Thickness measurement at material testing
A DIC system with two cameras allows to measure 3D discplacement, 3D deformation, strain field and object geometry with high accuracy. Due the the full field measurement technique and the scalability of the measurement volume a Q400 system can be used for many different applications. The range covers simple tensil tests to complex multiaxial loading of specimen or components in Aerospace, Automotive, research, development etc. The optical accessibility of the measured surface is the main requirement to use a DIC system.
Additional cameras provide at complex object geometries a better surface coverage and a generally higher accuracy: 8 cameras allow e.g. to measure 360° of a cylindrical surface..
Multi camera setup are supported in the DIC software ISTRA4D through a special cluster approach:
- The cameras can be arranged free in space. This allows to optimize the view and perspective of all cameras optimally to the measured surface geometry.
- All cameras are calibrated by an automatic calibration process in one common coordinate system.
- Every camera, that "sees" a surface point contributed in the correlation and increases the measurement accuracy at this point.
The camera setup with two cameras at the front and two camera at the back side provides additionally full field informations about the specimen thickness and thickness changes during the test. Relevant material parameters can therefore be determined for inhomogenous and structured materials. The double sided measurement allows also to measure unwanted bending moments that are induced e.g. by the specimen clamps.
As an example are shown the measurement results of a homogenous polymer specimen and a rolled aluminium tensile specimen. Längsdehnung = longitudinal strain, Querdehnung=transversal strain, Voderseite = front, Rückseite=back, Dicke=Thickness direction
The diagram shows the transversal strain versus longitudinal strain. The transversal strain is determined from width change and from thickness change. At the polymer specimen the transversal strain is similar in both directions. At the rolled aluminium specimen the transversal strain in thickness direction is much larger than the transversal strain in width direction.
The measurement of material parameters is very accurate with a DIC system and improves the knowledge about the material properties as the result date is full field. From the measurements material properties, e.g. Young's modulus, Poisson's ratio etc. are calculated. Measurements in temperatur chambers are possible and allow to determine temperature dependencies.
The strain measurement with multiple cameras gives meaningful Data and is used as the basis for the improvement of material cards and simulations.
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