Introduction to Time-Dependent Material Behavior

2005 ◽  
pp. 357-386
Author(s):  
Niels Saabye Ottosen ◽  
Matti Ristinmaa
Keyword(s):  
Material Behavior ◽  
Time Dependent

Improving the Long-Term Performance of Elastomeric Seals by Material Behavior Design

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Ryan B. Sefkow ◽  
Nicholas J. Maciejewski ◽  
Barney E. Klamecki
Keyword(s):  
Energy Density ◽  
Contact Pressure ◽  
Strain Energy ◽  
Applied Pressure ◽  
Material Behavior ◽  
Time Dependent ◽  
Ring Section ◽  
Stiff Material ◽  
Elastomeric Seals

Previously it was shown that including smaller inset regions of less stiff material in the larger O-ring section at locations of high stress results in lower strain energy density in the section. This lower energy content is expected to lead to improved long-term seal performance due to less permanent material deformation and so less loss of seal-housing contact pressure. The shape of the inset region, the time-dependent change in material properties, and hence change in seal behavior over time in use were not considered. In this research experimental and numerical simulation studies were conducted to characterize the time-dependent performance of O-ring section designs with small inset regions of different mechanical behaviors than the larger surrounding section. Seal performance in terms of the rate of loss of contact pressure of modified designs and a baseline elastic, one-material design was calculated in finite element models using experimentally measured time-dependent material behavior. The elastic strain energy fields in O-ring sections were calculated under applied pressure and applied displacement loadings. The highest stress, strain, and strain energy regions in O-rings are near seal-gland surface contacts with significantly lower stress in regions of applied pressure. If the size of the modified region of the seal is comparable to the size of the highest energy density region, the shape of the inset is not a major factor in determining overall seal section behavior. The rate of loss of seal-housing contact pressure over time was less for the modified design O-ring sections compared with the baseline seal design. The time-dependent performance of elastomeric seals can be improved by designing seals based on variation of mechanical behavior of the seal over the seal section. Improvement in retention of sealing contact pressure is expected for seal designs with less stiff material in regions of high strain energy density.

Characterization and Modeling of Time-Dependent Behaviour of Braided Packing Rings

2016 ◽  
Author(s):  
Mehdi Kazeminia ◽  
Abdel-Hakim Bouzid
Keyword(s):  
Viscoelastic Behavior ◽  
Material Behavior ◽  
Time Dependent ◽  
Nonlinear Material ◽  
Dependent Behavior ◽  
Sealing Performance ◽  
Proposed Model ◽  
Packing Rings ◽  
Linear Viscoelastic Behavior ◽  
Linear Viscoelastic

The sealing performance of packed stuffing boxes used in valves and compressors depends on the ability of the structure to maintain a minimum threshold contact pressure through a sufficient period of time. Packing rings exhibit combined creep and relaxation behavior due to internal disordered porous structure and nonlinear material behavior in addition to the interaction with other structural components. A comprehensive understanding of the time-dependent behavior of packing rings is essential for increasing the sealing performance. In this paper, the time-dependent linear viscoelastic behavior of packing material is constitutively simulated. The experimental investigation is carried out in a special test bench which was designed and developed to study the characteristics of the time-dependent behavior of packing rings. The results show that the proposed model can successfully be exploited to determine the time-dependent behavior of packing rings for application in the design of packed stuffing boxes.

Time Dependent Carcass-Liner Interface Load Model

2017 ◽  
Author(s):  
Geir Skeie ◽  
Roger Wold ◽  
Nils Sødahl
Keyword(s):  
Closed Form ◽  
Failure Mode ◽  
Load Capacity ◽  
Closed Form Solution ◽  
Material Behavior ◽  
Time Dependent ◽  
Critical Parameters ◽  
Thermal Shrinkage ◽  
Closed Form Expression ◽  
Load Model

Flexible risers in operation may experience large forces between the carcass and the polymer liner. Especially, cool-down of a pressurized riser results in thermal shrinkage of the liner layer and will transfer tensile loading of the carcass at the end fixation. Two aspects are then important to explore; the structural load capacity of the carcass structure and the balancing load effects acting on the carcass and liner. The current paper addresses the latter: the carcass load model. This has been presented in a previous publication in form of closed form expression for the long term quasi-static axial loading [1]. The model is extended to include the time dependent evolution of the carcass-liner interface force taking account of the time dependent material behavior in the liner and the time variation of the driving forces acting on the carcass and liner. The extension expresses the axial force as a convolution integral. In all but for the simplest cases the integral needs to be evaluated through appropriate quadrature rules. The closed form solution represents a reduced, efficient and robust scheme for evaluating the critical load level of a newly discovered failure mode. Further, the model enables identification of the critical parameters driving this failure mode.

