Theoretical Deformation Model Research Articles

Stiffness-tunable and self-sensing integrated soft machines based on 4D printed conductive shape memory composites

Through the synergy of nervous system and the self-regulation of muscle stiffness, living organisms are capable of quickly adjusting movements and actively adapting to dynamic environments. Likewise, the stiffness-changing and self-sensing functionalities are critical to empower soft robots with adjustable load capacity and agile movement. This work presents a paradigm for the design and fabrication of soft actuators with stiffness tunability and intrinsic self-sensing feedback through 4D printing method. The integration of 4D printed conductive composite into soft actuator body allows for stiffness adjustment within three orders of magnitude and ensures real-time stiffness-sensing, bending-sensing and pressure-sensing feedback. By constructing the theoretical deformation models and decoupling the resistance signals by machine learning methods, information on the stiffness, deformation and pressure of the material at different temperatures can be obtained. Cardiac-mimicking actuator and active therapeutic insoles are fabricated as proof-of-concept demonstrations, among which the active therapeutic insoles can perceive plantar pressure changes and conduct pressure-releasing actuation to ease the pain of patient at walk. It demonstrates the potential of this design approach for versatile applications such as medical assistive devices, artificial muscles, soft robotics, etc.

Surface residual stress detection method for aero-engine blades based on active thermal deformation excitation

ABSTRACT Surface residual stress is made on the aero-engine blades by shot peening to improve the fatigue life of the blades. As the service time increases, the surface residual stress is decreasing due to thermomechanical relaxation and the centrifugal load caused by high-speed rotation. Therefore, the surface residual stress detection is of great importance for predicting the remaining life of aero-engine blades. Up to now, efficient and non-contact detection of surface residual stress is still a challenge. In this paper, an active thermal deformation excitation (ATDE) method for surface residual stress is proposed. According to the thermal deformation theory, the thermal deformation of the material is positively correlated with the surface residual stress, and by measuring the thermal deformation the surface residual stress can be detected and evaluated. The theoretical deformation model was established, and simulation models with different surface residual stresses were constructed. A detection system was proposed to detect the blade deformation with different surface residual stresses. Results show that there was a linear relationship between the blade deformation and the surface residual stress from −636 Mpa to −1403 Mpa.

Structural response of the U-type corrugated core sandwich panel used in ship structures under the lateral quasi-static compression load

This paper addresses a study on the structural deformation mechanism of the U-type corrugated core sandwich panel used in ship structures under the lateral quasi-static compression load through the experimental, numerical and analytical methods. Based on the results from quasi-static experiment and the finite element simulation, the deformation characteristics of the U-type corrugated core sandwich panel under the lateral quasi-static compression load are analyzed. The results show that the deformation of the U-type corrugated core sandwich panel can be divided into two processes according to whether the core is in contact during the compression process. And the deformation process has little influence on the variation trend of the structural resistance curve. Based on this, the deformation mode of the U-type corrugated sandwich panel is summarized, and the analytical formula of the deformation resistance of the U-type corrugated core sandwich panel is developed. It is shown that the proposed theoretical deformation model can reflect the main deformation process, and the analytical results match well with the experimental and numerical results.

Numerical simulation analysis for deformation deviation and experimental verification for an antenna thin-wall parts considering riveting assembly with finite element method

In the process of thin-wall parts assembly for an antenna, the parts assembly deformation deviation is occurring due to the riveting assembly. In view of the riveting assembly deformation problems, it can be analyzed through transient and static simulation. In this work, the theoretical deformation model for riveting assembly is established with round head rivet. The simulation analysis for riveting deformation is carried out with the riveting assembly piece including four rivets, which comparing with the measuring points experiment results of riveting test piece through dealing with the experimental data using the point coordinate transform method and the space line fitting method. Simultaneously, the deformation deviation of the overall thin-wall parts assembly structure is analyzed through finite element simulation; and its results are verified by the measuring experiment for riveting assembly with the deformation deviation of some key points on the thin-wall parts. Through the comparison analysis, it is shown that the simulation results agree well with the experimental results, which proves the correctness and effectiveness of the theoretical analysis, simulation results and the given experiment data processing method. Through the study on the riveting assembly for thin-wall parts, it will provide a theoretical foundation for improving thin-wall parts assembly quality of large antenna in future.

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.

