Search results for "Continuous cooling transformation"
showing 10 items of 11 documents
Physical Cross Links in Amorphous PET, Influence of Cooling Rate and Ageing
2003
A Continuous Cooling Transformation (CCT) procedure can be used to distinguish the initial “state” of the amorphous PET samples produced upon solidification from the melt at different cooling rates. The material frozen at this stage behaves as a rubber when brought above the Tg due to the onset of physical cross links. The rubber is not a stable network, however, since physical cross links may eventually dissolve. Their size distribution, and possibly their number, depend on cooling rate and ageing. Some may be even stable above the glass transition and act as nuclei for further crystallization from the glass. Upon increasing cooling rate, size distribution becomes smaller and stability of …
Artificial Neural Networks to correlate Hot Deformation Cooling Rate and Deformation Temperature on Continuous Cooling Transformation of 22MnB5 Steel
2016
The 22MnB5 steel is a hot stamping steel developed with the aim to satisfy the increasing request of the automotive industries to apply materials able to guarantee higher passive safety and weight reduction. The hot stamping process is an innovative forming technique in which the deformations are carried out at elevated temperature and allows to achieve high strength components. The experimental characterization of the material response, at different values of the main variables of process, may result both expensive and time consuming, but the mutual effects evaluation of the deformation parameters and the phase transformations are necessary to produce components within the desired properti…
Relating morphology to nanoscale mechanical properties: from crystalline to mesomorphic iPP
2005
Abstract A nanoindentation technique using an atomic force microscope (AFM) was applied to characterize the mechanical behaviour of several isotactic polypropylene (iPP) samples. The samples were solidified from the melt with a CCT (continuous cooling transformation) procedure spanning a wide range of cooling rates thanks to a fast quenching apparatus developed by the authors. The influence of instrumental parameters on the nanoscale mechanical properties (indentation depth, Young's modulus) shows that for modulus determination one has to rely on simpler methods of force curve analysis based on trace curve alone. Structure homogeneity up to the scale of macroscopic samples used to evaluate …
Effect of Plastic hot deformation on the hardness and continuous cooling transformations of 22MnB5 micro-alloyed boron steel
2009
The strains, transformation temperatures, microstructure, and microhardness of a microalloyed boron and aluminum precoated steel, which has been isothermally deformed under uniaxial tensile tests, have been investigated at temperatures between 873 and 1223 K, using a fixed strain rate value of 0.08 s−1. The effect of each factor, such as temperature and strain value, has been later valued considering the shift generated on the continuous cooling transformation (CCT) diagram. The experimental results consist of the starting temperatures that occur for each transformation, the microhardness values, and the obtained microstructure at the end of each thermomechanical treatment. All the thermome…
Solidification of syndiotactic polystyrene by a continuous cooling transformation approach
2007
Syndiotactic polystyrene (sPS) was solidified from the melt under drastic conditions according to a continuous cooling transformation methodology developed by the authors, which covered a cooling rate range spanning from approximately 0.03 to 3000 °C/s. The samples produced, structurally homogeneous across both their thickness and surface, were analyzed by macroscopic methods, such as density, wide-angle X-ray diffraction (WAXD), and microhardness (MH) measurements. The density was strictly related to the phase content, as confirmed by WAXD deconvolution. The peculiar behavior encountered (the density first decreasing and then increasing with the cooling rate) was attributed to the singular…
Influence of plasticizers and cryogenic grinding on the high-cooling-rate solidification behavior of PBT/PET blends
2015
Two structurally different plasticizers (cyclic and linear) and the effect of cryogenic grinding on the solidification behavior at high cooling rates by a continuous cooling transformation approach of poly(butylene terephthalate)/poly(ethylene terephthalate), PBT/PET, blends are described. The solidification curve (density versus cooling rate) is confirmed as an effective tool to compare the differences in crystallization behavior under conditions mimicking processing. In comparison to the bulky cyclic plasticizer, the linear oligomeric one was found to have a more pronounced influence on the crystallization behavior. A 60/40 by weight PBT/PET blend shows a drop-off of density at ∼50 K/s. I…
The continuous cooling transformation (CCT) as a flexible tool to investigate polymer crystallization under processing conditions
2009
An experimental route for investigating polymer crystallization over a wide range of cooling rates (from 0.01 to 1000◦C/s) and pressures (from 0.1 to 40 MPa) is illustrated, using a method that recalls the approach adopted in metallurgy for studying structure development in metals. Two types of experimental setup were used, namely an apparatus for fast cooling of thin films (100–200 μm thick) at various cooling rates under atmospheric pressure and a device (based on a on-purpose modified injection molding machine) for quenching massive samples (about 1–2 cm3) under hydrostatic pressure fields. In both cases, ex situ characterization experiments were carried out to probe the resulting struct…
The solidification behavior of a PBT/PET blend over a wide range of cooling rate
2009
In recent years, much attention has been paid to the development of high-performance polyester blends, among which blends of polybutylene terephthalate/polyethylene terephthalate (PBT/PET) are expected to exhibit remarkable properties as far as their crystallization behavior is concerned. Through trial and error, appropriate commercial compositions have been chosen which could not be otherwise explained by a suitable interpretation of the mechanisms determining their solidification behavior. The solidification behavior of a 60/40 w/w PBT/PET blend was studied in a wide range of cooling conditions, according to a continuous cooling transformation (CCT) procedure developed previously, aiming …
Influence of plasticizers suggests role of topology in polymer solidification at high cooling rates
2012
Although solidification in processing deter- mines short- and long-term properties, methods for under- standing polymer crystallization mostly rely on real time experiments. Their evidences being drawn on time scales farther apart with respect to those experienced in process- ing. Nor significant outcomes have been so far drawn with approaches mimicking the typical processing times, the Continuous Cooling Transformation methods. Use of these techniques has indeed been limited to a heuristic interpretation of the structure developed under extreme solidification conditions without suggesting alternative routes to the understanding or even clues to the many open questions on polymer crystalliz…
Design, build-up and optimization of a fast quenching device for polymeric thin film
2014
In this work an innovative apparatus for the characterization of polymer solidification under very high cooling rates (up to thousand of K/s) is described, according to the continuous cooling transformation approach adopted in metallurgy for studying structure development in metals. The proposed model experiment is addressed to design a method for the characterization of non-isothermal solidification behaviour, encompassing typical cooling conditions of polymer processing. Only temperature history determines the structure formed, as melt solidification takes place in quiescent conditions. With respect to the device previously developed by the authors [1, 3] the present equipment presents th…