An Assessment of In-Service Stress Relaxation of a Work-Hardened Aluminum Magnesium Alloy

2004 ◽  
Vol 126 (2) ◽  
pp. 157-163 ◽  
Author(s):  
L. Zhu ◽  
A. J. Beaudoin ◽  
S. R. MacEwen
Keyword(s):  
Mechanical Properties ◽  
Magnesium Alloy ◽  
Stress Relaxation ◽  
Permanent Deformation ◽  
Time Dependent ◽  
Bending Test ◽  
Relaxation Processes ◽  
Simple Analysis ◽  
Time In Service ◽  
Aluminum Magnesium Alloy

Time-dependent relaxation processes continue after forming of sheet metal components. Mechanical properties and even the shape of the part may evolve with time. Beverage can ends, made of an aluminum-magnesium alloy, provide one example of relaxation in a metal product. Ends are manufactured in a series of forming operations, and the can end buckle pressure plays an important role in the design. It has been established that buckle pressure decreases with time in service. In this work, we outline a simple bending test to study relaxation at stress levels well below the usual 0.2 percent offset yield stress. The evolution of stress and development of plastic strain with time are assessed through a simple analysis of springback. The microplastic processes that lead to permanent deformation of the bent beam are well characterized by a model developed by Garmestani and Hart.

scholarly journals Evolution of Network Structure and Mechanical Properties in Autonomous-Strengthening Dental Adhesive

Polymers ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2076 ◽  
Author(s):  
Rizacan Sarikaya ◽  
Linyong Song ◽  
Qiang Ye ◽  
Anil Misra ◽  
Candan Tamerler ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Network Structure ◽  
Permanent Deformation ◽  
Hydrolytic Stability ◽  
Time Dependent ◽  
Rational Approach ◽  
Aqueous Environment ◽  
Experimental Sample ◽  
Dental Resins ◽  
By Products

The inherent degradation property of most dental resins in the mouth leads to the long-term release of degradation by-products at the adhesive/tooth interface. The by-products increase the virulence of cariogenic bacteria, provoking a degradative positive-feedback loop that leads to physicochemical and mechanical failure. Photoinduced free-radical polymerization and sol‒gel reactions have been coupled to produce a novel autonomous-strengthening adhesive with enhanced hydrolytic stability. This paper investigates the effect of network structure on time-dependent mechanical properties in adhesives with and without autonomous strengthening. Stress relaxation was conducted under 0.2% strain for 8 h followed by 40 h recovery in water. The stress‒time relationship is analyzed by nonlinear least-squares data-fitting. The fitted Prony series predicts the sample’s history under monotonic loading. Results showed that the control failed after the first loading‒unloading‒recovery cycle with permanent deformation. While for the experimental sample, the displacement was almost completely recovered and the Young’s modulus increased significantly after the first test cycle. The experimental polymer exhibited higher degree of conversion, lower leachate, and time-dependent stiffening characteristics. The autonomous-strengthening reaction persists in the aqueous environment leading to a network with enhanced resistance to deformation. The results illustrate a rational approach for tuning the viscoelasticity of durable dental adhesives.

High Temperature Mechanical Properties of a Crystallized BaO-B2O3-Al2O3-SiO2 Glass Ceramic for SOFC

2009 ◽  
Author(s):  
Hsiu-Tao Chang ◽  
Chih-Kuang Lin ◽  
Chien-Kuo Liu
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Stress Relaxation ◽  
Flexural Strength ◽  
Glass Ceramic ◽  
Testing Temperature ◽  
Bending Test ◽  
High Temperature Mechanical Properties ◽  
Four Point Bending ◽  
The Given

The high temperature mechanical properties in a glass-ceramic sealant of BaO-B2O3-Al2O3-SiO2 system was studied by four-point bending test at room temperature, 550°C, 600°C, 650°C, and 700°C, to investigate the variation of Young’s modulus, flexural strength, and stress relaxation. Weibull statistic analysis was applied to describe the fracture strength of the given glass ceramic. The crystalline phase was produced by controlled heat treatment and analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that the flexural strength was enhanced at high temperatures when the testing temperature was below the glass transition temperature (Tg). This was presumably due to a crack healing effect taking place at high temperature. Significant stress relaxation for the given glass ceramic was observed to generate extremely large deformation without breaking the specimens when the testing temperature was set at 700°C.

