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According to the 3-phase model, semi-crystalline thermoplastics consist of a mobile amorphous fraction (MAF), a rigid amorphous fraction (RAF), and a crystalline fraction (CF). For the two polyesters Polybutylene Terephthalate (PBT) and Polyethylene Terephthalate (PET), the composition of these phases was investigated using the largest possible variation in the isothermal and non-isothermal boundary conditions. This was performed by combining the conventional Differential Scanning Calorimetry (DSC) with the Fast Scanning Calorimetry (FSC). From the results it can be deduced that the structural composition of both polymers is characterised by a large fraction of the rigid amorphous phase. This is mainly formed either during the primary crystallization in the low temperature range or during the subsequent secondary crystallization that follows primary crystallization in the high temperature range. Depending on the thermal history, the fraction of the mobile amorphous phase of both polymers approaches a minimum, which does not appear to be undercut.

The behavior of glass-fiber reinforced phenolic resin in the presence of the wall surface during injection molding under various processing parameters has been studied with a rather simple but effective and useful method, namely, the spotwise painting of the mold wall surface. The experimental results show clearly a strong slip of the phenolic melt on the cavity surface. The occurrence of slip begins immediately when the phenolic melt contacts the wall surface. This technique was applied to study the slip of thermoplastic melts inside a rectangular mold. However, completely opposite results found between the flow behavior of thermosets and thermoplastics on the cavity surface raise the questions concerning the applicability of thermoplastics injection molding concepts and rheological property testing methods, respectively, simulation packages for thermosets.

Intelligent light weight concepts are increasingly designed as multi-material systems in order to achieve optimized properties through a targeted combination of materials. For these applications, the market demands joining technologies that make it possible to join foreign materials reliably (e.g., incompatible thermoplastics, thermoplastic-metal and thermoplastic-thermoset). In view of these industrial challenges, thermoplastic staking is an established forming process. At present, computer-aided development and precise FE-simulation (finite element-simulation) of these processes are not state-of-the-art. Accordingly, the previous design is based on subjective empirical values and empirical tests of the component. Within the framework of the paper, these gaps are to be closed by the development of numerical models for the heating and forming behavior of thermal plastic rivets (hot air staking) and the associated experimental validation. This requires the experimental development of the cause-effect relationships between melt formation and the resulting forming behavior. Finally, the numerical simulation shows a high conformity to the experimental data and allows an evaluation of the minimum heating time as well as initial approaches to evaluating the resulting structures by the simulation.

Injection molding is one of the most commonly applied processing methods for plastic components. Heat transfer coefficient (HTC), which describes the heat conducting ability of the interface between a polymer and cavity wall, significantly influences the temperature distribution of a polymer and mold during plastic component injection molding. This study focuses on HTC under diverse processing situations. On the basis of the heat conducting principle, a theoretical model for calculating the average HTC within an injection cycle was presented. Experimental injection studies were also performed to acquire necessary temperature data. The heat quantity and HTC across the interface between a polymer and cavity wall was on the basis of the results of the experimental injection studies. The factors influencing the HTC were analyzed on the basis of the factor weight during injection molding cycle. Finally, the surface roughness of plastic components obtained from disparate processing situations was measured and compared with the surface roughness of inserts. The surface roughness results are in good agreement with the HTC value and can be used to interpret the cause of variation. The results of this study will be beneficial for understanding the heat transfer process comprehensively, predicting the temperature field, arranging the cooling system, and offering precise HTC for numerical simulation.

The filling process of a micro‐cavity was analyzed by modeling the compressible filling stage by using pressure‐dependent viscosity and adjusted heat transfer coefficients. Experimental filling studies were carried out at the same time on an accurately controlled microinjection molding machine. On the basis of the relationship between the injection pressure and the filling degree, essential factors for the quality of the simulation can be identified. It can be shown that the flow behavior of the melt in a micro‐cavity with a high aspect ratio is extremely dependent on the melt compressibility in the injection cylinder. This phenomenon needs to be considered in the simulation to predict an accurate flow rate. The heat transfer coefficient between the melt and the mold wall that was determined by the reverse engineering varies significantly even during the filling stage. With increasing injection speed and increasing cavity thickness, the heat transfer coefficient decreases. It is believed that the level of the cavity pressure is responsible for the resulting heat transfer between the polymer and the mold. A pressure‐dependent model for the heat transfer coefficient would be able to significantly improve the quality of the process simulation. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers

A completely opposite injection molding filling behavior of thermosets and thermoplastics by an effective and useful method developed by the authors was found. Specifically, for the thermoset injection molding, there is a strong slip between the thermoset melt and wall surface, which is not found for the injection molding of thermoplastic materials. In addition, the variables, such as the filler content, the mold temperature, the injection speed, and the surface roughness that could lead to or influence the slip phenomenon of thermoset injection molding compounds, were also investigated. Furthermore, microscopy was conducted to verify the correlation between the mold wall slip and fiber orientation. The results obtained in this paper open challenges in the field of the calculation, analysis, and simulation of mold filling behavior of highly glass fiber-reinforced thermoset resins in the injection molding process with consideration of wall slip boundary conditions.

