•Flaking life from 15-μm-diameter defects decreased with increasing defect length.•SR micro CT imaging detected vertical and horizontal cracks with defects.•FEA simulated a higher stress intensity ...factor of vertical crack with longer defects.•FEA results implied the mechanism of the above experimental results.•Flaking life from 50-μm-diameter defects was constant regardless of defect lengths.
The objective of the present paper is to clarify the effect of shapes of circular hole defects, orientated perpendicular to the surface, on rolling contact fatigue (RCF) crack initiation and propagation in high strength steel. RCF test and synchrotron radiation micro computed tomography (SR micro CT) imaging were conducted. In the case of a 15-μm-diameter defect, the number of cycles of rolling contact to flaking occurring (flaking life) decreased with increasing defect length. In a comparison of the CT image and the SEM view, the shapes of defects and the locations of the horizontal cracks were almost the same respectively. The mechanism of RCF crack propagation was discussed by finite element (FE) analysis. Defects led to higher tensile residual stress than that without defects in the region where the defect exists. The shear stress range at 0.1mm in depth on the middle line of the defect and the range of mode II stress intensity factor at the bottom of a vertical crack increased with increasing defect length. In the case of a defect 50μm in diameter, defect length does not affect flaking life. The reason for this is probably that the horizontal cracks form and propagate before vertical cracks grow to an effective size.
•Synchrotron radiation micro-computed tomography imaging detects rolling contact fatigue cracks.•Detected cracks are composed of vertical and horizontal cracks originating from artificial ...defects.•Finite element analyses simulating the above observation results are conducted.•The possibility of mode II and III propagation of vertical and horizontal cracks is revealed.•Interaction between vertical and horizontal cracks plays key role in the propagation of cracks.
The objectives of the present paper are to clarify the rolling contact fatigue (RCF) crack path in high strength steel with artificial defects using synchrotron radiation micro-computed tomography (SR micro CT) imaging and to discuss the mechanism of RCF crack propagation by finite element (FE) analysis. Two crack types, a vertical crack and a horizontal crack, were observed around the artificial defect by SR micro CT. The stress intensity factor (SIF) of horizontal cracks, calculated by FE analysis, increased by the existence of vertical cracks. The interaction between these two crack types dominates RCF crack propagation originating from artificial defects.
•A laminography technique using ultra-bright synchrotron radiation (SRCL) was developed for steels.•Formation and propagation of rolling contact fatigue (RCF) tests were observed by SRCL.•Effects of ...inclusion size and orientation on the RCF life were clarified.•New mechanism for flaking process in RCF was proposed.
Since rolling contact fatigue (RCF) is known to be affected by non-metallic inclusions, the RCF crack initiation and propagation mechanisms in high-strength steels were observed using ultrabright synchrotron radiation laminography. The material of the sample was a high-carbon chromium bearing steel, which intentionally contained a high concentration of sulfur to enable the observation of crack initiation from MnS inclusions. To conduct an RCF test nearby the experimental hatch of a beam line of a synchrotron radiation facility, a special RCF testing machine was developed. Fatigue tests were interrupted to conduct laminography. The fatigue life for flaking depended on the length, width, and orientation of inclusions. For every length and orientation of inclusions, vertical cracks, whose faces were perpendicular to the rolling direction, first appeared, then horizontal cracks, whose faces were parallel to the sample surface, were formed after the vertical cracks reached a critical length. The initiation life of the vertical cracks and horizontal cracks depended on the length, width, and orientation of the MnS inclusions. The depth of horizontal crack initiation site, however, was almost independent of these parameters. The mechanism of the flaking process, which was directly observed by laminography using synchrotron radiation, was completely different from that previously supposed from observations by conventional microscopy.
The objective of the present paper is to clarify the effect of defect length in depth direction on rolling contact fatigue (RCF) crack propagation in high strength steel. RCF test and synchrotron ...radiation micro computed tomography (SR micro CT) imaging were conducted. In the case of the defect with the 15 ?m diameter, flaking life decreased with increasing defect length. In a comparison of the CT image and the SEM view, the shapes of defects and the locations of the horizontal cracks were almost the same respectively. The mechanism of RCF crack propagation was discussed by finite element (FE) analysis. Defects led to higher tensile residual stress than that without defects in the region where the defect exists. The shear stress range at 0.1 mm in depth on the middle line of the defect and the range of mode II stress intensity factor at the bottom of a vertical crack increased with increasing defect length.
The rolling contact fatigue (RCF) tests were performed on a high-strength steel by a newly developed compact rolling contact fatigue test machine, and the formation and propagation of cracks were ...observed by the synchrotron radiation computed laminography (SRCL). An increase in the sulfur concentration, i.e., increase in inclusion length, resulted in an increase in the variation of flaking life, and materials with horizontal inclusion showed large variation compared to those with vertical inclusion although average flaking lives are almost identical. In the flaking process, cracks, those were perpendicular to the rolling surface and rolling direction, first formed from an inclusion that was adjacent to the rolling surface. Then, the crack propagated in the depth direction. After the vertical crack propagated to a critical depth, a horizontal crack formed, whose face was parallel to the rolling surface. Finally, the horizontal crack propagated to form flaking.
