Plastic Coupling and Stress Relaxation During Nonproportional Axial-Shear Strain-Controlled Loading

2000 ◽  
Vol 123 (1) ◽  
pp. 81-87
Author(s):  
Cliff J. Lissenden ◽  
Steven M. Arnold ◽  
Atef F. Saleeb
Keyword(s):  
Stress Relaxation ◽  
Shear Strain ◽  
Stress Reduction ◽  
Large Range ◽  
Axial Stress ◽  
Axial Strain ◽  
Time Dependent ◽  
Load Path ◽  
Percent Reduction ◽  
Material Parameters

A nonproportional strain-controlled load path consisting of two segments was applied to the cobalt-based alloy Haynes 188 at 650°C. The first segment was purely axial; the axial strain was then held constant while the shear strain was increased during the second segment. The alloy exhibited about a 95-percent reduction in axial stress (298 to 15 MPa) during shear straining. This reduction was due primarily to plastic coupling, but time-dependent stress relaxation also occurred. A rate-independent plasticity model approximated the stress reduction due to plastic coupling reasonably well, but as expected was unable to account for time-dependent stress relaxation. A viscoplasticity model capable of predicting the interaction between stress relaxation and plastic coupling also predicted the plastic coupling reasonably well. The accuracy of the viscoplastic model is shown to depend greatly upon the set of nonunique material parameters, which must be characterized from a sufficiently large range of load histories.

scholarly journals Time-Dependent Response of a Recycled C&D Material-Geotextile Interface under Direct Shear Mode

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 3070
Author(s):  
Fernanda Bessa Ferreira ◽  
Paulo M. Pereira ◽  
Castorina Silva Vieira ◽  
Maria de Lurdes Lopes
Keyword(s):  
Shear Stress ◽  
Stress Relaxation ◽  
Shear Displacement ◽  
Time Dependent ◽  
Shear Behaviour ◽  
Displacement Rate ◽  
Shear Mode ◽  
Direct Shear ◽  
Constant Displacement ◽  
Shear Box

Geosynthetic-reinforced soil structures have been used extensively in recent decades due to their significant advantages over more conventional earth retaining structures, including the cost-effectiveness, reduced construction time, and possibility of using locally-available lower quality soils and/or waste materials, such as recycled construction and demolition (C&D) wastes. The time-dependent shear behaviour at the interfaces between the geosynthetic and the backfill is an important factor affecting the overall long-term performance of such structures, and thereby should be properly understood. In this study, an innovative multistage direct shear test procedure is introduced to characterise the time-dependent response of the interface between a high-strength geotextile and a recycled C&D material. After a prescribed shear displacement is reached, the shear box is kept stationary for a specific period of time, after which the test proceeds again, at a constant displacement rate, until the peak and large-displacement shear strengths are mobilised. The shear stress-shear displacement curves from the proposed multistage tests exhibited a progressive decrease in shear stress with time (stress relaxation) during the period in which the shear box was restrained from any movement, which was more pronounced under lower normal stress values. Regardless of the prior interface shear displacement and duration of the stress relaxation stage, the peak and residual shear strength parameters of the C&D material-geotextile interface remained similar to those obtained from the conventional (benchmark) tests carried out under constant displacement rate.

Combined-Stress Tests on 24S-T Aluminum-Alloy Tubes

1947 ◽  
Vol 14 (2) ◽  
pp. A147-A153
Author(s):  
W. R. Osgood
Keyword(s):  
Aluminum Alloy ◽  
Hoop Stress ◽  
Axial Stress ◽  
Axial Strain ◽  
Maximum Deviation ◽  
Shearing Stress ◽  
Stress Tests ◽  
Combined Stress ◽  
Stress Strain ◽  
Shearing Strain

Abstract Combined-stress tests were made on five 24S-T aluminum-alloy tubes, 1 3/4 in. ID × 0.05 in. thick. The ratios of circumferential (hoop) stress to axial stress were 0, 1/2, 1, 2, and ∞. The tubes were tested to failure and sufficient measurements of circumferential strain and axial strain were taken to plot stress-strain curves almost up to rupture. The results are presented in the form of two sets of stress-strain curves for each ratio of stresses, namely, maximum shearing stress plotted against maximum shearing strain, and octahedral shearing stress plotted against octahedral shearing strain. In each plot the maximum deviation of the curves is about ± 5 per cent. A method of evaluating small octahedral shearing strains from the data is given which does not assume Poisson’s ratio to be 1/2.

