Short Term Relaxation of Stuffing Box Packings

2007 ◽  
Author(s):  
Mohammed Diany ◽  
Abdel-Hakim Bouzid
Keyword(s):  
Contact Pressure ◽  
Threshold Value ◽  
Element Model ◽  
Packing Material ◽  
Ansys Software ◽  
Short Term ◽  
Creep Properties ◽  
Contact Pressures ◽  
Key Parameter

The long term tightness performance of stuffing box packings, used in valves, is conditioned by the capacity of its material to maintain a contact pressure to a predetermined minimal threshold value. Due to creep, this contact pressure decrease with time depending on the creep properties and the stiffness of the housing. Assessing relaxation is a key parameter in determining the tightness performance of the stuffing box packing over time. Using Ansys software, an axisymmetric 2D finite element model is developed to assess the contact pressures between the packing material and the stem and the housing and its variation with time. The assessment of the packing relaxation is a major obstacle to the good leakage performance of the Stuffing Box Packing.

Short Term Relaxation Modeling of Valve Stem Packings

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Mohammed Diany ◽  
Abdel-Hakim Bouzid
Keyword(s):  
Contact Pressure ◽  
Analytical Model ◽  
Viscoelastic Behavior ◽  
Threshold Value ◽  
Element Model ◽  
Creep Properties ◽  
Valve Stem ◽  
Sealing Material ◽  
Important Design

The long term tightness performance of stuffing-box packings, used in valves, is conditioned by the capacity of its sealing material to maintain a contact pressure to a predetermined minimal threshold value. Due to the creep, this contact pressure decreases with time depending on the creep properties and the stiffness of the housing. Assessing relaxation is a key parameter in determining the tightness performance of a valve stem packing over time. An analytical model based on the packing viscoelastic behavior is developed to assess the contact pressures between the packing material and the stem and the housing and their variation with time. In parallel, an axisymmetric 2D finite element model was build to validate and support the analytical model. The valve stem packing relaxation performance is an important design parameter to consider when selecting compression packings.

Effect of load type on temperature rise of a disc brake

2014 ◽  
Vol 5 (1) ◽  
pp. 30-44 ◽  
Author(s):  
Qing-rui Meng
Keyword(s):  
Contact Pressure ◽  
Temperature Rise ◽  
Axial Direction ◽  
Sine Wave ◽  
Practical Application ◽  
Ansys Software ◽  
Content Type ◽  
Load Types ◽  
Load Simulation ◽  
Contact Pressures

Purpose – The purpose of this paper is to reveal the temperature rise characteristics of the disc and pads under different load types. Design/methodology/approach – Evolutions of the disc and pads temperature under a stable, gradual changing and sine-wave contact pressures widely used at present are analyzed numerically by using ANSYS software. Findings – The results show that during the loading process, the temperature increases most rapidly under a stable contact pressure, most slowly under a gradual changing contact pressure; the disc temperature rise curves expose saw-shaped character, the closer it is to the friction surface, the more serious the fluctuations will be, the pads temperature rise curves are rather smooth; temperature gradient in the axial direction is higher than that in the other two directions under all of the three types of contact pressure and shows a sine-wave variation under a sine-wave contact pressure. Originality/value – It indicates that a gradual changing contact pressure should be adopted preferentially in practical application. The simulation results of this work provide theoretical basis for load simulation.

Analysis of Premium Connection of Connecting and Sealing Ability Loaded by Axial Tensile Loads

2012 ◽  
Vol 268-270 ◽  
pp. 737-740
Author(s):  
Yang Yu ◽  
Yi Hua Dou ◽  
Fu Xiang Zhang ◽  
Xiang Tong Yang
Keyword(s):  
Finite Element ◽  
Contact Pressure ◽  
Tensile Load ◽  
Element Model ◽  
Sealing Ability ◽  
Axial Tensile ◽  
High Level ◽  
Maximum Contact ◽  
Contact Pressures ◽  
The Finite Element Model

It is necessary to know the connecting and sealing ability of premium connection for appropriate choices of different working conditions. By finite element method, the finite element model of premium connection is established and the stresses of seal section, shoulder zone and thread surface of tubing by axial tensile loads are analyzed. The results show that shoulder zone is subject to most axial stresses at made-up state, which will make distribution of stresses on thread reasonable. With the increase of axial tensile loads, stresses of thread on both ends increase and on seal section and shoulder zone slightly change. The maximum stress on some thread exceed the yield limit of material when axial tensile loads exceed 400KN. Limited axial tensile loads sharply influence the contact pressures on shoulder zone while slightly on seal section. Although the maximum contact pressure on shoulder zone drop to 0 when the axial tensile load is 600KN, the maximum contact pressure on seal section will keep on a high level.

