A macroscopic yield criterion for crystalline polymers

Yield studies including uniaxial tension, uniaxial compression and biaxial stress states (developed with internally pressurized thin wall tubes) were conducted with high density polyethylene. The experimental results are compared with a predicted yield locus based upon a pressure-modified von Mises criterion. Agreement was quite reasonable although a slight degree of anisotropy was noted in the test material. Since this same yield criterion has earlier been shown to provide excellent agreement with glassy amorphous polymers it appears unnecessary to employ different criteria for different polymers if one is concerned with macroscopic yielding.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33777/1/0000030.pd

Yield locus studies of oriented polycarbonate An anisotropic and pressure-dependent solid

Uniaxial and biaxial stress states were employed so as to investigate the yield behavior of oriented polycarbonate. These experimental results are compared with a theoretical yield locus based upon a yield criterion proposed for solids that are both anisotropic and pressure dependent in regard to macroscopic yield behavior. A good correlation between theory and experiment was found.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22244/1/0000680.pd

A yield criterion for anisotropic and pressure dependent solids such as oriented polymers

The anisotropic yield criterion first posed by Hill has been modified to account for differences in tensile and compressive yield strengths in a given direction; additionally, the influence of hydrostatic pressure on yielding is also considered. Predictions using this new criterion are compared with published experimental results involving oriented polymers and excellent agreement is found. It is suggested that this criterion is more correct on fundamental grounds than those put forth in earlier publications.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44783/1/10853_2004_Article_BF00754900.pd

Macroscopic yielding behavior of polymeric materials

http://deepblue.lib.umich.edu/bitstream/2027.42/7199/5/bad1125.0001.001.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/7199/4/bad1125.0001.001.tx

Amorphous structure heat: Molecular structure from solution heats of polymethylmethacrylate in orthodichlorobenzene

The heats of solution in orthodichlorobenzene were measured as a function of temperature for both as‐reprecipitated and quenched atactic polymethylmethacrylate. The as‐reprecipitated curve decreases linearly with a slope of 0.096 cal∕g°C from room temperature to 90°C, and above 110°C has a constant value of +1.5 cal∕g. The quenched material data decreases linearly with a slope of 0.12 cal∕g°C from room temperature to 55°C, jumps +2 cal∕g at 55°C, and continues the linear decrease with a slope of 0.096 cal∕g°C from 55 to 90°C. The data suggests that isotactic stereochemical impurities in the atactic material are able to crystallize at 55°C which is the Tg of i‐PMMA, and therefore must be associated as i‐PMMA islands in a rigid atactic‐syndiotactic PMMA matrix. This also suggests that the β transition in PMMA may be associated with the isotactic impuritiesPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70426/2/JAPIAU-45-10-4155-1.pd

Amorphous structure heat: Molecular mechanisms from solution heats of poly(2,6‐dimethyl‐p‐phenylene oxide) in orthodichlorobenzene

The heats of solution in orthodichlorobenzene were measured as a function of temperature for both quenched and as‐received polyphenylene oxide. The curves are linear below 110°C with slopes of 0.098 cal∕g°C and linear above 110°C with slopes of 0.032 cal∕g°C. The inflection at 110°C is attributed to a β transition. The plot for the as‐received material is displaced vertically from that of the quenched material by 2.75 cal∕g which is attributed to the fact that the as‐received material contains about 27.5% crystallinity. The major component of the heats of solution is the exothermic contribution from the solvent‐induced freeing or relaxation of the constrained molecular motions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70773/2/JAPIAU-45-10-4151-1.pd