Time-dependent strength

Depending on construction and orientation of stress relative to reinforcement, it may not be necessary to provide extensive data on time-dependent stiffness properties since their effects may be small and can frequently be considered by rule of thumb using established practical design approaches. When time dependent strength properties are required, creep and other data are used most effectively. There are many RP products that have had super life spans of many decades. Included are products that have been subjected to different dynamic loads in many different environments from very low temperatures to very high corrosive conditions, etc. An example is aircraft primary structures (10,14,62). 

Keywords Crazing Creep Molecular deformation mechanisms Disentanglement Time-dependent strength Toughness... 

Macrofracture is a kinetic process of accumulation of microevents. It can be characterized by some average waiting time or by time-dependent strength of a sample at the given load. If an elementary fracture step is the break of one chemical bond, the average waiting time X at stresscf is ... 

Sheikh-Salem M, Fell JT. The influence of magnesium stearate on time dependent strength changes in tablets. Drug Dev Ind Pharm 1981 7 669-674. 

R.H. Borden, Time-Dependent Strength and Stress-Strain Behavior of Silicate-Grouted Sand," Ph.D. Dissertation, Department of Civil Engineering, Northwestern University, Evanston, Illinois. 

Sayir, A. 1993. Time dependent strength of sapphire fibers at high temperatures. Pp. 691-702 in Advances in Ceramic Matrix Composites. Vol. 38 in Ceramic Transactions, N. Bansal (ed). Westerville, Ohio American Ceramic Society. 

H. Klemm and G. Pezzotti, Fracture Toughness and Time-Dependent Strength Behavior of Low- Doped Silicon Nitrides for Applications at 1400°C , J. Am. Ceram. Soc., 77,1994, 553-61. 

Aveston, J. and Silwood, J.M., Time dependent strength of uni directional glass reinforced plastics in air, water and dilute sulphuric acid. Proc. SrdRiso Int Symp. on Metallurgy Materials Science, 1982. 

S. Manley, B. Davidovitch, N.R. Davies, L. Cipelletri, A.E. Bailey et al.. Time-dependent strength... 

The result of most fatigue testing is the generation of S-N curves. These curves plot stress S against the number of cycles to failure N. The data are obtained by testing many specimens to failure at different stress levels. As with any type of time-dependent strength property, the life to failure increases as the stress is decreased. Also, an endurance limit is reached, i.e., a maximum stress above which the material will not withstand cyclic stress indefinitely. For experimental convenience and time required, fatigue tests are usually discontinued if failure has not occurred by 10 million cycles. 

It is assumed that chain scission is a thermo-mechanically activated process. A chain segment containing weakest bonds of energy Uq, and carrying at its ends a constant stress xpo will, on the average, break after time Tc- One refers to as the time-dependent strength of a chain segment ... 

Generally the third result is technologically desirable. In order to define the region of permissible loads a study of the delayed failure, i.e. of the time-dependent strength, is indispensable. 

Owing to its fundamental importance the time-dependent strength of load-bearing polymers has been extensively investigated with temperature as the principal para-... 

FIGURE 10.15 Time-dependent strength for polymeric and nonpolymeric materials 1, silver chloride 2, poly(vinyl chloride) 3, aluminum 4, PMMA 5, zinc 6, celluloid 7, rubber 8, nitro-ceUuloid, 9, platinum 10, silver 11, phosphoric bronze 12, nylon 6 (oriented). (Data from Hsaio, C. C Phys. Today, 19, 49, March 1966.)... 

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