Determination of elastomeric foam parameters for simulations of complex loading

Objective To explore the establishment of 3D thoracic model by finite element methods, and study the mechanical mechanism of minimally invasive surgery for correcting the chest wall deformity, and provide personalized surgery solution in the future. Methods According to admission and exclusion criteria, we selected 10 cases of pectus carinatum that received chest CT scan. The finite element model of pectus carinatum was established and analyzed by Mimics, ABAQUS, etc. The validity of finite element method for chest wall was verified by comparing the sternal displacement between the simulated values and actual values with the same force. Results The 3D finite element model of pectus carinatum was successfully established and analyzed. The stress distribution of the 10 cases in the posterior ribs was mainly in the 1-6 ribs on both sides, mostly concentrated in the 4th to 6th ribs, and the stress was symmetrical on both sides. Statistical analysis showed that the displacement value of the sternum was correlated, and the validity of the model was verified. Conclusion Mimics, ABAQUS and other finite element modeling and analysis software can effectively establish the thoracic 3D finite element model and mechanical analysis, which can help the further development of personalized minimally invasive surgery for correcting chest wall deformities. Key words: Pectus carinatum; Chest wall deformity; Finite element analysis

Finite element analysis (FEA) is widely used to investigate the crushing performance of thin-walled tubes, and carry out parametric studies. However, simulation results are not always in good agreements with experimental results especially in terms of deformation modes in published literature. In this paper, a systematic FEA study will be conducted to evaluate two main simulation techniques using indentation triggers and buckling modes to introduce imperfections in FEA. Axial compressive tests were first carried out on three types of thin-walled circular tubes with different geometrical parameters. The finite element models were subsequently developed and used to explore the effects of indentation triggers and buckling modes on the deformation modes and force–displacement curves of thin-walled tubes. The influences of indentation depths and indentation positions on the crushing performance were investigated. Similarly, the effects of the order of buckling modes and scale factors on the crushing characteristics were examined as well. It has been found that for thin-walled circular tubes, a suitable simulation technique with indentation triggers or buckling modes can be employed to precisely mimic the deformation mode and corresponding force–displacement curve. This study is expected to provide some practical techniques and insights into the numerical simulation of circular tubes.

A double scalar elastic damage constitutive model of ice materials

A finite element analysis (FEA) model is established to investigate the concrete-encased concrete-filled steel tubular (CFST) column to reinforced concrete (RC) beam joints under cyclic loading. The feasibility of the FEA model is verified by a set of test results, consisting of the failure modes, the exposed view of connections, the crack distributions and development, and the hysteretic relationships. The full-range analysis is conducted to investigate the stress and strain development process in the composite joint by using this FEA model. The internal force distributions of different components, as well as the deformation distributions, are analyzed under different failure modes. The proposed connections are investigated under dimensional and material parameters, and the proper constructional details of the connections are recommended. Parameters of the beam-column joints, including material strength, confinement factor, reinforcement ratio, diameter of steel tube to sectional width ratio, beam to column linear bending stiffness ratio and beam shear span ratio are evaluated. Furthermore, the key parameters affecting the failure modes and the corresponding parameters ranges are proposed in this paper.

The layer of non-impregnated aramid fibers is widely used in the containment systems of aircraft gas turbine engines. Such systems are found to be especially cost-effective and light weight for mitigating engine debris during a fan blade-out event. This is mostly because non-impregnated aramid fibers have a high strength per unit weight. Moreover, it is inexpensive to manufacture such a containment system compared to traditional metallic systems. To properly utilize this advantage, it is necessary to have a finite element (FE) analysis modeling methodology for daily design tasks. Non-impregnated aramid fibers winding for fan case modeling for engine containment systems is a difficult task. This research implied both experimental and modeling techniques, and data characterizing the behavior of fabric materials for engine containment systems. This research was aimed at addressing engine containment modeling issues. Thus this work has resulted in the following major accomplishments: • Experimental Characterization of Non-impregnated Aramid Fibers: the fabric material model originally was created during this phase. The independent laboratory tests conducted at NPO Saturn form the basis of this model. These material models are general enough to be used as the constitutive model for both static and dynamic/explicit FE analyses. • Static Ring Tests: Static tests of containment wraps subjected to loads through a blunt nose impactor were performed at NPO Saturn. Ballistic tests of containment wraps subjected to a high-velocity projectile were performed at NPO Saturn. These tests provided the test cases (the benchmark results) to validate the developed FE methodology. • FE Material Model Development: The material models were used by the research team in the FE simulation of static and ballistic tests. The static test results have been validated by NPO Saturn using the ANSYS FE program. The ballistic test results were validated by NPO Saturn using the LS-DYNA FE program. • Engine Fan Blade-Out (FBO) Simulation: The knowledge gained from previous tasks was used by NPO Saturn for the the numerical simulation of real engine FBO events involving the existing production engine models and compared to the test results (employing thelayer of non-impregnated aramid fibers containment). • Combined Fan and Metal Case Comparison: The relative comparison between the non-impregnated aramid fibers and the metal materials in engine FBO containment systems has been carried out in order to ascertain that the non-impregnated aramid fibers case is more advantageous.

The present study aimed to identify the optimal design of the unicompartmental femoral component through parameter analysis and stability evaluation. A finite element (FE) analysis was applied to analyse and adjust the parameter combinations of the anterior tilt angle of the posterior condyle resection surface, the position of the peg, the length of the pegand the inclination angle of the peg, resulting in 10 different FE models. Setting three knee flexion angles of 8.4° (maximum load state during walking), 40° (maximum load state during stair climbing)and 90° (maximum load state during squatting exercise), quantitatively analysing the micromotion values of the bone-prosthesis interfaceand defining a weighted scoring formula to evaluate the stability of different FE models. The validity of the FE analysis was verified using the Digital Image Correlation (DIC) device. The errors between the FE analysis and the DIC test at three flexion angles were 5.6%, 1.7%and 11.1%. The 10 different femoral component design models were measured separately. The FE analysis demonstrated that the design with a 0° anterior tilt angle of the posterior condyle resection surface, both pegs placed on the distal resection surface, lengthened 5 mm pegsand a 10° peg inclination angle provided the best stability. The current study proposed a method for evaluating the stability of the femoral component design. The optimal intersurface stability design of the unicompartmental femoral component was achieved with two pegs placed on the distal resection surface, a 5-mm peg length incrementand a 10° peg inclination. These results might provide a reference for the selection of unicompartmental femoral components in clinical practice and therefore improve the survival rate of future unicompartmental knee arthroplasty. Level III.

Intelligent finite element method: An evolutionary approach to constitutive modeling

A computationally efficient method is proposed for the steady-state performance simulation of brushless permanent-magnet (PM) motors. Only a minimum number of magnetostatic finite-element (FE) analysis (FEA) solutions are used in conjunction with space-time transformations, which are based on the periodicity specific to synchronous machines. For an example electronically controlled interior PM (IPM) motor with six teeth per pole and a distributed winding, a single nonlinear magnetostatic FE solution was employed to estimate the flux density time waveforms in the stator teeth and yoke. Other results include core losses, back electromotive force, and torque. The extension of the method to fractional-slot topologies with reduced number of teeth and concentrated (non-overlapping) coils is discussed with reference to a nine-slot six-pole IPM motor example. The computational time is reduced by one to two orders of magnitude as compared with more laborious time-stepping FEA. Successful validation was performed against experimental data and detailed FEA results.

Elastic-plastic deformation behavior of austenitic, martensitic, and austenitic-martensitic high-Mn steels is investigated by using crystal plasticity theory. The development of expandable pipes made of two-phase steel for oil and gas well applications is needed for improved and efficient recovery of hydrocarbons from difficult reservoirs. The current research is aimed at improving the down-hole post-expansion material properties of expandable pipes. A mathematical model is first developed based on finite-deformation crystal plasticity theory assuming that slip is the prime mode of plastic deformation. The developed model is then numerically implemented by using the finite element software ABAQUS, through a user defined subroutine. Finite element simulations are performed for austenitic, martensitic, and austenitic-martensitic steels having different proportions of martensite in an austenite matrix. Three primary modes of loading are considered: uniaxial tension, compression and simple shear. The variation in yield strength, hardening pattern and dissipated energy is observed and analyzed.

Tensile behavior of an auxetic structure: Analytical modeling and finite element analysis

Field investigation and finite element analysis on expansion and shrinkage strains of expansive concrete structures

In the hot forging process of aluminum piston using water-soluble lubricants, the lubricant layer is often peeled off due to excessive deformation of the material during forming, which may result in direct contact between the material and the die, thereby partially increasing the friction. The constant friction in the Finite element (FE) analysis of this process sometimes results in a completely different result from the actual material flow. Therefore, this study was designed to investigate the friction condition to accurately predict the material flow in the FE analysis. The FE analysis was performed for various material temperatures and friction parameters and the proper friction condition was also derived to remove forging defects. Finally, the forging test was carried out for the initial specimens produced by three different methods to verify the analytical results and eliminate the forging defects. The results showed that the friction depends on the effective strain in the FE analysis and the critical value to increase friction is approximately 1.5–1.8. In addition, among the three different specimens, the shot peened specimen can remove the forging defect by increasing the amount and uniformity of the lubricant on its surface.