Basic Study on Creep Properties of Eucalyptus Wood

2014 ◽  
Vol 911 ◽  
pp. 232-237
Author(s):  
Yuan Rong Ma ◽  
Xian Jun Li ◽  
Biao Deng ◽  
Ying She Luo
Keyword(s):  
Model Parameters ◽  
Short Term ◽  
Basic Study ◽  
Burger Model ◽  
Creep Properties ◽  
Eucalyptus Plantation ◽  
Moisture Contents ◽  
Creep Curves ◽  
Term Creep

The study tested the short-term bending creep curves of Eucalyptus Plantation Wood under different loads, moisture contents and temperatures, analyzed the influence of load, moisture content and temperature on creep of Eucalyptus. Guided by the rheological theory, the study adopted the Burger rheological model to do the curve fitting and solved the model parameters. A defect found from Burger model in simulating long-term creep properties of wood was preliminary discussed and remedied. The equivalence of creep test and relaxation one was discussed.

A Mathematical Model of Short-Term Memory

SIMULATION ◽  
1964 ◽  
Vol 3 (6) ◽  
pp. 46-51
Author(s):  
W. Ross Adey ◽  
N.V. Findler
Keyword(s):  
Electromagnetic Waves ◽  
Short Term Memory ◽  
Threshold Value ◽  
Long Term Memory ◽  
Short Term ◽  
Term Memory ◽  
Neuron Density ◽  
Receptor Neurons ◽  
The Brain

It is attempted in this paper to give a mathematical description of the short-term memory. Instead of using the microscopic properties of individual neu rons, such as the number of interconnections, neuron density, threshold value, etc., the cerebral cortex is regarded as a "neuron gas" that is a vast conglomer ate of neurons with statistically distributed charac teristics. Stimuli from the environment cause the receptor neurons to emit virtual electromagnetic waves into the brain. A self-optimizing process of the brain tis sue is here described by which the useful, informa tion-carrying energy reaching the long-term memory tends to maximum. It is emphasized that in the following a brain model is described and the physical processes in volved may have no direct equivalent in reality.

Properties of Pavement Bitumens Assessed Using European and American Approach

2017 ◽  
Vol 737 ◽  
pp. 554-559
Author(s):  
Pavel Coufalik ◽  
Ondrej Dasek ◽  
Petr Hyzl ◽  
Iva Krcmova
Keyword(s):  
United States Of America ◽  
Fatigue Behavior ◽  
Asphalt Binder ◽  
The United States ◽  
Asphalt Binders ◽  
Short Term ◽  
European Standards ◽  
Unites States ◽  
Key Parameter

This paper compares the different approaches to assessing asphalt binders used in Europe and the Unites States. A series of pavement bitumens is assessed using European standards and also by the Performance Graded Asphalt Binder Specification based on AASHTO MP 1, which was developed as part of the Strategic Highway Research Program (SHRP) in the United States of America. The results show that the European approach places high requirements on the pavement bitumens in relation to their behavior at low-temperatures, while in case of the American approach, the key parameter is fatigue behavior after short-term and long-term aging. It is evident that it is necessary to evaluate properties of pavement bitumens after long-term aging in Europe, too.

The Effect of Ageing on the Micro-Creep Properties of Radiation Cross-Linked Materials

2016 ◽  
Vol 368 ◽  
pp. 134-137
Author(s):  
Martin Řezníček ◽  
Martin Ovsík ◽  
Adam Škrobák ◽  
David Manas
Keyword(s):  
Mechanical Properties ◽  
Polymeric Materials ◽  
Term Effect ◽  
Short Term ◽  
Creep Properties ◽  
Long Term Effect ◽  
Radiation Crosslinking ◽  
Positive Effect

Radiation crosslinking of polymeric materials have placed and nowadays in the field of long-term use of loaded products. This article aims to identify the long-term effect of radiation crosslinking on micro-creep properties. The article compares the micro-creep properties of HDPE measured two years ago with the results of tests conducted under the same conditions and on the same samples now. The effect of time on the mechanical properties of the radiation crosslinked materials was demonstrated in short-term tests. These findings demonstrate the positive effect of time on the evaluated parameters.

scholarly journals Evaluation of Patellar Contact Pressure Changes after Static versus Dynamic Medial Patellofemoral Ligament Reconstructions Using a Finite Element Model

2019 ◽  
Vol 8 (12) ◽  
pp. 2093 ◽  
Author(s):  
Vicente Sanchis-Alfonso ◽  
Gerard Ginovart ◽  
Diego Alastruey-López ◽  
Erik Montesinos-Berry ◽  
Joan Carles Monllau ◽  
...  
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Contact Pressure ◽  
Maximum Stress ◽  
Medial Patellofemoral Ligament ◽  
Quadriceps Tendon ◽  
Element Model ◽  
Fixation Techniques ◽  
Static Versus Dynamic ◽  
Contact Pressures

