Sound and vibrations in structures with air enclosures

Vibrations in thin shell structures and sound fields in enclosures are investigated as well as the interaction between such structures and the enclosed sound field. Optical, non-contacting methods as TV holography, shearography and laser scanning vibrometry are used to investigate vibrations of thin shell structures with air enclosures. The sound radiation from vibrating structures is also measured with more traditional sound intensity techniques. The techniques used are briefly presented and compared in this thesis. Structural vibrations in organ pipes made of different materials are investigated as well as the sound distribution from the pipes. Operating deflection shapes of a complete violin are investigated, and the effect of enclosed air on structural vibrations is measured on a violin model. Aerial standing waves inside three cavities are measured and visualised with an optical technique. The response of the shell structures due to aerial standing waves is also measured. From the investigations it is found that the enclosed air has a significant effect on, above all, the lowest eigenmodes. It is also shown that non-contacting measuring techniques have advantages in that they do not to disturb the measured object and in that they are field methods. In numerical comparisons to the measurements it is found that the enclosed air should be included in the numerical model to predict correct results. Two different finite element models of the enclosed air are tested.Godkänd; 1999; 20061117 (haneit)</p

Vibrations and sound from structures with air enclosures

Godkänd; 1997; 20070418 (ysko)</p

Evaluation of non-destructive testing methods for automatic quality checking of spot welds

Car bodies are today more often made of high strength steel. In high strength steel spot welds are more friable and it is necessary to have higher demands on the inspections of spot welds. Quality control of spot weld can be either destructive or non-destructive. Destructive testing is still the most common method to test spot weld. The non-destructive methods that are investigete in this project are visual inspektion (VT), penetrant testing (PT), eddy current testing (ET), ultrasonic testing (UT), magnetic paticle testing (MT) and X-ray testing (RT). Other NDT methods are acoustic emission (AE), digital sheargraphy and IR-termography (IRT). These methods are investigated with focus on the possibility to detect Lens Diameter, stick welds, expulsions, porosity and cracks. And the possibility to automation of the method with focus on size and weight of the system, protection equipment, contact or contactless, one or two sided, position accuracy, and result in real-time. Only tree NDT methods, UT, RT and IRT, can detect all discontinuities that we looking for in RSW. The thermography system has the largest potential to be a NDT system for spot weld in the future, mainly because the method is non-contact, which helps when you have the opportunity to searching on a surface instead of a specific position. The main problem with this method is that there is no software for analysing the results to obtain lens diameter.SpotLigh

Model based compensation of systematic errors in an inductive gap measurement method

A model-based correction of systematic errors to improve the measurement of gap dimensions in a recently presented method is described. Using one inductive coil on each side of the gap to measure distance and liftoff, the method detects zero width gaps and shows position error less than 0.1 mm. The correction model relies on observations of experimental data, and is calibrated to a small set of measurements. From the initial measurement of gap dimensions, the model estimates errors in each coil to calculate new values for gap width, alignment and height. The errors in the compensated results are within 0.1 mm except for gap width, which still suffers from the effect of combined gap width and misalignment. The method is intended for gap measurement in laser keyhole welding, where the laser beam and the resulting weld seam are very narrow, requiring high precision in alignment and gap preparation.CC BY-NC-ND 4.0Corresponding author at: University West, Nohabgatan 18A, SE-461 53 Trollhättan, Sweden. E-mail address: [email protected] (E. Svenman).The authors gratefully acknowledge the financial support from the Research School SiCoMaP, funded by the Knowledge Foundation, and GKN Aerospace Engine Systems.</p

Experimental validation of an inductive probe for narrow gap measurement based on numerical modelling

Experimental validation of numeric results for an inductive probe shows that narrow gaps between two plates can be measured with accuracy suitable for laser beam welding. A two-coil inductive probe for measurement of the gap was built based on finite element modelling results. The individual coils were calibrated using a complex response method, and results from the physical coils closely match the numerical results regarding distance to gap and lift-off above the plate. The measurement of a realistic gap shows results that can be used in industrial applications for position, plate height and height alignment.

