Tensile deformation of anisotropic porous copper with directional pores

2010 ◽  
Vol 25 (10) ◽  
pp. 1975-1982 ◽  
Author(s):  
M. Tane ◽  
R. Okamoto ◽  
H. Nakajima
Keyword(s):  
Tensile Deformation ◽  
High Stress ◽  
Stress Triaxiality ◽  
Strain Curve ◽  
Peak Stress ◽  
Localized Deformation ◽  
High Stress Concentration ◽  
Porous Copper ◽  
Fracture Crack ◽  
Cylindrical Pores

The tensile deformation of anisotropic porous copper with unidirectionally oriented cylindrical pores was investigated by an acoustic emission method. In the loadings parallel and perpendicular to the orientation direction of the pores, many cracks are formed after yielding and they strongly affect the deformation. The formed cracks rapidly grow and connect with each other near the peak stress of the stress–strain curve, thereby leading to final fracture. Crack formation is easier under perpendicular loading than under parallel loading, because high stress concentration and stress triaxiality occurs around the pores. As a result, the strength and elongation for perpendicular loading are much smaller than those for parallel loading. Furthermore, in the case of perpendicular loading, the localized deformation around pores drastically decreases the plastic Poisson's ratio. These results indicate that a porous copper macroscopically behaves as a semibrittle material under perpendicular loading, while the porous copper exhibits ductility under parallel loading.

Anisotropic Tensile Deformation of Lotus-Type Porous Copper

2011 ◽  
Vol 695 ◽  
pp. 545-548
Author(s):  
Masakazu Tane ◽  
Rika Okamoto ◽  
Hideo Nakajima
Keyword(s):  
Cross Section ◽  
Tensile Deformation ◽  
Tensile Specimen ◽  
Copper Matrix ◽  
Constant Volume ◽  
Incompressibility Condition ◽  
Orientation Direction ◽  
Porous Copper ◽  
Cylindrical Pores ◽  
The Matrix

The tensile deformation of lotus-type porous copper with cylindrical pores oriented in one direction was investigated. Deformation was occured homogeneously in the copper matrix for loadings parallel to the orientation direction of pores (pore direction), while deformation was localized in the matrix around pores for loadings perpendicular to the pore direction. In the case of parallel loading the decrease in cross section of tensile specimen was smaller than that of nonporous copper, because of the constant-volume law (i.e. incompressibility condition) for deformation was not applicable to the deformation of pores. In the case of perpendicular loading, the deformed regions were disconnected and constant-volume law holds only in the matrix around the pores, and thus, the cross section hardly decreases during the tensile deformation.

Development of Design Curve for Sweepolet Subjected to Acoustic Induced Vibration

2016 ◽  
Author(s):  
Yuqing Liu ◽  
Philip Diwakar ◽  
Dan Lin ◽  
Ismat Eljaouhari ◽  
Ajay Prakash
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Fatigue Failure ◽  
High Stress ◽  
Peak Stress ◽  
Acoustic Energy ◽  
Piping System ◽  
Element Analysis ◽  
Design Curve ◽  
High Stress Concentration

High acoustic energy has the potential to cause severe Acoustic Induced Vibration (AIV) that leads to fatigue failure at high stress concentration regions such as fittings in a piping system. Sweepolet fittings have been extensively used as mitigation to counteract the risk of fatigue failure caused by AIV. The advantages of a sweepolet are its integrally reinforced contoured body and low stress concentration. However, there are inconsistencies in published standards and regarding the design limits for sweepolet subjected to AIV. In this paper, Finite Element Analysis is conducted to simulate high frequency pipe shell wall vibration caused by acoustic energy inside the pipe. Peak stress and the associated minimum fatigue life are calculated for sweepolet and sockolet under the same acoustic excitation. By comparing the stress level to that of a sockolet whose design limit to AIV had been published, the design curve and fatigue life equation for sweepolet are developed.