A multiscale simulation method for the determination of mechanical properties of semi-crystalline polymers is presented. First, a four-phase model of crystallization of semi-crystalline polymers is introduced, which is based on the crystallization model of Strobl. From this, a simulation on the nanoscale is derived, which models the formation of lamellae and spherulites during the cooling of the polymer by using a cellular automaton. In the solidified state, mechanical properties are assigned to the formed phases and thus the mechanical behavior of the nanoscale is determined by a finite element (FE) simulation. At this scale, simulations can only be performed up to a simulation range of a few square micrometers. Therefore, the dependence of the mechanical properties on the degree of crystallization is determined by means of homogenization. At the microscale, the cooling of the polymer is simulated by a cellular automaton according to evolution equations. In combination with the mechanical properties determined by homogenization, the mechanical behavior of a macroscopic component can be predicted.

In the injection molding process, weld line regions occur when a molten polymer flow front is first separated and then rejoined. The position, length, and angle of weld lines are dependent on the gate location, injection speed, injection pressure, mold temperature, and, especially, the direction and degree of the polymer melt velocity in the mold-filling process. However, the wall surface velocity of the thermoset melt in the mold-filling process is not zero, which is not found for thermoplastic injection molding. The main reason leading to this difference is the slip phenomenon in the filling phase between the thermoset melt and the wall surface, which is directly affected by the filler content. In this study, commercial thermoset phenolic injection molding compounds with different amounts of filler were employed to investigate not only the mechanism of weld line formation and development behind an obstacle in the injection molding process but also the flow disturbance of the thermoset melt in the spiral flow part. In addition, the effect of the wall slip phenomenon on the flow disturbance characterization and the mechanism of weld lines of selected thermoset materials was carefully considered in this research. Furthermore, the generated material data sheet with the optimal developed reactive viscosity and curing kinetics model was imported into a commercial injection molding tool to predict the weld line formation as well as the mold-filling behavior of selected thermoset injection molding compounds, such as the flow length, cavity pressure profile, temperature distribution, and viscosity variation. The results obtained in this paper provide important academic knowledge about the flow disturbance behavior as well as its influence on the mechanism of weld line formation in the process of thermoset injection molding. Furthermore, the simulated results were compared with the experimental results, which helps provide an overview of the ability of computer simulation in the field of the reactive injection molding process.

The aim of this study is concentrated on the experimental investigation of crack initiation during dynamic wear process and its correlation with fatigue crack growth of reinforced rubber materials. The analyzed rubber compounds suitable for applications such as treads for truck tires were based on natural rubber (NR) and polybutadiene rubber (BR). The dynamic wear behavior has been studied using an own developed testing equipment based on gravimetric determination of mass loss of test specimen. Fatigue crack growth (FCG) analysis was performed under pulse loading in accordance with real dynamic loading conditions of rolling tires using the Tear Analyser (TA). We show the crack initiation process during dynamic wear with respect to different impact energies and correlate the liability of crack initiation with FCG data at given tearing energy as a function of the rubber compositions. We demonstrate the higher crack initiation resistance of rubber blends with increased content of BR, while a predominant influence of NR improves the resistance against crack propagation especially at higher strain levels due to strain induced crystallization.

The filling process of a micro-cavity was analyzed by modeling the compressible filling stage by using pressure-dependent viscosity and adjusted heat transfer coefficients. Experimental filling studies were carried out at the same time on an accurately controlled microinjection molding machine. On the basis of the relationship between the injection pressure and the filling degree, essential factors for the quality of the simulation can be identified. It can be shown that the flow behavior of the melt in a micro-cavity with a high aspect ratio is extremely dependent on the melt compressibility in the injection cylinder. This phenomenon needs to be considered in the simulation to predict an accurate flow rate. The heat transfer coefficient between the melt and the mold wall that was determined by the reverse engineering varies significantly even during the filling stage. With increasing injection speed and increasing cavity thickness, the heat transfer coefficient decreases. It is believed that the level of the cavity pressure is responsible for the resulting heat transfer between the polymer and the mold. A pressure-dependent model for the heat transfer coefficient would be able to significantly improve the quality of the process simulation. POLYM. ENG. SCI., 50:165-173, 2010. [C] 2009 Society of Plastics Engineers