Explicit robust schemes for implementation of a class of principal value-based constitutive models: Symbolic and numeric implementation

The issue of developing effective and robust schemes to implement a class of the Ogden-type hyperelastic constitutive models is addressed. To this end, special purpose functions (running under MACSYMA) are developed for the symbolic derivation, evaluation, and automatic FORTRAN code generation of explicit expressions for the corresponding stress function and material tangent stiffness tensors. These explicit forms are valid over the entire deformation range, since the singularities resulting from repeated principal-stretch values have been theoretically removed. The required computational algorithms are outlined, and the resulting FORTRAN computer code is presented

Explicit robust schemes for implementation of general principal value-based constitutive models

The issue of developing effective and robust schemes to implement general hyperelastic constitutive models is addressed. To this end, special purpose functions are used to symbolically derive, evaluate, and automatically generate the associated FORTRAN code for the explicit forms of the corresponding stress function and material tangent stiffness tensors. These explicit forms are valid for the entire deformation range. The analytical form of these explicit expressions is given here for the case in which the strain-energy potential is taken as a nonseparable polynomial function of the principle stretches

On the symbolic manipulation and code generation for elasto-plastic material matrices

A computerized procedure for symbolic manipulations and FORTRAN code generation of an elasto-plastic material matrix for finite element applications is presented. Special emphasis is placed on expression simplifications during intermediate derivations, optimal code generation, and interface with the main program. A systematic procedure is outlined to avoid redundant algebraic manipulations. Symbolic expressions of the derived material stiffness matrix are automatically converted to RATFOR code which is then translated into FORTRAN statements through a preprocessor. To minimize the interface problem with the main program, a template file is prepared so that the translated FORTRAN statements can be merged into the file to form a subroutine (or a submodule). Three constitutive models; namely, von Mises plasticity, Drucker-Prager model, and a concrete plasticity model, are used as illustrative examples

Kinetics analysis of solidification process of 1035 steel at different cooling rates

It is of great theoretical significance to study the solidification kinetics of metal materials for improving the microstructure and properties. In this paper, the Differential Scanning Calorimetry (DSC) was used to measure the enthalpy change of solidification process of 1035 steel at different cooling rates. The activation energy of the solidification process was determined by the equal conversion method based on the data of enthalpy. The mechanism function of the solidification process was also determined. It is shown that the value of the activation energy of solidification process varied with the solidification fraction, and the mechanism functions of solidification process are different in different temperature ranges, which are –ln(1– α) for 1 504-1 502 °C –ln(1–α)1/2 for 1 500-1 942 °C and –ln(1– α)2/5 for_1 490 °C respectively

Kinetics analysis of solidification process of 1035 steel at different cooling rates

It is of great theoretical significance to study the solidification kinetics of metal materials for improving the microstructure and properties. In this paper, the Differential Scanning Calorimetry (DSC) was used to measure the enthalpy change of solidification process of 1035 steel at different cooling rates. The activation energy of the solidification process was determined by the equal conversion method based on the data of enthalpy. The mechanism function of the solidification process was also determined. It is shown that the value of the activation energy of solidification process varied with the solidification fraction, and the mechanism functions of solidification process are different in different temperature ranges, which are –ln(1– α) for 1 504-1 502 °C –ln(1–α)1/2 for 1 500-1 942 °C and –ln(1– α)2/5 for_1 490 °C respectively

Cardiac rhythm analysis during ongoing cardiopulmonary resuscitation using the Analysis During Compressions with Fast reconfirmation technology

BACKGROUND Pauses in chest compressions (CCs) have a negative association with survival from cardiac arrest. Electrocardiographic (ECG) rhythm analysis and defibrillator charging are significant contributors to CC pauses. OBJECTIVE Accuracy of the Analysis During Compressions with Fast Reconfirmation (ADC-FR) algorithm, which features automated rhythm analysis and charging during CCs to reduce CC pauses, was retrospectively determined in a large database of ECGs from 2701 patients with out-of-hospital cardiac arrest. METHODS The ADC-FR algorithm generated a total of 7264 advisories, of which 3575 were randomly assigned to a development data set and 3689 to a test data set. With ADC-FR, a high-pass digital filter is used to remove CC artifacts, while the underlying ECG rhythm is automatically interpreted. When CCs are paused at the end of the 2-minute cardiopulmonary resuscitation interval, a 3-second reconfirmation analysis is performed using the artifact-free ECG to confirm the shock/no-shock advisory. The sensitivity and specificity of the ADC-FR algorithm in correctly identifying shockable/nonshockable rhythms during CCs were calculated. RESULTS In both data sets, the accuracy of the ADC-FR algorithm for each ECG rhythm exceeded the recommended performance goals, which apply to a standard artifact-free ECG analysis. Sensitivity and specificity were 97% and 99%, respectively, for the development data set and 95% and 99% for the test data set. CONCLUSION The ADC-FR algorithm is highly accurate in discriminating shockable and nonshockable rhythms and can be used to reduce CC pauses