Teflon-pad shaping process of circular metal blanks into quasi-cup specimens by theoretical and experimental methods

Teflon-pad shaping process of circular metal blanks into quasi-cup specimens is investigated by theoretical and experimental methods in the quasi-static condition. In the experiments, circular metal sheets are formed into the quasi-cup samples by compressing them between a Teflon-filled die and a rigid punch with desirable shape. To investigate influences of different parameters on the forming progress, 12 rigid punches with different dimensions, two blank material types of aluminum and galvanized iron, three blank thicknesses of 0.6, 1.1 and 1.5 mm, and two Teflon-fillers of PVC and polyurethane are used in several experimental tests. In the analytical part, theoretical deformation models of metal blank and Teflon-filler are introduced and based on energy method, energy absorptions by the blank and Teflon-filler are calculated to derive a theoretical formula for predicting total required energy of the forming process. For this purpose, several energy absorption mechanisms are considered in the blank and filler. Furthermore, predictions by theoretical equation are compared with the corresponding experimental tests to study the verity of the calculated formulas. Theoretical and experimental results illustrate change trend of forming energy with respect to blank thickness. Also, the performed forming tests show that when external cone angle of rigid punch with respect to the horizontal direction increases, forming energy increases nonlinearly; and when the depth of spherical part of rigid punch increases, the probability of rupture increases. Additionally, the experiments demonstrate that there is a direct relationship between the forming energy and flow stress of the blanks. Furthermore, experimental observations illustrate that forming energy of a certain blank with PVC Teflon-filler is higher than that of a similar specimen with polyurethane Teflon-filler; but, the probability of wrinkling decreases when PVC Teflon-pad is used as the filler; and it is advantage of PVC Teflon-filler with respect to polyurethane Teflon.

Ballistic limit velocity of empty rectangular metal columns under a blunt projectile penetration

This paper studies the ballistic limit velocity of empty rectangular columns under a blunt projectile penetration, theoretically and numerically. The deformation mechanism of the empty column is considered as plugging. The projectile is assumed to be a flat-ended cylinder without deformation. A new theoretical model of deformation is introduced, and based on the energy method, a theoretical formula is derived to estimate the ballistic limit velocity of the process. Numerical simulations of the penetration process of a blunt solid cylinder into the empty metal columns are performed using the LS-DYNA explicit solver. Different empty columns are used as the targets, and these columns are made from Weldox 460E steel and have different wall thicknesses (6, 7, 8 and 9 mm) and internal column edge lengths (60, 70, 80 and 90 mm). To validate the derived relation for the ballistic limit velocity, the results of the numerical simulations are compared with the corresponding theoretical predictions. Finally, the effects of some geometrical characteristics such as projectile diameter and mass on the perforation process and the ballistic limit velocity are discussed.

Bioinspired fabrication and characterization of a synthetic fish skin for the protection of soft materials.

The scaled skin of fish is a high-performance natural armor that represents a source of inspiration for novel engineering designs. In this paper, we present a biomimetic fish skin material, fabricated with a design and components that are simple, that achieves many of the advantageous attributes of natural materials, including the unique combination of flexibility and mechanical robustness. The bioinspired fish skin material is designed to replicate the structural, mechanical, and functional aspects of a natural teleost fish skin comprised of leptoid-like scales, similar to that of the striped red mullet Mullus surmuletus. The man-made fish skin material consists of a low-modulus elastic mesh or "dermis" layer that holds rigid, plastic scales. The mechanics of the synthetic material is characterized under in-plane, bending, and indentation modes of deformation and is successfully described by theoretical deformation models that have been developed. This combined experimental and modeling approach elucidates the critical mechanisms by which the composite material achieves its unique properties and provides design rules that allow for the engineering of scaled skins. Such artificial scaled skins that are flexible, lightweight, transparent, and robust under mechanical deformation may thus have potential as thin protective coatings for soft materials.

The Resistance of Ship Web Girders in Collision and Grounding

Ship web girders play an important role in ship structure performance during collision and grounding accidents. The behavior of web girders subjected to in-plane concentrated load is investigated by numerical simulation and theoretical analysis in this paper. A numerical simulation based on previous experiment is conducted to give insight to the deformation mechanism of crushing web girders. Some new important deformation characteristics are observed through the simulation results. A new theoretical deformation model is proposed featured with these deformation characteristics, and a simplified analytical method for predicting the instantaneous and mean resistances of crushing web girders is proposed. The proposed method is verified by two previous experiments and a series of numerical simulations. The agreement between the solutions by the proposed method and the experiment results is good. The comparison results between the proposed analytical method and numerical simulation results are satisfactory for most cases. The proposed analytical method will contribute to the establishment of an efficient method for fast and reliable assessment of the outcome of ship accidental collisions and grounding events.

Elastic-Plastic Deformation of Milling Thin Wall Part

Aircraft components are mostly made by aluminum alloy as thin wall types. These parts are usually end milled to required thicknesses and tight tolerances in specific areas. The thin wall parts are difficult to machine because they are easy to vibrate and deformed due to their lower rigidity. This paper proposes a new elastic-plastic deformation model which is suitable for prediction of machining deformations of end milled thin wall parts. The theoretical deformation model is established on the basis of the equations of Von Kármán. The part deformations are simulated using FE analysis and Matlab. The results show that the deformations for the end milling of thin wall parts can be captured with very high accuracy using the proposed elastic-plastic deformation prediction model.

Empty circular metal tubes in the splitting process – theoretical and experimental studies

This article derives some theoretical relations to predict the instantaneous axial force of the circular metal tubes during the splitting process under the axial compression by the theoretical and experimental methods. A new theoretical model of splitting deformation of the circular tube as a thin-walled structure subjected to the axial loading is introduced and based on the deformation model and using the energy method, some analytical formulas are derived to estimate the instantaneous axial load, maximum splitting load, steady force and curl radius of the tubes. To verify the present theory, some aluminum, mild steel and brazen tubes with the circular cross-section and different geometrical and material characteristics were prepared and axially compressed on conical dies with the different cone angles. Comparison of the theoretical predictions and the experimental measurements shows a good correlation and it affirms verity of the new theoretical deformation model and the present theory. Also, based on the experimental results, the effects of wall thickness and inner radius of the tubes and also, number and length of initial slits and semi-angle of conical die are studied on the axial load and maximum splitting load.

Axial compression of the empty capped-end frusta during the inversion progress

This paper introduces a new theoretical model of plastic deformation during the inversion process on the capped-end frusta using a solid cylindrical punch. Based on the theoretical deformation model, the instantaneous axial load versus the displacement during the inversion process of the capped-end frusta is predicted. In the analytical model, the inversion process is divided into two different stages including plastic deformation of the frusta bottom and inversion of the frusta wall. Also, instantaneous absorbed energy versus the axial displacement and maximum inversion load during the process are estimated using the theoretical model. Some axial inversion experiments were carried out on capped-end conical tubes with different materials and geometrical dimensions to verify the present theory. A good agreement between the theoretical predictions and the experimental results affirms precision and accuracy of the new theoretical model and the analytical formulas.

Theoretical and experimental studies of the external inversion process in the circular metal tubes

This article introduces a new theoretical model of deformation and based on the energy method derives a new theoretical relation to predict the axial load versus the axial displacement during the external inversion process in the circular metal tubes. Several deformation mechanisms are assumed in the theoretical model: bending around circular hinge line, bending in normal to meridian direction and circumferential expansion. A total inversion process in the tubes is divided to three different stages versus the inversion angle, θ: 0⩽θ⩽π, π⩽θ⩽2π and after θ=2π. In each stage, the total dissipated energy is calculated by different deformation modes. The different strain components are calculated and based on the principle of energy conservation; some theoretical relations are derived to predict the instantaneous inversion force. Then, some circular brazen tubes are used in the external inversion tests with die radiuses of R=2.85mm and 4mm and diagrams of axial load versus the axial displacement are sketched. Comparison of the theoretical predictions and the experimental results shows a reasonable correlation. The theoretical relations can predict variations of the axial load versus the axial displacement of three considered stages during the whole inversion process with a good agreement. Comparison of the theoretical and experimental curves shows a better correlation in the horizontal part and position of start point of the inversion process with the die radius of R=4mm, comparing with the inversion process with the die radius of R=2.85mm. Also, the theoretical analysis shows that the absorbed energy and the axial load during the inversion process in the circular tubes depend on the wall thickness and diameter of the tube, tube material type, and the die radius.

Prediction of the mean folding force during the axial compression in foam-filled grooved tubes by theoretical analysis

In this article, some theoretical relations are derived to predict the mean folding force, total absorbed energy per unit of tube length and specific absorbed energy per unit of total mass by the polyurethane foam-filled grooved tubes with circular cross section under the axial compression process. During the folding process, a new theoretical model of deformation is introduced for the polyurethane foam-filler. The theoretical analysis is developed on the basis of the energy method. Some foam-filled grooved specimens were prepared and axially compressed to obtain the experimental diagram of the folding force versus the axial displacement. Comparison of the theoretical predictions with the experimental results showed a good agreement. Then, by considering the interaction effect between the polyurethane foam and the inner wall of grooved tubes, a semi-empirical relation was derived. Predictions along with considering the interaction factor obtained from the semi-empirical relation indicate a better correlation with those of the experiments.

Experiments and Simulation of Elastic-Plastic Deformation in Thin Wall Part Milling

Aircraft components are mostly made by aluminum alloy as thin wall types. These parts are usually end milled to required thicknesses and tight tolerances in specific areas. The thin wall parts are difficult to machine because they are easy to vibrate and deformed due to their lower rigidity. This paper proposes a new elastic-plastic deformation model which is suitable for prediction of machining deformations of end milled thin wall parts. The theoretical deformation model is established on the basis of the equations of Von Kármán. The effect of bending springback is also taken into account. The part deformations are simulated using FE analysis and Matlab. Milling experiments on a CNC machining center are performed. The experimental results show that the deformations for the peripheral milling of thin wall parts can be captured with very high accuracy using the proposed elastic-plastic deformation prediction model.

