Slow Crack Growth in Dental Composites

1985 ◽  
Vol 55 ◽  
Author(s):  
G. M. Montes-G. ◽  
R. A. Draughn ◽  
T. H. Simpson
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
Slow Crack Growth ◽  
High Stress ◽  
Torsion Test ◽  
Stable Crack Growth ◽  
Test Method ◽  
Volume Percent ◽  
Stick Slip ◽  
Model Composite

ABSTRACTThe fracture properties of selected commercial composite dental restorative materials and a model composite system were studied to determine the influences of the reinforcing phase, exposure to water, and particle/polymer adhesion on crack propagation. The content of inorganic fillers ranged from 36 to 62 volume percent. In the model system the polymer phase approximated that of the commercial products, a constant size distribution of quartz fillers was used, and polymer/particle adhesion was varied. The double torsion test method was employed to measure relationships between applied stress intensity factor and velocity of crack propagation during stable crack growth. In all systems, cracks propagated through regions of high stress concentration at the low end of the velocity range studied (10−7 m/sec to 10−3 m/sec). Wet materials fractured at lower stress intensities than dry materials at all velocities. At high velocities unstable (stick-slip) growth occurred in dry materials with strong filler/matrix interfaces and in wet specimens with initially strong interfaces and less than 41 volume percent filler. In wet conditions, materials with poorly bonded fillers fractured by slow crack growth at stress intensities 10% to 30% below the levels of composites with strong interfaces.

Crack Growth During Full Scale Reeling Simulation of Pipes With Girth Welds

2004 ◽  
Author(s):  
Oddvin O¨rjasaeter ◽  
Olav Jan Hauge ◽  
Guy Ba¨rs ◽  
Per Egil Kvaale
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
High Strain ◽  
High Stress ◽  
Strain Range ◽  
Full Scale ◽  
Small Scale ◽  
Final Fracture ◽  
Lack Of Fusion ◽  
Girth Welds

Installation of pipelines by reeling has proved to be an effective method. However, the pipe bending results in very high stress and strain and cannot be handled by conventional design rules, as stated in design codes, e.g. [2]: High strain crack growth must be assessed according to specific case-by-case selected criterions. In the present work the performance of 10” and 12 3/4” pipes with typical weld defects is studied — from initiation of cracks at notches to final fracture. Information was obtained from several sources: full scale cyclic bending of pipes, FE simulations, and small-scale tests. The plasticity during reeling operations results in substantial non-linear behavior due to varying cross section properties, cyclic creep, and different material response at tensile and compression side of the pipe. Hence, a full scale reeling simulation must be carefully planned and include sufficient tolerances. Critical cracks in pipe girth welds initiate mainly from the surface (undercuts, lack of penetration, or lack of fusion), but potentially also internally (lack of fusion or large pores). Various configurations of these parameters were investigated in full scale pipe tests. It was possible to verify both crack propagation during the reeling cycles, and the point of final fracture (for ECA verifications). In pipe design on must assure safe conditions for both reeling operations and for later in-service loading. Proper design tools must be available. Several methods for high strain crack growth analysis were considered and also compared to small-scale specimen data. Conventional strain-life methodology failed to predict the crack propagation accurately. A new approach including a tensile strain range parameter offered promising results.

Finite Element Modeling for Energy Release Rate in Human Cortical Bone

Volume 2 ◽  
2004 ◽  
Author(s):  
Saiphon Charoenphan ◽  
Apiwon Polchai
Keyword(s):  
Finite Element ◽  
Crack Propagation ◽  
Finite Element Modeling ◽  
Energy Release Rate ◽  
Cortical Bone ◽  
Energy Release ◽  
Crack Growth ◽  
Release Rate ◽  
Slow Crack Growth ◽  
Finite Element Models

The energy release rates in human cortical bone are investigated using a hybrid method of experimental and finite element modeling techniques. An explicit finite element analysis was implemented with an energy release rate calculation for evaluating this important fracture property of bones. Comparison of the critical value of the energy release rate, Gc, shows good agreement between the finite element models and analytical solutions. The Gc was found to be approximately 820–1150 J/m2 depending upon the samples. Specimen thickness appears to have little effect on the plane strain condition and pure mode I assumption. Therefore the energy release rate can be regarded as a material constant and geometry independent and can be determined with thinner specimens. In addition, the R curve resulting from the finite element models during slow crack growth shows slight ductility of the bone specimen that indicates an ability to resist crack propagation. Oscillations were found at the onset of the crack growth due to the nodal releasing application in the models. In this study light mass-proportional damping was used to suppress the noises. Although this techniques was found to be efficient for this slow crack growth simulation, other methods to continuously release nodes during the crack growth would be recommended for rapid crack propagation.

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