The tool point frequency response function(FRF) is commonly obtained by impacting test or semi-analytical techniques.Regardless of the approach,it is assumed that the workpiece system is rigid.The assumption is valid ...The tool point frequency response function(FRF) is commonly obtained by impacting test or semi-analytical techniques.Regardless of the approach,it is assumed that the workpiece system is rigid.The assumption is valid in common machining,but it doesn’t work well in the cutting processes of thin-wall products.In order to solve the problem,a multi-degree-of-freedom dynamic model is employed to obtain the relative dynamic stiffness between the cutting tool and the workpiece system.The relative direct and cross FRFs between the cutting tool and workpiece system are achieved by relative excitation experiment,and compared with the tool point FRFs at x and y axial direction.The comparison results indicate that the relative excitation method could be used to obtain the relative dynamic compliance of machine-tool-workpiece system more actually and precisely.Based on the more precise relative FRFs,four evaluation criterions of dynamic stiffness are proposed,and the variation trend curves of these criterions during the last six months are achieved and analyzed.The analysis results show that the lowest natural frequency,the maximum and the average dynamic compliances at x axial direction deteriorate more quickly than that at y axial direction.Therefore,the main cutting direction and the large-size direction of workpieces should be arranged at y axial direction to slow down the deterioration of the dynamic stiffness of machining centers.The compliance of workpiece system is considered,which can help master the deterioration rules of the dynamic stiffness of machining centers,and enhance the reliability of machine centers and the consistency of machining processes.展开更多
The existing studies have primarily focused on the effect of cyclic load characteristics(namely,cyclic load ratio and amplitude ratio)on cyclic lateral response of monopiles in sand,with little attention paid to the e...The existing studies have primarily focused on the effect of cyclic load characteristics(namely,cyclic load ratio and amplitude ratio)on cyclic lateral response of monopiles in sand,with little attention paid to the effect of pile−soil relative stiffness(K_(R)).This paper presents a series of 1-g cyclic tests aimed at improving understanding of the cyclic lateral responses of monopiles under different pile−soil systems.These systems are arranged by two model piles with different stiffness,including four different slenderness ratios(pile embedded length,L,normalized by diameter,D)under medium dense sand.The K_(R)-values are calculated by a previously proposed method considering the real soil stress level.The test results show that the lateral accumulation displacement increases significantly with the increment of the K_(R)-value,while the cyclic secant stiffness performs inversely.The maximum pile bending moment increases with the cycle number for the rigid pile−soil system,but shows a decreasing trend in the flexible system.For an uppermost concern,an empirical model is proposed to predict the accumulated displacement of arbitrary pile−soil systems by combining the results from this study with those from previous experimental investigations.The validity of the proposed model is demonstrated by 1-g and centrifuge tests.展开更多
The study on property degradation of damaged composite laminates is extendedto anisotropic laminates with matrix cracking. In (I) of the paper, an idea of 'stiffnesspatition' is proposed to deal with the puzz...The study on property degradation of damaged composite laminates is extendedto anisotropic laminates with matrix cracking. In (I) of the paper, an idea of 'stiffnesspatition' is proposed to deal with the puzzle that the in-plane normal response iscoupled with the shear response of the laminates. For (θm/90n.), laminates containingtransversely cracked layers under general in-plane loading, the constitutive relationsare derived and the effective stiffnesses are expressed as the function of crack density.展开更多
The description in the abstract lacks clear logic and a comprehensive summary of this study, so please revise and improve it according to the design theme and main content of this study, and describe it in the order o...The description in the abstract lacks clear logic and a comprehensive summary of this study, so please revise and improve it according to the design theme and main content of this study, and describe it in the order of (research background), purpose/aim, method, results and conclusions. The introduction of the abstract and preface is rather lengthy, but the summary of the whole study and the presentation of the research background are not perfect (mainly because the logic of the context is not clear and orderly), so it will appear a bit messy. Hope to be able to modify (this has been mentioned in the preliminary opinion). Cardiovascular events (CVE) pose a significant threat to individuals with end-stage renal disease (ESRD), yet these patients are often excluded from cardiovascular clinical trials, leaving prognostic factors associated with CVE in ESRD patients largely unexplored. Recent human studies have demonstrated elevated circulating aldosterone levels in ESRD patients, correlating with left ventricular hypertrophy. Additionally, animal models have shown improvements in uremic cardiomyopathy with spironolactone therapy, prompting interest in assessing the efficacy of spironolactone or eplerenone in reducing mortality and improving cardiovascular function in dialysis patients. Clinicians have historically been cautious about prescribing mineralocorticoid receptor antagonists (MRAs) to congestive heart failure patients with chronic kidney disease (CKD) due to hyperkalemia risk. However, the emergence of finerenone, a novel MR antagonist with a favorable safety profile and lower hyperkalemia risk, has renewed interest in MRA therapy in this population. Heart disease, including coronary artery disease, hypertension, and left ventricular failure, is alarmingly prevalent in dialysis patients, contributing significantly to elevated mortality rates compared to the general population. Arterial stiffness, as indicated by pulse wave velocity (PWV), progressively worsens with advancing CKD stages, peaking in severity among ESRD patients undergoing dialysis. High PWV serves as a crucial risk stratification tool in ESRD. Elevated NT-proBNP and BNP levels in ESRD patients are well-documented, with significant associations observed between baseline peptide concentrations and cardiovascular morbidity and mortality. By incorporating finerenone into our study, we aim to investigate its potential benefits in reducing arterial stiffness, lowering blood pressure, and ultimately mitigating heart-related mortality among hemodialysis patients. This study holds substantial implications for hypertension and cardiovascular risk management in this vulnerable patient population. Eligible participants must have been on chronic hemodialysis for at least three months, with ACE inhibitors or angiotensin receptor blockers included in their therapy at maximum tolerable doses. Serum potassium levels 5.7 mmol/L, left ventricular ejection fraction 50%, and PWV higher than age-estimated values are also prerequisites for study entry. Randomized allocation will be conducted using a permuted block design, stratified by center, with allocation communicated via signed study forms during initial examinations. All steps of this research will be conducted in accordance with the principles of the Helsinki Declaration.展开更多
Curved-beams can be used to design modular multistable metamaterials(MMMs)with reprogrammable material properties,i.e.,programmable curved-beam periodic structure(PCBPS),which is promising for controlling the elastic ...Curved-beams can be used to design modular multistable metamaterials(MMMs)with reprogrammable material properties,i.e.,programmable curved-beam periodic structure(PCBPS),which is promising for controlling the elastic wave propagation.The PCBPS is theoretically equivalent to a spring-oscillator system to investigate the mechanism of bandgap,analyze the wave propagation mechanisms,and further form its geometrical and physical criteria for tuning the elastic wave propagation.With the equivalent model,we calculate the analytical solutions of the dispersion relations to demonstrate its adjustability,and investigate the wave propagation characteristics through the PCBPS.To validate the equivalent system,the finite element method(FEM)is employed.It is revealed that the bandgaps of the PCBPS can be turned on-and-off and shifted by varying its physical and geometrical characteristics.The findings are highly promising for advancing the practical application of periodic structures in wave insulation and propagation control.展开更多
基金supported by National Natural Science Foundation of China(Grant No.51175208)National Key Basic Research Program of China(973 ProgramGrant No.2011CB706803)
文摘The tool point frequency response function(FRF) is commonly obtained by impacting test or semi-analytical techniques.Regardless of the approach,it is assumed that the workpiece system is rigid.The assumption is valid in common machining,but it doesn’t work well in the cutting processes of thin-wall products.In order to solve the problem,a multi-degree-of-freedom dynamic model is employed to obtain the relative dynamic stiffness between the cutting tool and the workpiece system.The relative direct and cross FRFs between the cutting tool and workpiece system are achieved by relative excitation experiment,and compared with the tool point FRFs at x and y axial direction.The comparison results indicate that the relative excitation method could be used to obtain the relative dynamic compliance of machine-tool-workpiece system more actually and precisely.Based on the more precise relative FRFs,four evaluation criterions of dynamic stiffness are proposed,and the variation trend curves of these criterions during the last six months are achieved and analyzed.The analysis results show that the lowest natural frequency,the maximum and the average dynamic compliances at x axial direction deteriorate more quickly than that at y axial direction.Therefore,the main cutting direction and the large-size direction of workpieces should be arranged at y axial direction to slow down the deterioration of the dynamic stiffness of machining centers.The compliance of workpiece system is considered,which can help master the deterioration rules of the dynamic stiffness of machining centers,and enhance the reliability of machine centers and the consistency of machining processes.
基金This work was financially supported by the National Natural Science Foundation of China(Grant Nos.51808112,51878160,and 52078128)the Natural Science Foundation of Jiangsu Province(Grant No.BK20180155).
