Strength,Fracture and Complexity

The International Congress on Fracture (ICF) was created through the vision of Takeo Yokobori in Sendai, Japan in 1965. The primary emphasis of Yokobori was to join the micro- and macro-mechanics aspects of fracture research. The outstanding growth of ICF demonstrates that the founding effort was the right approach to the right topic at the right time. The “ICF Brand” is now recognised around the world as one of the leading international societies in the broad field of structural integrity, fracture, fatigue, creep, corrosion and reliability – from biological to geophysical materials, from nano to macro scales, from basic science to practical engineering and technology and systems modelling. In this paper we trace the history of the development of fracture research and of ICF via the many threads of, for example, the E24/E9 committees of ASTM; the US Committee on Ship Steel linked to work on the Liberty Ships in the Engineering Laboratories, Cambridge, England; early work in Germany, France and Japan – culminating in the MIT Swampscott Fracture Conference of 1959 (“ICF0”), the pre-cursor to ICF1 in Sendai in 1965. We then examine the impact of the ICF quadrennial series of international fracture conferences from ICF1 through to ICF12 in Ottawa, Canada in 2009. The key is the original research presented in some 5000 scientific papers and to be made available online on the new ICF website (www.icf-wasi.org). Finally we examine the evolution of ICF since 2009 towards ICF13 in Beijing, China in 2013 (www.ICF13.org) and forward for the next decade and beyond.

The concept of EBSD (Electron Back Scattering Diffraction) strain analysis was proposed and applied to investigate the parameter for accumulated permanent strain during creep or creep-fatigue damage process. The EBSD strain analysis was based on the dislocation theory with a simplified model of estimating dislocation density within the EBSD unit pixel and dislocation mobile distance. EBSD analyses were conducted on experimentally creep and creep-fatigue damaged austenitic SUS304HTB boiler tube steel and ferritic Mod.9Cr piping steel. Creep damage was imposed under 650°C, 130 and 100 MPa stress, and creep-fatigue damage was imposed by an electric hydraulic servo testing machine with induction heater under the condition of 650°C, 1% strain range and 10 min tensile strain hold. The longitudinal mid-section of specimen was observed by EBSD equipment with IPF (Inverse Pole Figure) maps, KAM maps, GAM (Grain Average Misorientation) maps and GOS (Grain Orientation Spread) maps. Apparent reduction of misorientation and growth of block size was observed for damaged Mod.9Cr steel, while increase of misorientation was observed for SUS304HTB steel. Among EBSD strain parameters M_ε,ΔKAMave, M_ε,ΔGAMave and M_ε,GOSave, those two contradictory trends were turned to the almost similar linear correlations with accumulated permanent strain both for creep and creep-fatigue by M_ε,GOSave.

High Cr ferritic heat resistant steels are used for boiler components in ultra-super critical thermal power plants. In weld components of these steels, Type-IV creep damages formed in the fine-grained heat-affected zone (HAZ), causing their creep strength to decrease at high temperatures. To assist the standardization of the testing method for creep crack growth in weld components, we conducted round robin tests using ASME Grade 92 steel as part of the VAMAS TWA31 collaboration. The CCG tests were carried out using the CT specimen and the circumferentially notched round bar specimen for both the base metal and weld joint of Gr. 92 steel. The effects of specimen configuration, temperature, load and stress triaxiality conditions on the crack initiation and growth properties were investigated.

This paper presents the notch effect in low cycle fatigue of Mod.9Cr-1Mo steel under multiaxial loading. Tension–torsion multiaxial low cycle fatigue tests were performed using three types of circumferential notched specimens of the steel and crack initiation, failure and propagation lives were experimentally obtained. Two proportional and nine nonproportional strain waveforms were used in low cycle fatigue tests. The superposition of torsion loading on tension loading reduced the three lives but they little decreased with elastic stress concentration factor. The three lives in nonproportional loading were smaller than those in proportional loading but showed smaller reduction with elastic stress concentration factor. Local strains at the notch root were estimated by finite element analyses and Neuber's rule. Mises strain range and maximum principal strain range conservatively estimated the crack initiation lives of the notched specimens.

The Ni-base superalloy IN738LC developed as a heat-resistant material has excellent high temperature strength, but at the same time it has a brittle property. As a result, any evidence of creep degradation such as deformation of components or initiation of creep voids has hardly made an appearance by the end of its available creep life.

This paper investigates the possibility that creep damage can be evaluated by using the electron backscatter diffraction (EBSD) method to analyze misorientation which is considered to be caused by creep strain. The use of an in-situ observational testing machine with a notched specimen allowed creep-EBSD round tests which consisted of creep tests in the in-situ observational testing machine and EBSD observations using scanning electron microscopy (SEM) alternately against an identical specimen.

