Effects of pre-tension on fatigue behavior of rolled magnesium alloy

Park, Sung Hyuk,Hong, Seong-Gu,Lee, Jeong-Hun,Kim, Sang-Hoon,Cho, Young-Rae,Yoon, Jonghun,Lee, Chong Soo Elsevier 2017 Materials science & engineering. properties, micro Vol.680 No.-

<P><B>Abstract</B></P> <P>The effects of pre-tension on the fatigue properties of a rolled Mg-3Al-1Zn (AZ31) alloy were investigated by imposing 2%, 5%, and 10% tensile strains along the rolling direction before low-cycle fatigue tests. The investigation showed that the applied pre-tension increased the dislocation density and introduced a small number of twins into the material. Although the as-rolled sample and all the pre-tensioned samples exhibited asymmetric hysteresis loops owing to the alternation of twinning and detwinning during each cycle, the tensile and compressive peak stresses increased with an increase in the amount of pre-tension during the first cycle. With an increase in the number of cycles, however, the flow stress, mean stress, plastic strain energy density, and hysteresis loop of the samples became similar irrespective of the amount of pre-tension, which is attributed to cyclic strain softening or hardening behavior depending on the initial dislocation density. Despite the relatively large pre-deformation, the pre-tensioned samples exhibited a fatigue life equivalent to that of the as-rolled sample because of an early extinction of the difference in the cyclic stress-strain response caused by pre-tension. This result demonstrates that the pre-tension process can improve the yield strength of rolled Mg alloys without a loss of their low-cycle fatigue resistance.</P>

Comparative Study between Structural Properties of Pre-Tensioned Inverted T-Girder and Actual Post-Tensioned Box Girder in Bridge Construction

Mohammad Omar Faruk Murad,Zamri Chik,B. M. Nural Absar,Kamal Hossain Shikdar,Khairul Anuar Mohd Nayan 대한토목학회 2016 KSCE Journal of Civil Engineering Vol.20 No.6

In this study a full scale 3D analysis of post-tensioned box section and pre-tensioned inverted T-girder section is carried out by considering only vertical loadings. The aim of this research is to investigate long span box Girder Bridge with pre-tensioned inverted T-girder using splicing technique. 4 lanes of 150m long (3 spans @ 50 m) post-tensioned box girder bridge with 12 cells and 13.54 m wide deck is considered as the bridge model and that the equivalent box section consists of 13 numbers of inverted pre-tensioned girder having two different lengths spliced at the points of inflection of continuous length of the bridge. The inverted T-girders are used to support the deck panel with superimposed load on it. The structural analysis of the bridge is done using CSi Bridge employing Integrated 3D Bridge Design Software based on finite element method for both longitudinal and transverse direction. In the analysis, AASHTO LRFD-2006 is used by subjecting Uniformly Distributed Load (UDL), edge loads, knife edge loads, and heavy vehicles load on the bridge deck. Moving vehicles load is placed at different locations to determine the maximum and minimum moments, stresses and flexural effects. Actual post-tensioned box section flexure, shear, torsion and stress in both longitudinal and transverse analyses showed lower values when compared to pre-tensioned inverted T-girder section. Assuming monolithic behaviour, the actual box section provided better stiffness rather than equivalent one. Nevertheless composite behaviour of the equivalent section can be accepted as an alternative solution for long span continuous box Girder Bridge where cost is a major factor in particular.

Pre-tension Effects from Tightening the Ligature on Spinous Process Fracture Risk in Interspinous Process Device Implantation

Park, Won Man,Choi, Dae Kyung,Kim, Yoon Hyuk,Kim, Kyungsoo Korean Society for Precision Engineering 2014 International Journal of Precision Engineering and Vol.15 No.12

Ligatures are used with many types of interspinous process devices to prevent instability in flexion movement by wrapping around upper and lower spinous processes. In this study, the effects of the pre-tension by tightening the ligature on the spinous process fracture were investigated using a finite element method. Five different interspinous process devices, Coflex-F<TEX>$^{(R)}$</TEX>, Wallis<TEX>$^{TM}$</TEX>, Diam<TEX>$^{TM}$</TEX>, Viking, and Spear<TEX>$^{(R)}$</TEX>, were chosen, and implanted after creating a defect consisting of bilateral facetectomy with a resection of the ligamentum flavum. Flexion and extension motions were simulated with various pre-tension values of the ligatures in the range of 0 to 400 N at 100 N increments. While stability at the surgical level in the flexion increased with increasing pre-tension of the ligatures, the spinous process fracture risk also increased with increasing ligature pre-tension. Furthermore, the fatigue life of the spinous process also decreased. Thus, the amount of pre-tension of the ligatures should be carefully selected depending on the materials and design of implants.

