Joints compressive strength

The Barton-Bandis (BB) model represents the change in the normal and shear stiffness due to the stress change by using JRC (Joint Roughness Coefficient) and JCS (Joint Compression Strength). By using the JRC and JCS (MPa) which is the mean values for each set /, the initial normal stiffness of joint, K i (MPa/mm), is calculated for each set /,... 

For Case HM, pairs of joint roughness coefficient (JRC) and joint compressive strength... 

Ceramic materials typically have low tensile strengths compared to compressive strengths which arc five to ten times higher. Therefore, the ccramic-to-mctal joint construction should only impose compressive stress on the ceramic-metal interface. This, for example, can be achieved through the use of a metallic bellow. By joining the bellow directly to the porous ceramic element and welding the bellow under compressive conditions to the module or reactor housing, the joint will stay at all times under a compressive force [Velterop and Keizer, 1991]. To reinforce the joint, a dense... 

Recently, a cellular, structural biomaterial comprised of 15 to 25% tantalum (75 to 85% porous) has been developed. The average pore size is about 550 p,m, and the pores are fully interconnected. The porous tantalum is a bulk material (i.e., not a coating) and is fabricated via a proprietary chemical vapor infiltration process in which pure tantalum is uniformly precipitated onto a reticulated vitreous carbon skeleton. The porous tantalum possesses sufficient compressive strength for most physiological loads, and tantalum exhibits excellent biocompatibility [Black, 1994]. This porous tantalum can be mechanically attached or diffusion bonded to substrate materials such as Ti alloy. Current commercial applications included polyethylene-porous tantalum acetabular components for total hip joint replacement and repair of defects in the acetabulum. 

FIFE tape is used in many applications, including sealing joints, insulating conductive wires, and protecting materials from corrosive elements. FIFE demonstrates a good chemical and heat resistance, electrical insulation characteristics, as well as a low coefficient of friction. However, in general, it has less than desirable mechanical properties, in particular with respect to abrasion resistance and compression strength. 

Figure 8. Variation of compressive strength ratio with joint frequency for specimen of POP with joints at difrerent inclination...

The effect of frequency and orientation of joints is clearly depicted in Figure 8. This figure shows the variation of compressive strength ratio with joint frequency for jointed rock specimen at live different inclinations 0°, 30°, 50°, 70°, 90° and clearly shows the reduction of strength with the increase with the number of joints. The maximum reduction of strength is observed for the specimen with 30°joint inclination. The observed reduction in strength for single joint at P=30° is relatively... 

Figure 9. Variation of compressive strength ratio ofPOP specimen with orientation of a single joint...

POP mixed with 10% Portland cement by weight was also used to prepare cylindrical specimens to have relatively higher uniaxial compressive strength and to represent higher wall strength, in case of jointed specimens. A total of 110 gm mixture was taken containing 11 gm Portland cement and was thoroughly dry mixed with a stirrer. This POP with cement mix was then mixed with specific quantity of water (always kept constant for every sample) to cast cylindrical specimens with split moulds similar to POP without cement mix specimens. These specimens of POP with ce-... 

UNIAXIAL COMPRESSIVE STRENGTH/ELASTIC MODULUS OF JOINTED ROCKS... 

It is attempted to evaluate uniaxial compressive strength (UCS) and elastic modulus of rock mass as a function of UCS or elastic modulus of intact rock and j oint factor. Figure 14 shows the variation of (the ratio of UCS of jointed rock to the intact rock) with joint factor (Jj.) for tested material. The term joint factor (Jj.), introduced by Ramamurthy (1993), which reflects the combined effect of j oint frequency, joint inclination and joint roughness (or wall strength) and is expressed as ... 

With the help of these equations the uniaxial compressive strength/elastic modulus of jointed rocks can be determined for known values ofjoint factor and uniaxial compressive strength/elastic modulus of intact rock. It is observed that the ratios of both static and dynamic elastic modulus decreases with an increase inthe jointfactorunder unconfinement. The test results of POP and the POP-cement mix specimens are given in Table 5. Figure 14 shows the experimental values of uniaxial compressive strength ratio versus joint factor along with a fitted curve. 

The plots of ratio of elastic modulus with the joint factor derived from the experimental data, for unconfined, are shown in Figure 15. The plots of ratio of dynamic elastic modulus with the joint factor are shown in Figure 16, which shows the variation of experimental values of uniaxial compressive strength ratio with joint factor for POP-... 

Specimen Joint inclination parameter (n) Joint strength parameter (r) Joint frequency (Jn) Joint factor (Jf) Uniaxial compressive strength ratio (or) Ratio of elastic modulus (Er) Ratio of dynamic elastic modulus... 

Figures 20. Variation of uniaxial compressive strength ratio with joint factor 1...

Exponential correlations were established for the prediction of uniaxial compressive strength ratio/ratio of static and dynamic elastic modulus of rock mass from the intact rock uniaxial compressive strength/elastic modulus and joint factor (Ramamurthy, 1993), which includes joint frequency, joint inclination andjoint strength. These relations are useful in characterisation of jointed rock mass by knowing the intact rock properties and the joint factor. 

In this paper the compressive strength/elastic modulus of the jointed rock mass was estimated as a function of intact rock strength/modulus and joint factor. The joint factor reflects the combined effect of joint frequency, joint inclination and joint strength. Therefore, having known the intact rock properties and the joint factor, jointed rock properties can be estimated. The test results indicated that the rock mass strength decreases with an increase in the joint frequency and a sharp transition was observed from brittle to ductile behaviour with an increase in the number of joints. It was also found that the rocks with planar anisotropy exhibit the highest strength in the direction perpendicular to the anisotropy and the lowest at an inclination of 30o-45o in jointed samples. The anisotropy of the specimen influences the dynamic elastic modulus more than the static elastic modulus. The results were also compared well with the published works of different authors for different type of rocks. 

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