Rapid loading

The concept of a ductile-to-brittle transition temperature in plastics is well known in metals where notched metal parts cause brittle failure when compared to unnotched specimens. There are differences such as the short time moduli of many plastics compared with those in metals that may be 200 MPa (29 x 10 psi). Although the ductile metals often undergo local necking during a tensile test, followed by failure in the neck, many ductile plastics exhibit the phenomenon called a propagating neck. 

There are different methods used to determine the impact resistance of plastics. They include pendulum methods (Izod, Charpy, tensile impact, falling dart, Gardner, Dynatup, etc.) and instrumented techniques. In the case of the Izod test, what is measured is the energy required to break a test specimen transversely struck (the test can be done either 

An impact test on products requires setting up an approach on how it should be conducted. The real test is after the product has been in service and field reports are returned for evaluation. Regardless, the usual impact tests conducted on test samples can be useful if they are properly related with product requirements. 

Test and service data with PVC both rate low in notched Izod impact tests and performs well in normal service applications that involve impact loading. Another example is with some grades of rubber-modified high impact PSs that show up well in the Izod test fail on impact under field test conditions. These results have led to continual reexamination of the tests used to determine the toughness of plastics. 

TPs impact properties can be improved if the material selected does not have sufficient impact strength. One method is by altering the composition of the material so that it is no longer a glassy plastic at the operating temperature of the product. In the case of PVC this is done by the addition of an impact modifier which can be a compatible plastic such as an acrylic or a nitrile rubber. The addition of such a material lowers the Tg (glass transition temperature) and the material becomes a rubbery viscoelastic plastic with improved impact properties (Chapter I). 

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Rapid loading - shear stresses set up in impaet may be aeeompanied by high normal stresses whieh exeeed the eleavage strength of the material... 

Unlike gases and liquids, the temperatures induced by the rapid loading of solids can be relatively modest. Only at pressures greater than many tens of gigapascal (GPa) are the temperatures of major importance in solid density samples. In porous solid compacts, significantly higher temperatures may be encountered, but, even in this case at lower pressures, mechanical rather than thermal effects may often be dominant. 

Solvent usage is drastically reduced due to several factors. The feed can be flowed through the ChiraLig columns nearly continuously and high feed concentrations can be used as needed. Rapid loading occurs due to reasonable binding kinetics. The subsequent release (elution) step is accomplished in just a few bed volumes, with... 

Fig. 2-47 Relation of rapid loading strain rates to those developed in other methods of testing.

Fig. 2-49 Examples of rapid loading or high speed tests.

Stress- and thermal-related cracks develop caused by rapid load swings. 

Very variable and rapid load swings, often taking place when the boiler is on manual... 

Rapid loading of cross-linked PS Wang resin (4-(benzyloxy)benzyl alcohol PS) with a selection of /3-ketoesters was shown to reach completion within 1-10 min if microwave irradiation at 170 °C was employed. The conventional thermal method for acetoacetylation of hydroxymethyl-functionalized polystyrene resins takes several hours therefore, microwave heating allowed for... 

The term shatter fracture applies to a situation where the applied energy is well in excess of that necessary for fracture. Many regions of the particle are overloaded under these conditions, yielding a comparatively large number of particles with a wide distribution of sizes. This type of fracture occurs under conditions of rapid loading such as those obtained in a high-velocity impact. 

A systematic investigation of an electrolyzer response to rapid load variation was performed by operating the electrolyzer according to 1 s power data from a wind turbine, then according to 10,60, and 150 s averages as well as under the mean constant power for a time period of 24 h each [52]. The pressure and temperature values were not affected by... 

Rapid loading dose for the management and treatment of CHF control ofventricular rate In patients with atrial fibrillation-, treatment and prevention of recurrent paroxysmal atrial tachycardia PO Initially, 0.5-0.75 mg, additional doses of 0.125-0.375 mg at 6-to8-hr intervals. Range 0.75-1.25 mg. IV 0.6-1 mg. 

Cartridge, Clip. A sheet-metal item intended to hold together a number of cartridges at their bases in order to facilitate rapid loading into the magazine of a rifle or pistol Refs l)Funk Wagnails, "New Standard Dictionary", NY (1958), 410 2)Glossary of Ord (1959), 72... 

A rapid and simple assay for the analysis of OTC, TC, CTC, and DXC in milk was established using an on-line sample cleanup. Coexisting substances in milk were removed by the precolumn head-cut-loading method, and TCs were rapidly loaded on an analytical column after changing the eluent (ion-pair mobile phase containing octanesulphonic acid). This method could be carried out after deproteinization with TFA only. The authors reported recoveries ranging from 80% to 104% (49). 

Initial and Final Creep Mismatch Ratio At low temperatures, or during rapid loading, the stress in the fibers and matrix can be estimated from a simple rule-of-mixtures approach this gives the elastic stress distribution between the fibers and matrix. During creep, the stress distribution is time dependent and is influenced by both the initial elastic stress distribution and the creep behavior of the constituents. Immediately after applying an instantaneous creep load (i.e., at t = 0+), the CMR, =0+ can be found by substituting ef0 = Af (E/ Ec)a-C nf and emfi = Am (Em/Ec)[Pg.176]

Fig. 5.9 Influence of initial loading rate on fiber and matrix stress and microstructural damage mode in materials where CMR< 1. Under rapid loading, the matrix stress may achieve a level sufficient to initiate matrix fracture.

Figure 5. Hyperbolic load-duration curve with rapid loading and longtime loading trends for bending (12,13).

Conventional laboratory tests used to guarantee that the grouted soil meets specification requirements typically lead to failure of a specimen in only 5-10 min. The strength of grouted soil determined under such a rapid load rate can be two or more times that which the grouted soil can develop if it is loaded over a one-or two-day period. 

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