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Overflow is usually used to keep fluid continuously flowing to avoid the fluid from changing flow direction and subsequently inducing large stresses. To explore the mechanism of flow-induced stress evolution, a flow model was established in terms of compressible, non-isothermal, and viscoelastic flow. Based on the Leonov model and the mid-plane approach, a pseudo-Poisson type equation for pressure was derived to decouple the interdependence between velocity and pressure. To improve computational efficiency, a numerical approach involving double iterations was proposed to solve the flow problem. Two kinds of mold cavities, with and without overflow, were designed and manufactured. Molding experiments were conducted, and corresponding simulations based on the proposed model and algorithm were performed. The results show that the simulated contours of flow-induced stress are in good agreement with the photoelastic streaks. The use of overflow can significantly reduce flow-induced stresses. If the slot thickness is set to a proper value, the flow-induced stress can be reduced by more than 80%. On the other hand, a slot that is too thick does not have significant reducing effects. Therefore, using overflow to reduce flow-induced stresses during transparent part production is a promising approach if the material cost is worthy of the quality. Highlights * A double iteration method is proposed for viscoelastic flow problem. * Overflow can reduce the stress as much as 80% if the dimension is properly set. * The simulated stress streaks are in good agreement with photoelasticities. KEYWORDS finite element method, flow-induced stress, Leonov model, overflow, viscoelastic, 1 | INTRODUCTION Injection molding (IM) is the most efficient mass-production technology for manufacturing polymers in complex and detailed geometries with high precision. In view of these advantages, most transparent [...]

Daytime radiative cooling material provides a low‐energy way of cooling because it can reflect sunlight and radiate heat without consuming any energy. However, there are still great difficulties in manufacturing low‐cost, high‐efficiency, sustainable, and biodegradable daytime radiative cooling materials. In this paper, poly (vinyl alcohol)/boron nitride (PVA/BN) composite aerogels were prepared by freeze‐drying technology. By adjusting the PVA concentration and BN content, the aerogel can achieve high sunlight reflectivity (96%), high mid‐infrared emissivity (96%) and good thermal insulation performance. Therefore, the temperature of the aerogel can be reduced to 12.5°C lower than the ambient temperature at night, and 5.5°C lower than the ambient temperature under the direct sunlight of 900 W/m2. This aerogel opens an environmentally sustainable pathway for radiative cooling applications. [ABSTRACT FROM AUTHOR]

To describe uncured rubber melt flow, a modified Phan–Thien–Tanner (PTT) model was proposed to characterize the rheological behavior and a viscoelastic one-dimensional flow theory was established in terms of incompressible fluid. The corresponding numerical method was constructed to determine the solution. Rotational rheological experiments were conducted to validate the proposed model. The influence of the parameters in the constitutive model was investigated by comparing the calculated and experimental viscosity to determine the most suitable parameters. The uncured rubber viscosity was 3–4 orders larger than that of plastic and did not have a visible Newtonian region. Compared with the Cross-Williams-Landel-Ferry (Cross-WLF) and original PTT models, the modified PTT model can describe the rheological characteristics in the entire shear-rate region if the parameters are set correctly.

This work presents a tunable receiver analog front-end (AFE) circuit, capable of achieving data rates between 14 Gb/s and 28 Gb/s. The circuit is implemented using the TSMC 65 nm CMOS technology. The circuit incorporates a continuous-time linear equalizer (CTLE), a transimpedance amplifier (TIA) and an output buffer. A g m -boosted technique is employed within the CTLE for bandwidth and gain enhancement, while the TIA leverages a super source follower (SSF) structure to combat parasitic output node issues. By adjusting the tunable structures in the circuit, the proposed AFE can achieve variable DC gain at 14 GHz. Simulation results reveal that the AFE can compensate for the channel loss at the 14 GHz Nyquist frequency, delivering eye diagram spreads of approximately 0.85 UI and 0.78 UI at 14 Gb/s and 28 Gb/s, respectively. The complete post-simulation layout area is only 0.0026 mm2. Operating with a power consumption of 10.5 mW, the AFE exhibits an exceptional FoM of 11.8 pJ/bit/dB. [ABSTRACT FROM AUTHOR]

