Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Deformation inelastic

Argon A S 1993 Inelastic deformation and fracture of glassy solids Materials Science and Technology vol 6 (Weinheim VCH) pp 462- 508... [Pg.2540]

The theory is initially presented in the context of small deformations in Section 5.2. A set of internal state variables are introduced as primitive quantities, collectively represented by the symbol k. Qualitative concepts of inelastic deformation are rendered into precise mathematical statements regarding an elastic range bounded by an elastic limit surface, a stress-strain relation, and an evolution equation for the internal state variables. While these qualitative ideas lead in a natural way to the formulation of an elastic limit surface in strain space, an elastic limit surface in stress space arises as a consequence. An assumption that the external work done in small closed cycles of deformation should be nonnegative leads to the existence of an elastic potential and a normality condition. [Pg.118]

It should be noted that the normality conditions, arising from the work assumption applied to inelastic loading, ensure the existence and uniqueness of solutions to initial/boundary value problems for inelastic materials undergoing small deformations. Uniqueness of solutions is not always desirable, however. Inelastic deformations often lead to instabilities such as localized deformations. It is quite possible that the work assumption, which is essentially a stability postulate, is too strong in these cases. Normality is a necessary condition for the work assumption. Instabilities, while they may occur in real deformations, are therefore likely to be associated with loss of normality and violation of the work assumption. [Pg.139]

Carroll, M.M., A Rate-Independent Constitutive Theory for Finite Inelastic Deformations, J. Appl. Mech. 54, 15-21 (1987). [Pg.170]

Rather than bearing an infinite stress at the crack tip, yielding occurs resulting in a volume of inelastically deformed material along the crack front called the process zone, as shown in Fig. 2. The size of the inelastic zone, r j , under a monotonic tensile stress, o , can be approximated by substituting o = Oj into eq. 2 for the horizontal plane, 0 = 0... [Pg.492]

In metals, inelastic deformation occurs at the crack tip, yielding a plastic zone. Smith [34] has argued that the elastic stress intensity factor is adequate to describe the crack tip field condition if the inelastic zone is limited in size compared with the near crack tip field, which is then assumed to dominate the crack tip inelastic response. He suggested that the inelastic zone be 1/5 of the size of the near crack tip elastic field (a/10). This restriction is in accordance with the generally accepted limitation on the maximum size of the plastic zone allowed in a valid fracture toughness test [35,36]. For the case of crack propagation, the minimum crack size for which continuum considerations hold should be at least 50 x (r ,J. [Pg.495]

The piezoelectric response investigation also provides direct evidence that significant inelastic deformation and defect generation can occur well within the elastic range as determined by the Hugoniot elastic limit. In quartz, the Hugoniot elastic limit is 6 GPa, but there is clear evidence for strong nonideal mechanical and electrical effects between 2.5 and 6 GPa. The unusual dielectric breakdown phenomenon that occurs at 800 MPa under certain... [Pg.95]

In this chapter studies of physical effects within the elastic deformation range were extended into stress regions where there are substantial contributions to physical processes from both elastic and inelastic deformation. Those studies include the piezoelectric responses of the piezoelectric crystals, quartz and lithium niobate, similar work on the piezoelectric polymer PVDF, ferroelectric solids, and ferromagnetic alloys which exhibit second- and first-order phase transformations. The resistance of metals has been investigated along with the distinctive shock phenomenon, shock-induced polarization. [Pg.136]

Dow and Rosen s results are plotted in another form, composite material strain at buckling versus fiber-volume fraction, in Figure 3-62. These results are Equation (3.137) for two values of the ratio of fiber Young s moduius to matrix shear modulus (Ef/Gm) at a matrix Poisson s ratio of. 25. As in the previous form of Dow and Rosen s results, the shear mode governs the composite material behavior for a wide range of fiber-volume fractions. Moreover, note that a factor of 2 change in the ratio Ef/G causes a factor of 2 change in the maximum composite material compressive strain. Thus, the importance of the matrix shear modulus reduction due to inelastic deformation is quite evident. [Pg.182]

The most common conditions of possible failure are elastic deflection, inelastic deformation, and fracture. During elastic deflection a product fails because the loads applied produce too large a deflection. In deformation, if it is too great it may cause other parts of an assembly to become misaligned or overstressed. Dynamic deflection can produce unacceptable vibration and noise. When a stable structure is required, the amount of deflection can set the limit for buckling loads or fractures. [Pg.203]

Inelastic deformation can cause product failure arising out of a massive realignment of the plastic s molecular structure. A product undergoing inelastic deformation does not return to its original state when its load is removed. It should be remembered that there are plastics that are sensitive to this situation and others that are not. [Pg.203]

The magnitude of the pull-off force depends on the natnre of the tip-sample interaction during contact. Adhesion depends on the deformation of the tip and the sample, because attractive forces are proportional to the contact area. Quantifying the work of adhesion is difficult. The measured magnitude of A7 is strongly dependent on environment, surface roughness, the rate of pull-off, and inelastic deformation surrounding the contact. [Pg.30]

