scholarly journals FATIGUE CRACK INITIATION IN A CARBON BLACK–FILLED NATURAL RUBBER

2016 ◽  
Vol 89 (1) ◽  
pp. 126-141 ◽  
Author(s):  
Bertrand Huneau ◽  
Isaure Masquelier ◽  
Yann Marco ◽  
Vincent Le Saux ◽  
Simon Noizet ◽  
...  
Keyword(s):  
Crack Initiation ◽  
Carbon Black ◽  
Natural Rubber ◽  
Energy Dispersive Spectrometry ◽  
Chemical Nature ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Fatigue Tests ◽  
X Rays ◽  
The Matrix

ABSTRACT A detailed study of the initiation of fatigue cracks in carbon black–filled natural rubber is conducted. Interrupted fatigue tests are performed and fatigued samples are observed with a scanning electron microscope. This procedure first enables the quantification of the morphology, spatial distribution, and evolution of crack initiation sites for different strain levels, which gives some statistical data for each strain level. It also permits analysis of the chemical nature of inclusions inducing crack initiation thanks to energy dispersive spectrometry of X-rays. It is shown that fatigue damage initially occurs generally on carbon black agglomerates or oxides such as ZnO. However, those two types of inclusions correspond to different crack initiation mechanisms, and most of the time, only the initiations on carbon black agglomerates are followed by crack propagation that leads to failure. This difference is probably because carbon black agglomerates have a stronger cohesion than ZnO inclusions and a stronger adhesion to the matrix.

Fatigue Crack Initiation and Growth in Stainless Steel Pipe Welds

2009 ◽  
Author(s):  
D. Green ◽  
R. D. Smith ◽  
J. P. Taggart ◽  
D. Beardsmore ◽  
S. Robinson
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Thermal Loading ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Cyclic Hardening ◽  
Element Model ◽  
Fatigue Tests ◽  
Welded Pipe ◽  
Pipe Work

Thermal fatigue cracks have been found in austenitic pipe work in many pressurised water reactors, caused by thermal cycling due to the passage of water at different temperatures along the pipe inner surface. The rates of crack initiation and growth for this situation are not well understood because of the stochastic nature of the temperature fluctuations. Therefore, large allowances must be made when assessing the integrity of this pipe work to this failure mechanism. Improved assessment of crack initiation and growth could enable increased plant availability, and better safety cases. A programme of work has been completed consisting of fatigue tests on thick 304L butt-welded pipe specimens, and accompanying predictions of crack initiation and growth. In each test, uniform thermal cycles were generated using a water jet on a small area of the pipe. The magnitude of the cycles differed between the tests. Crack initiation and growth were monitored using a dye penetrant technique, applied to the pipe inner and outer surfaces, together with destructive examination. Crack initiation predictions were made using fatigue data derived from mechanical fatigue tests on the same material as in the pipe specimens. Good predictions were made using a strain-life endurance curve at a temperature corresponding to the average temperature of the metal surface during the thermal cycle. Crack growth predictions were based on an inelastic finite-element model accounting for cyclic hardening, and an enhanced R5 procedure (1) with crack closure taken into account. A linear elastic fracture mechanics definition of a Paris law for crack growth was used, and plastic redistribution effects were included. Predictions were good for all of the experimental scenarios carried out. A further experimental and analytical programme is in hand using the same experimental arrangements, concerning variable amplitude thermal loading.

Research on the Mechanism of Fatigue Crack Initiation of X60 Pipeline Steel after Per-Tension Deformation

2012 ◽  
Vol 197 ◽  
pp. 798-801
Author(s):  
Yu Rong Jiang ◽  
Mei Bao Chen
Keyword(s):  
Fatigue Crack ◽  
Cyclic Loading ◽  
Brittle Fracture ◽  
Crack Initiation ◽  
Pipeline Steel ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Fracture Characteristics ◽  
Metallic Inclusions ◽  
The Matrix

It is impossible to keep pipelines free from defects in the manufacturing, installation and servicing processes. In this paper, pre-tension deformation of X60 pipeline steel was employed to experimentally simulate the influence of dents and the mechanism of fatigue crack initiation of X60 pipeline steel after per-tension deformation under cyclic loading were investigated. The results indicate that the mechanism of fatigue crack initiation is the typical cleavage fracture characteristics and the cracks mainly initiates from the non-metallic inclusions which was the local brittle fracture materials such as MnS inclusion. With the pre-tension deformation increase, the yield strength of the matrix was increased and the toughness decreased due to the work-hardening effect. With the effects of the non-metallic inclusions larger, the fatigue cracks initiated from the non-metallic inclusions easier.

