Some Chemical Effects in Fatigue Cracking of Vulcanized Rubbers

1963 ◽  
Vol 36 (2) ◽  
pp. 399-406 ◽  
Author(s):  
A. N. Gent
Keyword(s):  
Fatigue Life ◽  
Natural Rubber ◽  
Crack Growth ◽  
Crack Tip ◽  
Fatigue Cracking ◽  
Substantial Proportion ◽  
Oxidative Deterioration ◽  
Chemical Effects ◽  
Oxidation Inhibitors ◽  
Mechanical Rupture

Abstract An apparatus is described for studying the fatigue of rubber strips under repeated simple extensions in different atmospheres. The fatigue life is shown to be greatly increased in vacuo for vulcanizates of natural rubber and SBR. The effect of oxidation inhibitors and radical acceptors has been examined; they are found to prolong the life in air, but have little effect in vacuo. The results suggest that a substantial proportion of crack growth in air is due to oxidative deterioration of the rubber at the crack tip, probably initiated by mechanical rupture.

scholarly journals Fatigue Life Enhancement of Welded Steel-Steel Composite during Crack Growth from Weak to Strong Steel: An Experimental Validation

2009 ◽  
Vol 417-418 ◽  
pp. 825-828
Author(s):  
Sunil Bhat ◽  
Vijay G. Ukadgaonker
Keyword(s):  
Fatigue Life ◽  
Crack Growth ◽  
Load Transfer ◽  
Electron Beam Welding ◽  
Fatigue Testing ◽  
Crack Tip ◽  
Compact Tension ◽  
Welded Steel ◽  
Maraging Steels ◽  
Bimetallic Composite

Strength mismatch effect across weld interfaces, generated by welding weak and strong steels, influences fatigue and fracture properties of a welded bimetallic composite. Advancing fatigue crack tip in weak parent steel is shielded from the remote load when it reaches near the interface of ultra strong weld steel. Entry of crack tip plasticity into weld steel induces load transfer towards weld which dips crack growth rates thereby enhancing the fatigue life of the composite. A computational model for fatigue life prediction of strength mismatched welded composite under K dominant conditions is validated by experimental work in this paper. Notched bimetallic compact tension specimens, prepared by electron beam welding of weak alloy and strong maraging steels, are subjected to fatigue testing in high cycle regime.

Relaxation Processes in Vulcanized Rubber. II. Secondary Relaxation Due to Network Breakdown

1963 ◽  
Vol 36 (2) ◽  
pp. 389-398 ◽  
Author(s):  
A. N. Gent
Keyword(s):  
Molecular Structure ◽  
Experimental Study ◽  
Natural Rubber ◽  
Relaxation Process ◽  
Relaxation Processes ◽  
Secondary Relaxation ◽  
Oxidative Deterioration ◽  
Vulcanized Rubber ◽  
Oxidation Inhibitors ◽  
Natural Rubber Vulcanizates

Abstract An experimental study is described of a “secondary” relaxation process in stretched vulcanizates, which becomes dominant after long periods at normal temperatures. It is shown to be affected markedly by the temperature, the atmosphere in which the test is conducted, and the presence of oxidation inhibitors. It is therefore attributed to oxidative deterioration of the molecular structure. In some vulcanizates, however, a similar or even greater relaxation is found to occur in vacuo, and this is attributed to the failure of specific crosslink structures. The extent of recovery on releasing the extended testpieces has also been investigated for a number of natural rubber vulcanizates.

Fracture Resistance of Ship Longitudinal Members Including Fatigue Crack

2013 ◽  
Author(s):  
Yann Quéméner ◽  
Chien-Hua Huang ◽  
Chi-Fang Lee
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Crack Length ◽  
Crack Growth ◽  
Fracture Resistance ◽  
Crack Tip ◽  
Critical Crack ◽  
Critical Crack Length ◽  
Extreme Loads

This study investigates the fracture failure of longitudinal members including cracks. Specifically, this study employs the failure assessment diagram methodology to assess the conditions of failure at the crack tip. Based on various crack configurations, this study establishes the analytical formulations of the crack-tip condition that are validated using finite element analyses. In addition, the material toughness is expressed in terms of crack-tip opening displacement. This study evaluates the failure stress of representative cracked members as a function of the crack length. This enables determining critical crack lengths corresponding to the maximum stresses derived from extreme loads. Finally, this study uses simplified fatigue crack growth analyses to characterize the critical crack length in terms of fatigue life. For members located in the deck and bottom regions, the critical crack lengths correspond to the end of the assessed fatigue life. Therefore, the fracture resistance of the longitudinal members is satisfactory as it will not cause the premature loss of the component. This study also provides analytical formulations for crack-tip conditions that could be employed in a reliability study linking fatigue crack growth and fracture under extreme loads.

Improved Fatigue Life Assessment of Lighting Poles

2014 ◽  
Vol 891-892 ◽  
pp. 149-154
Author(s):  
Clark W.K. Hyland ◽  
W. George Ferguson ◽  
Katalin Csikasz
Keyword(s):  
New Zealand ◽  
Fatigue Life ◽  
Crack Growth ◽  
Design Method ◽  
Fatigue Cracking ◽  
Life Assessment ◽  
Response Analysis ◽  
Wind Speeds ◽  
Proof Testing ◽  
Wind Response

