A Vibrational Technique for Stress Measurement in Films

1990 ◽  
Vol 188 ◽  
Author(s):  
A. Jagota ◽  
S. Mazur ◽  
R. J. Farrisf
Keyword(s):  
Material Parameter ◽  
Natural Frequencies ◽  
Stress Measurement ◽  
Random Noise ◽  
Vibrational Analysis ◽  
Silver Films ◽  
State Of Stress ◽  
A New Technique ◽  
Membrane Vibrations ◽  
Measured Response

ABSTRACTThis paper presents a new technique for the measument of stress in films based on the classical theory of membrane vibrations. The specimens for vibrational analysis are prepared by removing a circular or square piece of the substrate far from any edge of the film (this operation preserves the state of stress in the film). The specimen is mechanically excited by random noise and its natural frequencies are peaks in the measured response of the membrane. The natural frequencies increase as the square root of stress in the film. The only material parameter needed to determine stress from the natural frequency is the density of the film. The technique has been used to measure stress in two different systems: urethane cured epoxies and silver films under different environmental conditions (temperature and humidity).

Vibrational Analysis of Human Femur Bone

2018 ◽  
Author(s):  
Reza Sadeghi ◽  
Firooz Bakhtiari-Nejad ◽  
Taha Goudarzi
Keyword(s):  
Natural Frequencies ◽  
Vibrational Analysis ◽  
Bone Geometry ◽  
The Body ◽  
Mode Shapes ◽  
Pelvic Bone ◽  
Cross Sectional ◽  
Femur Bone ◽  
Bone Structures ◽  
Elderly Falls

Femur bone is the longest and largest bone in the human skeleton. This bone connects the pelvic bone to the knee and carries most of the body weight. The static behavior of femur bone has been a center of investigation for many years while little attention has been given to its dynamic and vibrational behavior, which is of great importance in sports activities, car crashes and elderly falls. Investigation of natural frequencies and mode shapes of bone structures are important to understand the dynamic and vibrating behaviors. Vibrational analysis of femoral bones is presented using finite element method. In the analysis, the bone was modeled with isotropic and orthotropic mechanical properties. The effect of surrounding bone muscles has also been accounted for as a viscoelastic medium embedding the femur bone. Natural frequencies extracted considering the effects of age aggravated by weakening the elastic modulus and density loss. The effects of real complex bone geometry on natural frequencies are studied and are compared with a simple circular cross-sectional model.

scholarly journals Vibrational Analysis of Composite Beam Embedded with Nitinol Shape Memory Alloy Wires

2018 ◽  
Vol 7 (3.4) ◽  
pp. 143
Author(s):  
Omer Muwafaq Mohmmed Ali ◽  
Rawaa Hamid Mohammed Al-Kalali ◽  
Ethar Mohamed Mahdi Mubarak
Keyword(s):  
Shape Memory Alloy ◽  
Shape Memory ◽  
Frequency Response ◽  
Response Curve ◽  
Natural Frequencies ◽  
Damping Ratio ◽  
Vibrational Analysis ◽  
Laminated Composite ◽  
Vibration Modes ◽  
Frequency Response Curve

In this paper, laminated composite materials were hybridized with fibers (E-glass) and shape memory alloy wires which considered a smart material. The effect of changing frequency on the (acceleration- frequency) response curve, the damping ratio of the vibration modes, the natural frequencies of the vibration mode, the effect of shape memory alloy wires number on the damping characteristics were studied. Hand lay-up technique was used to prepare the specimens, epoxy resin type was used as a matrix reinforced by fiber, E-glass. The specimens were manufactured by stacking 2 layers of fibers. Shape memory alloy, type Nitinol (nickel-titanium) having a diameter (1 and 2mm), was used to manufacture the specimens by embedding (1,2 and 3) wires into epoxy. Experimentally, the acceleration- frequency response curve was plotted for the vibration modes, this curve was used to measure the natural frequencies of the vibration modes and calculate the damping ratio of the vibration modes. ANSYS 15- APDL was used to determine the mode shape and find the natural frequencies of the vibration modes then compared with the experimental results. The results illustrated that, for all specimens increasing the natural frequency leads to decreasing the damping ratio. Increasing the number of shape memory alloy wires leads to increase the values of the damping ratio of the vibration modes and the natural frequencies of the vibration modes at room temperature. 

scholarly journals Dynamic Force Identification for Beamlike Structures Using an Improved Dynamic Stiffness Method

1996 ◽  
Vol 3 (3) ◽  
pp. 183-191 ◽  
Author(s):  
S.L. Chen ◽  
M. Géradin
Keyword(s):  
Dynamic Stiffness ◽  
Random Noise ◽  
Parameter Extraction ◽  
Dynamic Force ◽  
Modal Parameter ◽  
Force Identification ◽  
Entire Structure ◽  
Stiffness Method ◽  
Dynamic Stiffness Method ◽  
Measured Response

