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41.
Experimental identification and mathematical modeling of viscoplastic material behavior 总被引:1,自引:0,他引:1
Uniaxial torsion and biaxial torsion-tension experiments on thin-walled tubes were carried out to investigate the viscoplastic behavior of stainless steel XCrNi18.9. A series of monotonic tests under strain and stress control shows nonlinear rate dependence and suggests the existence of equilibrium states, which are asymptotically approached during relaxation and creep processes. Strain controlled cyclic experiments display various hardening and softening phenomena that depend on strain amplitude and mean strain. All experiments indicate that the equilibrium states within the material depend on the history of the input process, whereas the history-dependence of the relaxation and creep behavior appears less significant. From the experiments the design of a constitutive model of viscoplasticity is motivated: The basic assumption is a decomposition of the total stress into an equilibrium stress and a non-equilibrium overstress: At constant strain, the overstress relaxes to zero, where the relaxation time depends on the overstress in order to account for the nonlinear rate-dependence. The equilibrium stress is assumed to be a rate independent functional of the total strain history. Classical plasticity is utilized with a kinematic hardening rule of the Armstrong-Frederick type. In order to incorporate the amplitude-dependent hardening and softening behavior, a generalized arc length representation is applied [14]. The introduction of an additional kinematic hardening variable facilitates consideration of additional hardening effects resulting from the non-radiality of the input process. Apart from the common yield and loading criterion of classical plasticity, the proposed constitutive model does not contain any further distinction of different cases.The experimental data are sufficient to identify the material parameters of the constitutive model. The results of the identification procedure demonstrate the ability of the model to represent the observed phenomena with satisfactory approximation. 相似文献
42.
Julien Rouleau Alexandre Korovitch Claude Lion Miryana Hémadi Nguyêt-Thanh Ha-Duong Jean-Michel El Hage Chahine Thierry Le Gall 《Tetrahedron》2013
Potential metal chelators containing one or several acyltetronic acid moieties were prepared from cyclic or acyclic amines and polyamines, and from bis(phenols) by reaction with 1–4 equiv of 3-bromoacetyltetronic acid in the presence of potassium carbonate. The affinity constants of the chelating agents for toxic metallic cations Cd2+, Cs+, and Pb2+ and for dimethylarsinic acid were measured, at pH 7.5 and 9.3. Compound 4, an acyclic triamine containing four acyltetronic moieties, was found to complex efficiently all the tested species. 相似文献
43.
G. Rima J. Satge H. Sentenac-Roumanou M. Fatome J. D. Laval C. Lion O. Alazard P. Chabertier 《应用有机金属化学》1994,8(5):481-490
New germa- and silathiazolidines or germa- and siladithioacetals with N-allyl-substituted cysteamine and methylcysteamine ligands have been synthesized and their pharmacological properties (toxicity, radioprotective activity) have been studied. A notable decrease in the toxicity and a rather large increase in the radioprotective activity of these new organometallic derivatives compared to N-allyl-substituted cysteamine and methylcysteamine were observed. 相似文献
44.
Bourdreux Y Nowaczyk S Billaud C Mallinger A Willis C Murr MD Toupet L Lion C Gall TL Mioskowski C 《The Journal of organic chemistry》2008,73(1):22-26
A short, convergent synthesis of the mushroom pigment norbadione A is described. The construction of an appropriately substituted naphtholactone intermediate involved a regioselective Diels-Alder reaction between a bis(triisopropylsilyloxy)diene and 2,6-dichlorobenzo-1,4-quinone. A double Suzuki-Miyaura cross-coupling between a diboronate and two identical enol triflates was another key feature of the synthesis. 相似文献
45.
In order to represent the chemical ageing behaviour of rubber under finite deformations a three-dimensional theory is proposed. The fundamentals of this approach are different decompositions of the deformation gradient in combination with an additive split of the Helmholtz free energy into three parts. Its first part belongs to the volumetric material behaviour. The second part is a temperature-dependent hyperelasticity model which depends on an additional internal variable to consider the long-term degradation of the primary rubber network. The third contribution is a functional of the deformation history and a further internal variable; it describes the creation of a new network which remains free of stress when the deformation is constant in time. The constitutive relations for the stress tensor and the internal variables are deduced using the Clausius–Duhem inequality. In order to sketch the main properties of the model, expressions in closed form are derived with respect to continuous and intermittent relaxation tests as well as for the compression set test. Under the assumption of near incompressible material behaviour, the theory can also represent ageing-induced changes in volume and their effect on the stress relaxation. The simulations are in accordance with experimental data from literature. 相似文献
46.
To simulate the frequency-dependent behaviour of nonlinear viscoelastic structures under loadings which consist of a finite predeformation in combination with a superimposed harmonic deformation with small amplitude, frequency-domain formulations of the constitutive models are needed. For this purpose, a recently developed approach of finite viscoelasticity is considered and the corresponding dynamic modulus tensors are derived. The constitutive equations are geometrically linearized in the neighbourhood of the predeformation and evaluated in the frequency-domain. This procedure is applicable to arbitrary constitutive models and can be used to derive their frequency-domain formulations for finite element implementations as proposed by Morman and Nagtegaal [Morman, K.N., Nagtegaal, J.C., 1983. Finite element analysis of sinusoidal small-amplitude vibrations in deformed viscoelastic solids. International Journal for Numerical Methods in Engineering, 19, 1079–1103]. 相似文献
47.
By coupling photorefractive holography with speckle shearography, it is possible to simultaneously perform both coherent imaging and strain measurement. Use of the photorefractive effect, which is insensitive to incoherently scattered light, is a significant advantage in coherent imaging as described. Experimental results obtained from a centrally loaded steel plate are presented. 相似文献
48.
49.
Claude Lion Jacques-Emile Dubois J.Anthony Macphee Yayé Bonzougou 《Tetrahedron》1979,35(17):2077-2079
The reaction of n-propyllithium with a number of hindered aliphatic carboxylic esters in ether at 0° produces cleanly the corresponding carboxylic acid in satisfactory yields. This reaction represents a facile dealkylation of hindered carboxylic esters. The mechanistic aspects are briefly examined. 相似文献
50.
Abstract— The UV photolysis of tryptophan (Trp) and Trp-containing peptides in aerated aqueous solutions has been studied by ESR and spin-trapping techniques using f-nitrosobutane as the spin-trap. The photolysis of Trp alone at 290 nm gave rise to the addition of the spin-trap to carbon 3 of the indole ring. A large ESR signal from the hydronitroxide spin-adduct was also observed revealing the formation of hydrated electrons. Generally, the photolysis of Trp-containing dipeptides generated the deamination radical of the N-terminal amino acid followed by addition to the spin-trap. In the case of lysyl-Trp, a deamination radical from the side chain of lysine was proposed. A sensitization experiment with Trp as sensitizer and glycine (Gly) as substrate led to the generation of the deamination radical of Gly. Most of the observed free radicals resulting from the photolysis of Trp-containing peptides can be explained in terms of hydrated electrons reacting with the carbonyl group followed by deamination of the N-terminus. 相似文献