No abstract

A new method to measure the movement of the flexible bag used in vacuum infusion is presented. The method is based on an in‐house developed stereoscopic digital speckle photography system (DSP). The advantage with this optical method, which is based on cross‐correlation, is that the deflection of a large area can be continuously measured with a great accuracy (down to 10 μm). The method is at this stage most suited for research but can in the long run also be adopted in production control and optimization. By use of the method it was confirmed that a ditch is formed at the resin flow front and that there can be a considerable and seemingly perpetual compaction after complete filling. The existence of the ditch demonstrates that the stiffness of the reinforcement can be considerably reduced when it is wetted. Hence, the maximum fiber volume fraction can be larger than predicted from dry measurements of preform elasticity. It is likely that the overall thickness reduction after complete filling emanates from lubrication of the fibers combined with an outflow of the resin. Besides, the cross‐linking starts and the polymer shrinks. Hence, the alteration in height will continue until complete cross‐linking is reached.

A technique to measure two-dimensional deformation fields of a layer inside materials during dynamic events such as impact experiments is presented. Even optically opaque materials like cement can be evaluated when flash x rays are used. Blocks of polyester and cement were prepared with a layer of x-ray-absorbing lead particles. The specimens were then hit by a 9-mm-diameter steel sphere (ball bearing) fired from a 9-mm-bore gas gun at a velocity of 373.5 +/- 3.0 ms(-1). A 30-ns-long x-ray pulse exposed one radiograph before impact; another radiograph was exposed a short time after the impact on the specimen. The two-dimensional displacement field was obtained when the x-ray radiographs were digitized by a conventional flatbed scanner, and a digital speckle photography algorithm was used to calculate the displacements. The flash x-ray technique allowed examination of the deformation at the layer inside the material during failure, thus giving interesting data about the material flow field around the impactor.

A metrology system is presented that measures internal three-dimensional (3-D) displacement fields. The system uses a stereo pair of flash x-ray heads and correlation analysis to measure the true deformation of a layer of x-ray-absorbent particles inside the specimen. The 3-D deformation field inside blocks of polyester was determined. The polyester blocks were impacted by a 9-mm steel ball bearing fired from a 9-mm-bore gas gun at a speed of 373.5 +/- 3.0 m s(-1). At a given time after impact, a short-duration (30 ns) flash x-ray pulse exposes the x-ray radiographs and freezes the events during impact. Thereafter, the x-ray radiographs are scanned into a personal computer and analyzed as in digital speckle photography.

Projected random patterns have been used to measure the shape of discontinuous objects. A sequence of independent random patterns are projected onto the object. These images are analyzed by use of the technique called temporal digital speckle photography (DSP) that is introduced here. With temporal DSP the spatial resolution of the shape measurement is improved considerably compared with previously reported results with projected random patterns. A calibration procedure is described that uses a sequence of independent random patterns to calibrate measurement volume. As a result, independent space coordinates for each subimage are obtained. The accuracy is of the order of 1/1000 of the field of view where a subimage size of 8 pixels seems to be a good compromise between reliability and spatial resolution. The technique is illustrated with a measurement of an electrical plug and a 9-V battery.