Tensile Stress Relaxation Tests Research Articles

Tensile properties of articular cartilage are altered by meniscectomy in a canine model of osteoarthritis.

Loss of or damage to the meniscus alters the pattern of loading in the knee joint and frequently leads to cartilage degeneration and osteoarthritis. The mechanical properties of articular cartilage have been shown to reflect the extent of cartilage degeneration in human osteoarthritis and in experimental models of joint disease, but there is little experimental data documenting changes in cartilage mechanics following meniscectomy. We hypothesized that the tensile properties of the surface zone of articular cartilage are altered following total medial meniscectomy. Twelve mongrel dogs underwent complete resection of the medial meniscus in the right knee, and the femoral cartilage was studied 12 weeks after the operation. We performed uniaxial, tensile stress-relaxation tests to determine the equilibrium tensile modulus of surface-zone cartilage. Water and glycosaminoglycan content were also measured at site-matched locations. The tensile moduli of the cartilage decreased significantly following meniscectomy. The linear region modulus decreased by 40%, from 25.5 +/- 7.7 to 15.3 +/- 7.2 MPa. There was a weak (r = -0.45), but significant, correlation between the linear region modulus and the gross morphological grade for cartilage damage. Water and glycosaminoglycan content did not change following meniscectomy. Composition was not correlated with mechanical properties or morphological grade, suggesting that cartilage structure may play a more important role than composition in determining the mechanical properties. The observed decrease in cartilage material properties provides a quantitative measure of the loss of cartilage function following meniscectomy and reflects a pattern of change that is consistent with damage to the collagen-proteoglycan solid network.

Viscoelastic Properties of Nylon 6 Fibers and Corresponding Fiber Assemblies

The viscoelastic properties of nylon 6 fibers are studied in terms of stress relaxation and dynamic mechanical analysis. Single fibers are subjected to tensile stress relaxation tests at room temperature in air and water after rapid straining to between 5 and 40%; the duration of these tests is between 0.1 to 105 seconds. Dynamic mechanical tests are done on a Rheometrics dynamic tester at frequencies between 0.1 to 10 Hz and at various static prestrains. Results are compared with those from similar tests in com pression on waddings made of corresponding fibers. In general, correlations are good between fiber properties and wadding properties.

Effects of age and location on the biomechanical and biochemical properties of canine tracheal ring cartilage in dogs

SUMMARY Objective To evaluate effects of age (immature vs adult) and location along the trachea on the biomechanical properties (via a tensile stress relaxation test) and biochemical properties (water content and total proteoglycan content) of canine tracheal ring cartilage. Sample population Entire trachea from 8 immature and 8 adult dogs. Procedure A section of each tracheal ring from 8 immature dogs (6 months old) and 8 adult dogs (2 to 3 years old) was tested biomechanically (maximal stress, equilibrium stress, equilibrium modulus, and percentage of relaxation) and processed for biochemical analysis (water content and total proteoglycan content). Two rings from each trachea were prepared for histologic analysis (H&E or safranin-O staining). Results Biomechanical and biochemical parameters were not different between cervical and thoracic rings of either age group. Mean maximal stress, equilibrium stress, and equilibrium modulus were significantly higher for adult, compared with immature, dogs. However, percentage of relaxation for adult dogs was significantly lower. Tracheal rings of adult dogs had a significantly higher proteoglycan content and a significantly lower water content than did those of immature dogs. Water content and biomechanical parameters were significantly correlated, and proteoglycan content and biomechanical properties were significantly but weakly correlated. On histologic sectioning, a qualitative decrease in safranin-O staining in the rings of immature dogs also was observed. Conclusions and Clinical Relevance Biomechanical and biochemical properties of the canine tracheal ring cartilage are altered with age. However, location of the ring along the trachea did not affect these properties for either age group. Results lend support to the theory that proteoglycan content has some effect on tensile properties of tracheal rings and may explain increased compliance observed in rings from dogs with collapsed trachea. (Am J Vet Res 1998;59:18–22)

Environmental effects on the static strength and stress relaxation of a quartz fabric–reinforced, cyanate resin–matrix composite

AbstractEnvironmental effects are an important consideration when one is designing polymer matrix composites (PMC). The mechanical behavior of a quartz fabric–reinforced, cyanate resin–matrix composite was studied by tensile tests, compression tests, and stress relaxation tests. Compression and tensile strength as well as smaller relaxation spectra were obtained after exposing the material to different environments involving printed wire board (PWB) in aviation systems: Skydrol hydraulic oil (25°C), salt spray (5% NaCl at 95°F), alkaline solution (45 g/l 50°C), and nitric acid (304 g/l 25°C). Although only a small amount of environmental liquid was absorbed, it nonetheless had an acute effect on the mechanical properties and lifetime of the material.

Viscoelastic behavior of flexible slabstock polyurethane foams: Dependence on temperature and relative humidity. I. Tensile and compression stress (load) relaxation

AbstractThe relaxation behavior of the load in compression and the stress in tension was monitored at constant temperature and/or relatively humidity for a set of four slabstock foams with varying hard‐segment content as well as two of the compression molded plaques of these foams. The majority of the compression relaxation tests were done at a 65% strain level in order to be consistent with the common ILD test. The tensile stress relaxation tests were performed at a 25% strain level. Over the 3‐h testing period, a linear relationship between the log of compressive load or the log of tensile stress versus log time is observed for most testing conditions. For linear behavior, the values of the slope or the load/stress decay rate are comparable in both the tension and compression modes with the values being slightly higher in magnitude for the compression mode. These rates of decay are in the range of −2.2 × 10 −2 to −1.7 × 10 −2 for a 21 wt % hard‐segment foam and −3.2 × 10−2 to −2.4 × 10−2 for a 34 wt % hard‐segment foam. Increasing %RH at a given temperature does bring about a steady decrease in the initial load or initial stress as well as a slight increase in the rate of relaxation. The effect of temperature on the relaxation behavior is most significant at temperatures near 125°C and above. The FTIR thermal analysis of the plaques indicates that this significant increase is due to additional hydrogen bond disruption and possible chain scission taking place in the urea and urethane linkages that are principally present in the hard segment regions. The relaxation behavior in both tension and compression is believed to be mostly independent of the cellular texture of the foam at the strain levels given above. This conclusion is based on the similar relaxation behavior between the plaques and the foams. © 1994 John Wiley & Sons, Inc.

Viscoplastic properties of an FeCrPC amorphous alloy

The homogeneous flow of amorphous Fe 76Cr 5C 11P 8 (obtained by melt spinning) was examined in tensile creep and bend stress relaxation tests. The stress dependence of the steady-state homogeneous plastic flow rate was measured over a large stress range. We observed a transition from linear Newtonian viscous flow to a non-linear regime. This transition depends on temperature and stress. We also observed that during the first stage of creep the viscosity increased linearly with time, and that the rate of increase exhibited an Arrhenius-type temperature dependence with an activation energy of 27 kJ mol −1. The isoconfigurational viscosity in various states of structural relaxation was investigated over a wide temperature range. It was found to depend on thermal history and was non-Arrhenian. The stress relaxation rate is characterized by a linear decrease in ln( σ/ σ 0) with ln t. The rate of change of the viscosity computed from the slope of these linear regions agrees with the creep results.

Initial Agehardening and Thermally Activated Process in Al–Zn Alloys

Measurements of the electrical resistivity, Simple tensile tests and stress relaxation tests are made to investigate the hardening mechanism at the early stage of ageing in Al–Zn alloys. There exists a good linear relationship between the flow stress and the square root of the plastic strain, ε1⁄2, at any stage of ageing for pure Al and Al–Zn alloys deformed at \dotε=10−4s−1 and 77 K. The strain independent flow stress σ0 obtained by extrapolating ε1⁄2 to zero increases drastically in the concentrated alloys as ageing proceeds. This initial agehardening can be explained by the increment in internal stress due to the interaction between dislocations and the coherent strain fields as proposed by Gerold et al.The strain exponent n of the activation volume for dislocation motion is obtained to be n1=−0.3 and n2=−0.6 on both sides of a certain strain εc for the alloys on the assumption that V*∝εn. The dislocation intersection mechanism can give a satisfactory explanation for n2\simeq−1⁄2. The reason why n1 does not coincide with n2 may be that parallel processes of the dislocation intersection and the shearing of GP zones by dislocations rate-controll the deformation in the strain region less than εc.