Polymer film melt stretching exhibits a unique stress–strain behavior, featuring a stress plateau followed by a sudden increase with increasing the strain. This phenomenon poses a challenge to conventional melt-extension theories and methods. To address this, we derive a simplified flow theory according to the symmetric characteristics of thin melt-stretching, and propose a modified multi-mode Leonov model (m-Leonov) that accounts for molecular orientation effects, a crucial factor in accurately simulating the process. In order to improve the computational efficiency, an iterative algorithm was developed to decouple the interdependence between governing and constitutive equations. The computational results reveal that the viscoelastic nature of the film contributes to a delay in the transformation of stretching forces, leading to the observed stress plateau. Significantly, our m-Leonov model successfully predicts both the plateau and the subsequent abrupt increase in stress, across various temperatures and stretching rates. These simulations closely agree with experimental data, underlining the robustness of our approach. Our findings would enhance the understanding of rheological complexities in film stretching, offering potential applications in various materials and polymer processing. [ABSTRACT FROM AUTHOR]

Flow-induced stress in compression stage is complex because compression flow combines both shear flow and extensional flow characters and involves the boundary change in melt front and compressing directions. To describe this kind of flow effectively, the theoretical model was established in terms of three-dimensional compressible and viscoelastic fluid, and the material derivative which includes mesh moving velocity was introduced to modify the convective terms in governing and constitutive equations based on Arbitrary Lagrangian Eulerian description. The corresponding variational equations were derived via Gauss formula and the finite element method was used to discretize the flow variables with mixed elements. In order to decouple the interdependence of velocity, stress, and temperature, a new approach involves twofold iterations was proposed to solve nonlinear flow problem. A new mesh updating scheme was presented to keep consistent with compressed regions. Numerical results indicate the compression can reduce the flow-induced stress significantly compared to conventional injection molding, increase compressing velocity enlarges flow-induced stress, and high temperature decreases flow-induced stress. The proposed method was verified by photoelastic pictures and measured pressures and temperatures during molding., INTRODUCTION The residual flow-induced stress is responsible for the anisotropy of mechanical, thermal, and optical properties, and affects the long-term dimensional stability. Less or free stress manufacturing has attracted an [...]

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A series of rotary rheological experiments were conducted for high-impact polystyrene (PS-HI) under different temperatures to analyze the precision of conventional obtained from usually used viscous models. Then, a flow theory based on Phan-Thien Tanner (PTT) model was established and the corresponding algorithm was constructed to study the viscoelastic characteristics of rubber-like state PS-HI. Both theoretical and numerical results indicated that the Cross and Carreau-Yasuda models could describe the rheological characteristics of PS-HI better compared to other viscous models. The viscoelastic PTT model exhibited a significant improvement in precision, indicating that PS-HI presented some elasticity in the rubber-like state. [ABSTRACT FROM AUTHOR]

This study presents a self‐designed foaming apparatus and routes to manufacture foamed isotactic polypropylene (iPP) blends with uniform and dense cells, using styrene‐ethylene‐butadiene‐styrene (SEBS) block copolymer as toughening additive. The addition of SEBS can clearly enhance the impact strength of solid iPP, iPP blends with a 20 wt% SEBS has obtained high notched impact strength of 75 kJ/m2, which is ca. 16 times larger than that of neat iPP. Relatively fine microcellular iPP‐SEBS foams with the average cell size of several micrometers, and the cell density of 109 cells/cm3 were fabricated using a batch foaming procedure. Moreover, using our self‐designed mold and compression foaming method, iPP‐SEBS foams with balanced mechanical properties were produced. With the increasing of SEBS, tensile strength and flexural strength were slightly decreased, but the impact strength was increased clearly. The balanced mechanical properties between stiffness and toughness were achieved after compression foaming. [ABSTRACT FROM AUTHOR]