QUASI-LINEAR VISCOELASTIC MODELLING OF UNCURED PREPREGS UNDER COMPACTION

2021 ◽  
Author(s):  
SIDDHESH S. KULKARNI ◽  
KAMRAN A. KHAN ◽  
REHAN UMER
Keyword(s):  
Stress Relaxation ◽  
Relaxation Function ◽  
Soft Tissues ◽  
Volume Fraction ◽  
Time Dependent ◽  
Strain History ◽  
Manufacturing Processes ◽  
Fiber Volume ◽  
Consolidation Process ◽  
Thermoset Resin

Reinforcement compaction sometimes referred as consolidation process and is one of the key steps in various composite manufacturing processes such as autoclave and out-of-autoclave processing. The prepregs consist of semi-cured thermoset resin system impregnating the fibers. hence, the prepreg shows strong viscoelastic compaction response, which strongly depends on compaction speed and stress relaxation. modeling of time-dependent response is of utmost importance to understand the behavior of prepregs during different stages of composites manufacturing processes. The quasilinear viscoelastic (QLV) theory has been extensively used for the modeling of viscoelastic response of soft tissues in biomedical applications. In QLV approach, the stress relaxation can be expressed in terms of the nonlinear elastic function and the reduced relaxation function. The constitutive equation can be represented by a convolution integral of the nonlinear strain history, and reduced relaxation function. This study adopted a quasilinear viscoelastic modeling approach to describe the time dependent behavior of uncured-prepregs under compression. The model was modified to account for the compaction behavior of the prepreg under a compressive load. The deformation behavior of the prepreg is usually characterized by the fiber volume fraction, V . In this study, the material used was a 2/2 Twill weave glass prepreg (M26T) supplied by Hexcel® Industries USA. We performed a compaction experiment of the uncured prepreg at room temperature at different displacement rate and subsequent relaxation to describe the viscoelastic behavior of the prepreg. The model parameter calibration was performed using the trust-region-reflective algorithm in matlab to a selected number of test data. The calibrated model was then used to predict the rate dependent compaction and relaxation response of prepregs for different fiber volume fractions and strain rates.

New strength metrics for containerboards: influences of basic papermaking factors

2018 ◽  
Vol 33 (4) ◽  
pp. 592-602
Author(s):  
Amanda Mattsson ◽  
Tetsu Uesaka
Keyword(s):  
Time Dependent ◽  
New Method ◽  
Creep Tests ◽  
Material Parameters ◽  
Dependent Failures ◽  
Short Term Strength ◽  
New Material ◽  
End Use ◽  
Future Work ◽  
Operating Window

Abstract In end-use, containerboard is subjected to a variety of loading histories, such as seconds of loading/unloading, hours of vibration, days of creep load. The fundamental question is whether the commonly measured static strength represents “strength” under these conditions. Another question is, since those time-dependent failures are notoriously variable, how to describe the probabilistic aspect. This study concerns the characterisation of these different facets of “strength”. In our earlier work, we have investigated the theoretical framework for time-dependent, probabilistic failures, and identified three material parameters: (1) characteristic strength, {S_{c}}, representing short-term strength, (2) brittleness/durability parameter, ρ, and (3) reliability parameter, β. We have also developed a new method that allows us to determine all these parameters much faster than typical creep tests. Using the new method, we have started investigating effects of basic papermaking variables on the new material parameters. Among the samples tested, the parameter ρ varied from 20 to 50, and β from 0.5 to 1.0. This suggests that, even within the current papermaking practice, there is a wide operating window to tune these new material parameters. The future work is, therefore, to find specific manufacturing variables that can systematically change these new material parameters.

