<title>Miniaturization of speckle interferometry for rapid strain analysis</title>

Abstract

Today's industry demands high-performance components meeting toughest mechanical features and ultimate safety standards. Especially in automotive and aircraft industry the development focuses on tailor-made design and solutions according to customer specifications. To reconcile economy, light-weight construction has become a key issue. Many companies are looking for new advanced strain/stress analysis techniques to improve cost efficiency and the limitations of classical methods. Detection of weak points and fatigue tests are carried out mainly with strain gauges which need careful application and experience. ESPI (electronic peckle pattern interferometry) allows a rapid, full field and 3D-measurement without contact. This paper presents the principle and application of a new miniaturized laser optical sensor combining contour and deformation measurement. In it's basic employment ESPI is an interferometric method measuring deformations at modern working materials with high accuracy. Here also a module for contouring was developed and integrated into a single interferometer. Therefore even at complex components it is possible to measure and display strain-fields and -gradients with respect to the underlying contour. The new sensor is a unique device for flexible strain-analysis at weldedmaterials, extrusions, engines, car-bodies, etc. Without preparation and due to the full field and 3D-measurement 'hot spots' are shown, reducing the testing procedure and increasing the reliability of complex component testing significantly.In this paper the recent development of a miniaturized ESPI-interferometer for strain and stress measurement is described. Advanced features according to classical techniques are specified and new applications in material and component testing are presented.

Noncontact Inspection Method to Determine the Transfer Length in Pretensioned Concrete Railroad Ties

“…To measure the transfer length more quickly and accurately, a non-contact method based on laser- (Wegner 1999). This makes it impractical for the ESPI technique to be used for strain 13 measurement on pre-tensioned concrete ties in the harsh manufacturing environment where the 14 stringent alignment of the sensor is hard to achieve.…”

Optical Sensor Developments for Measuring the Surface Strains in Prestressed Concrete Members

“…To protect the optical sensor from damage, it is necessary to remove the sensor after the initial reading from the concrete surface prior to the detensioning process. These extreme conditions prevent some optical strain sensors, originally designed to be attached to the specimen surface throughout the measurement/detensioning processes, from being applied to the prestressed concrete applications [10]. Secondly, the prestressed concrete surface strain is in the range of several hundred micro‐strains within few hours and up to 30 to 60 days, which means the strain sensor must be able to cover fairly large dynamic ranges.…”

<title>Novel laser grating interferometer (LES) for industrial applications</title>

“…requirements. Most of them are based on speckle pattem interferometry (ESPI) or ESPI based shearography (ESPSI) [1,2]. The main disadvantage of ESPI systems is the high level of noise in the output data and restricted range of continuos measurement due to decorelation problem.…”