Determination of Notched Input for Equipment Under Random Vibrations

Equipment that is mounted on a spacecraft is subjected to random vibration tests to verify whether they can withstand the specified random loads. These tests are generally carried out by using shaker systems during which equipment experiences very high responses at the natural frequencies of the equipment. To reduce such over-testing, notching of the input is done. Notching of the input is normally carried out by considering the force generated at the base and limiting it to a specified value. To accomplish the notching, the force spectrum to be limited and measurement of base force during the tests are needed. This work shows that the acceleration input at the interface of equipment gets reduced at its resonance frequency and this feature can be utilized in arriving at the notched input. An expression to determine the depth of notching is derived and the results are compared with those obtained using numerical simulations. The depth of the notch increases with the response of the oscillator and it is sensitive to the stiffness ratios rather than the mass ratios of the oscillator and the mounting panel. This behavior and the expressions derived can be effectively used in arriving at the notched input for an equipment without the need for measuring the base force, especially for random vibration testing, which is demonstrated with an example.

Vergleichende Untersuchung der Verschleißbilder von Steckverbindern aus Reibverschleiß- und Vibrationsprüfungen mit unterschiedlichen Prüfrichtungen

In this study a comparison between the wear patterns of electrical connectors resulting from two different test types, namely fretting corrosion test and vibration test, is conducted. In both tests, the excitation directions include the mating direction as well as the orthogonal directions corresponding to the mating direction. Different measurement techniques are used to identify similarities and differences between the wear resulting from these test types. The results show fundamentally different critical directions with regard to wear for the respective test types. Furthermore, it is shown that the induced movement of the fretting tests lead to a higher degree of wear than the vibration tests. Also, it is not adequately possible to establish a direct relationship between the induced movement and the excitation amplitude caused by the attached wires since there is a superposition of several movements in the case of real applications.

Finite Element Analysis and Preliminary Dynamic Tests of Laboratory Bridge Model

A preliminary dynamic test of a two-span continuous girder bridge is reported in this paper, including the design specifications, the numerical model, and the modal identification result. This laboratory bridge is made of aluminum plates and connected via bolts. The finite element method is applied to build a numerical model of the bridge to aid the design and test plan. Several ambient vibration tests are conducted to extract the modal parameters, e.g., modal frequencies, damping ratios, and mode shapes, of the constructed bridge, and the Bayesian FFT algorithm is used for modal identification. We compare the identified results with those predicted by the finite element model and vary the magnitude of load to investigate its potential influence on the modal parameters. Damage cases by loosening structure members are also considered, and significant changes are observed in modal frequencies. The constructed model will be used as a benchmark for damage identification, model updating, and condition assessment, etc.

Characterization of Woven Composite Material Properties by Using an Inverse Technique Based on Vibration Tests

A mixed numerical-experimental technique based on vibration tests is modified and applied to determine the elastic material properties of woven composites. This non-destructive technique consists of physical experiments, numerical modelling and material identification procedure. For the purpose of characterization, two carbon fiber panels were prepared by manual layout technology. An evaluation of the accuracy of woven composite elastic properties is executed comparing the numerical and experimentally obtained resonant frequencies.

Effect of Crack Orientation on Laminated CFRP Composites Using Vibration and Numerical Analysis

Crack orientation, a critical parameter, significantly affects the dynamic properties of composite structures. Experimental free vibration tests were conducted on carbon fiber–reinforced polymer (CFRP) composite plates at room temperature with different crack orientations. Dynamic properties such as damping ratio, natural frequency, and storage modulus were measured using a four-channel dynamic pulse analyzer. Multi-sensors were mounted on the test plate to pick up the vibration signals. Experimental modal analysis was performed to identify the first three mode shapes of the defective plates. A numerical model using ANSYS software was developed via parametric investigation to predict the correlation between crack orientation and resonant frequencies with corresponding mode shapes. The orientation of the introduced cracks had a significant effect on the dynamic properties of CFRP composites. Vertical cracks had the most significant influence on the eigenvalues of the mode shape frequencies. Furthermore, the damping ratio was an effective method to detect the cracks in CFRP composites.