The outcome of these experiments was that crystal orientation change tendencies corresponding to the creep strain were continuously observed. It has been found that there was a good correlation between the creep strains and the misorientations referenced to the average orientation in the grain, the parameter of Grain Reference Orientation Deviation (GROD) defined by TSL EBSD system. Consequently, this study shows that the creep damage could be estimated by analyzing misorientations using the EBSD system automatically. Also, it has been found that crystal orientation changes appeared around notches in the direction of maximum shearing stress, which implies that the misorientation development was caused by the crystallographic lattice rotation.

In the Joule heat welding of two metallic wires, the melting phenomenon at the nanocontact between the wires is very important. If the current supply is insufficient, the nanocontact does not melt and the phenomenon is similar to the crack problem in linear elastic fracture mechanics where a crack does not propagate if the applied force is too low. From the seeming analogy between the melting phenomenon and the crack problem, a parameter which governs the melting phenomenon at the nanocontact is considered.

Evaluation of cracks in the ceramic coatings is very important to insure the reliability of the coating itself and the coated materials, parts and whole systems. Laser acoustic emission (AE) method was applied to enable a non-contact and in-situ monitoring of cracks in the ceramic coating immediately after plasma spraying. In this study, originally developed Continuous Wave Memory (CWM) was used as an AE measurement system to enable the continuous waveform recording during plasma spraying process. AE signals due to cracks could be successfully distinguished from large noise components such as mechanical vibration and laser scattering during the process. The AE events during plasma spraying revealed correlation with the dynamic temperature fluctuation on the surface of the specimen which was generated by the scanning of the plasma torch. Furthermore, the larger temperature fluctuation brought higher active AE signals.

This paper deals with the fatigue strength of a paper-based friction material under the cyclic shear–compressive loading which is regarded as a real loading condition in an automotive automatic transmission. The paper-based friction material are composed of aramid fibers and phenolic resin. Static fracture and fatigue tests are carried out under various shear and compressive stress conditions. The S–N curves of the paper-based friction material under shear–compressive stresses are described by straight lines in a log–log diagram. The static fracture strength and fatigue strength are higher when the compressive stress is more dominant. The pure compressive cyclic deformation tests are also carried out to explain the fatigue strength of the paper-based friction material under compressive-dominant stress condition. From the tests, it is made clear that with increasing compressive stress, the friction materials becomes dense and the Young's modulus or slope of cyclic stress–strain relation becomes high, and as a result the strain range of the cyclic stress–strain relation remains as constant low value. Therefore, it is considered that the fatigue strength of the paper-based friction material is remarkably high under the compressive-dominant stress condition.

Drug-eluting stent (DES) is tiny wire mesh tubes coated with drug used to open narrowed and diseased coronary arteries. DES releases drug slowly to prevent scar tissue growth in the artery, which causes in-stent restenosis. However, clinical problems remain such as stent fractures and polymer coating detachment. During the balloon catheter expansion, DES has to undergo the plastic deformation. Moreover, after implantation, stent has to undergo the load given by the heart pulse. In this study, fatigue behavior of stent is investigated and morphologies of polymer coating in relation to stent expansion and cyclic strain were observed using scanning electron microscope (SEM) to assess the reliability of DES. Fatigue test of stent indicated that there were no significant differences in fatigue behavior between DES and bare-metal stent (BMS). From the SEM appearance, two kinds of irregularities caused by expansion process were observed in the coating of DES, that is, crack and delamination. Additionally, no significant increase of irregularities was found in the coating of DES after fatigue test.

A new sensor called “smart stress-memory patch” which can measure the stress amplitude and the number of fatigue cycles and the maximum stress related to a structure subjected to fatigue loading for efficient structural health monitoring has been proposed. However, there are two problems in the real applications of smart patch. Firstly, when the sensor is adhered to the structure, the sensing property of smart patch may change because the restrained condition of the sensor would be intricately changed. Secondly, high-precision crack measurement of smart patch by optical microscope is too cumbersome in the real field. In this study, thin electrodeposited (ED) Cu specimen was prepared and attached to steel bar as a sensor of smart patch. The fatigue test was performed to examine the fatigue crack growth of the sensor attached to the structure. Furthermore, wireless devices using low power wireless modules have been developed for efficient crack measurements, and wireless devices results give close agreement with the results by microscope.

The problems of diffusion in solid are widely treated as those of numerical analyses such as mechanisms of hydrogen diffusion which causes embrittlement, boundary micro crack initiation and growth under high temperature creep condition and stress and electro-migration due to vacancy diffusion in LSI circuit. In this paper, the significance of α multiplication method which we proposed to analyze the particle diffusion problems under potential gradient and the results obtained from this method were discussed for the problems of hydrogen embrittlement, vacancy diffusion which results in creep crack damage and deformation, and line failure in LSI circuit. Furthermore, temperature characteristic of the sensitivity of particle diffusion and concentration such as hydrogen and vacancy were discussed based on this proposed analysis.