqueous solution. The printed and sintered ceramic foam honeycombs possess low relative density (∼6%). By tailoring their microstructure and geometry, we created honeycombs with different modes of deformation, exceptional specific stiffness, and stiffness values that span over an order of magnitude. This capability represents an important step toward the scalable fabrication of hierarchical porous materials for applications, including lightweight structures, thermal insulation, tissue scaffolds, catalyst supports, and electrodes.

Theoretical study of absorbed energy by empty and foam-filled composite tubes under lateral compression

This paper is an attempt for introduction of new theoretical relations in order to predict energy absorption behavior of empty and polyurethane foam-filled composite tubes, which are made of woven fiber fabrics, during lateral compression between two rigid plates. Such theoretical relations can be used to specify portion of different deformations that are happened during crushing process in total energy absorption of the structures. Knowing these data may help the designers to reinforce the energy absorbers more effectively. Also, several experiments are conducted on empty and polyurethane foam-filled circular E-glass/Vinylester composite tubes in order to validate the theoretical relations. The specimens are laterally compressed between two rigid plates during a quasi-static process. According to experimental studies, the composite tubes collapse with different modes of deformation during lateral flattening. Different relations are introduced for prediction of the absorbed energy of tubes with different deformation modes. The theoretical and experimental energy-displacement diagrams and total absorbed energy by the composite tubes are compared and good agreements are found. Finally, theoretical relations are compared with each other and effects of different energy absorption mechanisms on total energy absorption are discussed based on the presented relations.

Numerical Simulation of Crushing and Energy Absorption Behavior of Twisted Tubes under Impact Loading

Thin-walled tubes are light in weight and has shown good energy absorption potential. Geometry of such tubes is a key in deformation modes and energy absorption under impact loading. Energy absorption can further be enhanced by implementing improved geometrical configurations. In the present investigation, crushing and energy absorption behavior of twisted aluminum tubes are test simulated under impact loading. The nonlinear finite element simulation is carried out using commercially available software ABAQUS®. The analysis is carried out with three different thicknesses and three different velocities for twisted tubes. Different modes of deformation, load-displacement curve are developed and analyzed. The investigation shows that energy absorption marginally decreases with increase in velocity whereas, it increases with increase in thickness of the tubes. The tubes deform in concertina mode and value of maximum first peak force is evaluated for various thicknesses and impact velocities. This study helps in design of the crush tubes in automotive sector wherein sudden rise of peak force is undesirable from passenger safety viewpoint.

Enhancement of Formability of AA5052 Alloy Sheets by Electrohydraulic Forming Process

Formability of lightweight materials like Al and Mg alloys is a major concern for their application in automobiles. Forming limit diagram (FLD) and strain distribution are extremely useful in the assessment of overall formability of sheet metals. At very high strain rates, the deformation behavior of Al alloys and the safe forming window could be different from quasi-static conventional forming. In this paper, formability of Al 5052 alloy sheets of 0.5 mm thickness has been assessed in electrohydraulic forming (EHF) in terms of FLD and strain distribution and compared with formability in conventional forming by punch-stretching experiments. EHF is a high strain rate forming process which utilizes energy released from a capacitor bank to generate shockwaves in a fluid medium. Experiments have been conducted at different energy levels to identify the highest safe strains in different modes of deformation. From the experimental results, it has been observed that the limit strains increased by nearly 45-50% in all the three regions of the FLD (tension-tension, plane strain and tension compression). Unlike in the case of conventional forming, no clear necking due to strain localization has been observed prior to failure due to very high strain rates of the order of 103/s. The strain distribution has been found to be more uniform in the case of EHF with a single strain peak at the pole. Absence of friction in EHF also leads to higher degree of biaxiality leading to higher limit strains in biaxial tension. In the case of EHF, the effective strain and hardness are maximum at the pole and their variation correlated well with the findings from the strain distribution analysis. In all modes of deformation, the features of fractured surface in EHF appeared different from a normal ductile failure.

Foam-Filled Grooved Tubes with Circular Cross-Section Under Axial Compression: A Theoretical Analysis

In this article, some theoretical relations are derived to predict the instantaneous folding force and the absorbed energy by the empty and polyurethane foam-filled grooved tubes with circular cross-section during the first fold formation under the axial loading. Five different modes of deformation are considered in the theoretical model of deformation: bending around two internal circular hinge lines, bending around an external circular hinge line, extensional deformation in the folding arms, axial compression of the polyurethane foam, and interaction effects between polyurethane foam and inner wall of the grooved tube. Also, based on the experiments, a semi-empirical relation is suggested to predict the effective axial displacement at the end of a complete fold creation in the polyurethane foam-filled grooved tubes. To verify the theoretical analyses, some axial compression tests were carried out on the empty and filled grooved tubes. Comparison of the theoretical predictions with the corresponding experimental results showed a good correlation.

Modeling of the inhomogeneity of grain refinement during combined metal forming process by finite element and cellular automata methods

The potential of discrete cellular automata technique to predict the grain refinement in wires produced using combined metal forming process is presented and discussed within the paper. The developed combined metal forming process can be treated as one of the Severe Plastic Deformation (SPD) techniques that consists of three different modes of deformation: asymmetric drawing with bending, namely accumulated angular drawing (AAD), wire drawing (WD) and wire flattening (WF). To accurately replicate complex stress state both at macro and micro scales during subsequent deformations two stage modeling approach was used. First, the Finite Element Method (FEM), implemented in commercial ABAQUS software, was applied to simulate entire combined forming process at the macro scale level. Then, based on FEM results, the Cellular Automata (CA) method was applied for simulation of grain refinement at the microstructure level. Data transferred between FEM and CA methods included set of files with strain tensor components obtained from selected integration points in the macro scale model. As a result of CA simulation, detailed information on microstructure evolution during severe plastic deformation conditions was obtained, namely: changes of shape and sizes of modeled representative volume with imposed microstructure, changes of the number of grains, subgrains and dislocation cells, development of grain boundaries angle distribution as well as changes in the pole figures. To evaluate CA model predictive capabilities, results of computer simulation were compared with scanning electron microscopy and electron back scattered diffraction images (SEM/EBSD) studies of samples after AAD+WD+WF process.

Effect of geometrical parameters on mode shape and critical buckling load of dished shells under external pressure

A conical shell frustum with flat circular top is called dished shell. These type of shell find application in many aerospace and rocket industries. These type shells undergo a special type of buckling phenomenon similar to arches and spherical caps, which needs to be studied in detail. In the present study, an Eigen value buckling analysis of dished shallow shell is attempted. Two types of dished shallow shells are chosen: with a stiff top, and with a flexible top. Finite element analysis is done to find out the effect of various geometrical parameters such as shell thickness, height, top flat region radius and various boundary conditions on the mode shape and critical buckling load under uniform external pressure. It is found that mode shape and critical buckling pressure changes with variation in geometrical parameters of shells. It is also observed that shells having stiff central flat circular region show different harmonics in conical region for different modes of deformation and the values of critical pressure for different modes are very close to each other. However, for dished shallow shells with flexible top critical buckling pressures are significantly different for various modes except conjugate ones. The numerical analysis results for dished shell with flexible top and fixed boundary condition is compared with analytical solutions of an equivalent spherical cap and for stiff top condition with analytical solutions of an externally pressurized conical frustum. The information obtained from this study, can be used for design improvement and failure mode analysis of dished shells.

Energy dissipation in thin metallic shells under projectile impact

Abstract The ballistic performance of hemispherical aluminium shells was studied and the energy absorption in different modes of deformation has been computed. The experiments were performed wherein blunt and ogive nosed steel projectiles of 19 mm diameter were fired on 0.7–1.5 mm thick 1100-H12 aluminum hemispherical shells of different effective spans. The mechanics of deformation and energy absorption capacity was found to be significantly influenced by the shell thickness and projectile nose shape. The ogive nosed projectile caused failure through perforation by petal formation. Against blunt nosed projectile, however, the shells underwent significant dishing and reverse bending and thus defeated the projectile by dissipating its energy in global plastic deformation. The experimental findings were reproduced numerically on ABAQUS/Explicit finite element code. The numerical results were further employed for the computation of plastic strain energy in stretching in polar, radial, elevation and shear directions of the shell in order to eventually extract the total energy absorbed in plastic deformation. For a given span diameter and thickness of shell, the energy dissipation was found maximum in shear stretching while it was minimum in polar stretching of the material.

Cell Mechanics: Combining Speed with Precision

The mechanical response of cells is a powerful biophysical marker for cell state. Information on a cell’s elasticity can, for instance, be used to distinguish between different cell phenotypes, or between healthy and diseased cells.

Influence of mode of deformation on microstructural heterogeneities in Ni subjected to large strain deformation

In the present work, the effect of deformation mode (uniaxial compression, rolling and torsion) on the microstructural heterogeneities in a commercial purity Ni is reported. For a given equivalent von Mises strain, samples subjected to torsion have shown higher fraction of high-angle boundaries, kernel average misorientation and recrystallization nuclei when compared to uniaxially compressed and rolled samples. This is attributed to the differences in the slip system activity under different modes of deformation.

Vibration of thin-walled laminated composite beams having open and closed sections

An efficient technique based on one dimensional beam finite element analysis for vibration of thin-walled laminated composite beams having open and closed sections is proposed in this paper. The developed technique is quite generic which can accommodate any stacking sequence of individual walls and considers all possible couplings between different modes of deformation. The formulation has accommodated the effect of transverse shear deformation of walls as well as out of plane warping of the beam section where the warping can be restrained or released. The inclusion of shear deformation has imposed a problem in the finite element formulation of the beam which is solved successfully utilising a concept developed by one of the authors. A number of numerical examples of open section (I and C sections) beams and closed section box beams are solved by the proposed technique and the results predicted by the proposed model are compared with those obtained from literature as well as detailed finite element analysis using a commercial code. The results show a very good performance of the proposed modelling technique.