Papers by Author: Guo Xiang Song

Abstract: Fracture surface observations and statistical deriving are applied for the present investigation on the random fatigue crack growth rates of China grade B cast steel wheel. Results reveal that: the crack grows with relative regular initial tip companied fabric like stripes along the growth direction but few of fatigue striations, and then, cleavage flowers appearing on the district of transient fracture with few of dimples. It indicates that sharp notched structural crack behaviour acts as a few of plastic dissipation process. Non-linear statistical modeling covering entire three pieces of fatigue crack growth is constructed for describing the random crack growth rates. Scattered randomness of the growth rates has been well characterized.

Abstract: Fracture surface observations and statistical deriving are applied for investigating the random critical fracture toughness values of China grade B cast steel wheel. Results reveal that: the crack grows to show fabric like stripes along the growth direction with few of dimples. Cleavage flowers appear under higher magnification. Cracked structural damage process is verified with few of plastic dissipation. At the same time, code based evaluated results indicate that significant scatter exists for the toughness values. Lognormal modeling is constructed appropriately with a comprehensive statistical comparison method. It is verified that random characters and quantitative measurements have been well depicted for the present critical fracture toughness values.

Abstract: Fracture surface observations and statistical deriving are applied experimentally for the present investigation on random fatigue cracking thresholds of China grade B cast steel wheel. Results reveal that: the crack grows with relative regular initial tip companied fabric like stripes along the growth direction but few of fatigue striations and then, cleavage flowers appearing on the district of transient fracture with few of dimples. This indicates that sharp notched structures may be subjected to a little plastic dissipation process. In the same time, non-linear statistical modeling is constructed for describing the random crack growth and then, random fatigue cracking thresholds are measured at specified growth rate. The measurements hold a same growth rate which can not be obtained directly from test results.

Abstract: Cyclic deformation behaviour is experimentally investigated using an incremental step method under a spectrum straining block loading mode for China grade B cast steel wheel. Results reveal that the material acts cyclically as non-Masing behaviour with a Bausinger effect. Different from monotonic tensile situation, material under fatigue loads was subjected to a plastic dissipation process without a yielding sign. Fatigued areas of specimen fracture surfaces are around 35%. Cyclic stress-strain (CSS) curve exhibits constant lower than monotonic tensile curve. Difference is enlarged as strain level increasing in elastic regime of the monotonic deformation. And this difference sustains a level of around 100 MPa as over yielding point. In addition, randomness is also observed for the present cyclic deformations. It indicates that random CSS relations should be comprehensively applied even if under stress based fatigue analysis.

Abstract: Random mechanical properties are experimentally studied on China grade B cast steel wheel. Significant dimples and fabric-like tearing signs were observed firstly and then, lotus flower-like cleavage fracture faces were appeared to indicate the material subjected to a plastic dissipation process under monotonic load. Randomness appears in the deformation process companied with a similarity in total and significant differences in local. Appropriate statistical description is explored with a comprehensive statistical comparison method. Lognormal distribution is excavated out by comparison from seven possible statistical models. Random characters and quantitative measurements have been given for the mechanical properties of China grade B cast steel wheel.

Abstract: Chemical composition and physical properties are measured and inspected for China railway grade B cast steel wheel. The wheel shows slight higher for chemical elements C and Cr, much higher for Al and Mo, and significant lower for P and S comparing to the AAR code. Gross pearlites plus net-like continuum ferrites appear in wheel hub; ferrites exhibit also net-likely but dis-continuously in web with a shot peening effect; and in rim, dis-continuous ferrites with few of net-like signs distribute randomly due to a quenching and tempering effect. Bigger hardness values appear in rim; and the values in web and hub appear a decrease in sequence. Major flaw affecting material condense is shrinkage porosities. Flawed content is closely between hub and web. More condense appears in rim. Material inclusions are non-metallic compounds of MnS and Al2O3. They appear sphere-like shapes having around 8 μm diameters.

Abstract: Critical safety wheel wear size is investigated through considering the fatigue safety effect on RD2 type axle of China railway freight cars. The wheel wear size increase results in a rise of the wheel-rail contact forces, which increase the fatigue stress history of the axle in service. Therefore, the size must be controlled to maintain the axle safety in service before the next overhaul inspection. A field investigation was firstly made on the wear size change regularity. Then, the size related wheel-rail impact forces are solved by a non-linear Hertzian contact theory with a vehicle multi-body dynamic model. In addition, a statistical method is further developed for incorporating the impact forces into the wheelset service load history. Finally, a wear size related critical state equation is established for ensuring the axle safety in service. A stationary solution is statistically obtained for the critical wear sizes with respect to the axle circumferential crack and semi-elliptical crack. It is concluded that the critical safety wear size should be controlled in the range of 100 mm at the statistical level of survival probability 0.99 and confidence 95%.

Abstract: Critical fatigue safety state is investigated on RD2 type axle of China railway freight cars. Attention is paid on the grooves near axle boxes, where more fatigue cracks were early appeared even result in at least six derailed accidents. Load history was obtained by vehicle dynamics simulation combining with on-line inspection. Braking loads and effects of maintenance and off-round of wheels are also incorporated. Semi-elliptical and external circumferential cracks are employed for crack growth simulation. Crack shape change and shear stressing of the semi-elliptical crack are taken into account. New crack growth rate modeling in which covers from cracking threshold to toughness related fracture state is applied for residual life evaluation. Critical fatigue safety state is defined as the crack size from which the axle can be safely operated to next overhaul inspection. Critical crack size is estimated step-by-step with the crack shape change. Results show that the external circumferential crack is more dangerous than the semi-elliptical crack. Application more than two years in production verifies that the present assessment is available and reliable.