Testing methods optical microscopy

The optical microscope is a valuable tool in the laboratory and has numerous applications in most industries. Depending on the type of data that is required to solve a particular problem, optical microscopy can provide information on particle size, particle morphology, color, appearance, birefringence, etc. There are many accessories and techniques for optical microscopy that may be employed for the characterization of the physical properties of materials and the identification of unknowns, etc. Utilization of a hot-stage accessory on the microscope for the characterization of materials, including pharmaceutical solids (drug substances, excipients, formulations, etc.), can be extremely valuable. As with any instrument, there are many experimental conditions and techniques for the hot-stage microscope that may be used to collect different types of data. Often, various microscope objectives, optical filters, ramp rates, immersion media, sample preparation techniques, microchemical tests, fusion methods, etc., can be utilized. 

Ultimate tensile strength, stifihess, and strain-to-failure were determined quasi-statically for each class of as-received material in accordance with ASTM D 3039 Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials using a deflection rate of 2.5 mm/min (0.10 in./min). A total of thirty samples were tested, ten of each material type. In addition, two samples of each material were set aside for crack density analysis using x-ray and optical microscopy techniques. 

Les] Stationary-drop method tests of wettabiUty, optical microscopy, electron microscopy, EPMA Adhesive characteristics and formation of phase boundaries in Cu rich composite materials manufactured by powder metallurgical process at 1100-1300°C... 

The CNB test specimen does not require crack length measurement, thereby providing some convenience to the user. However the SEPB and SCF test methods require quality measurements if accurate fracture toughness estimates are expected. For the SEPB test specimen, the precrack front is very difficult to delineate unless it leaves a crack arrest line. An arrest line is easily detected if the crack tip turns out of plane or is hooked, thereby making the precrack and fast fracture plane non-coplanar, as shown in Figure 7. In one study, some cracks were so planar that the front could not be detected with conventional optical microscopy [12]. In such cases, the use of dye penetrants have been successful as shown in Figure 8, however, in some cases penetrants tend to bleed on the fracture surface and the measurements must be made immediately. Dye penetrants must be used with caution as they may cause environmentally assisted crack growth. 

There are no nondestructive testing methods that can measure the efficiency of a stress-relief cycle other than direct measurement of residual stresses by x-ray diffi action. No significant changes in microstructure due to stress-relieving heat treatments can be detected by optical microscopy. 

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