Pre-tension Effects from Tightening the Ligature on Spinous Process Fracture Risk in Interspinous Process Device Implantation

박원만,김윤혁,최대경,김경수 한국정밀공학회 2014 International Journal of Precision Engineering and Vol. No.

Ligatures are used with many types of interspinous process devices to prevent instability in flexion movement by wrapping aroundupper and lower spinous processes. In this study, the effects of the pre-tension by tightening the ligature on the spinous processfracture were investigated using a finite element method. Five different interspinous process devices, Coflex-F®, WallisTM, DiamTM,Viking, and Spear®, were chosen, and implanted after creating a defect consisting of bilateral facetectomy with a resection of theligamentum flavum. Flexion and extension motions were simulated with various pre-tension values of the ligatures in the range of0 to 400 N at 100 N increments. While stability at the surgical level in the flexion increased with increasing pre-tension of the ligatures,the spinous process fracture risk also increased with increasing ligature pre-tension. Furthermore, the fatigue life of the spinousprocess also decreased. Thus, the amount of pre-tension of the ligatures should be carefully selected depending on the materials anddesign of implants.

Biomechanical Effect of Tunnel Positions and Pre-tension Forces on Implanted Graft Stress and Strain During Outside-in ACL Reconstruction Surgery: A Simulation Study

Tae Soo Bae,Byeong Chan Cho 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.21 No.3

The selection of surgical site for the femoral tunnel during anterior cruciate ligament (ACL) reconstruction surgery remains controversial. However, it is not only surgical site that lacks scientific consensus but also the level of pre-tension force applied during implanted graft fixation. This study aims to propose the optimal femoral tunnel position considering appropriate pre-tension in ACL reconstruction surgery. To select the optimal position, the stress and strain on the implanted graft in 40 cases was calculated by testing combinations of 10 recommended tunnel positions on the femoral epicondyle and four pre-tension forces (0, 10, 20, and 30 N) using multi-flexible body dynamics. The lowest implanted graft stress and strain was found in a posterior proximal site at 15 mm from the lateral femoral epicondyle; the pre-tension force here showed no significance. In conclusion, changes in stress on the implanted graft were affected more by tunnel position than by pre-tension.

Load deformation characteristics of shallow suspension footbridge with reverse profiled pre-tensioned cables

Huang, Ming-Hui,Thambiratnam, David P.,Perera, Nimal J. Techno-Press 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.21 No.4

Cable supported structures offer an elegant and economical solution for bridging over long spans with resultant low material content and ease of construction. In this paper, a model of shallow cable supported footbridge with reverse profiled pre-tensioned cables is treated and its load deformation characteristics under different quasi-static loads are investigated. Effects of important parameters such as cable sag and pre-tension are also studied. Numerical results performed on a 3D model show that structural stiffness of this bridge (model) depends not only on the cable sag and cross sectional areas of the cables, but also on the pre-tension in the reverse profiled cables. The tension in the top supporting cables can be adjusted to a high level by the pre-tension in the reverse profiled bottom cables, with the total horizontal force in the bridge structure remaining reasonably constant. It is also evident that pre-tensioned horizontally profiled cables can greatly increase the lateral horizontal stiffness and suppress the lateral horizontal deflection induced by eccentric vertical loads.

Automatic measurement and warning of tension force reduction in a PT tendon using eddy current sensing

Kim, J.M.,Lee, J.,Sohn, H. Butterworth-Heinemann 2017 NDT AND E INTERNATIONAL Vol.87 No.-

