Fracture of Elastomers by Gas Decompression

1995 ◽  
Vol 68 (2) ◽  
pp. 197-211 ◽  
Author(s):  
Andrew Stevenson ◽  
Glyn Morgan
Keyword(s):  
Crack Growth ◽  
Fundamental Problem ◽  
Finite Thickness ◽  
Gas Permeation ◽  
Experimental Results ◽  
Internal Flaw ◽  
Tearing Energy ◽  
Elastomeric Seals ◽  
Permeation Kinetics ◽  
Surfaces Of Weakness

Abstract A study has been made of gas decompression failures in elastomeric seals using a fracture mechanics approach and considerations of gas permeation. An equation is proposed for the tearing energy associated with crack growth from internal gas bubbles in a finite thickness elastic media. When applied to a model experiment where an internal flaw of known size was pressurized up to failure, the equation agreed with experimental results. A series of seals were then subjected to high gas pressures (up to 69 MPa or 10,000 psi) for a range of temperatures between 20 and 230°C and the amount of crack growth was measured after decompression. The trends in crack growth were correctly accounted for when values for tearing energy and modulus were used that were appropriate for the temperature of decompression. The effect of mechanical boundary constraint was studied by varying the compression on the seal in specially designed test holders. The effect of decompression rate is also considered. The conditions under which failure will occur are created by a complex balance of the available tearing energy and the gas permeation kinetics. A fundamental problem is the unknown size of the initial flaw from which crack growth and rupture occurs. This is discussed in the light of the experimental results and it is proposed that effective surfaces of weakness form in the elastomer phase of size to provide initiation sites for crack growth.

Guided Wave Acoustic Emission from Fatigue Crack Growth in Aluminium Plate

2006 ◽  
Vol 13-14 ◽  
pp. 23-28 ◽  
Author(s):  
C.K. Lee ◽  
Jonathan J. Scholey ◽  
Paul D. Wilcox ◽  
M.R. Wisnom ◽  
Michael I. Friswell ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Elastic Waves ◽  
Fatigue Cracks ◽  
Guided Wave ◽  
Experimental Results ◽  
Multiple Reflections ◽  
Alloy Plate

Acoustic emission (AE) testing is an increasingly popular technique used for nondestructive evaluation (NDE). It has been used to detect and locate defects such as fatigue cracks in real structures. The monitoring of fatigue cracks in plate-like structures is critical for aerospace industries. Much research has been conducted to characterize and provide quantitative understanding of the source of emission on small specimens. It is difficult to extend these results to real structures as most of the experiments are restricted by the geometric effects from the specimens. The aim of this work is to provide a characterization of elastic waves emanating from fatigue cracks in plate-like structures. Fatigue crack growth is initiated in large 6082 T6 aluminium alloy plate specimens subjected to fatigue loading in the laboratory. A large specimen is utilized to eliminate multiple reflections from edges. The signals were recorded using both resonant and nonresonant transducers attached to the surface of the alloy specimens. The distances between the damage feature and sensors are located far enough apart in order to obtain good separation of guided-wave modes. Large numbers of AE signals are detected with active fatigue crack propagation during the experiment. Analysis of experimental results from multiple crack growth events are used to characterize the elastic waves. Experimental results are compared with finite element predictions to examine the mechanism of AE generation at the crack tip.

Energy for crack growth in model rubber components

1972 ◽  
Vol 7 (2) ◽  
pp. 132-140 ◽  
Author(s):  
P B Lindley
Keyword(s):  
Fatigue Life ◽  
Crack Growth ◽  
Crack Surface ◽  
Uniform Stress ◽  
Numerical Techniques ◽  
Surface Displacements ◽  
Tearing Energy ◽  
Crack Growth Rates ◽  
Essential Prerequisite

The determination of tearing energy, i.e. the energy available for crack growth, is an essential prerequisite for the estimation of the fatigue life of rubber components. Three methods of determining tearing energy are considered: from changes in total energy, from crack surface displacements, and by comparison with known values for the same crack growth rates. It is shown by applying experimental and numerical techniques to plane-stress testpieces, not necessarily of uniform stress or thickness, that the methods are satisfactory.