The Experiment and Finite Element Analysis of Carbon Fiber Sandwich Beam With Pyramidal Truss Core Structure

2016 ◽  
Author(s):  
Jiguang Gu ◽  
Nana Yang ◽  
Zhanyi Guo ◽  
Xiongliang Yao
Keyword(s):  
Mechanical Properties ◽  
Carbon Fiber ◽  
Permanent Deformation ◽  
Sandwich Beam ◽  
Pressure Head ◽  
Bending Test ◽  
Face Sheet ◽  
Element Analysis ◽  
Truss Core ◽  
Pyramidal Truss

A new technology method is adapted to manufacture carbon fiber lattice sandwich beam with pyramidal truss core. The flat crush test experiment is to test the resistance to compression of the carbon fiber sandwich plate with pyramidal truss core. The result shows that after the pressure head contact the specimens adequately, and the stiffness of structure is the maximum. If the load is continuing increase, the pyramidal truss core may be destroyed, and both sides of the carbon fiber panel begin tottering. It emerges permanent deformation on the structures after an uninstall. The three-point bending test of lattice sandwich beam referred to ASTM C393-00 is designed to research the mechanical properties of face sheet and pyramidal truss core of lattice sandwich beam with theoretical analysis. Load-deflection curves of the middle of lattice sandwich beam in long span and in short span tests are retained, which are applied to obtain flexure stiffness of face sheet and shear strength of pyramidal truss core. It is found that span length has some influence on damage modes of lattice sandwich beam with pyramidal truss core. Debonding between face sheet and lattice core occurs when span is larger and core collapse appears when span is smaller. Crack expansion and fracture of resin base also both emerge in these two damage modes and the crack expansion consists of two different types which are crack expansion inside the resin base and crack expansion from the indenter to the support. Contrast with other lattice sandwich beam with similar or different shapes of core in the other references, the mechanical properties of this lattice sandwich beam by this new fabrication have obvious advantage at the same relative density.

scholarly journals Study on the Time-Dependent Mechanical Behavior and Springback of Magnesium Alloy Sheet (AZ31B) in Warm Conditions

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 3856
Author(s):  
Jae-Hyeong YU ◽  
Chang-Whan Lee
Keyword(s):  
Magnesium Alloy ◽  
Stress Relaxation ◽  
Dynamic Recrystallization ◽  
Mechanical Behavior ◽  
Alloy Sheet ◽  
Holding Time ◽  
Time Dependent ◽  
Die Set ◽  
Creep And Stress Relaxation ◽  
Springback Angle

In this study, the time-dependent mechanical behavior of the magnesium alloy sheet (AZ31B) was investigated through the creep and stress relaxation tests with respect to the temperature and pre-strain. The microstructure changes during creep and stress relaxation were investigated. As the tensile deformation increased in the material, twinning and dynamic recrystallization occurred, especially after the plastic instability. As a result, AZ31B showed lower resistance to creep and stress relaxation due to dynamic recrystallization. Additionally, time-dependent springback characteristics in the V- and L-bending processes concerning the holding time and different forming conditions were investigated. We analyzed changes of microstructure at each forming temperature and process. The uniaxial tensile creep test was conducted to compare the microstructures in various pre-strain conditions with those at the secondary creep stage. For the bending process, the change of the microstructure after the forming was compared to that with punch holding maintained for 1000 s after forming. Due to recrystallization, with the holding time in the die set of 60 s, the springback angle decreased by nearly 70%. Increased holding time in the die set resulted in a reduced springback angle.

scholarly journals Time-Dependent Mechanical Properties in Polyetherimide 3D-Printed Parts Are Dictated by Isotropic Performance Being Accurately Predicted by the Generalized Time Hardening Model

Polymers ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 678 ◽  
Author(s):  
A. G. Salazar-Martín ◽  
A. A. García-Granada ◽  
G. Reyes ◽  
G. Gomez-Gras ◽  
J. M. Puigoriol-Forcada
Keyword(s):  
Mechanical Properties ◽  
Stress Relaxation ◽  
Relaxation Behavior ◽  
Time Dependent ◽  
Secondary Creep ◽  
Stress Relaxation Behavior ◽  
Build Orientation ◽  
Fused Deposition ◽  
3D Printed ◽  
Generalized Time

The Fused-Deposition Modelling (FDM) technique has transformed the manufacturing discipline by simplifying operational processes and costs associated with conventional technologies, with polymeric materials being indispensable for the development of this technology. A lack of quantification of viscoelastic/plastic behavior has been noted when addressing FDM parts with Polyetherimide (PEI), which is currently being investigated as a potential material to produce functional end-products for the aerospace and health industry. Primary and secondary creep along with stress relaxation tests have been conducted on FDM PEI specimens by applying stresses from 10 to 40 MPa for 100 to 1000 min. Specimens were 3D printed by varying the part build orientation, namely XY, YZ, and XZ. Creep results were fitted to the Generalized Time Hardening equation (GTH), and then this model was used to predict stress relaxation behavior. FDM PEI parts presented an isotropic creep and stress relaxation performance. The GTH model was proven to have a significant capacity to fit viscoelastic/plastic performances for each single build orientation (r > 0.907, p < 0.001), as well as a tight prediction of the stress relaxation behavior (r > 0.998, p < 0.001). Averaged-orientation coefficients for GTH were also closely correlated with experimental creep data (r > 0.958, p < 0.001) and relaxation results data (r > 0.999, p < 0.001). FDM PEI parts showed an isotropic time-dependent behavior, which contrasts with previous publications arguing the significant effect of part build orientation on the mechanical properties of FDM parts. These findings are strengthened by the high correlation obtained between the experimental data and the averaged-coefficient GTH model, which has been proven to be a reliable tool to predict time-dependent performance in FDM parts.

