Digital design and thermomechanical process simulation for 3D printing with ABS and soyhull fibers reinforced ABS composites.

Recent demonstrations with fused filament fabrication (FFF) 3D printing have shown to produce prototypes as well as production components. Additionally, due to the FFF process platforms being low-cost and readily available there has been a high-demand to produce on-demand parts for various applications in automotive, in-space manufacturing and electronic industries. However, current limitations such as limited availability of advanced composites materials, and guidelines for design-for-manufacturing make the process prone to trial-and-error experiments both at the materials development, product design and manufacturing stage. In this work, new thermomechanical process simulations platform, Digimat-AM has been evaluated to address and demonstrate digital design and manufacturing of FFF process by performing simulation and experiments. With the use of Acrylonitrile butadiene (ABS) material and soyhull fibers reinforced ABS composite (ABS-SFRC) as a basis, an L9 Taguchi design-of-experiment (DOE) was setup by varying key process input parameters for FFF 3D printing such as layer thickness, melt temperature and extrusion multiplier were varied for three levels. A total of 9 DOE simulations and experiments were performed to compare part properties such as dimensions, warpage, and print time were analysed. Additionally, ANOVA analysis was performed to identify the optimum and the worst conditions for printing and correlate them with their effect on the mechanical properties of the printed samples. Furthermore, from the simulation results, a reverse warpage geometry, 3D model was generated that factors for part warpage, shrinkage, or other defects to enable 3D printing parts to design dimensions. Subsequently, using the generated reversed warpage geometry was used to perform 3D printed experiments and analyzed for part dimensions and defects. As a case study, a functional prototype [Two different geometries] was designed and simulated on Digimat-AM and using the above guide, 3D printing was performed to obtain part to specific dimensions. In addition to that, the thermomechanical properties of ABS-SFRC were needed to perform the Digimat simulation of geometries printed with ABS-SFRC. However, the materials property database of ABS-SFRC is very limited and experimental measurements can be expensive and time consuming. This work investigates models that can predict soyhull fibers reinforced polymer material composite properties that are required as input parameters for simulation using the Digimat process design platform for fused filament fabrication. ABS-SFRC filaments were made from 90%ABS 10% soyhull fibers feedstock using pilot scale filament extrusion system. Density, specific heat, thermal conductivity, and Young\u27s modulus were calculated using models. The modeled material properties were used to conduct simulations to understand material-processing-geometry interactions

Advanced Composite Materials and Structures

Composite materials are used to produce multi-objective structures such as fluid reservoirs, transmission pipes, heat exchangers, pressure vessels due to high strength and stiffness to density ratios and improved corrosion resistance. The mathematical concepts can be used to simulate and analyze the generated mechanical and thermal properties of composite materials regarding to the desired performances in actual working conditions.  To solve and obtain the exact solution of the developed nonlinear differential equations in the composite materials, analytical methods can be applied. Mechanical and thermal analysis of complex composite structures can be numerically analyzed using the Finite Element Method (FEM) to increase performances of composite structures in different working conditions. To decrease failure rate and increase performances of composite structures under complex loading system, thermal stress and effects of static and dynamic loads on the designed shapes of composite structures can be analytically investigated. The stresses and deformation of the composite materials under the complex applied loads can be calculated by using the FEM method in order to be used in terms of safety enhancement of composite structures. To increase the safety level as well as performances of the composite structures in different working conditions, crack development in elastic composites can be simulated and analyzed. To develop and optimize the process of composite deigning in terms of mechanical as well as thermal properties under different mechanical and thermal loading conditions, the advanced machine learning systems can be applied. A review in recent development of composite materials and structures is presented in the study and future research works are also suggested. Thus, to increase performances of composite materials and structures under complex loading systems, advanced methodology of composite designing and modification procedures can be provided by reviewing and assessing recent achievements in the published papers