In the resting conditions, narrowing the window of coronary pressure measurements from the whole cardiac cycle to diastole improves diagnostic performance of coronary pressure–derived physiological ...index. However, whether this also applies to the hyperemic conditions has not yet been thoroughly evaluated.
The purpose of this study was to assess whether diastolic fractional flow reserve (diastolic FFR) has better diagnostic performance in identifying ischemia-causing coronary lesions than conventional FFR in a prospective, multicenter, and independent core laboratory–based environment.
In this prospective multicenter registry at 29 Japanese centers, we compared the diagnostic performance of FFR, diastolic FFR, resting distal to aortic coronary pressure (Pd/Pa), and diastolic pressure ratio (dPR) using myocardial perfusion scintigraphy (MPS) as the reference standard in 378 patients with single-vessel coronary disease.
Inducible myocardial ischemia was found on MPS in the relevant myocardial territory of the target vessel in 85 patients (22%). In the receiver-operating curve analyses, diastolic FFR had comparable area under the curve (AUC) compared with FFR (AUCdiastolic FFR: 0.66; 95% confidence interval CI: 0.58-0.73, vs AUCFFR: 0.66; 95% CI: 0.58-0.74, P = 0.624). FFR and diastolic FFR showed significantly larger AUCs than resting Pd/Pa (0.62; 95% CI: 0.54-0.70; P = 0.033 and P = 0.046) but did not show significantly larger AUCs than dPR (0.62; 95% CI: 0.55-0.70; P = 0.102 and P = 0.113).
Diastolic FFR showed a similar diagnostic performance to FFR as compared with MPS. This result reaffirms the use of FFR as the most accurate invasive physiological lesion assessment. (Diagnostic accuracy of diastolic fractional flow reserve (d-FFR) for functional evaluation of coronary stenosis; UMIN000015906)
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Abstract
Background
In patients with stable angina pectoris (SAP), exact mechanism of plaque progression overtime is still unclear due to lack of histological evaluation. Directional coronary ...atherectomy (DCA) allows for the differential cutting of atherosclerotic lesions and for the histological examination.
Purpose
The aims of this study were to compare the histological features obtained by DCA and layered pattern (LP) by OCT, and to establish the prevalence and clinical characteristics of LP in culprit lesion form SAP patients.
Methods
SAP patients who underwent OCT imaging guide PCI in our medical school hospital between June 2016 and June 2018 were included into this study. This was two-fold histological and clinical studies. In a histological study, we evaluated histological features of 42 specimens from 18 patients who underwent DCA and compare OCT findings. Lesions were classified into the following categories based on the OCT finding before DCA cutting; homogeneous or heterogeneous group. Furthermore, lesions in heterogeneous group were classified into 2 categories; LP or non-LP group. In a clinical study, 205 target lesions form 205 patients were categorized as shown above at minimum lumen area (MLA) sites. Plaque characteristics were compared among these groups.
Results
In the histological study, 9 (21.4%) specimens were classified in homogeneous group and 33 (78.6%) in heterogeneous group. In 33 heterogeneous group, LP group were observed in 12 specimens (36.3%). Of 12 LP group, 10 LP group consisted of intramural thrombosis. In clinical study, 39 (19.0%) lesion were classified in homogeneous group and 166 (81.0%) in heterogeneous group. In 166 heterogeneous group, LP group were observed in 75 lesions (45.2%). Of heterogeneous group, LP group had significantly smaller MLA (1.5±0.9 mm2 vs 1.9±1.0 mm2, p<0.05) and higher rate of microchannels (57.3% vs 15.4%, p<0.05) than non-LP group.
A representative layered pattern case
Conclusions
LP in culprit lesion with SAP was significantly associated with intramural thrombosis. MLA sites in LP was significantly smaller than in non-LP group. These data suggest that thrombus formation and subsequent their organization overtime might contribute to the plaque progression even in SAP patients.
The purpose of this study was to analyze the ability of optical coherence tomography (OCT) to identify coronary arterial plaque diagnosed by histologic examination. We examined 166 sections from 108 ...coronary arterial segments of 40 consecutive human cadavers (24 men and 16 women; mean age 74 ± 7 years). The plaque type was classified as fibrous (n = 43), fibrocalcific (n = 82), or lipid-rich (n = 41). The accuracy of OCT and intravascular ultrasound (IVUS) in characterizing the plaque type was studied, with the histologic consensus diagnosis serving as the gold standard. OCT, as well as IVUS, had high sensitivity and specificity for characterizing the different types of atherosclerotic plaque. OCT had a higher sensitivity for characterizing lipid-rich plaques than IVUS (85% vs 59%, p = 0.03). In conclusion, the high resolution of OCT permitted evaluation of lipid-rich plaques more accurately than IVUS.
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