The Response of Human Skin to Small Tensile Loads in Vitro

1982 ◽  
Vol 11 (1) ◽  
pp. 43-46 ◽  
Author(s):  
W A B Wan Abas ◽  
J C Barbenel
Keyword(s):  
Mechanical Properties ◽  
Stress Relaxation ◽  
Human Skin ◽  
Tensile Modulus ◽  
Time Dependent ◽  
Anisotropic Stress ◽  
Linear Load ◽  
Load Cycling ◽  
Repeated Load

The mechanical properties of excised strips of human skin were investigated in the initial high compliant phase. The specimens showed preconditioning on repeated load cycling. The preconditioned specimen displayed a reproducible response, and a region of linear load-extension behaviour. The value of the tensile modulus and Poisson's ratio, both referred to the dimensions of the preconditioned specimens, are reported and the tissues shown to be anisotropic. Stress relaxation tests showed the properties of the tissues to be time dependent.

scholarly journals Evaluation of the Loading, Unloading, and Permanent Deformation of Newly Available Epoxy Resin Coated Ni-Ti Wires Using Self-Ligating Brackets

2017 ◽  
Vol 2017 ◽  
pp. 1-8
Author(s):  
Hazel Garro-Piña ◽  
María Cristina Jiménez-Cervantes ◽  
Ricardo Ondarza-Rovira ◽  
Roberto Justus ◽  
Salvador García-López
Keyword(s):  
Mechanical Properties ◽  
Epoxy Resin ◽  
Clinical Management ◽  
Permanent Deformation ◽  
Applied Force ◽  
Bending Test ◽  
Recovery Cycle ◽  
Three Point Bending ◽  
Significant Difference

Aim. The purpose of this study was to evaluate the load and unload deflection and permanent deformation of round 0.016′′ and rectangular 0.016′′×0.022′′ regular and coated Ni-Ti wires. Materials and Methods. Ni-Ti archwires produced by two manufacturers were evaluated. Both regular and coated round and rectangular Ni-Ti wire segments (n=15) from each group were submitted to a three-point bending test. Both types of wires were evaluated for permanent deformation at the end of a recovery cycle. Results. The coated round 0.016′′ Ni-Ti wires produced a significantly lower force in loading (p<0.01) and unloading (p<0.01) than regular wires of the same manufacturer and size. There was no significant difference in permanent deformation between coated and regular round Ni-Ti wires from the same company. For rectangular 0.016×0.022′′ Ni-Ti wires, there was a significant difference in the loading evaluation, but the unloading test presented no significant differences. The permanent deformation of the rectangular wires revealed no significant difference between them. Conclusion. The addition of an esthetic coating to these new Ni-Ti wires produced changes in their mechanical properties, manifested as a reduction in the applied force, which should be considered in clinical management.

scholarly journals Time dependent stress relaxation and recovery in mechanically strained 3D microtissues

2020 ◽  
Author(s):  
Matthew Walker ◽  
Michel Godin ◽  
James L. Harden ◽  
Andrew E. Pelling
Keyword(s):  
Mechanical Properties ◽  
Stress Relaxation ◽  
Single Cells ◽  
Collagen Matrix ◽  
Step Length ◽  
Linear Process ◽  
The Body ◽  
Time Dependent ◽  
Step Size ◽  
Length Changes

AbstractCharacterizing the time-dependent mechanical properties of cells is not only necessary to determine how they deform, but also to fully understand how external forces trigger biochemical-signaling cascades to govern their behavior. Presently mechanical properties are largely assessed by applying local shear or compressive forces on single cells in isolation grown on non-physiological 2D surfaces. In comparison, we developed the microfabricated vacuum actuated stretcher to measure tensile loading of 3D multicellular ‘microtissue’ cultures. With this approach, we assessed here the time-dependent stress relaxation and recovery responses of microtissues, and quantified the spatial remodeling that follows step length changes. Unlike previous results, stress relaxation and recovery in microtissues measured over a range of step amplitudes and pharmacological treatments followed a stretched exponential behavior describing a broad distribution of inter-related timescales. Furthermore, despite a performed compendium of experiments, all responses led to a single linear relationship between the residual elasticity and degree of stress relaxation, suggesting that these mechanical properties are coupled through interactions between structural elements and the association of cells with their matrix. Lastly, although stress relaxation could be quantitatively and spatially linked to recovery, they differed greatly in their dynamics; while stress recovery behaved as a linear process, relaxation time constants changed with an inverse power law with step size. This assessment of microtissues offers insights into how the collective behavior of cells in a 3D collagen matrix generate the dynamic mechanical properties of tissues, which is necessary to understanding how cells deform and sense mechanical forces in the body.

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