Properties deformation

The most serious obstacle in the design of plastic articles is the influence of stress concentrations, which should therefore he reduced to a minimum. 

In the category of deformation properties the phenomena of stress-strain behaviour, modulus and yield, stress relaxation and creep have been discussed already in Chap. 13. Here we want to give special attention to the long-term deformation properties. For a good design we need sufficiently reliable creep data (or stress-strain curves as a function of time and temperature). 

The usual design procedure is to couple a specific value of design stress with a conventional stress or strain analysis of the assumed structural idealisation. The uniaxial deformation behaviour is of special importance in thin-walled pipes, circular tanks and comparable systems under simple stress. 

We confine ourselves here to cylindrical tanks as an example. For free-standing liquid storage tanks the following formula applies to the design stress crD  

If one knows cr as a function of s, t and T, or the Young s modulus as a function of t and T, then the geometrical data can be calculated, e.g. the wall thickness at a given tank capacity. 

---

A. Ya. Gol dinaii, Prediction of the Deformation Properties of Polymeric and Composit Materials American Chemical Society, Washington (1994). 

Of the various parameters introduced in the Eyring theory, only r—or j3, which is directly proportional to it-will be further considered. We shall see that the concept of relaxation time plays a central role in discussing all the deformation properties of bulk polymers and thus warrants further examination, even though we have introduced this quantity through a specific model. 

Most authors who have studied the consohdation process of soflds in compression use the basic model of a porous medium having point contacts which yield a general equation of the mass-and-momentum balances. This must be supplemented by a model describing filtration and deformation properties. Probably the best model to date (ca 1996) uses two parameters to define characteristic behavior of suspensions (9). This model can be potentially appHed to sedimentation, thickening, cake filtration, and expression. 

N. McLachlan. The Modelling of Polycrystalline Graphite Fracture and Deformation Properties, Ph.D. Thesis, University of Exeter, UK, 1992. 

Pashley, M.D. and Tabor, D., Adhesion and deformation properties of clean and characterized metal micro-contacts. Vacuum, 31(10-1), 619-623 (1981). 

Conner has recently extended the longitudinal stress loading investigations of vitreous silica to shear loading, and shown that within the accepted elastic range the materials deformation properties are strongly influenced by shear [88C02]. 

Gulaev, V. M. The Strength and Deformation Properties of Vitreous Silica , Glass Ceramics, 30 No. 6, 279 (1973)... 

To characterize the mechanical properties of a material, one first needs a basic understanding of the concepts of stress, strain, and deformation, as they provide the tools necessary. The deformation properties of a material can be determined by applying a stress, either in compression or tension, and determining dimensional changes in the specimen. The applied stress will result in an elongation of the specimen, e = Al/l0. The elongation is called the strain, while the stress is defined as the applied load divided by the area over which it is applied. 

Plastic deformation, unlike elastic deformation, is not accurately predicted from atomic or molecular properties. Rather, plastic deformation is determined by the presence of crystal defects such as dislocations and grain boundaries. While it is not the purpose of this chapter to discuss this in detail, it is important to realize that dislocations and grain boundaries are influenced by things such as the rate of crystallization, particle size, the presence of impurities, and the type of recrystallization solvent used. Processes that influence these can be expected to influence the plastic deformation properties of materials, and hence the processing properties. 

The mechanical properties of materials, though not often studied in detail, can have a profound effect on solids processing. Clearly, tableting properties are influenced by the elastic and plastic deformation properties as well as the viscoelastic properties of a material. As we have pointed out, the powder flow properties are also affected, as well as the tendency of materials to set up on storage. Because of the importance of mechanical properties, it is important to be able to... 

Model simulating the hydrodynamic properties of a chain macromolecule consisting of a sequence of beads, each of which offers hydrodynamic resistance to the flow of the surrounding medium and is connected to the next bead by a spring which does not contribute to the frictional interaction but which is responsible for the elastic and deformational properties of the chain. The mutual orientation of the springs is random. 

The deformation properties of the drug substance and excipients will have a direct influence on the strength of the tablets that are produced. During the compaction process, as the powder flows from the hopper into the dies, the only force acting on the particles is due to the particles themselves. Then as the punches enter the dies, initially very low pressures are... 

Characterize the drug substance regarding deformation properties, compactibility, sticking tendency, ejection force, etc. 

Their poor viscosities and, consequently, low molecular weight characteristics make the synthesis of products with favourable strength and deformation properties problematic. 

Homologous series of networks, prepared under the same experimental conditions, and differing only by the length of their elastic chains have been made available, and were used to investigate their structure, their swelling behavior, and their mechanical deformation properties. It was assumed that within a homologous series of networks the crosslink functionality remains constant, an assumption which is supported by results on star-polymers11. ... 

In the definition of rheology there are two processes, deformation and flow. Deformation suggests the presence of solid-like behavior and flow suggests the presence of fluid-like behavior. Many foods have both solid and fluid properties. The objective of this section is to provide methods for the evaluation of the rheological properties of foods. In Chapter HI, flow properties of foods are the focus. In Chapter H2, deformation properties are the focus. 

Wium, H., Pedersen, P.S., and Qvist, K.B. 2003. Effect of coagulation conditions on the microstructure and the large deformation properties of fat-free Feta cheese made from ultrafiltered milk. Food Hydrocolloids 17, 287-296. 

Neubauer, C.M. (1997) On the Chemistry, Micro structure, and Deformation Properties of Cement Pastes Towards a New Strategy for Controlling Drying Shrinkage. PhD. Thesis, Northwestern University. 

Some plastic materials have different tensile and compressive characteristics. For example, polystyrene is tough under compressive load but very brittle in tension. However, for most elastoplastic materials, the stress-strain curves in compression are the same as in tension. Hence, the deformation properties of these materials in tension may also be applied to those in compression, which is of great interest to gas-solid flows. 

Fig. 12. Schematic deformation properties of nanophase ceramics. For ceramics, decreasing the grain size into the nanometer regime corresponds to an increase in grain boundary sliding, resulting in increased ductility of these materials. (Adapted and redrawn from Siegel, 1994.)...

There exists a substantial history of interest in flow and deformation properties of monolayers. Perhaps, the first is the theoretical formulation of hydrodynamic coupling between the monolayer and subphase by Harkins and Kirkwook in 1938 [129], in determination of steady shear viscosity of mono-layers, which has since been augmented by Hansen [130] and Goodrich [131]. A variation of the method based on the Maxwell model was proposed by Mannheimher and Schechter [132] in an oscillatory mode in a canal. Experimentally, the method was implemented by joint efforts in our laboratories for determinations of steady shear viscosity of monolayers through the canal... 

A number of polymeric systems exhibit domain formation. This results in some polymeric material being confined in regions between the domains. The deformation properties of these systems depend on the types of polymer chains lying between the domains, as well as on the shape and spatial arrangement of the domains. Several theories have been proposed to date for the contribution of the interdomain material to different deformation properties in semicrystalline polymers and block copolymers. We will present and analyze these theories herein. 

In the 1990s Northolt and Baltussen developed the so-called continuous chain model, which is able to describe the tensile deformation properties of well-oriented polymer fibres properly. We will not go into detail in describing this outstanding model, but for an exact description of this model the reader is referred to the many publications of these two authors and their co-authors in the years from 1995 to 2005, and in particular to the doctoral thesis (1996) by Baltussen, the 2002 paper by Northolt and Baltussen and the 2005 paper by Northolt et al. on the strength of polymer fibres. 

---