Numerical stimulation of stress-induced crystallization of injection molded semicrystalline thermoplastics

Injection molded semicrystalline plastic products exhibit variable morphology along their thickness directions. The processing conditions have a significant effect on the crystallinity distribution in the final parts. However, because of the lack of sound theoretical models for stress-induced crystallization kinetics in thermoplastics, simulations of the injection molding process of semicrystalline plastics with the consideration of stress-induced crystallization have been scarce. A stress-induced crystallization model for semicrystalline plastics is proposed based on the theory that stress induced orientation of polymer chains increase the melting temperature of the plastics, and hence, the supercooling which is the driving force for crystallization. By assuming that the effect of stress on crystallization is only by increasing the equilibrium melting temperature, the basic quiescent state crystallization equation can be directly applied to model stress-induced crystallization kinetics. A simple experimental technique such as rotational rheometric measurement, can be used to determine the melting temperature shift. The model predicts the most prominent features of stress-induced crystallization: with the application of shear stress, crystallization rate becomes higher, the crystallization temperature range is broadened and the peak of crystallization rate shifts to higher temperatures. The main advantage of the model is that the parameters in the quiescent state crystallization model do not change and the parameters in the equilibrium melting temperature shift model are easy to determine. And the unknown constants are kept to a minimum. The injection molding process of semicrystalline plastics was simulated with the proposed stress-induced crystallization model. A pseudo-concentration method was used to track the melt front advancement. The simple Maxwell stress relaxation model in combination with WFL equation was used to investigate the importance of stress relaxation on the development of crystallinity during the injection molding. Simulations were carried out under different processing conditions to investigate the effect of processing parameters on the crystallinity of the final part. Other results such as skin layer build-up and mold pressure were also simulated. The simulation results reproduced most of the features that were obtained by the experiments reported in the literature

The materials processing research base of the Materials Processing Center

The goals and activities of the center are discussed. The center activities encompass all engineering materials including metals, ceramics, polymers, electronic materials, composites, superconductors, and thin films. Processes include crystallization, solidification, nucleation, and polymer synthesis

Phase-field-crystal models for condensed matter dynamics on atomic length and diffusive time scales: an overview

Here, we review the basic concepts and applications of the phase-field-crystal (PFC) method, which is one of the latest simulation methodologies in materials science for problems, where atomic- and microscales are tightly coupled. The PFC method operates on atomic length and diffusive time scales, and thus constitutes a computationally efficient alternative to molecular simulation methods. Its intense development in materials science started fairly recently following the work by Elder et al. [Phys. Rev. Lett. 88 (2002), p. 245701]. Since these initial studies, dynamical density functional theory and thermodynamic concepts have been linked to the PFC approach to serve as further theoretical fundaments for the latter. In this review, we summarize these methodological development steps as well as the most important applications of the PFC method with a special focus on the interaction of development steps taken in hard and soft matter physics, respectively. Doing so, we hope to present today's state of the art in PFC modelling as well as the potential, which might still arise from this method in physics and materials science in the nearby future.Comment: 95 pages, 48 figure

Additive manufacturing of the high-performance thermoplastic : Experimental study and numerical simulation of the Fused Filament Fabrication

Additive manufacturing (AM) refers to a wide variety of manufacturing processes for rapid prototyping and production of final and semi-final products. In opposite to conventional orsubtractive processes, in additive manufacturing, the material is gradually added layer by layer to form the parts. AM enables the fabrication of complex parts which were impossible or not costeffective to manufacture with the traditional processes. Fused Filament Fabrication (FFF) is basedon the melting of a polymeric filament in an extruder; the filament is then deposited layer by layerto manufacture the final parts. Despite growing interest from industries and a large audience inrecent years, these manufacturing processes are still not well mastered, especially for not mass produced polymers. In this thesis, we will take an insight into the printability of PEEK(Polyetheretherketone). The aim is to find the printing conditions to obtain the best quality of theprinted parts by FFF process. In the first step, we have determined the polymer properties influencing the quality of the printed parts by FFF. The rheological properties, the surface tension,the thermal conductivity and thermal expansion have been determined experimentally. Then, thecoalescence phenomenon of the polymeric filaments has been studied by experimental, analyticaland numerical simulation. Furthermore, the stability of the filament and its flow properties when itexits from the extruder in the FFF process has been determined by experimental, analytical andnumerical simulation. Then, we have focused on the determination of the die swelling of PEEKextrudate. Lastly, the kinetics of isothermal and non-isothermal crystallization of PEEK has beenstudied by experimental study. The kinetics of crystallization has been applied to FFF process bynumerical simulation in order to determine the optimum environment temperature to control thecrystallization of printed parts. The crystallization of PEEK reaches its maximum value (about22%) of crystallization during the deposition

An Investigation of Enhanced Additive Manufacturing Incorporating Spatial Performance Property Control throughout Printed Products

The overall objective of this research is to investigate and develop a novel additive manufacturing technique that enables additive manufacturing to make products with customizable and gradient properties to match the consumer’s needs. This research inte

Process–Structure–Properties in Polymer Additive Manufacturing

Additive manufacturing (AM) methods have grown and evolved rapidly in recent years. AM for polymers is an exciting field and has great potential in transformative and translational research in many fields, such as biomedical, aerospace, and even electronics. Current methods for polymer AM include material extrusion, material jetting, vat polymerisation, and powder bed fusion. With the promise of more applications, detailed understanding of AM—from the processability of the feedstock to the relationship between the process–structure–properties of AM parts—has become more critical. More research work is needed in material development to widen the choice of materials for polymer additive manufacturing. Modelling and simulations of the process will allow the prediction of microstructures and mechanical properties of the fabricated parts while complementing the understanding of the physical phenomena that occurs during the AM processes. In this book, state-of-the-art reviews and current research are collated, which focus on the process–structure–properties relationships in polymer additive manufacturing