scholarly journals Mechanism of Fatigue Crack Initiation in Austenitic Stainless Steels in LWR Environments

2002 ◽  
Author(s):  
Omesh K. Chopra
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Stainless Steels ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Austenitic Stainless Steels ◽  
Fracture Morphology ◽  
Fatigue Tests ◽  
Temperature Level ◽  
Metallographic Examination

This paper examines the mechanism of fatigue crack initiation in austenitic stainless steels (SSs) in light water reactor (LWR) coolant environments. The effects of key material and loading variables, such as strain amplitude, strain rate, temperature, level of dissolved oxygen in water, and material heat treatment on the fatigue lives of wrought and cast austenitic SSs in air and LWR environments have been evaluated. The influence of reactor coolant environments on the formation and growth of fatigue cracks in polished smooth SS specimens is discussed. Crack length as a function of fatigue cycles was determined in air and LWR environments. The results indicate that decreased fatigue lives of these steels are caused primarily by the effects of the environment on the growth of cracks <200 μm and, to a lesser extent, on enhanced growth rates of longer cracks. A detailed metallographic examination of fatigue test specimens was performed to characterize the fracture morphology. Exploratory fatigue tests were conducted to enhance our understanding of the effects of surface micropits or minor differences in the surface oxide on fatigue crack initiation.

Notched Fatigue of Zr-Based Bulk Metallic Glass

2007 ◽  
Vol 345-346 ◽  
pp. 259-262 ◽  
Author(s):  
Yoshikazu Nakai ◽  
Naoki Sei ◽  
Bok Key Kim
Keyword(s):  
Crack Initiation ◽  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Shear Bands ◽  
Fatigue Tests ◽  
Propagation Mechanism ◽  
Shear Mode ◽  
Crack Propagation Mechanism

In the present study, fatigue tests of sharp-notched Zr-based bulk metallic glass (BGM), were conducted under fully reversed cyclic bending, and the fatigue crack initiation mechanisms were clarified by using AFM. The fracture surface was also observed to examine the crack propagation mechanism. The fatigue notch factor was 2.0, while the elastic stress concentration factor is 2.7. From the macroscopic observations of fractured specimen, either tension mode or shear mode fracture morphologies were observed. Either in smooth specimens or notched specimens, no prodigious sign of crack initiation were observed, i.e., fatigue cracks were initiated from shear bands those were formed just before the crack initiation.

Fatigue Crack Initiation Model of Type 316 Stainless Steel

2016 ◽  
Author(s):  
Terushi Ishizawa ◽  
Takao Nakamura ◽  
Takanori Kitada
Keyword(s):  
Crack Initiation ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Strain Range ◽  
Fatigue Tests ◽  
Statistical Dispersion ◽  
Crack Initiation Life ◽  
Using Data ◽  
Two Parameters ◽  
The Relationship

The fatigue tests under different conditions of strain range were conducted in air and the replica observation of fatigue cracks on specimen surface was also conducted. Using data obtained in fatigue tests, statistical dispersion of crack initiation life was quantified and modeled through an application of two-parameter Weibull distribution. The relationship between strain range and two parameters (s, shape parameter and Η, scale parameter) of crack initiation model was discussed. Thereby, the applicability of crack initiation model for arbitrary strain range was shown. Furthermore, the validation of P-curve applied crack initiation model was conducted by the simulation of fatigue life.

Effect of Maximum Temperature on the Thermal Fatigue Behavior of Superalloy GH536

2016 ◽  
Vol 853 ◽  
pp. 28-32 ◽  
Author(s):  
Jing Chen ◽  
Duo Qi Shi ◽  
Guo Lei Miao ◽  
Xiao Guang Yang
Keyword(s):  
Crack Initiation ◽  
Fatigue Test ◽  
Thermal Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Fatigue Tests ◽  
Maximum Temperature ◽  
Thermal Fatigue Crack ◽  
Thermal Fatigue Test

Thermal fatigue tests of superalloy GH536 were carried out at different maximum temperature. Three-dimensional numerical finite element computations were performed to simulate thermal fatigue test process. The crack initiation, propagation and thermal fatigue failure mechanism of GH536 plate at different maximum temperatures were obtained by experiments and numerical methods. Result shows that the crack initiation life is shortened and the crack growth rate is accelerated with the increase of the maximum temperature of thermal fatigue test. The numbers of appearing 1 mm length cracks are 180, 74 and 37, respectively, when the maximum temperature is 800°C, 850°C and 900°C respectively. So the thermal fatigue performance decreases with the increase of the maximum temperature. But in the thermal fatigue tests of different maximum temperature, the thermal fatigue crack initiation is all caused by a single crack initiation source, and the thermal fatigue cracks initiate transgranularly, develop and propagate intergranularly.