Objectives: To evaluate the effect of various medial patellofemoral ligament (MPFL) fixation techniques on patellar pressure compared with the native knee. Methods: A finite element model of the patellofemoral joint consisting of approximately 30,700 nodes and 22,200 elements was created from computed tomography scans of 24 knees with chronic lateral patellar instability. Patellar contact pressures and maximum MPFL graft stress at five positions of flexion (0°, 30°, 60°, 90°, and 120°) were analyzed in three types of MPFL reconstruction (MPFLr): (1) static/anatomic, (2) dynamic, using the adductor magnus tendon (AMT) as the femoral fixation, and (3) dynamic, using the quadriceps tendon as the attachment (medial quadriceps tendon-femoral ligament (MQTFL) reconstruction). Results: In the static/anatomic technique, the patellar contact pressures at 0° and 30° were greater than in the native knee. As in a native knee, the contact pressures at 60°, 90°, and 120° were very low. The maximum MPFL graft stress at 0° and 30° was greater than in a native knee. However, the MPFL graft was loose at 60°, 90°, and 120°, meaning it had no tension. In the dynamic MPFLr using the AMT as a pulley, the patellar contact pressures were like those of a native knee throughout the entire range of motion. However, the maximum stress of the MPFL graft at 0° was less than that of a native ligament. Yet, the maximum MPFL graft stress was greater at 30° than in a native ligament. After 30° of flexion, the MPFL graft loosened, similarly to a native knee. In the dynamic MQTFL reconstruction, the maximum patellar contact pressure was slightly greater than in a normal knee. The maximum stress of the MPFL graft was much greater at 0° and 30° than that of a native MPFL. After 30° of flexion, the MQPFL graft loosened just as in the native knee. Conclusions: The patellar contact pressures after the dynamic MPFLr were like those of the native knee, whereas a static reconstruction resulted in greater pressures, potentially increasing the risk of patellofemoral osteoarthritis in the long term. Therefore, the dynamic MPFLr might be a safer option than a static reconstruction from a biomechanical perspective.

Effects of a layered structure on the physicomechanical properties and extended creep behavior of bamboo-polypropylene composites (BPCs) determined by the stepped isostress method

Holzforschung ◽  
2018 ◽  
Vol 72 (7) ◽  
pp. 589-597 ◽  
Author(s):  
Chin-Yin Hsu ◽  
Teng-Chun Yang ◽  
Tung-Lin Wu ◽  
Ke-Chang Hung ◽  
Jyh-Horng Wu
Keyword(s):  
Creep Behavior ◽  
Bottom Layer ◽  
Short Term ◽  
Creep Properties ◽  
Polypropylene Composites ◽  
Plastic Composite ◽  
Accelerated Creep ◽  
Term Creep ◽  
Better Than

AbstractA layered bamboo-plastic composite (BPC) consisting of bamboo (Phyllostachys makinoi) particles and polypropylene was investigated. The influence of the layering conditions, including the thickness and bamboo content in various layers, was the focus in terms of the physicomechanical and creep properties of the BPCs. The results showed that a three-layered BPC (BPC3L) with a 1:3:1 thickness ratio and with top/bottom layer containing 40% bamboo exhibited the best specific flexural properties. An accelerated creep test approach was applied, known as the short-term stepped isostress method (SSM), to predict the long-term creep behavior of BPC3L. The results indicated that the creep master curves, which are constructed from different SSM testing parameters, agree well with the long-term experimental creep data and that the creep resistance of homogeneous single-layered BPC was better than that of BPC3L.

Clinical Replacement Strategies for Meniscus Tissue Deficiency

Cartilage ◽  
2021 ◽  
pp. 194760352110605
Author(s):  
Dean Wang ◽  
Erik Gonzalez-Leon ◽  
Scott A. Rodeo ◽  
Kyriacos A. Athanasiou
Keyword(s):  
Young Patients ◽  
Return To Sport ◽  
Short Term ◽  
Clinical Challenge ◽  
Meniscus Tissue ◽  
Collagen Meniscus Implant ◽  
Sport Activities ◽  
Joint Contact ◽  
Contact Pressures

Meniscus tissue deficiency resulting from primary meniscectomy or meniscectomy after failed repair is a clinical challenge because the meniscus has little to no capacity for regeneration. Loss of meniscus tissue has been associated with early-onset knee osteoarthritis due to an increase in joint contact pressures in meniscectomized knees. Clinically available replacement strategies range from allograft transplantation to synthetic implants, including the collagen meniscus implant, ACTIfit, and NUSurface. Although short-term efficacy has been demonstrated with some of these treatments, factors such as long-term durability, chondroprotective efficacy, and return to sport activities in young patients remain unpredictable. Investigations of cell-based and tissue-engineered strategies to treat meniscus tissue deficiency are ongoing.

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