Thermal non-destructive testing : modeling, simulation and experiments for improved localization of hidden defects

During the last decades, a substantial amount of research and practical work has been conducted on non-destructive testing of materials using thermography. The performed studies elucidate the potential of various types of thermal non-destructive testing (TNDT) for different materials and applications, including various types of defects. This paper presents a method for detecting in-depth defects in metallic materials and a simulation model for the heat transfer in the material. Experiments are performed on a test specimen with artificial defects (flat-bottom holes). The detection method exploits spatiotemporal analysis in order to find deviations from a model of normality, and shows novel results. Thermal modelling is performed in order to have a base-line simulation model enable us to (a) investigate affecting parameters without repeating the experiments and (b) generalize the results and extend their validity to other cases. Results show that there is an acceptable compliance between simulated and measured thermal data. SpotSimTUM

Automatic Inspection of Spot Welds by Thermography

The interest for thermography as a method for spot weld inspection has increased during the last years since it is a full-field method suitable for automatic inspection. Thermography systems can be developed in different ways, with different physical setups, excitation sources, and image analysis algorithms. In this paper we suggest a single-sided setup of a thermography system using a flash lamp as excitation source. The analysis algorithm aims to find the spatial region in the acquired images corresponding to the successfully welded area, i.e., the nugget size. Experiments show that the system is able to detect spot welds, measure the nugget diameter, and based on the information also separate a spot weld from a stick weld. The system is capable to inspect more than four spot welds per minute, and has potential for an automatic non-destructive system for spot weld inspection. The development opportunities are significant, since the algorithm used in the initial analysis is rather simplified. Moreover, further evaluation of alternative excitation sources can potentially improve the performance.Funding Agencies|Vinnova (the FFI program)</p

Weld gap position detection based on eddy current methods with mismatch compensation

The paper proposes a method for finding the accurate position of narrow gaps, intended for seam tracking applications. Laser beam welding of butt joints, with narrow gap and weld width, demand very accurate positioning to avoid serious and difficult to detect lack of fusion defects. Existing optical and mechanical gap trackers have problems with narrow gaps and surface finish. Eddy current probes can detect narrow gaps, but the accuracy is affected by mismatch in height above the surface on either side of the gap. In this paper a non-contact eddy-current method, suitable for robotic seam tracking, is proposed. The method is based on the resistive and inductive response of two absolute eddy current coils on either side of the gap to calculate a position compensated for height variations. Additionally, the method may be used to estimate the values of height and gap width, which is useful for weld parameter optimization. To investigate the response to variations in height, the method is tested on non-magnetic metals by scanning one commercially available eddy current probe across an adjustable gap and calculating the expected response for a two-probe configuration. Results for gap position are promising, while mismatch and gap width results need further investigation

Automated NDT cell for quality checking of spot welds

This report is written within Spotlight WP5 financed by the FFI programme within Vinnova. Thermography is a non-destructive testing method based on measurement of the heat distribution by an infrared camera. The method is suitable for automatic inspection since it is a full filed and non-contact method. A thermography system with an analysis tool developed by Termisk Systemteknik AB is investigated as an inspection method for spot weld. The system is able to detect spot welds, measure the diameter and separate a spot weld from a stick weld. The algorithms used in the analysis are rather simplified and the development opportunities are significant. A fully automated NDT-cell for spot weld inspection is presented. The automation includes a six axis industrial robot and communication for handling the information flow. This comprised the identification of the inspected spot weld and the reporting to the overall system as to the operator. A failure modes and effects analysis (FMEA) of the automated NDT-cell is accomplished and the most important actions are reported A business case for implementing a automated NDT-cell was included in the project. In this business case the most promising quality check concepts for NDT spot weld will be presented and compared with the other identified methods