Papers by Keyword: Rolling Wagon

Abstract: Fatigue S-N relations are investigated experimentally on the grade B cast steel for Chinese railway freight car bogie frames. Group test method was employed. Results reveal that the fatigue cracks were initiated from the material cast shrinking cavities with hot ties. Distinct fatigue striations, river-like flowers, and second cracks appeared on the fracture surface in perpendicular to the fatigue crack path. Lots of dimples in the transient fracture district indicate that present material is ductile. Considering both the scattered S-N relations and no fatigue limits under variable loads, the S-N relations are measured probabilistically in terms of continuous declined probabilistic S-N curves including super-long life regime (SLLR) of >107 cycles. Affordable novel approach, i.e. concurrent probability extrapolation method, was applied. The test S-N data in mid-long life regime (MLLR) and conventional fatigue limits are used. The curves are established by extrapolating the conventional S-N curves crossing the fatigue limits, in a concurrent probability manner, into the SLLR. Appropriate measurements have been given for the test data of the present material.

Abstract: Fatigue limit measurement is investigated experimentally on the grade B cast steel for Chinese railway freight car bogie frames. Small sample up-and-down test method was employed for the present study. Results reveal that fatigue cracks initiated mostly from the material cast shrinking cavities. Distinct river-like flowers and second cracks appeared on fracture surface in perpendicular to fatigue crack path. Lots of dimples are distributed in transient fracture district to indicate that present material is ductile. Maximum likelihood approach is applied for measuring the probabilistic fatigue limits, in which the limits are defined as the fatigue strengths following normal distribution at an expected fatigue life. Statistical parameters are then estimated by a likelihood function method. A comparison analysis to the existent conventional, Dixon-Mood and Zhang-Kececioglu approaches indicates that the maximum likelihood approach is the approach meeting the definition.

Abstract: Measurement on fatigue cracking thresholds is investigated to the grade B cast steel for China railway rolling wagon bogie frames. Compact tensional specimens are fatigued under a continuous decreasing loading mode for present study. Results reveal that the minimum test values have different crack growth rates without meeting the code-based rate requirement. Therefore, the test results can not be directly used for measuring the thresholds. A probabilistic modeling in the form of a non-linear law is developed for reflecting the scattered test data. The thresholds at specified reliability levels are then derived in meeting the threshold definition with a specified growth rate. The measurement for the present material has verified the availability of the present modeling.

Abstract: Compact tensional specimens are fatigued for modeling the fatigue crack growth rates of the cast steel for Chinese railway rolling wagon bogie frames. Typical fracture surface observations indicate that the fatigue cracks grew with distinct fatigue striations, river-like flowers, and second cracks in perpendicular to the fatigue crack path. Lots of dimples appeared in the transient fracture district to indicate that present material is ductile. Similar to the previous NASGRO’s exploration, a full modeling is proposed from fatigue cracking threshold to the transient fracture corresponding to the material fracture roughness. Availability has been verified to be applied for the present material. In addition, this modeling is very simple that the modeling can be performed by the conventional tests of fatigue cracking thresholds, growth rates, and fracture roughness values.

Abstract: Measurement on fracture roughness values is investigated to the grade B cast steel for China railway rolling wagon bogie frames. Due to be limited by production bogie frame geometry, a ductile fracture roughness measuring method is employed for the present study. Experiments reveal that, when crack growth increments are very scattered, the code based measurement of 0.2 mm crack growth increment for gauge ductile fracture roughness may be not reasonable. And a measurement of 90 % maximum ductile fracture roughness should be suggested to be an appropriate measurement. The new suggested 90 % maximum fracture roughness measurement is verified to be effective for the fracture roughness values of the present material.

Abstract: Cyclic deformation characters and description method are investigated to the grade B cast steel for Chinese railway rolling wagon bogie frames. Incremental step test method with 8 strain amplitude loading mode were employed. Results reveal that the material acts as non-Masing behaviour with a significant Bausinger’s effect and appears a slight cyclic softening. Great of dimples in the transient fracture district indicate that present material is ductile. Significant discrepancy between the monotonic and cyclic beaviour was revealed to indicate that there is different monotonic and cyclic deformation behaviour. The scattered cyclic stress-strain relations indicate that appropriate description for the cyclic deformation of present material should be a probabilistic modeling. And then, a probabilistic modeling with measurements of survival probability and confidence is developed to give a good description to the cyclic deformation behaviour.

Abstract: Scale-induced effect is investigated on the fatigue properties to the grade B cast steel for China railway rolling wagon bogie frame. Three kinds of structure-like specimens with production structural surfaces and different scales were fatigued in a manner of group tests at same stressing amplitude. Their fatigue properties are compared with those of material specimens. Fracture surface observations reveal that the fatigue cracks were initiated from the material casting shrinking cavities with/or hot ties. Distinct fatigue striations, river-like flowers, and second cracks appeared in perpendicular to the fatigue crack path. Lots of dimples appeared in the transient fracture zone to indicate a ductile fracture. Slight deference was observed that more dimples are for material specimen. To consider the scattered fatigue properties, effective sectional area-fatigue life relations are established for the structure-like specimens. And then, a probabilistic model is established for the scattered effect factors on fatigue lives. An effective application is given for constructing structural probabilistic S-N relations including super-long life regime from material S-N curves.