Cyclic Stress Relaxation (Csr) of Filled Rubber and Rubber Components

2009 ◽  
Vol 82 (1) ◽  
pp. 104-112 ◽  
Author(s):  
S. Asare ◽  
A. G. Thomas ◽  
J. J. C. Busfield
Keyword(s):  
Stress Relaxation ◽  
Line Graph ◽  
Cyclic Stress ◽  
Maximum Displacement ◽  
Real Component ◽  
Test Pieces ◽  
Filled Rubber ◽  
Straight Line ◽  
Relaxation Measurements ◽  
Number Of Cycles

Abstract Under repeated stressing it is well known that rubber materials exhibit cyclic stress relaxation (CSR). Previous work has shown that the amount of relaxation observed from cycle to cycle is significantly greater than that expected from static relaxation measurements. The reduction in the stress attained on the second and successive loading cycles as compared to the stress attained on the first cycle in a stress strain cyclic test of fixed amplitude has been measured for elastomer test pieces and engineering components. It is seen that the peak force, under cyclic testing to a specific maximum displacement, plotted against the number of cycles on logarithmic scales produces a straight line graph, whose slope correlates to the rate of cyclic stress relaxation per decade. The rate of cyclic stress relaxation was found to increase with displacement amplitude in all modes of deformation. Plotting the rate of stress relaxation per decade against the maximum average strain energy attained in the cycle reduces the data measured in different deformation modes for both simple test pieces and components to a single curve. This approach allows the cyclic stress relaxation in a real component to be predicted from simple laboratory tests.

Rate Dependent Constitutive Equations of Cyclic Softening

1985 ◽  
Vol 40 (7) ◽  
pp. 653-665
Author(s):  
J. S. Mshana ◽  
A. S. Krausz
Keyword(s):  
Stress Relaxation ◽  
Low Temperature ◽  
Constitutive Equations ◽  
Strain Softening ◽  
Structural Characteristics ◽  
High Stress ◽  
Cyclic Strain ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Stress Softening

Constitutive equations of cyclic strain and stress softening for materials with low internal stress levels are derived from the rate theory. The study shows that over the high stress and low temperature range where the description of plastic flow in cyclic softening can be approximated with activation over a single energy barrier, cyclic strain softening is well related to stress relaxation process while cyclic stress softening is related to creep process. The material structural characteristics for cyclic strain softening, cyclic stress softening and stress relaxation are identical. Subsequently, it is shown that cyclic stress and strain softening within the high stress and low temperature range can be evaluated from the constitutive equations using the material structural characteristics measured from a simple stress relaxation test.

Effects of T5 and T6 Heat Treatments Applied to Rheocast A356 Parts for Automotive Applications

2008 ◽  
Vol 141-143 ◽  
pp. 237-242 ◽  
Author(s):  
Mario Rosso ◽  
Ildiko Peter ◽  
R. Villa
Keyword(s):  
Fatigue Behaviour ◽  
Cyclic Stress ◽  
Industrial Applications ◽  
Fatigue Tests ◽  
Controlled Cooling ◽  
Test Analysis ◽  
Heat Treated ◽  
Mechanical Performances ◽  
Semi Solid ◽  
Number Of Cycles

The correlation between the evaluation of the mechanical and of the fatigue behaviour of the rheocast, T5 and T6 heat treated SSM A356 aluminium alloy with respect to the microstructures of the component has been investigated. The study has been carried out on a suspension arm injected in a rheocasting 800 tons plant in Stampal S.p.A. The new rheocasting is a process that allows obtaining the alloys in a semisolid state directly from the liquid state, by controlled cooling of the molten alloys. The resulting microstructures are very fine, free from defects and homogeneous: these characteristics improve the mechanical properties of the alloys and specially the response to cyclic stress, an important issue for a suspension component. After a preliminary tensile test analysis, axial high frequency fatigue tests have been carried out at room temperature on specimen cut out from the suspension arm to determine the Wöhler curve and the number of cycles to failure. The results of this work allow a comparison of the effects of heat treatment process, T5 or T6, on Semi-Solid components for industrial applications in the automotive field. On the basis of these analysis the correlation between microstructure and mechanical performances can be established.

scholarly journals Appraisal of the current standards for stress relaxation measurements in compression for rubbers

1986 ◽  
Vol 6 (2) ◽  
pp. 85-105 ◽  
Author(s):  
Arthur W. Birley ◽  
Kamal P. Fernando ◽  
Mohammed Tahir
Keyword(s):  
Stress Relaxation ◽  
Relaxation Measurements ◽  
Current Standards

scholarly journals Modern rheology and electric induction: multivalued index of refraction, splitting of eigenvalues and fatigue

1996 ◽  
Vol 39 (5) ◽  
Author(s):  
M. Caputo
Keyword(s):  
Constitutive Equations ◽  
Fractional Derivatives ◽  
Cyclic Stress ◽  
Index Of Refraction ◽  
Stress And Strain ◽  
Trans Form ◽  
Dielectric Media ◽  
Electric Induction ◽  
Frequency Domains ◽  
Number Of Cycles

