Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
The critical stress intensity factors for propagating cracks, K/sub ID/, was experimentally found to decrease with increasing crack velocity. K/sub ID/ was measured using rapidly wedged double cantilevered beam specimens. The crack length versus time was continuously recorded using electro-potential techniques. The specimens were fractured at temperatures well below the brittle to ductile transition temperature. The crack velocity in these specimens varies continuously but is typically in the range of 100 to 200 m/s. The analysis of fully dynamic crack propagation in double torsional beam specimens was solved in closed analytic form. The solutions for rotational rate loading and for constant applied torque, predict constant crack velocity. The crack velocity is given by the applied rate of rotation, the magnitude of the applied torque and specifics about the beam. The maximum crack velocity is the torsional wave speed. The use of the analysis is to deduce K/sub ID/ during crack propagation without measuring the crack velocity directly. The measurements of static, dynamic loading and propagating crack, stress intensity factors establishes that rate is an important variable in specifying the stress intensity factor for fracture. (auth).
Author: United States. Energy Research and Development Administration. Technical Information Center Publisher: ISBN: Category : Force and energy Languages : en Pages : 724
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
The slow, isothermal, propagation of cracks was analyzed by introducing the fracture mechanics concepts into molecular rate theory. Relations between thermodynamic variables and measurable quantities such as crack velocities, specimen temperature and crack extension force were derived. The shape and distribution of the rate controlling obstacles were left unspecified in the theory. The theory was applied to published crack propagation data in PMMA and agreement between theory and data is found. A literature survey of crack velocity data in a wide selection of materials including inorganic glasses, ceramics, polymers and metals shows the correlation that the crack extension force is inversely proportional to the crack activation area. In rapid crack propagation, a new technique, measuring the complimentary boundary condition to the applied boundary condition was used to deduce the stress intensity factor and the crack velocity during crack propagation in DCB specimens. The technique is easier to use and gives better results than the electro-potential methods of measuring crack length during rapid fracture. The shear force in a rapidly wedged DCB specimen is multiplied by the square root of the time after the wedge strikes the specimen, this product is nearly constant during fracture, from its slight time dependence we deduce how K/sub ID/ and the crack velocity vary as a function of time. Time is eliminated and K/sub ID/ is plotted versus crack velocity.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Energy balance methods have been used to find the crack driving force in elastic fractures. The fracture toughness of cracked steel bars have been measured using these techniques. Crack tip dislocations have been shown to protect the crack tip by having a stress intensity value that is opposite in sign from the applied stress intensity value. Thus, crack tip dislocation plasticity shields the crack from the external stress intensity factor. In the fatigue of LiF single crystals a relationship between monotonic and fatigue hardening responses has been established using a statistical model for fatigue deformation.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
A thermodynamic formulation for a crack driving force has been experimentally used in linear elastic fracture mechanics, elastic plastic fracture mechanics and creep fracture. In linear elastic and elastic plastic fracture mechanics, mechanical stability criteria are established from the load versus the load point displacement in two test specimens that differ only in crack area. These tests have also been used to measure the fracture toughness in several heat treated steels. Creep cracking of PMMA has shown that there is a sharp transition to unstable fracture in a plot of the log of the steady state crack velocity versus the crack driving force at several selected temperatures. In addition, it has been shown that the athermal crack driving force is independent of rate and temperature. A new method for electronically recording the crack driving force versus the crack area has been used on double cantilevered beam specimens. Temperature and crack rate dependences have been measured near the ductile to brittle transition temperature in a low carbon steel.
![Materials and Mechanics of Rate Effects in Brittle Fracture. Progress Report, October 1974--October 1975. [Stress Intensity Factors for Crack Propagation]. PDF](https://books.google.com/books/content/images/frontcover/HIvDwQEACAAJ?fife=w80-h100)
Author: 
Author: United States. Energy Research and Development Administration
Author: United States. Energy Research and Development Administration
Author: United States. Energy Research and Development Administration. Technical Information Center![Materials and Mechanics of Rate Effects in Brittle Fracture. Progress Report, October 1975--October 1976. [PMMA]. PDF](https://books.google.com/books/content/images/frontcover/NBTcwQEACAAJ?fife=w80-h100)
Author: 
Author: 
Author: 
Author: 
Author: J. R. Rice
Author: