Cracking Mechanism and Retrofit Design of Governing Stage Blades for a Steam Turbine

2008 ◽  
Vol 392-394 ◽  
pp. 967-974
Author(s):  
Z.L. Xu ◽  
S.N. He ◽  
Bo Shangguan
Keyword(s):  
High Cycle Fatigue ◽  
Natural Frequencies ◽  
Cycle Fatigue ◽  
Steam Turbines ◽  
Mode Shift ◽  
Assembly Tolerance ◽  
Right Reason ◽  
The Right ◽  
Retrofit Design ◽  
Electronic Microscope

Cracking of blade dovetails occurred in a governing stage of a 50MW steam turbines twice within 5 months. To find out the failure mechanism and measures to avoid the failure accident, one of the cracked blades has been inspected by the metallography and a scanning electronic microscope. The inspection results show that the cracking of the blade is caused by the high cycle fatigue. When governing stage blades are in operation, the vibration of blades can extend to platform or even to dovetail parts over radial supporting surfaces depending on temperature, centrifugal force and assembly tolerance. The calculated results by FEM show that not only natural frequencies of blades in operating are smaller than that in stationary but also the modal order shifts when the blade runs from stationary to operation states. The effect of mode shift on the failure was investigated. According to the conclusion, the blades have been retrofitted by increasing neck of dovetail to avoid dangerous resonance, and the blades have been operating in healthy condition for two years after the modification. Contrarily, if the phenomenon of mode shift were ignored, it would be difficult to find out the right reason of resonance and ways to retrofit the damaged blades.

Fracture Analysis and Retrofit Design of 1st Stage Blades for a Low-Pressure Steam Turbine

2003 ◽  
Author(s):  
Jong-Po Park ◽  
Zili Xu ◽  
Seok-Ju Ryu
Keyword(s):  
High Cycle Fatigue ◽  
Impact Test ◽  
Low Pressure ◽  
Cycle Fatigue ◽  
Steam Turbines ◽  
Fatigue Load ◽  
Pressure Steam ◽  
One Year ◽  
Fault Mechanism ◽  
Retrofit Design

Cracking of blade fingers occurred in a few numbers of 1st stage blades for low-pressure steam turbines. In order to find out the fault mechanism, one of the cracked blades has been inspected. The inspection results showed that the cracking blades has been inspected. The inspection results showed that the cracking of the blade finger was caused by high cycle fatigue. Vibratory modes of the blade group have been calculated and measured using a 3-D finite element S/W and impact test, respectively. The results showed that resonance of the second type group axial vibration mode with nozzle passing frequency was the source of high cycle fatigue load. To avoid the dangerous resonance, the blade groups have been modified into 10 blades per group. The new blade groups have been operated safely more than one year since the modification.

A Methodology for High Cycle Fatigue Characterization of Lead-Free Interconnects Under Simultaneous Harsh Environments of High Temperature and Vibration

2013 ◽  
Author(s):  
Pradeep Lall ◽  
Geeta Limaye
Keyword(s):  
High Temperature ◽  
High Speed ◽  
High Cycle Fatigue ◽  
Failure Modes ◽  
Elevated Temperatures ◽  
Natural Frequencies ◽  
Image Correlation ◽  
Lead Free ◽  
Cycle Fatigue ◽  
Increase With Increase

Current trends in the automotive industry warrant a variety of electronics for improved control, safety, efficiency and entertainment. Many of these electronic systems like engine control units, variable valve sensor, crankshaft-camshaft sensors are located under-hood. Electronics installed in under-hood applications are subjected simultaneously to mechanical vibrations and thermal loads. Typical failure modes caused by vibration induced high cycle fatigue include solder fatigue, copper trace or lead fracture. The solder interconnects accrue damage much faster when vibrated at elevated temperatures. Industry migration to lead-free solders has resulted in a proliferation of a wide variety of solder alloy compositions. Presently, the literature on mechanical behavior of lead-free alloys under simultaneous harsh environment of high-temperature vibration is sparse. In this paper, the reduction in stiffness of the PCB with temperature has been demonstrated by measuring the shift in natural frequencies. The test vehicle consisting of a variety of lead-free SAC305 daisy chain components including BGA, QFP, SOP and TSOPs has been tested to failure by subjecting it to two elevated temperatures and harmonic vibrations at the corresponding first natural frequency. The test matrix includes three test temperatures of 25C, 75C and 125C and simple harmonic vibration amplitude of 10G which are values typical in automotive testing. PCB deflection has been shown to increase with increase in temperature. The full field strain has been extracted using high speed cameras operating at 100,000 fps in conjunction with digital image correlation. Material properties of the PCB at test temperatures have been measured using tensile tests and dynamic mechanical analysis. FE simulation using global-local finite element models is thus correlated with the system characteristics such as modal shapes, natural frequencies and displacement amplitudes for every temperature. The solder level stresses have been extracted from the sub-models. Stress amplitude versus cycles to failure curves are obtained at all the three test temperatures. A comparison of failure modes for different surface mount packages at elevated test temperatures and vibration has been presented in this study.

Experimental and Numerical Investigation of Vibration Damping Using a Thin Layer Coating

2017 ◽  
Author(s):  
Imran Aziz ◽  
Sajjad Hussain ◽  
Wasim Tarar ◽  
Imran Akhtar
Keyword(s):  
Nickel Alloy ◽  
High Cycle Fatigue ◽  
Natural Frequencies ◽  
Damping Ratio ◽  
Rotating Machinery ◽  
Forced Response ◽  
Cycle Fatigue ◽  
Damping Characteristics ◽  
At Resonance ◽  
Vibration Shaker

High cycle fatigue (HCF) is the main cause of failure in rotating machinery especially in aircraft engines which results in the loss of human life as well as billions of dollars. More than 60 percent of aircraft accidents are related to High cycle fatigue. Major reason for HCF is vibratory stresses induced in the blades at resonance. Damping is needed to avoid vibratory stresses to reach the failure level. High speed rotating machinery has to pass through the resonance in order to reach the operational speed and chances of failure are high at resonance level. It is therefore required to suppress the vibrations at resonance level to avoid any damage to the structure. Application of coating to suppress vibrations is a current area of research. Various types of coatings have been studied recently. This includes plasma graded coatings, viscoelastic dampers, piezoelectric material damping, and magnetomechanical damping. In this research, the phenomenon of damping using a coating of nickel alloy on a steel beam is studied experimentally and numerically to reduce vibratory stresses by enhancing damping characteristics to avoid aircraft engine and rotating machinery failure. For this purpose, uncoated and nickel alloy coated steel beams are fabricated. The coating procedure was performed using plasma arc method. The beams were then mounted in a cantilevered position and bump and vibration shaker tests were conducted to determine the natural frequencies and mode shapes. One of the most important parameter to measure the damping of a system is the damping ratio. In order to determine the damping ratio, vibration analyzer mode was adjusted in time domain and beam was excited by using a hammer. The vibration analyzer showed the vibration decay as a function of time. Using that decay, damping ratio was calculated by using logarithmic decrement method. In order to investigate and compare the damping characteristics of un-coated and coated beams, forced response method was employed. In this method, beams were excited at 1st and 2nd bending mode natural frequencies using vibration shaker. Results were very encouraging and showed a significant improvement in damping characteristics. The experimental results were then endorsed by numerical results which were achieved by performing modal and forced response analysis using finite element analysis techniques.

A Diagnosis of Failure of a Compressor Blade

1987 ◽  
Author(s):  
J. A. Kubiak ◽  
J. M. Franco ◽  
A. Carnero ◽  
A. Rothhirsch L ◽  
J. Aguirre R.
Keyword(s):  
Finite Element ◽  
High Cycle Fatigue ◽  
Natural Frequencies ◽  
Welded Joint ◽  
Compressor Blade ◽  
Finite Element Code ◽  
Cycle Fatigue ◽  
Start Up ◽  
Load Conditions

The methodology and the procedure of diagnosis of a cracked stationary blade of a compressor due to high cycle fatigue is presented. The natural frequencies of the blades and a stator row were measured and an analysis of the casing vibrations during start-up and under load conditions of the compressor was conducted in a search for the cause of the failure. Using finite element code the natural frequencies and the vibratory stresses of the stator row blades (vanes) were computed. The computed maximum vibratory stresses in the vane were concentrated in the location of the crack which originated from the welded joint. It was concluded that the welded joint requires modification.

High Cycle Fatigue Life-Prediction for Lead-Free Interconnects Under Simultaneous High Temperature and Vibration

2013 ◽  
Author(s):  
Pradeep Lall ◽  
Geeta Limaye
Keyword(s):  
High Temperature ◽  
High Speed ◽  
High Cycle Fatigue ◽  
Failure Modes ◽  
Elevated Temperatures ◽  
Natural Frequencies ◽  
Image Correlation ◽  
Lead Free ◽  
Cycle Fatigue ◽  
Increase With Increase

Current trends in the automotive industry warrant a variety of electronics for improved control, safety, efficiency and entertainment. Many of these electronic systems like engine control units, variable valve sensor, crankshaft-camshaft sensors are located under-hood. Electronics installed in under-hood applications are subjected simultaneously to mechanical vibrations and thermal loads. Typical failure modes caused by vibration induced high cycle fatigue include solder fatigue, copper trace or lead fracture. The solder interconnects accrue damage much faster when vibrated at elevated temperatures. Industry migration to lead-free solders has resulted in a proliferation of a wide variety of solder alloy compositions. Presently, the literature on mechanical behavior of lead-free alloys under simultaneous harsh environment of high-temperature vibration is sparse. In this paper, the reduction in stiffness of the PCB with temperature has been demonstrated by measuring the shift in natural frequencies. The test vehicle consisting of a variety of lead-free SAC305 daisy chain components including BGA, QFP, SOP and TSOPs has been tested to failure by subjecting it to two elevated temperatures and harmonic vibrations at the corresponding first natural frequency. The test matrix includes three test temperatures of 25C, 75C and 125C and simple harmonic vibration amplitude of 10G which are values typical in automotive testing. PCB deflection has been shown to increase with increase in temperature. The full field strain has been extracted using high speed cameras operating at 100,000 fps in conjunction with digital image correlation. Material properties of the PCB at test temperatures have been measured using tensile tests and dynamic mechanical analysis. FE simulation using global-local finite element models is thus correlated with the system characteristics such as modal shapes, natural frequencies and displacement amplitudes for every temperature. The solder level stresses have been extracted from the sub-models. Stress amplitude versus cycles to failure curves are obtained at all the three test temperatures. A comparison of failure modes for different surface mount packages at elevated test temperatures and vibration has been presented in this study.

An Approach on Bladed-Disc Tuning

2009 ◽  
Author(s):  
Loc Duong ◽  
Kazem Kazerounian ◽  
Kevin D. Murphy
Keyword(s):  
High Cycle Fatigue ◽  
Natural Frequencies ◽  
Vibration Mode ◽  
Operating Speed ◽  
Cycle Fatigue ◽  
Finite Element Analyses ◽  
Excited Vibration ◽  
Structural Perturbations ◽  
Speed Range ◽  
Large Amplitude Vibrations

High cycle fatigue of rotating components, produced as the system is driven near to resonant conditions, is undesirable and is one of the major design concerns in engineering today. Structurally, it is imperative to tune the excited vibration mode out of the operating speed range to avoid large amplitude vibrations. It has been demonstrated that for a single blade with distinct eigenvalues, it is possible to tune the eigenvalue of choice out of the operating speed range while maintaining little change to other natural frequencies through structural perturbations. These perturbations usually come in the form of a redistribution of the stiffness and/or mass [1]. The focus of this paper is to extend this approach to the tuning of two adjacent excited frequencies of a bladed-disc by first reducing the inter-blade coupling through stiffening the disc structure followed by “individual” blade tuning. Due to the complexity of the bladed disc structure, results from direct finite element analyses are used based upon analytical eigen-perturbed expressions to investigate the dynamic inter-blade behavior of an impeller. A good correlation between analysis and laser vibrometry test measurements is obtained.

High Cycle Fatigue and Fatigue Crack Propagation Behaviors of Modified A7075-T73 Alloy

2014 ◽  
Vol 52 (4) ◽  
pp. 283-291 ◽  
Author(s):  
Gwan Yeong Kim ◽  
Kyu Sik Kim ◽  
Joong Cheol Park ◽  
Shae Kwang Kim ◽  
Young Ok Yoon ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
High Cycle Fatigue ◽  
Cycle Fatigue
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