Dynamic fracture energy

This approach does not address the higher frequency effects so an improved mass spring model has been proposed by Williams et al [8]. The calculation is somewhat cumbersome and for practical purposes has to be solved using a mathematics package such as MATHCAD. This improved model is used in this paper to calculate both the dynamic fracture toughness Kj and the dynamic fracture energy Gd. 

In the present section, attention will focus on the size of fragments created in a violent fragmentation event. The objective will be to explore some theoretical ideas which appear important to the dynamic fragmentation process. The two underlying phenomena that have dominated theoretical efforts in this area of dynamic fracture mechanics are the presence of an inherent flaw structure, and energy balance in the fracture process. 

Note that this product of the spall stress and time is a constant provided F itself is constant. This relation is also useful for estimating fracture energy from dynamic spall data. Also, from (8.30) and (8.31) a relation for the fragment size... 

Many variables used and phenomena described by fracture mechanics concepts depend on the history of loading (its rate, form and/or duration) and on the (physical and chemical) environment. Especially time-sensitive are the level of stored and dissipated energy, also in the region away from the crack tip (far held), the stress distribution in a cracked visco-elastic body, the development of a sub-critical defect into a stress-concentrating crack and the assessment of the effective size of it, especially in the presence of microyield. The role of time in the execution and analysis of impact and fatigue experiments as well as in dynamic fracture is rather evident. To take care of the specihcities of time-dependent, non-linearly deforming materials and of the evident effects of sample plasticity different criteria for crack instability and/or toughness characterization have been developed and appropriate corrections introduced into Eq. 3, which will be discussed in most contributions of this special Double Volume (Vol. 187 and 188). 

T. Nishioka and S. N. Atluri, Path-Independent Integrals, Energy Release Rates, and General Solutions of Near-Tip Fields in Mixed-Mode Dynamic Fracture Mechanics, Engineering Fracture Mechanics, 18, 1-22 (1983). 

Dynamic properties, fracture toughness, fracture energy, dynamic modulus, dynamic testing, impact tests, drop tower, high strain rate. 

Fig 8. Dynamic fracture toughness (from MSM and DKC) and fracture energy for PMMA... 

Instrumented Charpy impact tests on unnotched samples are conducted to determine the energy absorbing capability and dynamic fracture behaviour of the C/SiC composites. The dynamic fracture toughness (ak) is calculated using the following equation ... 

In contrast to equilibrium thermodynamics, the thermodynamics of irreversible processes portray the application of thermodynamic methods as dynamic and therefore time-dependent procedures. The name Prigo-gine must be mentioned in relationship to this—he received for his work in this area the Nobel Prize in the year 1977. A new, very complex thermodynamics originated from his examination method for chemical reactions, and was developed by us, to come to a successful description of heterogenous multiphase polymer systems. This theory interprets crazing fracture energy dissipation and fracture mechanism in a totally new way on the basis of dissipative structures in polymer blends and their dynamics, For a list of abbreviations used in this section sec page 610,... 

In this Section we will present the new model for impact modification in polymer blends. This new model is derived from the new non-equilibrium thermodynamical description of heterogeneous polymer systems and interprets crazing fracture energy dissipation and the fracture mechanism in a new way on the basis of dissipative structures in polymer blends and their dynamics. 

E. A. Lange and F. J. Loss, Dynamic Tear Energy—A Practical Performance Criterion for Fracture Resistance, NRL Report 6975, Naval Research Laboratories, Washington, D.C. (1969). 

Linear elastic fracture mechanics is no longer valid for dynamic fracture mechaiusms since continuous crack propagation addresses time dependent boundary conditions. The energy balance for the dynamic conditions can be written as... 

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