Analysis of the induced seismicity of the Lacq gas field (Southwestern France) and model of deformation

SUMMARY The goal of this paper is to propose a model of deformation pattern for the Lacq gas field (southwest of France), considering the temporal and spatial evolution of the observed induced seismicity. This model of deformation has been determined from an updating of the earthquake locations and considering theoretical and analogue models usually accepted for hydrocarbon field deformation. The Lacq seismicity is clearly not linked to the natural seismicity of the Pyrenean range recorded 30 km farther to the south since the first event was felt in 1969, after the beginning of the hydrocarbon recovery. From 1974 to 1997, more than 2000 local events (M L < 4.2) have been recorded by two permanent local seismic networks. Unlike previously published results focusing on limited time lapse studies, our analysis relies on the data from 1974 to 1997. Greater accuracy of the absolute locations have been obtained using a well adapted algorithm of 3-D location, after improvement of the 3-D P-wave velocity model and determination of specific station corrections for different clusters of events. This updated catalogue of seismicity has been interpreted taking into account the structural context of the gas field. The Lacq gas field is an anticlinal reservoir where 3-D seismic and borehole data reveal a pattern of high density of fracturing, mainly oriented WNW‐ESE. Seismicity map and vertical cross-sections show that majority of the seismic events (70 per cent) occurred above the gas reservoir. Correlation is also observed between the orientation of the pre-existent faults and the location of the seismic activity. Strong and organized seismicity occurred where fault orientation is consistent with the poroelastic stress perturbation due to the gas recovery. On the contrary, the seismicity is quiescient where isobaths of the reservoir roof are closed to be perpendicular to the faults. These quiescient areas as well as the central seismic part are characterized by a surface subsidence determined by repeated levelling profiles. Moreover, the temporal evolution of the distribution of the seismicity clearly exhibits a spatial migration from the centre to the boundaries of the reservoir. We conclude that the entire field is strained but this deformation is seismically expressed only where faults are parallel to the isobaths of the reservoir roof and where these faults plunge towards outside the field according to one of the two theoretical deformation models considered in our study. Then we propose a temporal scenario of deformation along the principal axis of seismic deformation.

Mechanical properties of 17-4PH stainless steel foam panels

Rectangular 17-4PH stainless steel sandwiched foam panels were fabricated using a commercial manufacturing technique by brazing two sheets to a foam core. Microstructural observations of the panels revealed large variations in the quality of the brazed areas from one panel to the next as well as within the same panel. Shear tests conducted on specimens machined from the panels exhibited failures either at poorly brazed face sheet–foam core interfaces or within foam cores of well-bonded specimens. Compression tests were conducted on the foam cores to evaluate their elastic and plastic deformation behavior. These data were compared with published data on polymeric and metallic foams, and with theoretical deformation models proposed for open cell foams.

Stress analysis of a cold forging process applied to a countersunk headed fastener

Cold forging processes are used frequently in the manufacture of high-strength headed fasteners. These processes are characterised often by high tool loads and stresses with the consequent risk of tool failure. Increasingly, engineers are attempting to develop a better understanding of the nature of the metal flow arising during closed-die cold-forging operations. This is being done in an effort to establish more reliable mathematical models of the process, to aid in the selection of the most appropriate forming machines, and in the design of the tooling to be used on these machines. The work reported in this paper involves an experimental and theoretical analysis of the metal deformation arising during the cold forging of countersunk headed fasteners. A set of expressions for the punch—workpiece interface and the mean forging pressure were derived by the author using the slab-analysis method. The predicted values for interface and mean forging pressures obtained using the derived slab-analysis equations were compared with results obtained using standard open-extrusion and cylinder-compression expressions. The results predicted using each of the theoretical deformation models were compared with those obtained from a series of experimental forging tests. It was found that the slab-analysis expressions predicted results that were in close agreement with those obtained experimentally. Furthermore, it was determined that the form of the derived equations was such that changes in both interfacial friction conditions and die angles could be catered for very easily.

Geometric Constraints on the Forming Path in Roll Forming Channel Sections

In roll forming, flat strip is progressively deformed by sets of rotating rolls; it is a commercially important metal forming process but not one that has been extensively studied on a scientific basis. This paper introduces a new method of indicating forming severity, the bend angle curve, which shows the bend angle distribution and the geometric restrictions imposed by the shape of the rolls, it includes and extends an existing theoretical model of deformation in the unsupported strip based on a modified minimum energy concept. Experiments were carried out in which a channel section was roll-formed and the shape of the strip measured along the whole deformation region. Good correlation was obtained with the predicted bending angle curve and the results demonstrate the influence of roll diameter as well as cross-sectional shape.