Inelastic deformation of any solid material is heterogeneous. That is, it always involves the propagation of localized (inhomogeneous) shear. The elements of this localized shear do not occur at random places but are correlated in a solid. This means that the shears are associated with lines rather than points. The lines may delineate linear shear (dislocation lines), or they may delineate rotational shear (disclination lines). The existence of correlation means that when shear occurs between a pair of atoms, the probability is high that an additional shear event will occur adjacent to the initial pair because stress concentrations will lie adjacent to it. This is not the case in a liquid where the two shear events are likely to be uncorrelated. [Pg.166]

During the transient load phase of an accidental explosion, when the shock duration is less than the time of maximum response of the structural elements, member end rotations are limited to one degree. Maximum inelastic deformation is limited to three times the member elastic limit deflection. Since this loading phase is suddenly applied, use of material dynamic increase factors based on strain rate of loading are also used. [Pg.250]

Fig. 8.4 Plots of relative change in electrical resistance against tensile deformation of a CNT/epoxy composite (a) shows the various characteristics of the piezoresistivity of nanocarbon networks linear resistance change in the elastic regime, nonlinear region after inelastic deformation and the permanent electrical resistance drop due to plastic deformation (image adapted from [30]) ... Fig. 8.4 Plots of relative change in electrical resistance against tensile deformation of a CNT/epoxy composite (a) shows the various characteristics of the piezoresistivity of nanocarbon networks linear resistance change in the elastic regime, nonlinear region after inelastic deformation and the permanent electrical resistance drop due to plastic deformation (image adapted from [30]) ...
A modeling study can avoid inelastic deformations by only searching conformation space close to the minima as in the pseudo-radial search method described in the preceding paper by Tran and Brady. That type of search mimics the thermal motion of a molecule. [Pg.196]

A rather different view of impact initiation to that of Bowden et al, is presented by the Russian school. The originator of this school appears to be Kholevo (Ref 6), supported by Andreev (Ref 7), with a recent and detailed presentation of this point of view provided by Afanas ev Bobolev (Ref 17) (from now on we will refer to these writers as A B without listing the Ref)- Briefly stated, A B consider that the prime mechanism of hot spot generation in solid explosives is by inelastic deformation of the entire impacted explosive sample (Kholevo (Ref 6) calls this flow )... [Pg.308]

The stress varies over the sample (compact) surface such that the peak stress is (2 to 2.5)P at the center and Ou/3 at the periphery (where P is the average stress on the sample). Since PCr Ou for most explosives, and the criticality condition is P>PCr, effective hot spots cannot form near the sample periphery. Effective hot spots are also not generated at the center of the sample because inelastic deformation of the sample is a minimum near its center. As will be shown, A B claim that non-uniform inelastic deformation of the entire sample generates hot spots... [Pg.309]

Furthermore, the fracture characteristics will be defined in the frame of linear elastic fracture mechanics (LEFM), assuming a purely elastic response of the material (stress proportional to infinitesimal strains). However, LEFM can be extended to materials that exhibit inelastic deformation around the crack tip, provided that such deformations are confined to the immediate vicinity of the tip [25]. [Pg.237]

In the above discussed theories, purely elastic deformation was assumed. In practice, the SFM tip can cause inelastic deformation or even move portions of the material away from the contact area. [Pg.100]

When the experimentalist set an ambitious objective to evaluate micromechanical properties quantitatively, he will predictably encounter a few fundamental problems. At first, the continuum description which is usually used in contact mechanics might be not applicable for contact areas as small as 1 -10 nm [116,117]. Secondly, since most of the polymers demonstrate a combination of elastic and viscous behaviour, an appropriate model is required to derive the contact area and the stress field upon indentation a viscoelastic and adhesive sample [116,120]. In this case, the duration of the contact and the scanning rate are not unimportant parameters. Moreover, bending of the cantilever results in a complicated motion of the tip including compression, shear and friction effects [131,132]. Third, plastic or inelastic deformation has to be taken into account in data interpretation. Concerning experimental conditions, the most important is to perform a set of calibrations procedures which includes the (x,y,z) calibration of the piezoelectric transducers, the determination of the spring constants of the cantilever, and the evaluation of the tip shape. The experimentalist has to eliminate surface contamination s and be certain about the chemical composition of the tip and the sample. [Pg.128]


See other pages where Deformation inelastic is mentioned: [Pg.157]    [Pg.492]    [Pg.494]    [Pg.502]    [Pg.502]    [Pg.82]    [Pg.90]    [Pg.33]    [Pg.62]    [Pg.65]    [Pg.52]    [Pg.56]    [Pg.178]    [Pg.513]    [Pg.515]    [Pg.523]    [Pg.523]    [Pg.102]    [Pg.193]    [Pg.193]    [Pg.196]    [Pg.197]    [Pg.199]    [Pg.500]    [Pg.128]   
See also in sourсe #XX -- [ Pg.193 ]

See also in sourсe #XX -- [ Pg.183 ]

See also in sourсe #XX -- [ Pg.341 ]




SEARCH



Inelastic

Inelastic deformation processes

Inelasticity

© 2024 chempedia.info