Development of upholstery electro-fabric for smart textile applications

Smart textile products developed by evaluating the human body’s data through sensors have become widespread in recent years. The majority of these products include textile-based information and communication technologies that integrate electronic components into clothing. People use seats, chairs, armchairs, etc., to sit constantly in vehicles, work or at home. The use of these items varies according to the requirements and purposes. In this study, an electro-textile-based upholstery fabric design was carried out to be used in sitting furniture. Electronic components containing capacitive sensors were placed in the designed fabric structure to make it usable in different areas where upholstery fabrics are used. In addition, the sensor connection circuit was developed to receive data from the fabric surface. The data taken from the fabric surface were made meaningful using the calibration and normalization algorithm. The 3D pressing map of the reaction on the fabric surface for different sitting positions was drawn. Electromagnetic field and vibration tests were carried out to examine the response behaviour in different environments where the fabric can be used. According to the findings, it was observed that the pressing areas formed on the surface were displayed in a significant way over the 3D pressing map, and the system was not affected by the electromagnetic field and vibrations. Besides, the fabric was applied on the various surfaces to test calibration and threshold algorithm. Obtained results and circumstances showed that the designed calibration and threshold algorithm were successful to obtained significant results. As a result of the study, upholstery electro fabric with a response time of 0.01 seconds in data collection was developed, which can be used in different environments such as home, workplace and vehicle. It can be used over furniture and in wet and dry conditions and is not affected by the electromagnetic field and vibration in the environment.

MONITORING AND PREDICTION OF TECHNICAL CONDITION OF STRUCTURAL UNITS OF BUILDINGS AND STRUCTURES

Рассмотрены вопросы анализа существующих подходов к мониторингу технического состояния строительных конструкций эксплуатируемых зданий и сооружений, описанные в нормативно-технической литературе. Рассмотрены и проанализированы типы мониторинга технического состояния зданий, особенности их проведения, имеющиеся несогласованности и разница в подходах к выполнению разных типов мониторинга. Проведено уточнение схемы мониторинга технического состояния строительных конструкций зданий и сооружений. Рассмотрены основные контролируемые параметры и их предельные значения с точки зрения проведения мониторинга, а также прогноза технического состояния несущих и ограждающих строительных конструкций зданий и сооружений различного назначения. Проведен анализ возможности использования предусмотренных в действующих нормативно-технических документах динамических испытаний строительных конструкций в условиях отсутствия объективных результатов при прогнозировании технического состояния конструкций по результатам вибрационных испытаний зданий. Выявлены значительные расхождения в подходах к проведению процедуры мониторинга технического состояния и мониторинга технического состояния зданий и сооружений, находящихся в ограниченно работоспособном или аварийном состоянии. Сделана попытка провести увязку требований и рекомендаций действующего ГОСТ 31937-2011 по проведению мониторинга, для обеспечения плавного перехода по ключевым контролируемым параметрам от общего мониторинга к мониторингу зданий, находящихся в ограниченно работоспособном или аварийном техническом состоянии. Рассмотрены пути прогнозирования дальнейшего развития технического состояния строительных конструкций зданий, с использованием обобщенных параметров, характеризующих текущее фактическое техническое состояние строительных конструкций, с использованием методов параметрического прогнозирования и экспертных методов. We considered the issues of analysis for existing approaches to monitoring technical condition of structural units of operated buildings and structures that are described in the normative and technical literature. We considered and analyzed different types of monitoring technical condition of buildings, features of their implementation, existing inconsistencies and difference in approaches to performing different types of monitoring. As a result we clarified the scheme of monitoring technical condition of structural units of buildings and structures. The main controlled parameters and their limit values are considered from the point of view of monitoring, as well as prediction of the technical condition of load-bearing and enclosing structural units of buildings and structures for various purposes. We carried out the analysis of the possibility of using dynamic tests of structural units provided in the current regulatory and technical documents in the absence of objective results when predicting the technical condition of structures based on the results of vibration tests of buildings. Significant discrepancies were revealed in the approaches to the procedure of monitoring technical condition of buildings and structures that are in a limited operational or emergency condition. We made an attempt to link the requirements and recommendations of the current GOST 31937-2011 for monitoring, to ensure a smooth transition in key controlled parameters from general monitoring to monitoring of buildings that are in a limited operational or emergency technical condition. The ways of predicting further development of the technical condition of structural units of buildings are considered, using generalized parameters that characterize the current technical condition of structural units, using parametric prediction and expert methods.