Taylor-Couette Flow of an Oldroyd-B Fluid in an Annulus Due to a Time-Dependent Couple

2011 ◽  
Vol 66 (1-2) ◽  
pp. 40-46 ◽  
Author(s):  
Corina Fetecau ◽  
Muhammad Imran ◽  
Constantin Fetecau
Keyword(s):  
Exact Solutions ◽  
Couette Flow ◽  
Bessel Functions ◽  
Time Dependent ◽  
Second Grade ◽  
Governing Equations ◽  
Material Parameters ◽  
Taylor Couette ◽  
Similar Solutions ◽  
Taylor Couette Flow

Taylor-Couette flow in an annulus due to a time-dependent torque suddenly applied to one of the cylinders is studied by means of finite Hankel transforms. The exact solutions, presented under series form in terms of usual Bessel functions, satisfy both the governing equations and all imposed initial and boundary conditions. They can easily be reduced to give similar solutions for Maxwell, second grade, and Newtonian fluids performing the same motion. Finally, some characteristics of the motion, as well as the influence of the material parameters on the behaviour of the fluid, are emphasized by graphical illustrations.

Performance of self-centering steel moment frame considering stress relaxation in prestressed cables

2020 ◽  
Vol 23 (9) ◽  
pp. 1813-1822
Author(s):  
Seyyed Morteza Asadolahi ◽  
Nader Fanaie
Keyword(s):  
Stress Relaxation ◽  
Stress Reduction ◽  
Original Position ◽  
Dissipated Energy ◽  
Moment Frame ◽  
Steel Moment Frame ◽  
Moment Resisting Frames ◽  
Moment Resisting Frame ◽  
Moment Resisting ◽  
Over Time

Buildings can be designed to limit the earthquake-induced damage to members that can easily be repaired. Self-centering moment-resisting frames can be used as effective structural systems for this purpose. Self-centering moment-resisting frames with prestressed cables are able to return the structure to its original position after the earthquake. The internal forces in self-centering moment-resisting frames are transferred between the beam and the column by post-tensioned cables. As a main member of self-centering connections, prestressed cables play a significant role in such systems. Cable tension decreases over time due to the effect of stress relaxation on the performance of the system. Stress relaxation is a time-dependent phenomenon causing stress reduction over time in the members prestressed at a constant strain. Therefore, the effect of stress relaxation on the performance of self-centering moment-resisting frames can be significant. In this article, after simulating and validating a moment-resisting frame with self-centering connections, stiffness and moment–rotation hysteresis diagrams were analyzed after 0, 1, 5, 10, and 20 years of cable prestressing. According to the results, two equations were presented to estimate the reduction in the connection stiffness and dissipated energy by the system based on prestressing level and the time after prestressing. The proposed equations could be used to model semi-rigid connections.

scholarly journals Further Insight into the Depth-Dependent Microstructural Response of Cartilage to Compression Using a Channel Indentation Technique

2013 ◽  
Vol 2013 ◽  
pp. 1-11 ◽  
Author(s):  
Ashvin Thambyah ◽  
Neil D. Broom
Keyword(s):  
Stress Relaxation ◽  
Axial Strain ◽  
Compressive Strain ◽  
Microstructural Analysis ◽  
Elastic Response ◽  
Axial Deformation ◽  
Aspect Ratios ◽  
The Matrix ◽  
Tissue System ◽  
Relaxation Responses

Stress relaxation and structural analysis were used to investigate the zonally differentiated microstructural response to compression of the integrated cartilage-on-bone tissue system. Fifteen cartilage-on-bone samples were divided into three equal groups and their stress relaxation responses obtained at three different levels of axial compressive strain defined as low (~20%), medium (~40%) and high (~60%). All tests were performed using a channel indenter which included a central relief space designed to capture the response of the matrix adjacent to the directly loaded regions. On completion of each stress relaxation test and while maintaining the imposed axial strain, the samples were formalin fixed, decalcified, and then sectioned for microstructural analysis. Chondron aspect ratios were used to determine the extent of relative strain at different zonal depths. The stress relaxation response of cartilage to all three defined levels of axial strain displayed an initial highly viscous response followed by a significant elastic response. Chondron aspect ratio measurements showed that at the lowest level of compression, axial deformation was confined to the superficial cartilage layer, while in the medium and high axial strain samples the deformation extended into the midzone. The cells in the deep zone remained undeformed for all compression levels.

Sign in / Sign up

Export Citation Format

Share Document