MICROSCOPY & IMAGING
I
n recent work, the School of Engineering at the University of Aberdeen carried out in situ experiments to study the failure mechanisms of syntactic foam, using both X-ray microcomputed tomography with uniaxial compression. X-ray microcomputed tomography was used to image the foam whilst it was under compressive strain to obtain 3D images of the internal microstructure and the changes that occurred.
Te material studied (polymer matrix syntactic foams) is a low-density composite material. Te foam is made by randomly filling hollow particles into a material matrix and is categorised as closed-cell, this is due to fact that the particles are not connected and that each pore is enclosed in the matrix. Te properties of syntactic foams are highly influenced by hollow particles. Syntactic foam microstructure is determined by the particle; material, volume fraction and wall thickness. Commonly, the hollow particles in polymer matrix syntactic foams are fabricated from glass, ceramic, carbon and
Fig.1. 3D images of the internal microstructure and failure process STAGE SUCCESS
Case study showcasing how a stage enables the University of Aberdeen to observe compressive damage mechanisms in syntactic foam
fly ash cenospheres. A real-life application of syntactic foams is their use as insulation in the offshore oil industry. Te foam helps combat the cooler temperatures and higher pressure during the extraction of oil from further out at sea or at greater depths.
Te material during these studies was syntactic foam that was provided by Trelleborg (a global engineering group focused on polymer technology). Te foam featured hollow glass spheres embedded within an epoxy matrix. Prismatic blocks were machined from a bar measuring 10x10x10mm³. To ensure flat surfaces and to reduce stress concentrations, the surfaces of the specimen were ground using abrasive paper.
Fig. 2. XZ images of the same process shown in Fig. 1.
58
www.scientistlive.com
Te X-ray microcomputed tomography was carried out on the Zeiss VersaXRM-410. A microtension/ compression testing stage was mounted to the X-ray machine’s stage. Te configuration can be seen in Fig. 1.
Te sample was loaded into the
Deben CT5000 stage inside the 3mm vitreous glassy carbon tube. Te dimensions of the sample were carefully determined to ensure that the load needed to reach beyond the elastic limited would not exceed the load cell’s capacity. Te dimensions also ensured that there was satisfactory X-ray transmission to obtain high-resolution images.
Te samples were subjected to unconstrained, uniaxial, quasi-static compression test and scanned at various different levels of strain. Te sample was placed within the grips of the testing machine and was secured at the top and bottom. Te top grip remained stationary and the bottom grip moved up to compress the sample. Te strain was held constant during each scan and then increased up before the next scan was taken. Te Deben stage control software allowed the applied load and displacement to be controlled.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72