scholarly journals In Vivo Properties of Uterine Suspensory Tissue in Pelvic Organ Prolapse

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
Jiajia Luo ◽  
Tovia M. Smith ◽  
James A. Ashton-Miller ◽  
John O. L. DeLancey
Keyword(s):  
Pelvic Organ Prolapse ◽  
Maximum Load ◽  
Pelvic Organ ◽  
Material Behavior ◽  
Time Dependent ◽  
Maximum Force ◽  
Knee Ligament ◽  
Uterosacral Ligaments ◽  
Servo Actuator

The uterine suspensory tissue (UST), which includes the cardinal (CL) and uterosacral ligaments (USL), plays an important role in resisting pelvic organ prolapse (POP). We describe a technique for quantifying the in vivo time-dependent force-displacement behavior of the UST, demonstrate its feasibility, compare data from POP patients to normal subjects previously reported, and use the results to identify the properties of the CL and USL via biomechanical modeling. Fourteen women with prolapse, without prior surgeries, who were scheduled for surgery, were selected from an ongoing study on POP. We developed a computer-controlled linear servo actuator, which applied a continuous force and simultaneously recorded cervical displacement. Immediately prior to surgery, the apparatus was used to apply three “ramp and hold” trials. After a 1.1 N preload was applied to remove slack in the UST, a ramp rate of 4 mm/s was used up to a maximum force of 17.8 N. Each trial was analyzed and compared with the tissue stiffness and energy absorbed during the ramp phase and normalized final force during the hold phase. A simplified four-cable model was used to analyze the material behavior of each ligament. The mean ± SD stiffnesses of the UST were 0.49 ± 0.13, 0.61 ± 0.22, and 0.59 ± 0.2 N/mm from trial 1 to 3, with the latter two values differing significantly from the first. The energy absorbed significantly decreased from trial 1 (0.27 ± 0.07) to 2 (0.23 ± 0.08) and 3 (0.22 ± 0.08 J) but not from trial 2 to 3. The normalized final relaxation force increased significantly with trial 1. Modeling results for trial 1 showed that the stiffnesses of CL and USL were 0.20 ± 0.06 and 0.12 ± 0.04 N/mm, respectively. Under the maximum load applied in this study, the strain in the CL and USL approached about 100%. In the relaxation phase, the peak force decreased by 44 ± 4% after 60 s. A servo actuator apparatus and intraoperative testing strategy proved successful in obtaining in vivo time-dependent material properties data in representative sample of POP. The UST exhibited visco-hyperelastic behavior. Unlike a knee ligament, the length of UST could stretch to twice their initial length under the maximum force applied in this study.

Fatigue Modeling of 508 LAS Under Variable Amplitude Loading: A Mechanistic Based Analytical Approach

2017 ◽  
Author(s):  
Bipul Barua ◽  
Subhasish Mohanty ◽  
William K. Soppet ◽  
Saurindranath Majumdar ◽  
Krishnamurti Natesan
Keyword(s):  
Material Behavior ◽  
Time Dependent ◽  
Plastic Behavior ◽  
Pressurized Water ◽  
Material Models ◽  
Variable Amplitude Loading ◽  
Variable Amplitude ◽  
Water Reactor ◽  
Material Parameters ◽  
Variable Amplitude Fatigue

A Chaboche-based evolutionary cyclic plasticity model is proposed to model the elastic-plastic behavior of 508 Low Alloy Steel (LAS), a commonly used material for Light Water Reactor (LWR), under variable amplitude loading. A novel parameter estimation technique is developed to incorporate the amplitude dependency of the material behavior into the earlier developed time-dependent material models based on constant amplitude fatigue test data. The resulting new material model can be referred as time-dependent-amplitude-independent material models. Variable amplitude fatigue tests under different environmental conditions (in air and pressurized water reactor (PWR) coolant water at 300°C) are analytically/mechanistically modeled. The analytical modeling results show that the time-dependent-amplitude-independent material parameters are able to capture the stress-strain state under variable amplitude fatigue loading. The developed model and reported material parameters can be utilized for more accurate stress analysis of safety-critical reactor components under real-life loading scenarios with variable/random loading transients. Recently a report on related 508 LAS material characterization work has been published by Argonne National Laboratory [1]. In this work a summary of the related work is presented.

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