In this study a procedure of dynamic force identification for beamlike structures is developed based on an improved dynamic stiffness method. In this procedure, the entire structure is first divided into substructures according to the excitation locations and the measured response sites. Each substructure is then represented by an equivalent element. The resulting model only retains the degree of freedom (DOF) associated with the excitations and the measured responses and the DOF corresponding to the boundaries of the structures. Because the technique partly bypasses the processes of modal parameter extraction, global matrix inversion, and model reduction, it can eliminate many of the approximations and errors that may be introduced during these processes. The principle of the method is described in detail and its efficiency is demonstrated via numerical simulations of three different structures. The sensitivity of the estimated force to random noise is discussed and the limitation of the technique is pointed out.

scholarly journals Vibrational analysis of Levy-type plates by using SEM

2018 ◽  
Vol 1 (1) ◽  
pp. 18 ◽  
Author(s):  
Shota Kiryu ◽  
Buntara Sthenly Gan
Keyword(s):  
Natural Frequencies ◽  
Vibrational Analysis ◽  
Element Model ◽  
Spectral Element ◽  
Thin Plates ◽  
Rigid Pavement ◽  
Structural Dynamic ◽  
Element Discretization ◽  
Stiffness Matrices ◽  
Vibrational Characteristics

The use of the frequency-dependent spectral method in structural dynamic related problems is known to provide very accurate solutions while reducing the number of degree-of-freedom to resolve the computational and cost drawbacks. This paper investigated the vibrational characteristics of a rigid pavement road which is modeled by an isotropic Levy-type rectangular thin plates. The Spectral Element Method (SEM) in the frequency domain is developed to formulate the free vibration problems of the plate. Transcendental stiffness matrices are well established in vibration, derived from the exact analytical solutions of the differential equations of a plate element. The present spectral element model has four line-type degree-of-freedoms (DOF) on each edge of the Levy-type rectangular plate. Natural frequencies are found using the Wittrick-Williams algorithm. Numerical examples are given to show the effectiveness, efficiency, and accuracy of the SEM by using one element, unlike the FEM, the SEM gives exact solutions of the natural frequencies of plates without element discretization procedures.

scholarly journals Changes in the Dynamic Characteristics of a Small-Scale Gymnasium Model Due to Simulated Earthquake Damage

2021 ◽  
Vol 16 (7) ◽  
pp. 1074-1085
Author(s):  
Jun Fujiwara ◽  
Akiko Kishida ◽  
Takashi Aoki ◽  
Ryuta Enokida ◽  
Koichi Kajiwara ◽  
...  
Keyword(s):  
Structural Damage ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Small Scale ◽  
Building Structures ◽  
Shake Table Tests ◽  
Large Span ◽  
Similarity Rule ◽  
Measured Response

In this study, the authors used shake-table tests to assess the modal parameters of a small-scale gymnasium model with simulated damage, the feasibility of estimating the damage to large-span building structures was studied. In Japan, large-span structures, such as gymnasiums, are expected to be used as evacuation shelters when a natural disaster occurs. As the shelter itself may be damaged in case of an earthquake, it is critical to determine whether damage has occurred, where it occurred, and how serious it is, before the shelter is used. The small-scale gymnasium was designed based on the similarity rule. Observed earthquake ground motions scaled to aftershock levels were applied to the model. The natural frequencies and mode shapes were obtained from the measured response accelerations. To study the influence of structural damage on the modal parameters, a gymnasium model with simulated damage was also tested. The results indicate that the modal parameters, e.g., natural frequencies and mode shapes, can be obtained from the response accelerations, and the damage patterns can be estimated from the changes in these modal parameters.

scholarly journals Measurement of Residual Stresses of Locomotive Wheel Treads During the Manufacturing Technological Cycle

2019 ◽  
Vol 27 (4) ◽  
pp. 236-241
Author(s):  
Vitaly V. Muravev ◽  
Olga V. Muraveva ◽  
Ludmila V. Volkova ◽  
Milan Sága ◽  
Zuzana Ságová
Keyword(s):  
Residual Stresses ◽  
Stress Measurement ◽  
The State ◽  
Rolling Stock ◽  
Wheel Pair ◽  
State Of Stress ◽  
Technological Cycle ◽  
Wheel Drive ◽  
Pulling Force ◽  
Simple Assembly

AbstractThe production of two-wheeled rolling stock represents, at first glance, a simple assembly process that significantly affects the overall functionality and safety of the vehicle. This is due to residual stresses that arise after assembly by pressing the wheel on the axle. The state of stress after assembly remains in the design has a decisive influence on the load-bearing capacity of the two-wheel drive, its lifespan but also the transfer of the pulling force in the case of locomotives. Therefore, it is very important to find suitable methods for determining residual stresses. Numerical and experimental approaches are already in place to gain information on the state of stress after compression, or during a real operation. The developed techniques and tools for estimation of residual stresses in locomotive wheel treads based on the acoustoelasticity effect using electromagnetic acoustic transformation are described in the paper. The original results of residual stress measurement in the treads during a technological cycle of locomotive wheel pair manufacturing are presented.

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