The Thermodynamics of the Glassy State

Rehage, G.; Borchard, W.

doi:10.1007/978-94-010-2355-9_2

Cited by 52 publications

(13 citation statements)

References 79 publications

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“…Examples include alumina reinforced with aluminum particles [18,19,20], silicon carbide containing aluminum [21], and tungsten carbide containing a dispersed binder phase of cobalt [22]. In these systems, the measured enhancement of toughness (usually in terms of fracture energy) is typically found to reach a factor of three or four times the matrix toughness, and is attributed to plastic deformation of bridging ligaments.…”

Section: Ceramic Matricesmentioning

confidence: 99%

Experimental investigations of crack trapping in brittle heterogeneous solids

Mower

Argon

1995

Mechanics of Materials

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Over the past two decades many mechanisms of toughening have been considered for brittle solids. Some of the most prominent ones applicable to either monolithic materials or fiberreinforced composites include deformation-induced local transformations, micro-cracking, crack trapping, crack bridging, and fiber pull-out. Few if any of these have been studied in the past in a manner which permitted evaluation of the effects of individual mechanisms in the absence of other interacting mechanisms. Here we present the development, analysis and results of an experimental study of toughening by the process of crack trapping by second-phase particles (spheres and fibers) of such toughness that make them impenetrable by probing cracks, forcing the cracks to bow around the obstacles with increasing applied load.The model fracture specimens employed here were wedge-loaded double cantilever beams cast of a brittle epoxy, containing macroscopic (3mm-diameter) inclusions of Nylon or polycarbonate having similar elastic properties to the matrix. The tests were performed at -60*C to achieve controlled, stable crack propagation. Images of the crack fronts advancing at velocities of about 10-4 M/s were recorded with good resolution, providing a continuous record of crack-front shapes during the evolution of the crack-trapping process from the initial pinning configuration through the transition to crack-flank bridging. Remarkable agreement between these images and crack-front shapes predicted by the numerical simulation of Bower & Ortiz is demonstrated. A parametric approach was adopted to study the influence of obstacle spacing, surface adhesion and thermally-induced residual stresses upon the observed crack-front behavior and enhanced stress intensity required to propagate the cracks past these obstacles. Analysis of the quantitative data has demonstrated that, in brittle matrices containing particle volume fractions of approximately 0.2, toughness enhancement by over a factor of two, relative to neat matrix values, may be achieved through the crack-trapping mechanism alone, provided that a high level of adhesion can be maintained between the matrix and the tough reinforcing particles.

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Section: Ceramic Matricesmentioning

confidence: 99%

Experimental investigations of crack trapping in brittle heterogeneous solids

Mower

Argon

1995

Mechanics of Materials

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“…Structural relaxation of glassy polymers has been widely studied in bulk materials, and it is now well understood [1][2][3][4][5]. Relaxation is important for explaining the long-term changes in physical properties (e.g., elastic modulus, dielectric strength, and refractive index) during the aging of a glass [1,2].…”

Section: Introductionmentioning

confidence: 99%

“…Relaxation is important for explaining the long-term changes in physical properties (e.g., elastic modulus, dielectric strength, and refractive index) during the aging of a glass [1,2]. In bulk polymer glasses, temperature-volume relationships have been thoroughly studied and are well documented.…”

Section: Introductionmentioning

confidence: 99%

Thickness dependence of structural relaxation in spin-cast, glassy polymer thin films

et al. 2004

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The isothermal structural relaxation of glassy, spin-cast polymer thin films has been investigated. Specifically, the thickness h of freshly cast poly(methyl methacrylate) thin films was measured over time using spectroscopic ellipsometry. The spin-cast films exhibit a gradual decrease in thickness, which is attributed to structural relaxation of the glass combined with simultaneous solvent loss. In all cases, h was found to be greater than the equilibrium thickness h ϱ , which is obtained by cooling slowly from the melt. It is observed that both the rate of the volume relaxation and the fractional departure from h ϱ (referred to as ␦ 0 ) increase with increasing film thickness. In the limit of very thin films, the initial h is close to h ϱ , and ␦ 0 is small, whereas in thick films ͑Ͼ500 nm͒, a plateau value of ␦ 0 of 0.16 is observed, which is close to the volume fraction of the solvent at the vitrification point. This dependence of ␦ 0 on thickness is observed regardless of the substrate, polymer molecular weight, or angular velocity during spin casting. Enhanced mobility near film surfaces could be leading to greater relaxation in thinner films prior to, and immediately after, the vitrification of the polymer during the deposition process.

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“…The presence of crystalline regions typically exhibits resistance to solvent penetration so decreases the moisture uptake, which has been widely reported by many researchers (Rehage and Borchard, 1973;Gagnon, 1986;Malucelli et al ., 2000). In addition water changes the structure of the amorphous regions as plasticizer.…”

Section: Discussionmentioning

confidence: 93%

“…Since most of the small pores are filled, the molecular relaxation in this region absorbs more moisture and makes volume change a higher dependence on relative humidity. In the high dependence region, the absorbed moisture acts like a plasticizer and induces starch plasticization, which takes more moisture content in return (Rehage and Borchard, 1973). In addition the saturation-caused phase transformation at T g (glass transition temperature) contributes more volume in expanding.…”

Section: Discussionmentioning

confidence: 99%

Volume Change Measurements of Rice by Environmental Scanning Electron Microscopy and Stereoscopy

2007

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The measurement of volume change, which is induced by changing the relative humidity, is performed on rice by using environmental scanning electron microscope (ESEM) and stereoscopy techniques. The typical DeltaV% approximately RH curve of rice in both sorption and desorption can be categorized into three regions: low, intermediate, and high dependence on relative humidity from low- to high-relative humidity. The volume changes faster for rice samples with lower crystallinity, which is because the amorphous component is easier to absorb moisture than the crystalline component. The volume change behavior in various relative humidity environments is comparable with rice isotherm curve in sorption process though discrepancies exist in desorption, which are thought to be the presence of small pores and microstructure changes at high relative humidity. The volume in the desorption branch is less than that in the sorption branch at the same relative humidity, which can be attributed to the collapse of interior structures, existence of small pores, surface topography loss, and amylose leach.

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The Thermodynamics of the Glassy State

Cited by 52 publications

References 79 publications

Experimental investigations of crack trapping in brittle heterogeneous solids

Experimental investigations of crack trapping in brittle heterogeneous solids

Thickness dependence of structural relaxation in spin-cast, glassy polymer thin films

Volume Change Measurements of Rice by Environmental Scanning Electron Microscopy and Stereoscopy

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