Modal Exciter Research Articles

Investigation of the Mechanical Properties of Spur Involute Gearing by Infrared Thermography

The work aims at validating a methodology for 3D printing of gears with involute gearing and evaluating their mechanical properties using infrared camera. A general methodology for the setup of 3D printing of gears made of polymeric materials has been developed, which can be used in technical practice in order to replace parts produced by conventional methods. An experiment was prepared determination of the distribution of the 1st invariant of the stress tensor and phase shift using a modal exciter and an IR camera. The values of the 1st invariant of the stress invariant were found. For these measurements, the lock-in thermography method was used, using a modal exciter we force loaded a gear in which the response to the load was registered. The aim was to obtain the distribution of the strain or stress field on the loaded tooth. The experimental method used also belongs to the field of non-destructive testing (NDT), and with suitable experimental parameters we can also obtain information from the layers below the surface, as demonstrated in the phase images. The practical benefit is to provide a competitive advantage to companies that will exploit the properties of polymeric materials by knowing the mechanical properties of these materials.

In-Situ Dynamic Response Measurement for Damage Quantification of 3D Printed ABS Cantilever Beam under Thermomechanical Load.

Acrylonitrile butadiene styrene (ABS) offers good mechanical properties and is effective in use to make polymeric structures for industrial applications. It is one of the most common raw material used for printing structures with fused deposition modeling (FDM). However, most of its properties and behavior are known under quasi-static loading conditions. These are suitable to design ABS structures for applications that are operated under static or dead loads. Still, comprehensive research is required to determine the properties and behavior of ABS structures under dynamic loads, especially in the presence of temperature more than the ambient. The presented research was an effort mainly to provide any evidence about the structural behavior and damage resistance of ABS material if operated under dynamic load conditions coupled with relatively high-temperature values. A non-prismatic fixed-free cantilever ABS beam was used in this study. The beam specimens were manufactured with a 3D printer based on FDM. A total of 190 specimens were tested with a combination of different temperatures, initial seeded damage or crack, and crack location values. The structural dynamic response, crack propagation, crack depth quantification, and their changes due to applied temperature were investigated by using analytical, numerical, and experimental approaches. In experiments, a combination of the modal exciter and heat mats was used to apply the dynamic loads on the beam structure with different temperature values. The response measurement and crack propagation behavior were monitored with the instrumentation, including a 200× microscope, accelerometer, and a laser vibrometer. The obtained findings could be used as an in-situ damage assessment tool to predict crack depth in an ABS beam as a function of dynamic response and applied temperature.

Operational Modal Analysis of the Laboratory Steel Truss Structure

Abstract Modal analysis in operational conditions is popular way for obtaining natural modes of civil structures such as bridges or dams nowadays. This approach called Operational Modal Analysis (OMA) overcomes difficulties with input forces used for excitation of the structure in Experimental Modal Analysis (EMA). In OMA the input forces are assumed to be stochastic. The paper presents the experimental measurement and analysis of the mode shapes and frequencies of the laboratory steel truss structure using output-only method based on Frequency Domain Decomposition (FDD). FDD technique for a decomposition of the spectral density function matrix in combination with a method for merging measured data from multiple measurement set-ups are both implemented into a data processing tool designed in LabVIEW. Modal exciter and random impulses in random points are used for the structure excitation. The results demonstrate the influence of different types of operational loading on identified modes.

ОЦЕНКА ЖЁСТКОСТИ МЕТАЛЛИЧЕСКОЙ РАМЫ МЕТОДОМ ДИНАМИЧЕСКИХ ИСПЫТАНИЙ

The article presents the method for assessing bending stiffness by dynamic testing using an example of the experienced metal frame. The source of forced oscillations during dynamic tests was a modal vibration exciter in the form of a mechanical oscillator with stepwise frequency control. The results of determining the natural frequencies of the frame, the frequency of forced oscillations of the exciter and logarithmic damping decrement are shown. Dynamic force and dynamic coefficient were calculated. Stiffness evaluation of the frame elements was carried out in comparison with its theoretical value specified in the finite element model. The model was compiled in the LIRA-SAPR design software 2013. For the frame elements, the curvature of a bend shape was calculated from experimental and model data. The experimental stiffness of elements on average was 8.81% less than the theoretical. The proposed approach allows realizing non-destructive testing of a bending stiffness of a structure at the measurement site.

Parameter effecting the experimental determination of modal properties

The investigation of structure dynamic behavior can be done by finding modal properties, which are based on the relation of force and vibration response. The information about exact force value is in most application unknown, but the investigation can be done for unit magnitude of force. In case of using modal exciter, the force applied to structure is transferred by connection between modal exciter and structure. The stiffness of connection part can affect the dynamic behavior and change the modal properties, or response of investigated part, because of additional modal properties of connection part. This article is focused on the influence of two different rod stiffness during modal properties identification. The modal exciter is used to find potential critical frequency during decreasing frequency. The affect is evaluated on the surface normal velocity as well as acoustic pressure. The stiffness of rod significantly affects the dynamic response of structure and based on that can add frequency, when the emitted noise is high.

The contribution to the modal analysis using an infrared camera

The paper deals with modal analysis using an infrared camera. The test objects were excited by the modal exciter with narrowband noise and the response was registered as a frame sequence by the high speed infrared camera FLIR SC7500. The resonant frequencies and the modal shapes were determined from the infrared spectrum recordings. Lock-in technology has also been used. The experimental results were compared with calculated natural frequencies and modal shapes.

