Crack growth stability

D. L. Davidson, J. B. Campbell, and J. Lankford, Fatigue Crack Growth through Partially Stabilized Zirconia at Ambient and Elevated Temperatures, Acta Metall. Mater., 39[6], 1319-1330 (1991). 

The electrolyte membrane presents critical materials issues such as high protonic conductivity over a wide relative humidity (RH) range, low electrical conductivity, low gas permeability, particularly for H2 and O2, and good mechanical properties under wet-dry and temperature cycles has stable chemical properties under fuel cell oxidation conditions and quick start-up capability even at subfreezing temperatures and is low cost. Polyperfluorosulfonic acid (PFSA) and derivatives are the current first-choice materials. A key challenge is to produce this material in very thin form to reduce ohmic losses and material cost. PFSA ionomer has low dimensional stability and swells in the presence of water. These properties lead to poor mechanical properties and crack growth. 

Discontinuous crack growth bands were first observed on the fracture surface of PVC specimens subject to cyclic loading by Elinck et al. The effect of molecular weight on band stability has been studied and some of the test results for three different molecular weights are displayed in Fig. 17. As M increases and the number of entanglements per chain rises, the data show that, for any given AK value, a greater... 

In summary, short cracks form epsilon CTPZ development, whereas long cracks usually lack the required shear components to generate the shear-band pair, niis creates the anomalous short crack behavior. When epsilon CTPZs form, the shear bands stabilize the crack, thus allowing the DCG process to continue to much higher apparent AK, values, further differentiating from the non-epsilon CTPZ DCG crack growth behavior. 

A stability analysis is presented for circumferential cracks of constant depth in cantilevered pipings. The analysis is based on the tearing modulus concept and the tearing stability criterion. Assuming that the cracked cross-section is subjected to limit moment the crack growth is studied in the case of pipings subjected to impact loading. 

Thus the condition of stability of the crack growth is given by [4,7,13]... 

Hutchinson, J.W. and Paris, P.C., (1979), Stability analysis of J-controlled crack growth. In J.D. Landes, J.A. Begley and G.A. Clarke (Eds), Elastic-Plastic Fracture, ASTM STP 668. American Society for Testing Materials, Philadelphia, 37. 

Matrix Particle growth Stability and crack formation Dissolution of y-LiA102 in the electrolyte Phase transformation from y to a variety Changes in the microstructure Increase in the ionic resistivity Decrease in the cell voltage Decrease in the cell life... 

Two types of stabilizers inhibit crack growth in rubbers microcrystalline waxes and alkylated phenylene diamines. A small quantity of the wax milled into a rubber will gradually diffuse to the surface where it will serve as a barrier impervious to ozone. A combination of wax and alkylated phenylene dicunine antiozonant is generally used for optimum protection. The exact function of antiozonant is still obscure but it is possible that it accelerates scission processes on the polymer surface producing a protective film of viscous products. 

In addition to their successful applications to fracture stability problems, the stress intensity factors have been widely used as correlation parameters in analyzing the subcritical crack growth rates da/dn (in fatigue) and dafdt (in corrosion), n and t referring to the number of... 

Figure 5. Regions of stable crack growth and overload observed in the Zr-stabilized 2014 aluminum alloy tested at 125 MPa fractured after 3.5 105 cycles.

Antiozonant Properties. Aromatic secondary diamines are the only class of organic chemicals able to reduce efficiently the ozone crack growth of vulcanizates under dynamic conditions and be acceptable at the same time from both the technical and toxicological points of view. The presence of a secondary aromatic amine moiety itself in a molecule is not a sufficient condition to attain antiozonants efficiency. (E.g., secondary monomaines are only antioxidants and flex-crack inhibitors without appreciable antiozonant activity. On the other hand, all N,N -disubstituted PD antiozonants are also efficient antoxidants and most of them also act as flex-crack inhibitors (1). Both these stabilization activities have to be considered in the complex antiozonant mechanism, together with some metal deactivating activity. 

Crack Stability. At low test speeds, stable crack growth with an extended stress-whitened plastic zone and crack blunting occur by the same mechanisms as those involved in the kinetics of the plastic zone, namely, rubber cavitation followed by shear deformation of the matrix. The ability of the matrix to shear is controlled by its relaxation behavior, which therefore determines its plasticity and the deformation imposed on rubbery particles distant from the notch. 

Can the properties that govern crack stability and growth be computed on the basis of hrst principles, or must they be determined experimentally How are these properties to be dehned, and how well can they be determined What are the variations in these properties If the failure load or crack growth life of a material can be measured, what degree of certainty can be attached to the prediction of safe operating load or serviceable life of a structural component made from that material ... 

Phase Transformation and Crack Growth in Yttria-Stabilized Zirconia... 

Interfacial stability is predicted using the ERR, which is defined as the mechanical energy that is released during an incremental increase in crack length. Crack advance occurs when the ERR reaches a critical value, often referred to as the interface toughness, denoted here as Fj. Thus, the crack growth criterion is G > Fj. The ERR is defined as [33]... 

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