An etiologic evaluation of children with short stature in Gorgan (Northeast Iran), 2005

Growth is an important biological process during childhood. Short stature is the most common cause of a child to be examined by an endocrinologist. This cross-sectional study was performed to determine the short stature causes in children aged 6-14 years old in 2005 who were referred to Talghani Medical-Educational Center. Demographic characteristics, history of any serious problem (prematurity), clinical feature, biochemical and endocrinological test results and radiological findings were evaluated. Standard Deviation Score (SDS) was calculated and written down in an information recording form. From 100 children under study (66%) were girls with the average age of 10.84 year. Their average of bone age was 8.4 year. Most common causes for short stature were constitutional (57%), growth hormone deficiency (30%) and familial (8%). There was not significant difference between two sexes in this view. According to the findings, after ruling out of Constitutional and familial causes, we strongly recommended the provocative growth hormone test for early detection and timely prevention of permanent short stature

A detailed model of high pressure torsion

High Pressure Torsion (HTP) is a popular physical simulator to produce ultra-fine grained materials. Existingsolutions of HPT predict a zero deformation and grain refinement near its sample’s longitudinal axis. However,experimental observations confirm that this is not typically the case. For a more realistic study of material’s flowduring the test, a detailed model was presented here in which the sample was represented as a “CylindricalSegment (CS)” with a small run-out. A HPT-CS model was developed which included a parametricrepresentation of the 3D problem and a kinematically admissible velocity field. The model was solved andthe effective strain rate and strain for the problem were formulated. To verify the HPT-CS solution, a specialcase with zero run-out and two general case solutions (non-zero run-out) were compared with the existingsolution of HPT as the reference. The sample comparisons confirmed the accuracy of the proposed solution.Distributions of effective strain rate and strain along the sample’s longitudinal axis were presented for thegeneral case solutions. These increased linearly from zero at the sample’s mid-plane to their maximum at itstop-plane. The maximum values for the second case were 0.138 s−1 and 0.290, respectively. An explanation forthe grain refinement near the sample’s centre was suggested based on the presented HPT-CS’ solution

A comprehensive method to identify the kinetics of static recrystallization using the hot torsion test results with an inverse solution

Many difficulties exist in directly following the static recrystallization of metals, particularly during hotworking. Indirect measurement of static recrystallization has been extensively performed in the literature where, for example, the recrystallization behavior of austenite in steels has commonly been measured indirectly using the fractional softening method. This method relies on the yield stress changes during recrystallization which are physically simulated by hot torsion or compression tests. However, the inherent heterogeneity of deformation during a mechanical test leads to a non-uniform static recrystallization distribution in the test sample. This, in turn, poses a serious question concerning the reliability of the measurement since the stress calculation techniques during recrystallization are not adequately developed in the existing literature. This paper develops a computer-based method to account for heterogeneous deformation during fractional softening measurements based on the hot torsion test data. The importance of the fractional softening gradient in determining the kinetics is emphasized and deficiencies in our understanding of the basic mechanisms are highlighted. A computer-based method is introduced to generate the experimental and computational components in a cost function. The cost function is then utilized by an inverse solution to calibrate the design parameters in a static recrystallization model

Conversion of the hot torsion test results into flow curve with multiple regimes of hardening

The method of Fields and Backofen has been commonly used to reduce the data obtained by hot torsion test into flow curves. The method, however, is most suitable for materials with monotonic strain hardening behaviour. Other methods such as St&uuml;we&rsquo;s method, tubular specimens, differential testing and the inverse method, each suffer from similar drawbacks. It is shown in the current work that for materials with multiple regimes of hardening any method based on an assumption of constant hardening indices introduces some errors into the flow curve obtained from the hot torsion test. Therefore such methods do not enable accurate prediction of onset of recrystallisation where slow softening occurs. A new method to convert results from the hot torsion test into flow curves by taking into account the variation of constitutive parameters during deformation is presented. The method represents the torque twist data by a parametric linear least square model in which Euler and hyperbolic coefficients are used as the parameters. A closed form relationship obtained from the mathematical representation of the data is employed next for flow stress determination. Two different solution strategies, the method of normal equations and singular value decomposition, were used for parametric modelling of the data with hyperbolic basis functions. The performance of both methods is compared. Experimental data obtained by FHTTM, a flexible hot torsion test machine developed at IROST, for a C&ndash;Mn austenitic steel was used to demonstrate the method. The results were compared with those obtained using constant strain and strain rate hardening characteristics.<br /

A heuristic model selection scheme for representing hot flow data using the hot torsion test results

The problem of &quot;model selection&quot; for expressing a wide range of constitutive behaviour adequately using hot torsion test data was considered here using a heuristic approach. A model library including several nested parametric linear and non-linear models was considered and applied to a set of hot torsion test data for API-X 70 micro-alloyed steel with a range of strain rates and temperatures. A cost function comprising the modelled hot strength data and that of the measured data were utilized in a heuristic model selection scheme to identify the optimum models. It was shown that a non-linear rational model including ten parameters is an optimum model that can accurately express the multiple regimes of hardening and softening for the entire range of the experiment. The parameters for the optimum model were estimated and used for determining variations of hot strength of the samples with deformation