A NEW RING STENT WITH GRADED GEOMETRY FOR TREATING COARCTATION OF CURVED AORTA ARTERIES

2021 ◽  
pp. 2150014
Author(s):  
XIAOWEN YIN ◽  
XIAOMIN HU ◽  
TONG LI ◽  
JIAYAO MA
Keyword(s):  
Stress Reduction ◽  
Maximum Stress ◽  
High Stress ◽  
Coarctation Of The Aorta ◽  
Peak Stress ◽  
Wave Crest ◽  
High Stress Concentration ◽  
Stent Restenosis ◽  
Graded Material ◽  
Curved Vessels

Ring stent implantation has been widely used to treat coarctation of the aorta (CoA) as an alternative to surgery. Currently adopted stents with uniform geometry may cause uneven stress distribution and high stress concentration in curved vessels, leading to in-stent restenosis (ISR). Inspired by functional graded material, here we propose a new ring-and-link stent, which has graded geometry in order to achieve a reduced peak stress when deployed in curved arteries. Numerical simulation of a single ring of the graded stent indicated that by varying the circumferential spacing of wave crest, the maximum stress exerted on the artery was reduced by as much as 27.86% in comparison with the uniform one. The effects of stent geometric parameters and artery curvature were also obtained through a parametric study. Finally, a whole stent was studied to verify the design, and a maximum stress reduction by 31.96% was achieved. In summary, the proposed graded ring stent shows great potential in clinical applications to reduce the risk of ISR.

scholarly journals Experimental Study on Biaxial Dynamic Compressive Properties of ECC

Materials ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1257
Author(s):  
Shuling Gao ◽  
Guanhua Hu
Keyword(s):  
Strain Rate ◽  
Lateral Pressure ◽  
Deformation Modulus ◽  
Strain Curve ◽  
Peak Stress ◽  
Pressure Level ◽  
Strain Rates ◽  
Peak Strain ◽  
Stress Strain Curve ◽  
Toughness Index

An improved hydraulic servo structure testing machine has been used to conduct biaxial dynamic compression tests on eight types of engineered cementitious composites (ECC) with lateral pressure levels of 0, 0.125, 0.25, 0.5, 0.7, 0.8, 0.9, 1.0 (the ratio of the compressive strength applied laterally to the static compressive strength of the specimen), and three strain rates of 10−4, 10−3 and 10−2 s−1. The failure mode, peak stress, peak strain, deformation modulus, stress-strain curve, and compressive toughness index of ECC under biaxial dynamic compressive stress state are obtained. The test results show that the lateral pressure affects the direction of ECC cracking, while the strain rate has little effect on the failure morphology of ECC. The growth of lateral pressure level and strain rate upgrades the limit failure strength and peak strain of ECC, and the small improvement is achieved in elastic modulus. A two-stage ECC biaxial failure strength standard was established, and the influence of the lateral pressure level and peak strain was quantitatively evaluated through the fitting curve of the peak stress, peak strain, and deformation modulus of ECC under various strain rates and lateral pressure levels. ECC’s compressive stress-strain curve can be divided into four stages, and a normalized biaxial dynamic ECC constitutive relationship is established. The toughness index of ECC can be increased with the increase of lateral pressure level, while the increase of strain rate can reduce the toughness index of ECC. Under the effect of biaxial dynamic load, the ultimate strength of ECC is increased higher than that of plain concrete.

Integrity Assessment and On-Site Repair of a Floating Production Platform

2005 ◽  
Author(s):  
Mauro G. Marinho ◽  
Alexandre M. Pope ◽  
Luiz Claudio Meniconi ◽  
Luiz Henrique M. Alves ◽  
Cesar Del Vecchio
Keyword(s):  
High Stress ◽  
Local Strain ◽  
Business Unit ◽  
Gusset Plates ◽  
Strain Measurements ◽  
Integrity Assessment ◽  
High Stress Concentration ◽  
Production Platform ◽  
Welding Defects ◽  
Classification Society

Following the warning of a flooded bow horizontal brace of a semi-submersible production platform, an inspection diving team was mobilized and cracks were found at both bow and aft K-joints. Analysis of the service life of the platform, together with the results of structural analysis and local strain measurements, concluded that cracking was caused by fatigue initiated at high stress concentration points on the gusset plates inserted in the tubular joints. As a consequence of the fractured plates other cracks were nucleated close to the intersection lines of the braces that compose the K-joints. Based on this analysis different repair possibilities were proposed. To comply with the production goals of the Business Unit it was decided to repair the platform on-site and in production in agreement with the Classification Society. The proposed repair contemplated the installation of two flanges on the gusset plates between the diagonal braces by underwater wet (UWW) welding. Cracks at the gusset plates were also removed by grinding and wet welding. Defects located at the braces are being monitored and repaired by the installation of backing bars, by wet welding, followed by grinding and welding from the inside. To carry out the job two weld procedures and ten welder-divers were qualified.