To determine nonlinear material properties of passive, diastolic myocardium using magnetic resonance imaging (MRI) tissue-tagging, finite element analysis (FEA) and nonlinear optimization. Alterations in the diastolic material properties of myocardium may pre-date the onset of or exist exclusive of systolic ventricular dysfunction in disease states such as hypertrophy and heart failure. Accordingly, significant effort has been expended recently to characterize the material properties of myocardium in diastole. The present study defines a new technique for determining material properties of passive myocardium using finite element (FE) models of the heart, MRI tissue-tagging and nonlinear optimization. This material parameter estimation algorithm is employed to estimate nonlinear material parameter sin the in vivo canine heart and provides the necessary framework to study the full complexities of myocardial material behavior in health and disease. Material parameters for a proposed exponential strain energy function were determined by minimizing the least squares difference between FE model-predicted and MRI-measured diastolic strains. Six mongrel dogs underwent MRI imaging with radiofrequency (RF) tissue-tagging. Two-dimensional diastolic strains were measured from the deformations of the MRI tag lines. Finite element models were constructed from early diastolic images and were loaded with the mean early to late left ventricular and right ventricular diastolic change in pressure measured at the time of imaging. A nonlinear optimization algorithm was employed to solve the least squares objective function for hte material parameters. Average material parameters for the six dogs were E = 28,722 +/- 15984 dynes/cm2 and c = 0.00182 +/- 0.00232 cm2/dyne. This parameter estimation algorithm provides the necessary framework for estimating the nonlinear, anisotropic and non-homogeneous material properties of passive myocardium in health and disease in the in vivo beating heart.

This paper deals with the cyclic elastoplastic analysis and stability evaluation of steel braces of hollow sections subjected to axial tension and compression. The inelastic cyclic performance of cold-formed steel braces of circular and box hollow sections is examined through finite element analysis using the commercial computer program ABAQUS. First some of the most important parameters considered in the practical design and ductility evaluation of steel braces of tubular hollow sections are presented. Then the details of finite element modeling and numerical analysis are described. Later the accuracy of the analytical model employed in the analysis is substantiated by comparing the analytical results with the available test data in the literature. Finally the effects of some important structural and material parameters on cyclic inelastic behavior of steel braces are discussed and evaluated. INTRODUCTION Steel braced frames are one of the most commonly used structural systems because of their structural efficiency in providing significant lateral strength and stiffness. The steel braces contribute to seismic energy dissipation by deforming inelastically during an earthquake. The use of this type of construction indeed avoids the brittle fracture found in beam-to-column connections in moment resisting steel frames that occurred in the Northridge earthquake in 1994 and the Kobe earthquake in 1995 (ASCE 2000, IGNTSDSS 1996). However, careful design of steel braced frames is necessary to avoid possible catastrophic failure by brace rupture in the event of a severe seismic loading. The current capacity design procedure adopted in most seismic design steel specifications (AISC 1997, CAN-CSAS16.1 1989), for concentrically braced frames requires yielding in the braces as primary members, whereas the secondary members of the frame should remain elastic and hence carry forces induced by the yielding members. The transition from current perspective seismic codes to performance-based design specifications requires accurate predictions of inelastic limit states up to structural collapse. The cyclic behavior of steel brace members is complex due to the influence of various parameters such as, material nonlinearity, structural nonlinearity, boundary condition, and loading history. The material nonlinearity includes structural steel characteristics such as, residual stresses, yield plateau, strain hardening and Bauschinger effect. The structural © 2008 ASCE 18th Analysis and Computation Specialty Conference Copyright ASCE 2008 18th Analysis and Computation Specialty Conference nonlinearity includes parameters such as, brace slenderness parameter, cross-section slenderness, width-to-thickness ratio of the cross-section’s component elements (or radius-to-thickness ratio of circular hollow sections), and initial out of straightness of the brace. The complex behavior results in various physical phenomena, such as, yielding in tension, buckling in compression, postbuckling deterioration of compressive load capacity, deterioration of axial stiffness with cycling, and low cycle fatigue fractures at plastic regions. Steel braces can be designed to resist only tensile forces, or to resist both tensile and compressive axial forces. Recent earthquakes and experiments have shown that the tensioncompression braces provide better performance under cyclic loading (during an earthquake) as compared with the tension-only braces having almost no compressive strength. Under severe earthquakes, the braces are subjected to cyclic axial forces and they are allowed to undergo compression buckling or tensile yield to dissipate the imposed energy while columns and collector beams respond elastically. Therefore, understanding the behavior of the bracing members under idealized cyclic loading is an important step in the careful design of steel braced frames. This paper deals with the cyclic elastoplastic analysis of steel braces. The most important parameters considered in the practical design and ductility evaluation of steel braces of tubular hollow sections are presented. The cyclic elastoplastic performance of steel braces is examined through finite element analysis using the computer program ABAQUS. The accuracy of the analytical model employed in the analysis is substantiated by comparing the analytical results with the available test data in the literature. The effects of some important structural and material parameters on inelastic cyclic behavior of steel braces are discussed and evaluated.

Computational evaluation of the axis-blade angle for measurements of implant positions in trochanteric hip fractures: A finite element analysis