<P>Post-tensioning (PT) using a bundle of pre-stressed strands is a critical process for assembling pre-fabricated and modularized bridge members. However, the tension force gradually diminishes over time due to such factors as corrosion, creep, and steel relaxation. Such changes compromise the overall safety of such structures. In this study, an eddy-current-based tension-force-loss warning (EC-TFLW) technique is proposed to detect and warn automatically of excessive loss of tension force in a PT tendon. A ring-type eddy-current sensor (ECS) is mounted on the outer surface of a wedge holding a tendon, and the level of eddy current measured by the ECS is related to the tension force of the tendon. The advantages of the proposed technique include: (1) low power consumption, (2) low cost, (3) simple installation, and (4) automated warning. The performance of the proposed EC-TFLW technique was validated experimentally in a full-scale lab test of a 3.3-m long, 15.2-mm diameter, mono-strand tendon that was tensioned using a universal testing machine (from 20 to 180 kN). Statistical hypothesis testing using the chi-square distribution was applied to the measured eddy current signals, and if the decline in tension exceeded a certain level, a warning was sent out automatically.</P>

프리텐셔닝 인장재를 적용한 CAP Deck 합성슬래브의 휨성능 실험

황슬기 ( Seul Ki Hwang ),김교천 ( Gyo Cheon Kim ),최성훈 ( Sung Hoon Choi ),경제환 ( Jae Whan Kyung ),최성모 ( Sung Mo Choi ) 한국복합신소재구조학회 2016 복합신소재구조학회논문집 Vol.7 No.2

These days, the Composite Slabs with Deep Deck plate was commonly used in domestic construction site, and, the application of the Slim Floor system was increased from the Enlargement and High-rise Building. But, Slim Floor system using the Deep Deck was shown safety problem caused by the deflection and local buckling in construction phase when used to more than 6m. Therefore, for solving the problem, the installation of the shores is essential. This study is realize the long span slab without shores from control the deflection through applied the pre-tensioning elements in CAP deck. In addition, by applying the pre-tensioning member as the tensile member of the CAP Deck slab, the pre-tensioning member for the shores tries to be used as the structural member. Accordingly, to determine the flexural performance of the CAP Deck slab through the pre-tensioning force in tensile member, and, the composite effect of the CAP Deck slab by the experiments.

Effect of external load on angular distortion in fillet welding

Park, J.U.,An, G.,Lee, H.W. Scientific and Technical Press ; Elsevier Science 2012 Materials & Design Vol.42 No.-

This paper studied the effects of the magnitude, the direction, and the release time of pre-tensioning stress on welding distortion and residual stress on thin steels for a ship in the pre-tensioning method above using the finite element method. It was found that pre-tensioning stress in the direction of weld path did not affect angular and longitudinal distortion but brought a decrease of 8% in the magnitude of welding residual stress which may affect the buckling strength. Meanwhile, pre-tensioning stress in the direction perpendicular to weld path resulted in a decrease of 40-60% in the magnitude of angular distortion. Also, when the pre-tensioning stress was released 60min after the completion of welding, it had a decreasing effect of 10-20% more in the magnitude of angular distortion than when released immediately after welding.

측면 충돌 시 B-Pillar 에서의 효과적인 센서 측정 방법에 대한 연구

김기석(Kiseok Kim),윤일성(Ilsung Yoon),임종현(Jonghyun Yim) 한국자동차공학회 2012 한국자동차공학회 학술대회 및 전시회 Vol.2012 No.11

Nowadays most of passenger vehicles equipped restraints system such as roof rail airbag and seat belt pre-tensioner at b-pillar area to protect passenger from crash accident, and the roof rail airbag and seat belt pre-tensioner are deployed by SDM firing signal during crash event. SDM firing signal is made by using vehicle pulse data - acceleration, velocity and displacement which are obtained by accelerometer attached body structure of test vehicle. In side impact test, these restraint systems cause a high frequency vibration at the b-pillar during roof rail airbag deployment and pre-tensioner firing. And it looks one of major reason to obtain anomaly acceleration data at the b-pillar. In this paper, simulation test were carried out with roof rail airbag deployment and seat belt pre-tensioner working. Then, accelerometer on the b-pillar obtained some data, even though test vehicle is not moved, and it makes b-pillar velocity which is bigger than zero velocity. To reduce this undesirable noise, some static tests as case study with a damping material - 2mm rubber plate and reinforcement - 2mm steel plate at accelerometer mounting position are performed. Finally, we could understand that increase of stiffness at the seat belt pre-tensioner mounting position can reduce maximum velocity and acceleration peak value. Increasing stiffness of mounting position can reduce amplitude under 4000Hz frequency which is cutoff frequency of data acquisition system. In case of rubber damper, it was effective to reduce vibration and reduce maximum velocity at the roof rail airbag mounting position but it was negative at the seat belt mounting position.