An Experimental Study of Cavity Nucleation During Superplastic Deformation

1990 ◽  
Vol 196 ◽  
Author(s):  
Jiang Xinggang ◽  
Cui Jianzhong ◽  
Ma Longxiang
Keyword(s):  
Grain Boundary ◽  
Superplastic Deformation ◽  
Thermomechanical Processing ◽  
High Stress ◽  
High Strength ◽  
Optical Microscope ◽  
Grain Boundary Sliding ◽  
Cavity Nucleation ◽  
High Stress Concentration ◽  
Voltage Electron

ABSTRACTCavity nucleation during superplastic deformation of a high strength aluminium alloy has been studied using a high voltage electron microscope and an optical microscope. The results show that cavities nucleation is due only to superplastic deformation and not to pre-existing microvoids which may be introduced during thermomechanical processing. The main reason for cavity nucleation is the high stress concentration at discontinuties in the plane of the grain boundary due to grain boundary sliding.

Comparison Analysis on the Mechanical Properties of HSC and NSC after the Action of High Temperatures

2014 ◽  
Vol 1014 ◽  
pp. 49-52
Author(s):  
Xiao Ping Su
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
High Temperatures ◽  
High Strength Concrete ◽  
Elasticity Modulus ◽  
Strain Curve ◽  
Peak Stress ◽  
High Strength ◽  
Peak Strain ◽  
Strength Concrete

With the wide application of high strength concrete in the building construction,the risk making concrete subject to high temperatures during a fire is increasing. Comparison tests on the mechanical properties of high strength concrete (HSC) and normal strength concrete (NSC) after the action of high temperature were made in this article, which were compared from the following aspects: the peak stress, the peak strain, elasticity modulus, and stress-strain curve after high temperature. Results show that the laws of the mechanical properties of HSC and NSC changing with the temperature are the same. With the increase of heating temperature, the peak stress and elasticity modulus decreases, while the peak strain grows rapidly. HSC shows greater brittleness and worse fire-resistant performance than NSC, and destroys suddenly. The research and evaluation on the fire-resistant performance of HSC should be strengthened during the structural design and construction on the HSC buildings.

A New Shaft Coupling Design for a High-Speed Rotor Wheel

1995 ◽  
Author(s):  
Tibor Kiss ◽  
Wing-Fai Ng ◽  
Larry D. Mitchell
Keyword(s):  
High Speed ◽  
High Stress ◽  
Critical Issue ◽  
Working Environment ◽  
Outer Diameter ◽  
Stress Concentrations ◽  
Coupling Region ◽  
Rotor Wheel ◽  
High Stress Concentration ◽  
Safety Margins

Abstract A high-speed rotor wheel for a wind-tunnel experiment has been designed. The rotor wheel was similar to one in an axial turbine, except that slender bars replaced the blades. The main parameters of the rotor wheel were an outer diameter of 10“, a maximum rotational speed of 24,000 RPM and a maximum transferred torque of 64 lb-ft. Due to the working environment, the rotor had to be designed with high safety margins. The coupling of the rotor wheel with the shaft was found to be the most critical issue, because of the high stress concentration factors associated with the conventional coupling methods. The efforts to reduce the stress concentrations resulted in an advanced coupling design which is the main subject of the present paper. This new design was a special key coupling in which six dowel pins were used for keys. The key slots, now pin-grooves, were placed in bosses on the inner surface of the hub. The hub of the rotor wheel was relatively long, which allowed for applying the coupling near the end faces of the hub, that is, away from the highly loaded centerplane. The long hub resulted in low radial expansion in the coupling region. Therefore, solid contact between the shaft and the hub could be maintained for all working conditions. To develop and verify the design ideas, stress and deformation analyses were carried out using quasi-two-dimensional finite element models. An overall safety factor of 3.7 resulted. The rotor has been built and successfully accelerated over the design speed in a spin test pit.

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