Vibration Fatigue Research Articles

Vibration Analysis and Fatigue Assessment of Floors. Part II: Mechanical Equipment

Vibration Analysis and Fatigue Assessment of Floors. Part II: Mechanical Equipment

Vibration Analysis and Fatigue Assessment of Floors. Part I: Human Rhythmic Activities

Vibration Analysis and Fatigue Assessment of Floors. Part I: Human Rhythmic Activities

Modeling ultrasonic vibration fatigue with unified mechanics theory

A series of ultrasonic vibration tests are performed on A656 grade steel samples, at a frequency of 20 kHz. A fatigue life model based on the unified mechanics theory is introduced to predict the very high cycle fatigue life of metals. Then, the fatigue life test data results are compared with the unified mechanics theory based model simulation results. It is shown that the physics-based unified mechanics theory can predict very high cycle fatigue life very well, without the need for the traditional empirical curve fitting a fatigue damage evolution function. The model does not require any curve fitting parameters obtained from fatigue test data. However, it does require deriving analytical thermodynamic fundamental equation of the material subjected to ultrasonic vibration fatigue. The thermodynamic fundamental equation of the material formulates the entropy generation mechanisms during the fatigue process. There are more than half a dozen entropy generation mechanisms during fatigue process. Entropy is an additive property, hence, the entropy generation due to all active mechanisms can be added.

Investigation of fatigue damage growth and self-heating behaviour of cross-ply laminates using simulation-driven dynamic test

Structural integrity of aerospace assets is paramount for both the safety and economy of aviation industry. The introduction of composites into the design of aero-structures generated several economic benefits but also led to several challenges, including fatigue damage growth and self-heating behaviour. Fatigue of metals is widely managed by calculations of damage accumulation and prediction of residual life. These techniques do not always apply to the fatigue of composites, where the onset and propagation of damage are still under investigation. Furthermore, vibration-induced fatigue is even less understood because of a handful of failure criteria available and, also, because it is biased by the self-heating conditions of the material itself. The authors have underpinned one failure criterion for vibration fatigue and mapped that against self-heating and environmental temperatures. Despite the advances, several research questions were left open because of the complex multiphysics behaviour of fatigue which outreached the experimental capacity. Therefore, this research suggests a Simulation-Driven Dynamic Test (SDDT) framework that deconstructs vibration fatigue experiments into step-wise steady-state analyses. This novel approach will enable (a) investigating the failure mode mixity of the underlying failure criterion, and (b) simulating the surface temperature during the delamination growth under vibration conditions.

A multi-axial vibration fatigue evaluation procedure for welded structures in frequency domain

Modeling of vibration fatigue of welded structures in the frequency domain can be particularly challenging. For instance, the stress singularity at weld locations causes finite element size sensitivity in stress determination. Furthermore, the interactions of multiple vibration modes at a weld location can generate non-proportional multiaxial stresses. Here we present a comprehensive procedure for modeling multiaxial fatigue behaviors of welded structures in the frequency domain to address some of these issues. The procedure utilizes a robust mesh-insensitive method and modal decomposition approach to determine the normal and shear traction stress responses. We proposed a non-proportionality correlation function to interrelate the resulting power spectrum density (PSD) of normal and shear traction stresses and their cross-PSD (CPSD) for establishing an effective stress parameter. The correlation function is determined and validated based on the well-established time-domain path-dependent maximum range (PDMR) method through a small-scale data-driven approach.

Performance of helical strakes in suppressing the FIV fatigue damage of two long flexible cylinders in a tandem configuration

Helical strakes are the most common vibration suppression devices for cylindrical structures undergoing vortex-shedding. Many problems with the performance of helical strakes on flow-induced vibration (FIV) fatigue damage suppression of two tandem cylinders have not been solved yet. The effectiveness of three-strand helical strakes with a pitch of 17.5D and a height of 0.25D (where D is the structural diameter) in suppressing fatigue damage of two tandem long flexible cylinders undergoing FIV was investigated in this paper. A constant spacing ratio (center-to-center distance to cylinder diameter) of 8.0 was selected. Four cases of the two cylinders, i.e., naked-naked, naked-straked, straked-naked and straked-straked, were executed under subcritical Reynolds number (Re ≤ 1.6 × 104). Based on the strain responses from the experimental tests, fatigue damage was estimated by using S–N curves and Miner's rule. To highlight the role of helical strakes in FIV fatigue damage suppression, an isolated naked cylinder was considered as a benchmark. It is shown that helical strakes exert substantially the same effect on FIV fatigue suppression of the upstream cylinder as they do on an isolated cylinder. The upstream cylinder significantly affects the performance of helical strakes on FIV fatigue suppression of the downstream cylinder. Both vortex breaking and prevention of interaction of two shear layers predominate the primary mechanism of the downstream straked cylinder when the upstream one is naked, which reinforces its cross-flow fatigue damage and hereby lowers the performance of helical strakes. In contrast, due to wake-induced vibration (WIV), the downstream straked cylinder laid behind a straked one might encounter much more serious fatigue damages in both the cross-flow and in-line directions than the case when the upstream cylinder is naked.

Two-phase flow-induced vibration fatigue damage of tube bundles with clearance restriction

Flow-induced vibration of the tube bundles in two-phase flow involves complicated interactions between the fluids and structures. Although a substantial number of studies have been devoted to investigating the flow-induced vibration and fluidelastic instability of the tube bundles subjected to two-phase cross-flow, the fatigue damage features of the tubes are not fully understood. In this paper, considering the effects of the turbulence random forces and the fluidelastic forces, a mathematical model of the tube bundles subjected to two-phase flow and the clearance restriction was developed. The vibration responses of the tube bundles within five void fraction conditions were calculated. The flow-induced vibration fatigue damages of the tubes were estimated based on S-N curves. The effects of the clearance restriction, the flow pitch velocity, and the void fraction of the two-phase flow on the fatigue damage were discussed. The numerical results demonstrate that the void fraction and flow pitch velocity of the two-phase flow have a significant influence on the fatigue damage of the tube bundles. And, the clearance restriction can change the location of the maximum fatigue damage.

Numerical and Experimental Investigation of Cumulative Fatigue Damage under Random Dynamic Cyclic Loads of Lattice Structures Manufactured by Laser Powder Bed Fusion

Lattice structures are lightweight engineering components suitable for a great variety of applications, including those in which the structural integrity under vibration fatigue is of paramount importance. In this work, we experimentally and numerically investigate the dynamic response of two distinct lattice configurations, in terms of fatigue damage and life. Specifically, Face-Centered-Cubic (FCC) and Diamond lattice-based structures are numerically studied and experimentally tested under resonant conditions and random vibrations, until their failure. To this end, Finite Element (FE) models are employed to match the dynamic behavior of the system in the neighborhood of the first natural frequency. The FE models are employed to estimate the structural integrity by way of frequency and tip acceleration drops, which allow for the identification of the failure time and a corresponding number of cycles to failure. Fatigue life under resonant conditions is well predicted by the application of conventional multiaxial high cycle fatigue criteria to the local state of stress. The same approach, combined with the Rainflow algorithm and Miner’s rule, provides good results in predicting fatigue damage under random vibrations.

Vibration Fatigue Assessment of Additive Manufactured Nickel Alloy With Inherent Damping

Abstract The fatigue life behavior and internal surface conditions of inherently damped additive manufactured (AM) specimens subjected to vibration bending are under investigation. This study supports research that demonstrated 95% vibration suppression due to damping capability of AM components with 1–3% internal volume of unfused powder; however, the viability of fatigue performance is unknown. The following effort explores whether internal wall damage caused by unfused powder particle motion debits fatigue life. Comparisons between the fatigue behaviors of unfused powder pocket and fully fused nickel based alloy 718 specimens confirms a long suspected powder interaction phenomena critical to damping performance.

Magnetic energy harvesting of transmission lines by the swinging triboelectric nanogenerator

With the development of smart grids, the demand for monitoring the condition of transmission is becoming high. Harvesting magnetic energy of transmission lines is a feasible approach to provide a sustainable power source for condition monitoring sensors. However, energy harvesting methods for transmission lines are constrained by size and service life. We report an antifatigue triboelectric nanogenerator based on a swinging structure (S-TENG) for magnetic energy harvesting. The S-TENG is composed of several magnets attached to a flexible substrate, which is laminated with a sponge layer, a copper film, and a polytetrafluoroethylene film. The laminated layer acts both as a tribo-layer and as a beam. The distinct structure without a stiff termination also avoids vibration fatigue and ensures the efficient contact of triboelectric layers with each other. The S-TENG presents a maximum peak power of 0.78 mW under 30 MΩ loading resistance. This work reveals the potential for harvesting alternating magnetic energy of transmission lines as an energy source for low-power electronic appliances.

Dirlik and Tovo-Benasciutti Spectral Methods in Vibration Fatigue: A Review with a Historical Perspective

The frequency domain techniques (also known as “spectral methods”) prove significantly more efficient than the time domain fatigue life calculations, especially when they are used in conjunction with finite element analysis. Frequency domain methods are now well established, and suitable commercial software is commonly available. Among the existing techniques, the methods by Dirlik and by Tovo–Benasciutti (TB) have become the most used. This study presents the historical background and the motivation behind the development of these two spectral methods, by also emphasizing their application and possible limitations. It further presents a brief review of the other spectral methods available for cycle counting directly from the power spectral density of the random loading. Finally, some ideas for future work are suggested.

Research on the transmission law of kurtosis of SDOF system under nonstationary and non-Gaussian random excitations

Vibration fatigue failure of structures under complex random excitations is a common problem in the field of engineering, and it seriously endangers the reliability and safety of major equipments and structures. It is particularly important to accurately predict the vibration fatigue life of structures under random excitations. Generally, it is assumed that the vibration excitation of engineering structures follows a stationary Gaussian distribution, but the actual excitation usually follows a nonstationary and non-Gaussian distribution, especially under harsh or variable working conditions. The vibration fatigue life of structures is closely related to the structural dynamic response characteristics, and the kurtosis of the structural response has a particularly obvious influence on the vibration fatigue life. In this paper, taking the single-degree-of-freedom system as an example and by decomposing complex random excitations in frequency segments, the dynamic response law of the system under nonstationary and non-Gaussian random excitations is studied in depth, and a mathematical model describing the transmission law of the kurtosis between the decomposed signal of excitation and response signal is established. The results show that there is a close linear relationship between the kurtosis of the structural dynamic response and the kurtosis of the decomposed signal obtained by frequency decomposition of the excitation signal by 3.2 times the half power bandwidth at the damped natural frequency of the structure. It is possible to quantitatively estimate the kurtosis of the structural response according to this relationship, which lays the foundation for accurately predicting the vibration fatigue life of structures under nonstationary and non-Gaussian random excitations.

Vibration Test Method of Aero-Engine 3D Printing Pre-Swirl Nozzle

According to the installation environment of the pre-swirl nozzle in the aero-engine, the equivalent constraint fixture is designed, which is the special fixture for vibration test. The equivalent constraint fixture has been checked in three aspects: stiffness simulation ring stiffness check, modal matching check and equivalent constraint fixture strength check. The modal characteristics of the pre-swirl are tested by hammering modal test method, and the natural frequency, mode shape and damping ratio are obtained within 2200Hz. By comparing the modal test results with the simulation results, the mode shapes are consistent. The maximum error of natural frequency is the 1st order 6 pitch diameter, , and the minimum error of the natural frequency is the 1st order 2 pitch diameter. The main frequency of the pre-swirl nozzle is determined to be 665.029Hz by frequency sweep test. The error of the result compared with the modal test result is 3.30%, and the error compared with the simulation result is only 1.59%. The excitation mode of pre-swirl nozzle formal durability test is determined by the pre-test. Finally, it is concluded that the vibration fatigue life of the pre-swirl nozzle can reach 5×10 7 times under a given stress level (120MPa).

Research on the fatigue failure behavior of 1Cr17Ni2 blades ground by abrasive belt with passivation treatment

As precision machining process of aero-engine blades, the surface integrity after abrasive belt grinding closely related to its fatigue resistance. In order to explore new anti-fatigue abrasive belt grinding methods, reveal the influence mechanism of blade surface integrity on anti-fatigue performance, and provide guidance for the anti-fatigue grinding, vibration fatigue tests were carried out on blades processed by different grinding process, and the effects of abrasive belt passivation treatment and feed speed on blade surface integrity and fatigue life were studied. Fatigue failure behavior of blades processed by different processes were also discussed from the fracture morphology and cross-section analysis. Results showed that blades processed by blunt grinding have different fatigue failure mechanisms, and the passivation treatment of abrasive belt and low feed speed can improve the surface integrity and fatigue life of aero-engine blades. The combination process of abrasive belt passivation treatment and slow feed speed were proposed for anti-fatigue grinding processing of aero-engine blades. In this research, compared with blades processed by new abrasive belt with feed speed 1000 mm/min, the fatigue life of blades processed by passivated abrasive belt at feed speed 100 mm/min was increased by 3.1 times.

Reliability Analysis of Solder Joints on Rigid-Flexible Printed Circuit Board for MEMS Pressure Sensors Under Combined Temperature Cycle and Vibration Loads With Continuously Monitored Electrical Signals

Abstract The reliability of lead-free solder joints on flexible printed circuit board (PCB) has created significant new challenges in the industry, especially in automotive electronics, and possibly for future wearable electronics. In the automotive industry, thermal cycling test and random vibration test need to be conducted to certify every electronic product to be used in harsh automotive environments. In order to accelerate the testing time, we may need to subject the electronic components, in particular, sensors to both loadings such as thermal cycling and vibration. During all the experiments, the electrical signals of each specimen were continuously monitored by using an event detector. One advantage of this method is that any individual soldering interconnect failure will result in the diagnostic signal of the circuit, which could be detected in real-time. A simulation was used to confirm the possibility of the stress concentration location caused by the vibration and thermal cycling loads. The influence of vibration frequency and acceleration on the vibration fatigue life of solid joints was investigated. In this paper, the submodeling technique was used to construct the finite element model of the rigid-flexible printed circuit board (rigid-flexible PCB) coupled with a MEMS pressure sensor subjected to temperature cycle and random vibration loadings. The research results are helpful to effectively characterize the performance of the MEMS sensors under both thermal cycling test and vibration test. Two kinds of land shapes and two kinds of PCB assemblies were selected. In order to investigate the crack growth in the solder joint, the solder joint is sliced and the crack on the cross section of the solder joint was observed. Results of finite element modeling analysis were consistent with the experimental results. Two design parameters have been identified in our research as being important to soldering usage in automotive environments: pad type (teardrop versus nonteardrop) and pad size (big versus small, matching size for Cu-wire and pad). Experimental results also showed that the solder joint with a big land shape presented a relatively good thermal fatigue resistance.

New Version of High-Damping PCB with Multi-Layered Viscous Lamina

In a previous study, a high-damping printed circuit board (PCB) implemented by multilayered viscoelastic acrylic tapes was investigated to increase the fatigue life of solder joints of electronic packages by vibration attenuation in a random vibration environment. However, the main drawback of this concept is its inability to mount electronic parts on the PCB surface area occupied by interlaminated layers. For the efficient spatial accommodation of electronics, this paper proposes a new version of a high-damping PCB with multilayered viscoelastic tapes interlaminated on a thin metal stiffener spaced from a PCB. Compared to the previous study, this concept ensures efficient utilization of the PCB area for mounting electronic parts as well as the vibration attenuation capability. Free vibration tests were performed at various temperatures to obtain the basic characteristics of the proposed PCB. The effectiveness of the proposed PCB was verified by random vibration fatigue tests of sample PCBs with various numbers of viscoelastic layers to compare the fatigue life of electronic packages.

Evaluation of tractor driving vibration fatigue based on multiple physiological parameters.

The vibration generated by tractor field operations will seriously affect the comfort and health of the driver. The low frequency vibration generated by the engine and ground excitation is similar to the natural frequency of human organs. Long term operation in this environment will resonate with the organs and affect drivers’ health. To investigate this possibility, in this paper we carried out a collection experiment of human physiological indicators relevant to vibration fatigue. Four physiological signals of surface electromyography, skin electricity, skin temperature, and photoplethysmography signal were collected while the subjects experienced vibration. Several features of physiological signals as well as the law of signal features changing with fatigue are studied. The test results show that with the increase of human fatigue, the overall physiological parameters show the following trends: The median frequency of the human body surface electromyography and the slope of skin surface temperature decreases, the value of skin conductivity and the mean value of the photoplethysmography signal increases. Furthermore, this paper proposes a vibration comfort evaluation method based on multiple physiological parameters of the human body. An artificial neural network model is trained with test samples, and the prediction accuracy rate reaches 88.9%. Finally, the vibration conditions are changed by the shock-absorbing suspension of a tractor, verifying the effectiveness of the physiological signal changing with the vibration of the human body. The established prediction model can also be used to objectively reflect the discomfort of the human body under different working conditions and provide a basis for structural design optimization.

Research on Path Planning for Reducing Vibration Fatigue of Precision Equipment Transportation

Abstract This paper analyzes the safety and reliability problems of large precision instruments and equipment in highway transportation, aiming at reducing the vibration fatigue damage of equipment to the greatest extent from the perspective of road planning. Based on the dynamic response model of the equipment, the relationship between the ground spectrum response and the cumulative fatigue damage of the equipment is analyzed. Based on the method of probability and statistics, an equipment fatigue prediction model is established. Based on the study of the relationship between the roughness of pavement grade and the reliability of equipment, the low-risk path planning is proposed. This paper adapts the Dijkstra shortest path algorithm. Not only the basic information such as the length of the highway is considered but also the road factors related to the reliability of the equipment and the environmental factors affecting the driving safety are considered. Try to avoid the adverse environment which has a great impact on the reliability of the equipment, reduce the vibration fatigue of the equipment in the process of transportation, and improve the quality of transportation. Using geographic information system secondary development, database, global positioning system positioning, and other technologies, this paper provides users with the shortest path and low-risk path planning for reference, which has a certain practical significance for highway transportation of high reliability products such as vulnerable products, precision instruments, and special equipment.

Bending fatigue of single-wall and double-wall corrugated paperboards under sinusoidal and random loads

The bending fatigue tests of single-wall and double-wall corrugated paperboards were conducted to obtain the εrms– N curves under sinusoidal and random loads in this paper. The εrms– N equation of corrugated paperboard can be described by modified Coffin–Manson model considering the effect of mean stress. Four independent fatigue parameters are obtained for single-wall and double-wall corrugated paperboards. The εrms– N curve under random load moves left and rotates clockwise compared with that under sinusoidal load. The fatigue life under random load is much less than that under sinusoidal load, and the fatigue design of corrugated box should be based on the fatigue result under random load. The stiffness degradation and energy dissipation of double-wall corrugated paperboard before approaching fatigue failure are very different from that of single-wall one. For double-wall corrugated paperboard, two turning points occur in the stiffness degradation, and fluctuation occurs in the energy dissipation. Different from metal materials, the bending fatigue failure of corrugated paperboard is a process of wrinkle forming, spreading, and folding. The results obtained have practical values for the design of vibration fatigue of corrugated box.

Vibration Fatigue Damage Estimation by New Stress Correction Based on Kurtosis Control of Random Excitation Loadings.

In the pioneer CAE stage, life assessment is the essential part to make the product meet the life requirement. Commonly, the lives of flexible structures are determined by vibration fatigue which accrues at or close to their natural frequencies. However, existing PSD vibration fatigue damage estimation methods have two prerequisites for use: the behavior of the mechanical system must be linear and the probability density function of the response stresses must follow a Gaussian distribution. Under operating conditions, non-Gaussian signals are often recorded as excitation (usually observed through kurtosis), which will result in non-Gaussian response stresses. A new correction is needed to make the PSD approach available for the non-Gaussian vibration to deal with the inevitable extreme value of high kurtosis. This work aims to solve the vibration fatigue estimation under the non-Gaussian vibration; the key is the probability density function of response stress. This work researches the importance of non-Gaussianity numerically and experimentally. The beam specimens with two notches were used in this research. All excitation stays in the frequency range that only affects the second natural frequency, although their kurtosis is different. The results show that the probability density function of response stress under different kurtoses can be obtained by kurtosis correction based on the PSD approach of the frequency domain.