Tensile menisci

This shrinkage mechanism occurs only in pores within a fixed range of sizes. In pores larger than 50 nm the tensile force in the water is too small to cause appreciable shrinkage and in pores smaller than 2.5 nm a meniscus cannot form [122]. The amount of cement-paste shrinkage caused by surface tension depends primarily on the water-cement ratio, but it is also affected by cement type and fineness and by other ingredients (such as admixtures, and supplementary cementing materials) which affect pore size distribution... 

IUPAC defines the lower limit of mesopores as 2 nm [1] which was considered as the limit below which the adsorption will occur by volume filling. However, in our recent article, based on the tensile stress hypothesis, we have shown that this limit is different than IUPAC limit. Using the mechanical stability criterion for the cylindrical meniscus (during adsorption), the critical size is obtained from... 

The essence of the above model is the assumption that pore segments of radius r in which the liquid is above the hysteresis temperature rH(/ i) cannot cause delayed desorption. This assumption is immediately plausible if 7h were to coincide with the pore critical temperature, as in this case the pore fluid is in a supercritical state above Tn, and thus the mass transport is not retarded by a gas/liquid meniscus. Some aspects of our model are remeniscent of the tensile strength hypothesis, although the concept of a pore critical temperature was not discussed at the time when that hypothesis was proposed. On the other hand, the present picture does not imply that the locus of lower closure points (p// o)L should be independent of the nature of the porous matrix. We conjecture that (/>/ o)l is given by the locus of pore hysteresis points of the fluid in open-pore systems of uniform pore size. A more comprehensive discussion of this model will be presented elsewhere."... 

As a result, the interface experiences a tensile force and behaves as membrane seeking to reduce its size. It is necessary to point out that representation of the interface as a smooth surface of the meniscus type where the concentration of molecules suffers a discontinuity is an idealization. Actually, this surface has... 

The macroscopic tensile strength of the entire meniscus was studied by Mathur et al [4] by gripping the horns of the meniscus, and stretching it to failure. The results suggested that the medial meniscus was significantly... 

Fithian, D.C., Zhu, W.B., Ratcliffe, A., Kelly, M.A. and Mow, V.C. (1989b) Exponential law representation of tensile properties of human meniscus. Proceedings of the Institute of Mechanical Engineers. The Changing Role of Orthopaedics, Mechanical Engineering Publications Limited, London, pp. 85-90... 

Anterior tibial spine fractures are more common in children than adults. They are caused by forced hyperextension of the knee with some rotation of the tibia on the femur. This results in a tensile force through the ACL, which has a broad attachment to the anterior tibial spine and the anterior horn of the medial meniscus. 

There is, however, a theory for the growth of crazes that is consistent with all the experimental evidence. Argon, Hannoosh and Salama [52] have proposed that the craze front advances by a meniscus instability mechanism in which craze tufts are produced by the repeated break-up of the concave air/polymer interface at the crack tip, as illustrated in Figure 12.15. A theoretical treatment of this model predicted that the steady-state craze velocity would relate to the five-sixths power of the maximum principal tensile stress, and support for this result was obtained from experimental results on polystyrene and PMMA [52]. 

As shown in Table 4.2, the asymmetric temperature distributions in the thickness direction in a flat disc and a meniscus lead to very different stresses after cooling under otherwise equal boundary conditions. In particular, the compressive stress in the y direction on the bottom is very strongly reduced in the meniscus in comparison with the flat disc. This means that the possibility to compensate for tensile stresses at the surface, which are caused by the crystal layer (see the following paragraph) or the support system, by annealing bulk stresses is significantly less with a meniscus-shaped disc than with a flat disc (called the meniscus effect in the following). 

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