Statement of problem: The application of elastomeric ligatures is one of the methods of archwires ligation to orthodontic brackets. Knowledge about modulus of Elasticity of these ligatures is useful for selecting a specific brand of elastomeric ligature for a special condition.Purpose: The purpose of this study was to compare Elastic modulus of seven commercially available elastomeric ligatures in the initial condition and after 28 days immersion in a simulated oral environment. Changes in the modulus of Elasticity were also surveyed for each brand of ligatures after 28 days.Materials and Method: 'In this experimental laboratory-based study, elastomeric ligatures were obtained from different companies and their modulus of Elasticity were measured in the initial condition and after 28 days immersion in a simulated oral environment using Zwick testing machine at 5mm/mm cross head speed. The data were analyzed using SPSS software and ANOVA, Duncan and student's t-test.Results: Different brands of elastomeric ligatures showed significant differences in Elastic modulus both in the as-received condition and after 28 days immersion in the simulated oral environment (p<0.05). Ligatures from American Orthodontics and Ortho Technology showed the lowest and ligatures from Dentaurum revealed the highest Elastic modulus in the as-received condition. modulus of Elasticity in the ligatures from American Orthodontics, Ortho Technology and ITO increased significantly while in ligatures from Dentaurum it was decreased significantly after 28 days immersion in the simulated oral environment (p<0.05).Conclusion: Ligatures from American Orthodontics and Ortho Technology are suitable for immediate use after bonding and in sliding mechanics while ligatures from Dentaurum are not suitable to use immediately after bonding.

Atomic force microscopy (AFM) is capable of imaging the surface of sample, as well as obtaining the information about mechanical properties of samples such as Elastic modulus. Nano indentation using the atomic force microscope makes it a powerful technique to determine Elastic properties like the Young's modulus for biological samples. JPK IP software is easy procedure and suitable to obtain Elastic data and calculate young modulus.

Complex nonlinear unloading behavior following plastic deformation on metals has been observed by researchers. However, a constant chord modulus has been used by most of the researchers to describe the unloading behavior. In this study, a new hypoElastic model is proposed in order to describe this complex nonlinear behavior. The Elastic modulus is assumed to be the initial Young’s modulus at the beginning of each loading reversal and is exponentially decreased with the Elastic deformation and finally saturates to a particular value at the start of plastic deformation. The model can be easily utilized in any plasticity constitutive law. Furthermore, its numerical implementation is fairly straightforward. As an example, a simple constitutive law was developed using the von-Mises yield function, isotropic hardening law and the proposed hypoElastic model. This constitutive law was implemented into ABAQUS commercial package via a user material subroutine UMAT. A comparison between the experimental response of DP980 and its simulated response showed that the model is able to describe the material response fairly well.

In order to use the design softwares for natural fibersthermoplastic composites in structural applications, precise determination of Elastic parameters is of importance. Regarding the viscoElastic properties of these materials and their nonlinear stress-strain curves, even at low loading levels, determination of precise Elastic parameters by common static tests is not simple. In the present study, methods of loadingunloading test was used to determine the Elastic modulus of a natural fiber-thermoplastic composite and the results were compared with the tangent modulus obtained from static compression test. Dynamic modulus was also obtained from ultrasonic test, and a regression relationship was proposed between dynamic modulus and the static one. Results showed that the composite had orthotropic nature and the dynamic modulus from ultrasonic test showed higher values compared with the two others. Also, with increasing modulus resulted from unloading test, the difference between dynamic and unloading modulus decreased linearly. Results also showed that using prevalent method of modulus determination for this material (i. e. tangent modulus at 10-40% of ultimate stress) leads to the Elastic modulus estimated much lower than the real value.

The results of over 100 geotechnical site investigations in different zones of Tehran alluvium in the south part of Tehran city were analyzed to determine the correlation of modulus between Elasticity and SPT number of soil in southern Tehran alluvium. The alluvial deposits in southern Tehran are composed mostly of fine-grained materials or coarse-grained soils with silt and clay particles. Based on the soil material properties, the study area is divided into three sections. In each section, the results of a large number of in situ and laboratory tests are classified and analyzed to determine the Elastic modulus of soil. The study shows that, for the first part of the area the modulus of Elasticity from plate load test correlates well with SPT number and for the second and third parts, the direct shear and triaxial tests have an acceptable correlation with SPT number. Formulas relating Elastic modulus to standard penetration test number are given and compared to those reported in the literature. Also, from the analysis of data it was seen that the Elastic modulus of soil is increased with increase of maximum soil particles. Finally average results for unconfined strengths of fine grained soil in alluvium of the south of Tehran are presented.

In this study, pressure-strain Elastic modulus, stiffness, distensibility, cross-sectional ‎compliance and Young modulus of the common carotid artery were evaluated in 30 ‎subjects, normal and atherosclerosis, non-invasively. The diameter changes and cross-‎sectional changes in systolic and diastolic phases of the carotid artery were measured ‎by real time B-mode sonography and color Doppler, respectively. Indirect blood ‎pressure measurement was made by manometer immediately after measurement of the ‎pulsatile vessel diameter and area. Elastic parameters were estimated from the ‎diameter relative changes, cross-section relative changes and the systolic and diastolic ‎blood pressure in the brachial artery. The relative diameter changes in mild stenosis ‎and severe stenosis compared to normal group are not expected‏.‏‎‎ The results of evaluation of Elastic parameters show that in mild stenosis, pressure-‎strain Elastic modulus, stiffness and Young modulus decreased but in severe stenosis ‎they increased relative to normal arteries. In mild stenosis, distensibility and cross-‎sectional compliance increased but in severe stenosis these parameters decreased ‎relative to normal. Of course, mechanical parameters of atherosclerotic group are ‎significantly different from the normal carotid artery. By applying this method, we ‎can detect atherosclerosis from normal carotid artery (Iranian Heart Journal 2003; 4 ‎‎(2,3): 68-74).‎