Rubber Fracture Characterization Using J-Integral

1988 ◽  
Vol 16 (1) ◽  
pp. 44-60 ◽  
Author(s):  
C. L. Chow ◽  
J. Wang ◽  
P. N. Tse
Keyword(s):  
Crack Initiation ◽  
Carbon Black ◽  
Natural Rubber ◽  
Fracture Parameter ◽  
J Integral ◽  
Specimen Length ◽  
Fracture Characterization ◽  
Premature Failure ◽  
Testing Procedures ◽  
Material Evaluation

Abstract The use of the J-integral to investigate fracture characterization in a carbon black reinforced natural rubber is described. Three applications to crack initiation are included: two based on the use of a hypothetical zero specimen length and one on conventional testing procedures for metals. While the validity of the zero-length methods is questionable, the conventional method yielded a consistent Jc value of 1.01 N/mm for a typical tire compound. This value was obtained from 24 combinations of varying specimen geometries and pre-crack lengths. The J-integral is revealed as a valid fracture parameter that is applicable not only for material evaluation but also for designing tire structures to resist premature failure. These conclusions disagree with those from an earlier investigation, so the causes for the discrepancies are examined and discussed.

Plastic Slip and Early Stage of Fatigue Damage in Polycrystals: Comparison between Experiments and Crystal Plasticity Finite Elements Simulations

2014 ◽  
Vol 891-892 ◽  
pp. 1711-1716 ◽  
Author(s):  
Loic Signor ◽  
Emmanuel Lacoste ◽  
Patrick Villechaise ◽  
Thomas Ghidossi ◽  
Stephan Courtin
Keyword(s):  
Fatigue Crack ◽  
Finite Elements ◽  
Crack Initiation ◽  
Fatigue Damage ◽  
Crystal Plasticity ◽  
Early Stage ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Plastic Slip

For conventional materials with solid solution, fatigue damage is often related to microplasticity and is largely sensitive to microstructure at different scales concerning dislocations, grains and textures. The present study focuses on slip bands activity and fatigue crack initiation with special attention on the influence of the size, the morphology and the crystal orientation of grains and their neighbours. The local configurations which favour - or prevent - crack initiation are not completely identified. In this work, the identification and the analysis of several crack initiation sites are performed using Scanning Electron Microscopy and Electron Back-Scattered Diffraction. Crystal plasticity finite elements simulation is employed to evaluate local microplasticity at the scale of the grains. One of the originality of this work is the creation of 3D meshes of polycrystalline aggregates corresponding to zones where fatigue cracks have been observed. 3D data obtained by serial-sectioning are used to reconstruct actual microstructure. The role of the plastic slip activity as a driving force for fatigue crack initiation is discussed according to the comparison between experimental observations and simulations. The approach is applied to 316L type austenitic stainless steels under low-cycle fatigue loading.

Short fatigue crack initiation and growth modeling in aluminum 7075-T6

2014 ◽  
Vol 229 (7) ◽  
pp. 1206-1214 ◽  
Author(s):  
M Amiri ◽  
M Modarres
Keyword(s):  
Crack Initiation ◽  
Damage Mechanics ◽  
Fatigue Crack Initiation ◽  
Estimation Method ◽  
Continuum Damage Mechanics ◽  
Fatigue Tests ◽  
Short Cracks ◽  
Al 7075 ◽  
Edge Notch ◽  
Aluminum 7075

A series of fatigue tests is carried out to investigate the behavior of microcrack initiation and propagation in Al 7075-T6. Plate specimens with semi-circular single edge notch are tested under uniaxial loading at different load amplitudes. Optical microscopy is used to detect the initiation and growth of short cracks. Continuum damage mechanics is used to model the crack initiation. After the initiation, crack growth is studied using fracture mechanics models. For both regions of crack initiation and growth, Bayesian estimation method is used to account for uncertainties in the parameters of the model. Results of the entire fatigue life, including initiation and growth, are compared with experiments. Good agreement is observed.

Sign in / Sign up

Export Citation Format

Share Document