Contributions of Time Dependent and Cyclic Crack Growth to the Crack Growth Behavior of Non Strain-Crystallizing Elastomers

2002 ◽  
Vol 75 (4) ◽  
pp. 643-656 ◽  
Author(s):  
J. J. C. Busfield ◽  
K. Tsunoda ◽  
C. K. L. Davies ◽  
A. G. Thomas
Keyword(s):  
Crack Growth ◽  
Growth Behavior ◽  
Time Dependent ◽  
Crack Growth Behavior ◽  
Wide Range ◽  
Dependent Component ◽  
Tearing Energy ◽  
Quasi Crystals ◽  
Crack Growth Rates ◽  
Time Dependent Crack Growth

Abstract Engineering components are observed to fail more rapidly under cyclic loading than under static loading. This reflects features of the underlying crack growth behavior. This behavior is characterized by the relation between the tearing energy, T, and the crack growth per cycle, dc/dn. The increment of crack growth during each cycle is shown here to result from the sum of time dependent and cyclic crack growth components. The time dependent component represents the crack growth behavior that would be present in a conventional constant T crack growth test. Under repeated stressing additional crack growth, termed the cyclic crack growth component, occurs. For a non-crystallizing elastomer, significant effects of frequency have been found on the cyclic crack growth behavior, reflecting the presence of this cyclic element of crack growth. The cyclic crack growth behavior over a wide range of frequencies was investigated for unfilled and swollen SBR materials. The time dependent crack growth component was calculated from constant T crack growth tests and the cyclic contribution derived from comparison with the observed cyclic growth. It is shown that decreasing the frequency or increasing the maximum tearing energy during a cycle results in the cyclic crack growth behavior being dominated by time dependent crack growth. Conversely at high frequency and at low tearing energy, cyclic crack growth is dominated by the cyclic crack growth component. A large effect of frequency on cyclic crack growth behavior was observed for highly swollen SBR. The cyclic crack growth behavior was dominated by the time dependent crack growth component over the entire range of tearing energy and/or crack growth rate. The origin of the cyclic component may be the formation/melting of quasi crystals at the crack tip, which is absent at fast crack growth rates in the unswollen SBR and is absent at all rates in the swollen SBR.

TACTICAL ROUTE PLANNING: NEW ALGORITHMS FOR DECOMPOSING THE MAP

1996 ◽  
Vol 05 (01n02) ◽  
pp. 199-218 ◽  
Author(s):  
J.R. BENTON ◽  
S.S. IYENGAR ◽  
W. DENG ◽  
N. BRENER ◽  
V.S. SUBRAHMANIAN
Keyword(s):  
Data Structures ◽  
Fundamental Problem ◽  
Route Planning ◽  
Decomposition Methods ◽  
Search Algorithms ◽  
Experimental Results ◽  
New Approach ◽  
Robotic Vehicles ◽  
New Algorithms ◽  
Large Grid

This paper defines a new approach and investigates a fundamental problem in route planners. This capability is important for robotic vehicles(Martian Rovers, etc.) and for planning off-road military maneuvers. The emphasis throughout this paper will be on the design and analysis and hieiaichical implementation of our route planner. This work was motivated by anticipation of the need to search a grid of a trillion points for optimum routes. This cannot be done simply by scaling upward from the algorithms used to search a grid of 10,000 points. Algorithms sufficient for the small grid are totally inadequate for the large grid. Soon, the challenge will be to compute off-road routes more than 100 km long and with a one or two-meter grid. Previous efforts are reviewed and the data structures, decomposition methods and search algorithms are analyzed and limitations are discussed. A detailed discussion of a hieraichical implementation is provided and the experimental results are analyzed.

