In situ deformation

Deformation experiments can be conducted within the microscope in order to assess the nature of the change in structure as a function of the specific deformation process. In this section, deformation will include not just fracture but also heating stages in various microscopes (cryostages will be considered in Section 4.9). Hot stages and deformation stages are commonly applied to optical microscopy 

An example of a study conducted using a tensile stage in the SEM is the evaluation of the ductile failure of poly(vinyl chloride) [534] in which stamped dumbbell shaped pieces of polymer from 1 mm thick sheets were extended to a neck in an Instron tester and then strained in the SEM. Low accelerating voltage was used for imaging of the uncoated specimens. These experiments showed that, after neck formation, fracture occurs by crack propagation from a flaw or cavity within the surface craze. The in situ deformation of amorphous polymers by shear deformation and craze growth has been observed in optical microscope studies by Donald and Kramer [509]. Thin films of various 

Understanding of the mechanisms in rubber modified polymers have benefited from methods used by Michler et al. [493-495] for the in situ deformation of rubber modified amorphous polymers and butadiene-styrene block copolymers. The techniques used were microscopic investigations of deformed samples, including in situ deformation of thin sections by TEM and AFM. Deformation tests in the SEM included investigation of the samples using special tensile devices at different temperatures (from -150°C to 200°C) in an SEM or ESEM. Deformation 

Rubbery materials are easily penetrated by an AFM probe, and the penetration depth can be evaluated as a relative measure of local stiffness and to know the depth of imaging. Bhushan [537] reviewed the use of indentation in conjunction with AFM to determine mechanical properties such as hardness and Young s modulus of elasticity on micro to picoscales. In nanoindentation, which is often applied for probing mechanical properties of polymer materials, with or without an AFM, stiff cantilevers and diamond tips are used. 

Scanning probe microscope techniques can be used in a variety of environments, including at elevated temperatures [52] and under various liquids. Use of a hot stage with AFM has been shown to provide information on the organiza- 

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Figure 3. Electron microscopic techniques used to study micromechanical processes in polymers (a) investigation of fracture surfaces by SEM (b) investigation by TEM of ultrathin sections prepared from deformed and selectively stained bulk material and (c) deformation of samples of different thicknesses (bulk, semithin, and ultrathin)9 using special tensile stages with SEM, HVEM, and TEM. The technique in (c) shows the possibility of conducting in situ deformation tests in the electron microscope.

Figure 14. Deformation of toughened PP, showing an increasing number of cavi-tated particles with increasing elongation (SEM image produced in an in situ deformation test). The deformation direction is horizontal.

Fig. 3.76 Dislocation structure during in situ deformation of Zr02-10 mol% Y2O3 at 1150 °C [37]. With kind permission of Elsevier and Professor Messerschmidt...

Fig. 2. Survey of (electron and scanning force) microscopic methods for investigating micromechanical processes in polymers, a indicates the applied tension stress and the arrows indicate area and direction of investigation in the microscope (see text for full details), (a) fracture surfaces— tension test, impact test, broken pieces (b) surfaces of deformed (loaded) bulk samples (c) in situ deformation of thin samples.

Some aspects of the first stage of deformation are visible in the in situ deformation test of a PE blend by sfm in Figures 16 and 17 and are also revealed by tern studies of crack-tip crazes in PE (48). 

Microfibril reinforced polymer-polymer composites (MRCs) based on two thermodynamically nonmiscible thermoplastics with different melting temperatures (T ) are prepared through a melt extrusion-hot stretching-quenching process, during which the high-melt-temperature component as the dispersed phase in situ deforms into microfibrils. The post... 

In the second case, the mechanical deformation method will not be standard, but suitable samples will be designed to fit the microscope. The in situ deformation of polymers is almost always conducted in the SEM at low magnification and is most often used for fibers and fabrics. Other microdeformation methods are used to prepare thin films for TEM observations, to model fiber structure or to investigate crazing. Since the mechanical deformation technique is... 

The in situ deformation of amorphous polymers by shear deformation and craze growth has been observed in optical microscope studies by Donald and Kramer [381]. Grids with thin films of various polymers and polymer blends were prepared on copper grids which were strained in air on a strain frame held in an optical microscope. The films were precracked in an electron microscope by a method more fully described by Lauterwasser and Kramer [382]. Many crazing studies are evaluated by in situ methods, and optical microscopy plays a major role in providing an overview of the deformation structure. Crazing studies will be more fully explored in the next section. 

Figure 4.13 HDPE/VLDPE (80/20) blend in an AFM in situ deformation test. Left before deformation middle and right after average deformation of 16% and 56%, respectively arrows with letters a, b, c, and d mark areas of different elongation at and between soft VLDPE particles (bright) [13]...

SBR filled with 50 phr carbon black, in situ deformation test ... 

Figure 5.9 Sequence of micrographs from an in situ deformation test of HIPS crack propagation in crazes and crack stop at rubber particles crack starts from above deformed SDS in HEM...

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