文摘The existing studies have primarily focused on the effect of cyclic load characteristics(namely,cyclic load ratio and amplitude ratio)on cyclic lateral response of monopiles in sand,with little attention paid to the effect of pile−soil relative stiffness(K_(R)).This paper presents a series of 1-g cyclic tests aimed at improving understanding of the cyclic lateral responses of monopiles under different pile−soil systems.These systems are arranged by two model piles with different stiffness,including four different slenderness ratios(pile embedded length,L,normalized by diameter,D)under medium dense sand.The K_(R)-values are calculated by a previously proposed method considering the real soil stress level.The test results show that the lateral accumulation displacement increases significantly with the increment of the K_(R)-value,while the cyclic secant stiffness performs inversely.The maximum pile bending moment increases with the cycle number for the rigid pile−soil system,but shows a decreasing trend in the flexible system.For an uppermost concern,an empirical model is proposed to predict the accumulated displacement of arbitrary pile−soil systems by combining the results from this study with those from previous experimental investigations.The validity of the proposed model is demonstrated by 1-g and centrifuge tests.
文摘The study on property degradation of damaged composite laminates is extendedto anisotropic laminates with matrix cracking. In (I) of the paper, an idea of 'stiffnesspatition' is proposed to deal with the puzzle that the in-plane normal response iscoupled with the shear response of the laminates. For (θm/90n.), laminates containingtransversely cracked layers under general in-plane loading, the constitutive relationsare derived and the effective stiffnesses are expressed as the function of crack density.
文摘The description in the abstract lacks clear logic and a comprehensive summary of this study, so please revise and improve it according to the design theme and main content of this study, and describe it in the order of (research background), purpose/aim, method, results and conclusions. The introduction of the abstract and preface is rather lengthy, but the summary of the whole study and the presentation of the research background are not perfect (mainly because the logic of the context is not clear and orderly), so it will appear a bit messy. Hope to be able to modify (this has been mentioned in the preliminary opinion). Cardiovascular events (CVE) pose a significant threat to individuals with end-stage renal disease (ESRD), yet these patients are often excluded from cardiovascular clinical trials, leaving prognostic factors associated with CVE in ESRD patients largely unexplored. Recent human studies have demonstrated elevated circulating aldosterone levels in ESRD patients, correlating with left ventricular hypertrophy. Additionally, animal models have shown improvements in uremic cardiomyopathy with spironolactone therapy, prompting interest in assessing the efficacy of spironolactone or eplerenone in reducing mortality and improving cardiovascular function in dialysis patients. Clinicians have historically been cautious about prescribing mineralocorticoid receptor antagonists (MRAs) to congestive heart failure patients with chronic kidney disease (CKD) due to hyperkalemia risk. However, the emergence of finerenone, a novel MR antagonist with a favorable safety profile and lower hyperkalemia risk, has renewed interest in MRA therapy in this population. Heart disease, including coronary artery disease, hypertension, and left ventricular failure, is alarmingly prevalent in dialysis patients, contributing significantly to elevated mortality rates compared to the general population. Arterial stiffness, as indicated by pulse wave velocity (PWV), progressively worsens with advancing CKD stages, peaking in severity among ESRD patients undergoing dialysis. High PWV serves as a crucial risk stratification tool in ESRD. Elevated NT-proBNP and BNP levels in ESRD patients are well-documented, with significant associations observed between baseline peptide concentrations and cardiovascular morbidity and mortality. By incorporating finerenone into our study, we aim to investigate its potential benefits in reducing arterial stiffness, lowering blood pressure, and ultimately mitigating heart-related mortality among hemodialysis patients. This study holds substantial implications for hypertension and cardiovascular risk management in this vulnerable patient population. Eligible participants must have been on chronic hemodialysis for at least three months, with ACE inhibitors or angiotensin receptor blockers included in their therapy at maximum tolerable doses. Serum potassium levels 5.7 mmol/L, left ventricular ejection fraction 50%, and PWV higher than age-estimated values are also prerequisites for study entry. Randomized allocation will be conducted using a permuted block design, stratified by center, with allocation communicated via signed study forms during initial examinations. All steps of this research will be conducted in accordance with the principles of the Helsinki Declaration.
基金supported by the National Natural Science Foundation of China(Nos.12172012 and 11802005)。
文摘Curved-beams can be used to design modular multistable metamaterials(MMMs)with reprogrammable material properties,i.e.,programmable curved-beam periodic structure(PCBPS),which is promising for controlling the elastic wave propagation.The PCBPS is theoretically equivalent to a spring-oscillator system to investigate the mechanism of bandgap,analyze the wave propagation mechanisms,and further form its geometrical and physical criteria for tuning the elastic wave propagation.With the equivalent model,we calculate the analytical solutions of the dispersion relations to demonstrate its adjustability,and investigate the wave propagation characteristics through the PCBPS.To validate the equivalent system,the finite element method(FEM)is employed.It is revealed that the bandgaps of the PCBPS can be turned on-and-off and shifted by varying its physical and geometrical characteristics.The findings are highly promising for advancing the practical application of periodic structures in wave insulation and propagation control.