Threshold stresses in amorphous alloys—I. Flow

The stress dependence of homogeneous flow in amorphous FeNiPB has been examined in tensile stress relaxation tests. The strain rate sensitivity m = [ d( lnγ)]/[ d( lnτ)] is found to be unity in an intermediate stress range and greater than unity at both high and low stress levels. The transition from linear stress-strain rate behavior ( m = 1) to a non-linear relationship ( m > 1) at high stress has previously been observed and explained by transition state theory. This new observation of linearity breakdown ( m > 1) at low stresses requires the introduction of a threshold stress and appropriate modification of the prior analysis. A physical interpretation of the stress threshold based on flow induced disordering will be discussed. The dependence of the threshold stress and the volume strain element on temperature and annealing time is presented. The implications of this new model on the transition from homogeneous to shear band flow is also discussed.

Creep, stress relaxation and structural change of amorphous alloys

The time, temperature and stress dependence of the homogeneous flow of amorphous FeNiPB and PdCuSi has been examined in tensile creep, tensile stress relaxation and bend stress relaxation tests. The results are shown to be entirely self-consistent, and are used to reconcile the discrepancies found in the literature data. In all cases, the viscosity increases linearly with time, the rate of increase being both temperature and composition dependent. The stress dependence of the strain rate follows a hyperbolic sine relation. The volume strain element appears to be a function of temperature and composition. A general empirical flow law for amorphous alloys is presented based on these observations. It is shown to be in agreement with all the available data.

Strain energy function of styrene butadiene rubber and the effect of temperature

AbstractBiaxial and uniaxial tensile stress relaxation tests were made on square sheet specimens of styrene butadiene rubber (SBR), mounted in a universal biaxial tester within a temperature‐controlled box, with the object of studying the effect of temperature on the strain energy function. The stress relaxation responses, usually for times up to 10 min, were obtained for various degrees of biaxiality, various extension ratios, and various temperatures within the limits of +25 to −45°C. The results indicated that if the Valanis–Landel representation of the strain energy function \documentclass{article}\pagestyle{empty}\begin{document}$ W = \sum\nolimits_{i = 1}^3 {w\left( {\lambda _i } \right)} $\end{document} is adopted, then time and strain are factorizable over the indicated temperature range, with time and temperature being related in the usual fashion. That is, changing the temperature does not affect the form of w(λi) but only that of G(t/αT), the temperature‐dependent relaxation modulus, aT being the regular Williams–Landel–Ferry (WLF) shift factor. The results verify the Valanis–Landel theory for various combinations of biaxiality

Investigation of the working region of kapron fibers

Kapron fibers with various stretch ratios have been subjected to tensile stress relaxation tests at constant clamped length. The relaxation constants — activation energy U0 and the coefficient γ — are calculated from the results of the experiments. It is shown that the fiber parameters U0 and γ depend on the given molecular orientation.

サーボ割算器を用いた定応力クリープ試験機

The tensile load was automatically controlled so as to satisfy the loading condition for constant stress creep tests, W=W0l0⁄l, where W is the tensile force, l is the gauge length of specimen and suffix 0 stands for initial values. The elongation of specimen was measured by means of differential transformers. The output signal (equivalent to l) was fed into a servo-divider and a signal (equivalent to W) being proportional to reciprocal l was calculated. There were two holes at the bottom of a water vessel to increase or decrease the volume of water whose weight was applied to the specimen. Automatic control of the dead load was performed by free drainage and the supply of water controlled by a pneumatic valve in accordance with the calculated value of W. The tensile force acting on the specimen being directly measured by means of a load cell connected in series with the specimen and an automatic balancing indicator, could be controlled accurately against various disturbances. Maximum tensile force being 100 kg, a deviation of the force from the calculated value during constant stress creep tests could be kept within 1%. This creep tester can be applied for vacuum creep tests (>3×10−6 Torr) and also for tensile tests and stress relaxation tests at elevated temperatures (<900°C). A new precise temperature controller has been developed for stress relaxation tests.

Effect of Stretching on the Properties of Rubber

Abstract The results of tensile stress-strain, stress relaxation, swelling, electric conductivity, and power factor tests show that the properties of pure vulcanizates are only slightly affected by previous stretching or flexing; on the other hand, the properties of vulcanizates containing reinforcing agents, or fillers which stiffen the rubber, may be considerably changed by previous stretching. The increases of stiffness, electric conductivity, and power factor produced by the incorporation of the fillers are destroyed by flexing or stretching. From most practical points of view these changes are of a permanent nature, as at normal temperatures the recovery towards the initial properties is slow. These effects are attributed to the breakdown of both agglomerates and chains of filler particles, and the adsorption of the filler particles on the rubber.