Competing Fracture Modes in Brittle Materials Subject to Concentrated Cyclic Loading in Liquid Environments: Monoliths

2005 ◽  
Vol 20 (8) ◽  
pp. 2021-2029 ◽  
Author(s):  
Yu Zhang ◽  
Sanjit Bhowmick ◽  
Brian R. Lawn
Keyword(s):  
Cyclic Loading ◽  
Crack Growth ◽  
Driving Forces ◽  
Slow Crack Growth ◽  
Finite Thickness ◽  
Brittle Materials ◽  
Soda Lime Glass ◽  
Growth Data ◽  
Fracture Modes ◽  
Maximum Contact

The competition between fracture modes in monolithic brittle materials loaded in cyclic contact in aqueous environments with curved indenters is examined. Three main modes are identified: conventional outer cone cracks, which form outside the maximum contact; inner cone cracks, which form within the contact; and median–radial cracking, which form below the contact. Relations describing short-crack initiation and long-crack propagation stages as a function of number of cycles, based on slow crack growth within the Hertzian field, are presented. Superposed mechanical driving forces—hydraulic pumping in the case of inner cone cracks and quasiplasticity in the case of median–radials—are recognized as critically important modifying elements in the initial and intermediate crack growth. Ultimately, at large numbers of cycles, the cracks enter the far field and tend asymptotically to a simple, common relation for center-loaded pennylike configurations driven by slow crack growth. Crack growth data illustrating each mode are obtained for thick soda-lime glass plates indented with tungsten carbide spheres in cyclic loading in water, for a range of maximum contact loads and sphere radii. Generally in the glass, outer cone cracks form first but are subsequently outgrown in depth as cycling proceeds by inner cones and, especially, radial cracks. The latter two crack types are considered especially dangerous in biomechanical applications (dental crowns, hip replacements) where ceramic layers of finite thickness are used as load-bearing components. The roles of test variables (contact load, sphere radius) and material properties (hardness, modulus, toughness) in determining the relative importance of each fracture mode are discussed.

COMPARISON OF SINE VERSUS PULSE WAVEFORM EFFECTS ON FATIGUE CRACK GROWTH BEHAVIOR OF NR, SBR, AND BR COMPOUNDS

2010 ◽  
Vol 83 (4) ◽  
pp. 391-403 ◽  
Author(s):  
G. Andreini ◽  
P. Straffi ◽  
S. Cotugno ◽  
G. Gallone ◽  
G. Polacco
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Natural Rubber ◽  
Crack Growth ◽  
Fine Tuning ◽  
Styrene Butadiene Rubber ◽  
Butadiene Rubber ◽  
Pulse Waveform ◽  
Tearing Energy ◽  
Styrene Butadiene

Abstract Fatigue crack growth experiments on carbon black-filled rubber compounds have been carried out to evaluate the influence of testing conditions over different compound formulations. Investigations on the influence of waveform, data acquisition, and compound formulation have been performed on strip-tensile specimens reproducing the mode I of crack opening. The response of three different compound formulations (based on either natural rubber, butadiene rubber, or styrene-butadiene rubber) to the application of two different waveforms, pulse and sine, has been analyzed, showing significant differences in fatigue behavior and ranking of the various compounds. Compared to the sinusoidal waveform, the use of a pulse waveform provided an improved correlation of the tearing energy with the crack propagation speed. This difference was particularly evident in the case of natural rubber and butadiene rubber, while it resulted negligible in the case of styrene-butadiene rubber. Such a different behavior could be attributed to differences in macromolecular chains orientation. Fine-tuning of video acquisition parameters provided an accurate observation of the crack growth process, as confirmed by the low standard deviation of the estimated tearing energy and crack growth rate.

Non-Relaxing Crack Growth and Fatigue in a Non-Crystallizing Rubber

1974 ◽  
Vol 47 (5) ◽  
pp. 1253-1264 ◽  
Author(s):  
P. B. Lindley
Keyword(s):  
Crack Growth ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Maximum Deformation ◽  
Fatigue Data ◽  
Tentative Explanation ◽  
Tearing Energy ◽  
Relationship Of ◽  
The Relationship ◽  
Unique Relationship

Abstract The crack growth behavior of a non-crystallizing rubber, SBR, is investigated in terms of the tearing energy T, the energy available for crack growth. For cyclic deformations in which the minimum tearing energy is zero (relaxing conditions), a unique relationship is obtained between the growth per cycle and T at the maximum deformation. This rubber also exhibits crack growth at constant tearing energies. The relationship of the crack growth rate as a function of tearing energy, when the minimum tearing energy of the cycle is not zero, can be superimposed on the relaxing relationship by scaling the rates, and a tentative explanation is proposed for the scaling factor. Fatigue data are consistent with this.

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