Fatigue cracking reported in a lighting pole on an elevated bridge structure near Wellington raised the question of how to better design for and predict the fatigue life of lighting poles subject to wind induced fatigue. There have been concerns as to the reliability and currency of the methods commonly used in New Zealand. The paper therefore reviews current international design methods and describes the development of an improved fatigue design method for lighting poles in New Zealand. The new method uses fracture mechanics based crack growth formulations in conjunction with a modified J.D. Holmes Method for wind response analysis of the pole to varying wind speeds. Cumulative crack growth is calculated iteratively rather than using an S-N curve based Palmegran-Miner summation. Wind spectra used in the method are developed from long term meteorological records at representative locations. Software has been prepared to enable quick assessment of the expected fatigue life of lighting poles, and associated gear openings and holding down bolts The method and software has been calibrated with reference to full scale laboratory fatigue proof testing of representative base stubs and natural wind response testing of a 12 m high lighting pole.

scholarly journals FATIGUE CRACK GROWTH BEHAVOR OF CARBON BLACK–REINFORCED NATURAL RUBBER

2021 ◽  
Author(s):  
Lewis B. Tunnicliffe
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Carbon Black ◽  
Natural Rubber ◽  
Crack Growth ◽  
Crack Tip ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Fatigue Crack Growth Behavior ◽  
Amplification Factors

ABSTRACT Fatigue crack growth behavior of carbon black–reinforced natural rubber is investigated. Rubber compounds of Shore A = 70 are prepared by varying the formulation loadings of a wide range of carbon black types based on their structure and surface area properties. The resulting fatigue crack growth behavior shows significant variation in β exponent values, depending on the properties of the carbon black. These variations are rationalized by considering the strain amplification of natural rubber by carbon black aggregates in the region of compound directly ahead of the crack tip. An assumption is made that little networking of the carbon black aggregates exists in this region of very high strain and that hydrodynamic calculations that consider occluded rubber can therefore provide realistic values for strain amplification. A reasonable scaling of power law crack growth parameters to calculated strain amplification factors is found, with the exponent, β, decreasing with increasing strain amplification. The implication here is that enhanced strain amplification promotes the formation of strain-induced crystallites in the crack tip region. Performance tradeoffs resulting from the crossover of crack growth data sets dependent on the carbon black type are discussed. Of practical significance is the fact that the strain amplification factors can be calculated directly from knowledge of carbon black type and loading in rubber formulations.

Crack growth mechanism of natural rubber under fatigue loading studied by a real-time crack tip morphology monitoring method

RSC Advances ◽  
2014 ◽  
Vol 4 (83) ◽  
pp. 43942-43950 ◽  
Author(s):  
Gengsheng Weng ◽  
Hong Yao ◽  
Aijun Chang ◽  
Kun Fu ◽  
Yanpeng Liu ◽  
...  
Keyword(s):  
Natural Rubber ◽  
Real Time ◽  
Crack Growth ◽  
Energy Dependence ◽  
Growth Mechanism ◽  
Crack Tip ◽  
Fatigue Loading ◽  
Monitoring Method ◽  
Crack Growth Mechanism

Tear energy dependence of NR crack tip morphology.

scholarly journals Effect of Electropulsing Treatment on the Fatigue Crack Growth Behavior of Copper

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2168 ◽  
Author(s):  
Yan Yin ◽  
Haibo Chen ◽  
Yasuyuki Morita ◽  
Yuhki Toku ◽  
Yang Ju
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Crack Tip ◽  
Cyclic Stress ◽  
Crack Growth Behavior ◽  
Electropulsing Treatment ◽  
Two Sides

Crack propagation was quantitatively evaluated to investigate the effect of electropulsing treatment (EPT) on fatigue crack growth of copper specimens. Varying fatigue cycles were obtained under six different load levels. The crack lengths were measured under two load levels to examine the effect of cyclic stress. The microhardness was measured around the vicinity of the crack tip. Furthermore, the fracture surface was observed by scanning electron microscopy. Results show that EPT with electric current density of 150 A/mm2 enhances the high-cycle fatigue life, and the effect tends to increase with the decrease in cyclic stress. Vickers microhardness (HV) near the crack tip decreases to normal levels after treatment, and the approaching cracks on two sides can be observed. Local annealing and recrystallization occur around the fatigue crack tip. Accordingly, crack propagation can be delayed, and fatigue life can be prolonged by EPT.

scholarly journals Simulation of Quasi-Static Crack Propagation by Adaptive Finite Element Method

Metals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 98
Author(s):  
Abdulnaser M. Alshoaibi ◽  
Yahya Ali Fageehi
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Fatigue Life ◽  
Stress Intensity ◽  
Crack Growth ◽  
Crack Tip ◽  
Intensity Factors ◽  
Linear Elastic ◽  
Elastic Fracture ◽  
Element Method

The finite element method (FEM) is a widely used technique in research, including but not restricted to the growth of cracks in engineering applications. However, failure to use fine meshes poses problems in modeling the singular stress field around the crack tip in the singular element region. This work aims at using the original source code program by Visual FORTRAN language to predict the crack propagation and fatigue lifetime using the adaptive dens mesh finite element method. This developed program involves the adaptive mesh generator according to the advancing front method as well as both the pre-processing and post-processing for the crack growth simulation under linear elastic fracture mechanics theory. The stress state at a crack tip is characterized by the stress intensity factor associated with the rate of crack growth. The quarter-point singular elements are constructed around the crack tip to accurately represent the singularity of this region. Under linear elastic fracture mechanics (LEFM) with an assumption in various configurations, the Paris law model was employed to evaluate mixed-mode fatigue life for two specimens under constant amplitude loading. The framework includes a progressive analysis of the stress intensity factors (SIFs), the direction of crack growth, and the estimation of fatigue life. The results of the analysis are consistent with other experimental and numerical studies in the literature for the prediction of the fatigue crack growth trajectories as well as the calculation of stress intensity factors.

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