Fractional-order positive position feedback compensator for active vibration control of a smart composite plate

In this paper, Active Vibration Control (AVC) of a rectangular carbon fibre composite plate with free edges is presented. The plate is subjected to out-of-plane excitation by a modal vibration exciter and controlled by Macro Fibre Composite (MFC) transducers. Vibration measurements are performed by using a Laser Doppler Vibrometer (LDV) system. A fractional-order Positive Position Feedback (PPF) compensator is proposed, implemented and compared to the standard integer-order PPF. MFC actuator and sensor are positioned on the plate based on maximal modal strain criterion, so as to control the second natural mode of the plate. Both integer and fractional-order PPF allowed for the effective control of the second mode of vibration. However, the newly proposed fractional-order controller is found to be more efficient in achieving the same performance with less actuation voltage. Moreover, it shows promising performance in reducing spillover effect due to uncontrolled modes.

Abstract 3345: Induction of apoptosis by high levels of oscillatory shear strain: proof of concept in a human colon cancer metastasis cell line.

Abstract Purpose / Introduction: Mechanotransduction is a biological process enabling cells to convert mechanical cues into biological responses[1]. The apoptotic status of many cell types is regulated by the mechanical conditions of their environment [2,3]. In this context, and due to the incompressible nature of tissues, it is theoretically thinkable to selectively induce cellular death by the controlled application of low frequency oscillatory shear strain. Unlike e.g. HIFU (high intensity focused ultrasounds), here the energy deposited would by far not be sufficient to mechanically rupture cells, but would instead trigger specific signals within the cell. We establish the proof of concept for this proclaimed effect in a cell line of colon cancer metastasis. Subjects and Methods: DHDK12 colon cancer metastasis cells were grown in conventional conditions. At confluency, one plate was subjected for 4 hrs to a 90Hz uniaxial sinusoidal motion parallel to the cell layer by a rigidly linked modal exciter. One control plate was left without any vibration. The strain levels induced in the cell monolayer were measured on a control plate loaded with a thin layer of agarose gel (2g/l) and covered with liquid to simulate the medium. Shear strain images were obtained on a 7T MRI system using a spin echo elastography sequence synchronized with a 90Hz vibration of the imaged plate (TE/TR = 39/1744 ms) with 4 wave offsets, 3 encoding directions and a 300 μm isotropic resolution. Strain was evaluated as the maximum shear strain (difference between maximum and minimum eigenvalues of the strain tensor). At the end of the experiment, cells were, colored with trypan blue and the proportion of colored vs. uncolored cells was estimated using a hematocytometer. Levels of caspase-3 were assessed by western blotting, using β-actin as the loading marker. Results: Using shear strain imagin, it was determined that the setup yielded very elevated maximum shear strains on the order of 5.5 ± 1.1 % in the first 300μm immediately above the plastic surface. Vibrations were sufficient to induce cell death, as observed by the 4.2X increase in the count of dead cells after vibrations (pre: 2.9±1.5%, post: 4.5±1.4% for the control plate, vs. pre: 5.3±2.6%, post: 22.3±3.9 % for the vibrated plate). Caspase-3 levels were elevated in the cells having undergone vibrations, indicating that an activation of the apoptosis pathway was involved in the observed increase in cell deaths. Discussion/Conclusion: We show that the application of 5% maximum shear strain at 90Hz for 4 hours has the ability to induce apoptosis in vitro on a human cell line of cancer metastasis. This proof of concept indicates that the selective application of high strain shear waves of low frequency may become a viable alternative for tumor therapy. [1] Ingber, FASEB 2006 20(7) [2] Jaalouk, Nat Rev Mol Cell Biol, 2009 10(1) [3] Cheng, PLOS One, 2009 4(2) Citation Format: Philippe Garteiser, Sabrina Doblas, Simon Lambert, Mouniya Mebarki, Valerie Vilgrain, Bernard E. Van Beers, Valerie Paradis, Ralph Sinkus. Induction of apoptosis by high levels of oscillatory shear strain: proof of concept in a human colon cancer metastasis cell line. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3345. doi:10.1158/1538-7445.AM2013-3345

Experimental Modal Analysis of an Automotive Powertrain

The work is devoted to study the dynamic properties of a powertrain, performing an experimental modal analysis (EMA). The aim is to determinate structural modes and frequency response function (FRF) using an experimental approach. Two types of excitation mechanism are applied and compared for the EMA: a modal exciter (electromagnetic shaker system) and an impact hammer. Both the analyses with modal shaker and with impact hammer are carried on measuring the acceleration of the structure in the same set of eighty-one points. In both cases, the excitation is performed along three directions (vertical, lateral and longitudinal with respect to the structure). The two different modal analysis methodologies are described, and results (modal parameters such as natural frequencies, damping ratios and modal shapes are identified with commercial software) are compared. The comparison is made in term of result accuracy, reliability and testing time required.

Studies in dynamic design of drilling machine using updated finite element models

The aim of the present work is to develop updated FE models of a drilling machine using analytical and experimental results. These updated FE models have been used to predict the effect of structural dynamic modifications on vibration characteristics of the drilling machine. Two studies have been carried out on the machine. In the first study, modal tests have been carried out on a drilling machine using instrumented impact hammer. Modal identification has been done using global method of modal identification. For analytical FE modeling of the machine, a computer program has been developed. The results obtained using FEM, have been correlated with the experimental ones using mode shape comparison and MAC values. Analytical FE model has been updated, with the help of a program, which has been developed using direct methods of model updating. In the second study, modal testing has been carried out using random noise generator and modal exciter. Global method has been used for modal identification. Analytical FE modeling has been done using I-DEAS software. Correlation of FE results with the experimental ones has been carried out using FEMtools software. Updating of the analytical FE model has also been done using the above software, based on an indirect technique viz. sensitivity based parameter estimation technique. The updated FE models, obtained from both the studies have been used for structural dynamic modifications (SDM), for the purpose of dynamic design and the results of SDM predictions are seen to be reasonably satisfactory.