Plasticity or ductility

In the following the major test methods for determination of the extrusion behaviour of ceramic bodies are introduced. The most important property for extrusion as a rheological parameter is the plasticity or ductility. Definitions of the term plasticity, or ductility, have been published amongst others by Haase, Moore and Astbury [7-9]. 

The mechanical properties of a new adhesive can be characterized in the lap shear test with small beech specimens connected with the new adhesive. The adhesive manufacturer needed some guidelines as to the results he should aim at. The authors presented him the calculated ideal curves of the shear stress r against the deformation v for both the elastic and the plastic adhesive layers (Fig. 7). The elastic adhesive layer should exhibit a linear relationship for r and v with a given slope. The plastic (or ductile) adhesive should exhibit an initial linear relationship between T and V, but it should yield when the shear stress reaches a value between 0.5 and 1.0 N/mm. ... 

At plastic or ductile deformation mechanism the value can be determined as follows [15] ... 

Wustite is plastic or ductile at temperatures above 700°C when deformed slowly, but its plasticity is partially lost if the strain rates and/or the strain amounts are too high. 

In addition to plastic deformation, materials may fail by either brittle fracture or ductile fracture fracture being the separation of a body into two or more parts. 

Most of the technical raw materials used in solid reactions are polycrystalhne, and these - when in solid form - undergo a range of modifications during milling. The first observation is the fracture of the solid into smaller pieces. The fracture mechanics are a topic of discussion, and fracture can be divided into two steps, namely crack formation and crack propagation . Depending on the ability of the material to undergo plastic deformation before fracture, either brittle or ductile fracture can be defined ... 

Landes and has since received wide attention. As yet, there are no published papers describing the direct measurement of. rubber-tou ened plastics or other particulate composites. Williams and co-workers have attempted to estimate Jjc for HIPS and ABS indirectly, from the work done at the crack tip in SEN specimens sulqected to tenaon or bending As the fracture surfaces were extensively whitened, these estimates were probably hi the 7/ criterion should strictly be applied to the point of crack initiation rather tiian to later stages of ductile tearing. 

For brittle materials, shear force is restricted to hammer mills, acting along with impact and attrition, as well as to toothed crushing rolls. The prerequisite for successful size reduction of particles is the existence of macro- or microstructure weaknesses (e.g., layered structure, schistosity) or differences in the characteristics of adjacent minerals (e.g., hardness, friability). Contrary to rocks and minerals, shear force is widely applied in soUd waste size reduction, as most of its constituents are soft, nonbrittle, plastic, and ductile, and, consequently, shear forces are effective. The various forms of shredders use shear force to reduce the size of solid waste constituents. 

Some properties of materials can vary according to the rate at which stress is applied some materials are plastic and ductile if the stress is applied slowly but can be elastic or brittle if the stress is applied by impact. The deformation mechanisms occurring during compaction of fines and agglomerated foods depend on the elastic and viscous flow, in addition to ductile yielding and brittle behavior common in pharmaceutical and food compaction processes (Barletta et al., 1993b). 

The term plastic also refers to a material that has the physical characteristics of plasticity and toughness. See ductility plasticity toughness, plastic, advanced A high-performance material. Also called advanced reinforced plastic or advanced plastic composite. See engineering plastic reinforced plastic, advanced. 

ASTM D256 Standard Test Methods for Determining the Izod Pendulum Impact Resistance of Plastics. Used to determine the resistance of a plastic specimen to impact by a pendulum-type hammer. Specimens contain a milled notch and depending upon the test method, failure may be brittle or ductile. Test results are reported in terms of energy absorbed per unit of specimen width or per unit of cross-sectional area under the notch. 

---