Poissons ratio and youngs modulus relationship counseling

For the cases I have looked at so far, the Young's modulus is proportional to the bulk modulus (because the Poissons's ratio is less than ). shear modulus (G) and Poisson's ratio (v) of soft hydrogels using a non- Noshir Langrana, for his unselfish commitment of time, conscientious advice, sincere effort synthetic polymers to prepare hydrogels, in the past couple of decades. Within the elastic limit of any material, there is a linear relationship between the When calculating the velocity of a shear wave, the shear modulus is used.

Defects such as dislocation and their density play an important role in the bioactivity of hydroxyapatite crystals. Dislocations have a major influence on the processes that leads to bone apposition on bioactive materials. Dislocations also have an important role in in vivo dissolution processes and in crystal maturation of biological apatites Porter et al.

Mechanical properties of hydroxyapatite single crystals from nanoindentation data

Dislocations allow plastic deformation through slip. Early studies using microscale compression tests along different crystallographic directions have shown that the hexagonal lattice of hydroxyapatite crystal exhibits highly anisotropic plastic deformation at high temperatures Nakano et al. In recent studies instrumented indentation experiments have been performed to investigate the mechanical properties of hydroxyapatite single crystals Viswanath et al. These studies exhibit interesting scale-dependent behavior.

At the microscale, hydroxyapatite crystals are very brittle and crack during microindentation Viswanath et al. Nanoindentation of hydroxyapatite single crystals along the [] and [] crystallographic directions exhibits anisotropic deformation behavior with the crystal being softer and more ductile along the [] crystallographic direction.

While the yield stress and hardness are lower along this direction, the fracture toughness is higher Saber-Samandari et al.

Other studies suggest that the mechanical properties of the hydroxyapatite crystals are a function of the crystal size Gao et al. At the nanoscale, the crystal mechanical properties become insensitive to defects and reach their theoretical maximum values. A study of the mechanical response of hydroxyapatite single crystal using atomistic simulations shows that when the defects in the crystal do not contribute to the deformation, the yield stress and hardness of the crystal significantly increase Ching et al.

Mechanical properties of hydroxyapatite single crystals from nanoindentation data

These simulations exhibit highly nonlinear anisotropic elastic-plastic deformation response with the crystal being softer along [] direction. Although the instrumented indentation studies provide valuable qualitative information about the overall mechanical properties of hydroxyapatite single crystals, quantitative data on the mechanical properties especially in the nonlinear regime is missing.

Number of studies have been focused to find the anisotropic elastic tensor of hydroxyapatite Hearmon, ; Katz and Ukrainck, ; Lees, ; Gilmore, ; Lopez et al. In a recent study, atomistic simulations have been performed to determine the elastic tensor of hydroxyapatite crystal Ching et al. However, to develop a nonlinear mechanical model of the elastic-plastic response, more detailed analysis of the indentation data along multiple crystallographic directions must be performed.

Significant research has been performed to determine the stress-strain response of a material using indentation data Cheng et al. It was found that metastatic nodes were stiffer than benign ones, and suggested that stiffness alone was accurate in diagnosing lymph node metastases, ex situ.

More recently, using the elastography technique, in vivo studies have been conducted on skin surface for superficial cervical nodes [ 19 - 22 ] or endoscopically for deep cervical, mediastinal and abdominal nodes [ 23 - 27 ], to study nodal stiffness. Elastographic color range of lymph nodes was reported to be between green and dark blue, which represents intermediate to hard tissue regions, depending on the degree of malignancy [ 212227 ].

Although operator dependence and perception error when visually grading subtle color differences can be overcome by computerized quantitative analysis [ 27 ], few studies have provided absolute values of the stiffness of lymph nodes [ 18 ].

Furthermore, biomechanical testing could extend our limited understanding of nodal tissue stiffness and such data were suggested being helpful in improving and validating elastography results [ 2027 ]. Therefore, the aim of the present study was to investigate the stiffness of lymph node tissues using a pig model.

In common with that of wildlife species such as dolphins, elephants and rhinoceroses, the lymph node of domestic pig is structurally inverted; with tissue characteristic of the medulla on the periphery and tissues characteristic of the cortex tissue in center [ 2829 ]. Indentation as a frequently used technique to study the biomechanical properties of biological tissues was adopted as a small indenter tip allows determination of any differences in tissue stiffness among selected regions.

It is expected that information obtained from this study could help understand better the lymph node from an anatomical aspect. Also, it may help to improve the interpretation of elastograms in the assessment of lymphadenopathy. All the specimens reached our lab within six hours after pigs were sacrificed.

In-vitro Strain and Modulus Measurements in Porcine Cervical Lymph Nodes

B-mode ultrasonography was conducted on the meat specimens to identify and locate suitable lymph nodes for investigation. The selected lymph nodes were resected from the surrounding tissues and measured and weighed with a digital calliper and an electronic scale respectively. Volume was determined by a water displacement method. Phantom Fabrication On the same day as resection, the lymph nodes were embedded in phantom of agar-gelatin blocks.

Fabrication of the tissue mimicking agar-gelatin background in this study was based on previous reports [ 30 - 32 ]. Briefly, gelatin Sigma-Aldrich Inc.

Relation among Young's modulus , Modulus of rigidity and Poisson's ratio - in HINDI - EduPoint

The lymph node was suspended using a thin thread to occupy a central position, with the long axis being orthogonal to the direction of slicing in preparation of specimens for the indentation test. In order for an easy slicing, two 2 mm longitudinal slits, 2 mm apart, was cut on opposite walls to guide a sharp knife Fig. Prior to pouring the agar-gelatin mixture into the mould, the slits were temporarily sealed using thin plastic sheets.