The modern constitutive equations of the rheology of analeptic media and of the polarization in dielectric media are discussed in the time and frequency domains. It is seen that the most appropriate form of the constitutive equations of these media is based on the convolution of the stress and strain, and of the electric field and induction respectively, with appropriate functions representing the memory of the medium to previous stress or induction. The most successful memory forma]ism in representing the observed phenomena is that of the derivative of fractional order which allows a variety of problems to be solved by means of the Laplace Trans- form. The consequent index of refraction, generally, is a set valued function which implies that a monochromatic wave generated in the medium is split into a set of waves with the same frequency but different wavelength which interfere and have a quasi periodically varying amplitude. The eigenfunctions of these media, associated to the ordinarily used principal values of the index of retraction, are split and so are the tree modes. The fatigue of anelastic media is studied using the new constitutive equations containing fractional derivatives; a phenomenological method is introduced to compute the number of cycles which gives fatigue for a strain or stress with given amplitude and frequency. The number of cycles which may cause fatigue is proportional to the amplitude and frequency of the applied strain or stress, or inversely proportional to the rate of stress or strain. A criterion is also established to see whether an applied cyclic stress or strain may cause fatigue. This criterion is tested with experimental data on steel and rocks verifying that, in general, it is consistent with the data although thc data are not always in the linear range. It is tentatively seen that fatigue docs not seem one of the causes of the release of the elastic energy stored in the Earth.

scholarly journals Numerical Modeling of the Degradation of the Normal Stress Under Large Number of Shearcycles

2021 ◽  
Vol 31 (3) ◽  
pp. 118-133
Author(s):  
Assia Bellayoune ◽  
Salah Messast ◽  
Marc Boulon
Keyword(s):  
Numerical Modeling ◽  
Normal Stress ◽  
Horizontal Stress ◽  
Cyclic Stress ◽  
Simple Expression ◽  
Shear Tests ◽  
Cyclic Shear ◽  
Explicit Formulation ◽  
Number Of Cycles

Abstract The evaluation of friction is an important element in the verification of stability and the determination of the bearing capacity of piles. In the case of cyclic stress, the soil-pile interface has a relaxation which corresponds to a fall in the horizontal stress which represents the normal stress at the lateral surface of the pile. This paper presents an explicit formulation to express the degradation of the normal stress after a large number of shear cycles as a function of cyclic parameters. In this study we are interested in the exploitation of the cyclic shear tests carried out by Pra-ai [1] with imposed normal rigidity (CNS) in order to demonstrate the phenomenon of falling of the normal stress. The approach presented in this paper consists in proposing a simple expression for estimating the degradation of normal stress as a function of cyclic shear parameters after a large number of cycles. The validation of this approach is verified by the application of this formulation to a real case where the comparison of the simulations made by this approach with those recorded on site shows the good adaptation of this approach to this type of problems.

scholarly journals Growth in the Lower Limb Following Chemotherapy for a Malignant Primary Bone Tumour: A Straight-Line Graph

Sarcoma ◽  
1997 ◽  
Vol 1 (2) ◽  
pp. 75-77 ◽  
Author(s):  
Paul Cool ◽  
Mark Davies ◽  
Rob J. Grimer ◽  
Simon R. Carter ◽  
Roger M. Tillman
Keyword(s):  
Lower Limb ◽  
Line Graph ◽  
Bone Tumour ◽  
Straight Line ◽  
Primary Bone Tumour ◽  
Primary Bone

Accelerated Heat-Aging Studies on Fluorosilicone Rubber

1975 ◽  
Vol 48 (5) ◽  
pp. 944-952 ◽  
Author(s):  
S. H. Kalfayan ◽  
R. H. Silver ◽  
A. A. Mazzeo
Keyword(s):  
Weight Loss ◽  
Stress Relaxation ◽  
Repeat Unit ◽  
Accelerated Aging ◽  
Basic Mechanism ◽  
Inert Atmosphere ◽  
Polymer Backbone ◽  
Aging Studies ◽  
Relaxation Measurements ◽  
Fluorosilicone Rubber

Abstract The accelerated aging of a vulcanizate of fluorosilicone rubber was studied by four methods: infrared spectroscopy, GPC, weight loss, and stress relaxation, with the object of gathering information pertinent to understanding the basic mechanism of its aging. No changes were observed in infrared spectra of the rubber aged in air up to 315°C although severe degradation took place, as evidenced by high weight loss and drastic change in the physical condition of the test samples. It was concluded that although the polymer degrades, there is no change detectable within the precision of the analytical methods in the structure of the repeat unit of the elastomer. The gel-permeation chromatogram of unheated rubber showed peaks at MW 450 000 (95%) and 630 (5%). The low-molecular-weight component is very likely the cyclic tetramer of λ,λ′,λ″-trifluoropropylmethylsiloxane, the principal monomer of the FVMQ used. Heat aging increased the concentration of the 630 MW component, but rate studies were prevented by complications resulting from solvent-induced rubber degradation. Rapid decrease in the MW of FVMQ, as found by GPC, indicated random scission in the polymer backbone, as opposed to ordered unzipping of the repeat unit. The same conclusion was reached from the effects of crosslink density on stress relaxation. Activation energies obtained from weight-loss measurements (104 kJ/mol) were lower than those obtained from stress-relaxation measurements, (150–155 kJ/mol), suggesting that the processes being measured in each case may not be the same. Chemical stress relaxation takes place more rapidly in the presence of air than in an inert atmosphere, and intermittent stress-relaxation measurements indicate that crosslinks form during thermal aging in air, their rate first increasing and then decreasing.

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