Advanced Composite Materials and Structures

Composite materials are used to produce multi-objective structures such as fluid reservoirs, transmission pipes, heat exchangers, pressure vessels due to high strength and stiffness to density ratios and improved corrosion resistance. The mathematical concepts can be used to simulate and analyze the generated mechanical and thermal properties of composite materials regarding to the desired performances in actual working conditions.  To solve and obtain the exact solution of the developed nonlinear differential equations in the composite materials, analytical methods can be applied. Mechanical and thermal analysis of complex composite structures can be numerically analyzed using the Finite Element Method (FEM) to increase performances of composite structures in different working conditions. To decrease failure rate and increase performances of composite structures under complex loading system, thermal stress and effects of static and dynamic loads on the designed shapes of composite structures can be analytically investigated. The stresses and deformation of the composite materials under the complex applied loads can be calculated by using the FEM method in order to be used in terms of safety enhancement of composite structures. To increase the safety level as well as performances of the composite structures in different working conditions, crack development in elastic composites can be simulated and analyzed. To develop and optimize the process of composite deigning in terms of mechanical as well as thermal properties under different mechanical and thermal loading conditions, the advanced machine learning systems can be applied. A review in recent development of composite materials and structures is presented in the study and future research works are also suggested. Thus, to increase performances of composite materials and structures under complex loading systems, advanced methodology of composite designing and modification procedures can be provided by reviewing and assessing recent achievements in the published papers

Manufacturing and properties of aramid-reinforced composites

The functional properties of the aramid-reinforced polymer composites depend primarily on the properties of the aramid reinforcing fibers, since the fraction of the fiber constituent in FRP is quite high, usually well above 30% by volume. The properties of the aramid fibers, in turn, depend on their chemical composition and manufacturing conditions: both of these determine the fibers physical structure and mechanical properties. The chapter will focus on these issues. Some specific problems related to the fiber-matrix nteraction.in aramid-containing FRP will also be addressed.Fundação para a Ciência e Tecnologia (FCT) - post-doctiral grant SFRH/BPD/45252/2008 (to Nadya Dencheva)Fundação para a Ciência e Tecnologia (FCT) - bolsa licença sabatica SFRH/BSAB/812/2008 (to Zlatan Denchev

A Review on the Mechanical Modeling of Composite Manufacturing Processes

© 2016, The Author(s). The increased usage of fiber reinforced polymer composites in load bearing applications requires a detailed understanding of the process induced residual stresses and their effect on the shape distortions. This is utmost necessary in order to have more reliable composite manufacturing since the residual stresses alter the internal stress level of the composite part during the service life and the residual shape distortions may lead to not meeting the desired geometrical tolerances. The occurrence of residual stresses during the manufacturing process inherently contains diverse interactions between the involved physical phenomena mainly related to material flow, heat transfer and polymerization or crystallization. Development of numerical process models is required for virtual design and optimization of the composite manufacturing process which avoids the expensive trial-and-error based approaches. The process models as well as applications focusing on the prediction of residual stresses and shape distortions taking place in composite manufacturing are discussed in this study. The applications on both thermoset and thermoplastic based composites are reviewed in detail

확률적 열화학 점탄성 모델을 적용한 탄소섬유 강화 적층 복합재료의 가상 RTM제조 시뮬레이션

학위논문 (석사) -- 서울대학교 대학원 : 공과대학 항공우주공학과, 2020. 8. 윤군진.Composite materials undergo a shrinkage process related to the curing kinetics of the matrix. This shrinkage effect, added to the material thermal expansion, results in geometric distortions and residual interlaminar stresses that affect negatively the mechanical response of the materials. This work addresses the effects of the manufacturing process on carbon fiber reinforced composite laminates used in aerospace structures. Here, computational tools are implemented to model a viscoelastic material with degree of cure and time-dependent properties. Additionally, probabilistic modeling tools are implemented in the interest of increasing the reliability of the results by considering the random nature of curing kinetics parameters. The model consists of a multiphysics system that couples the thermochemical and mechanical processes. First, the heat transfer analysis is performed by relating Fouriers heat conduction governing equations with Kamals model of curing kinetics. Then, for the mechanical analysis, a 9-element Generalized Maxwell Model is implemented to compute the viscoelastic behavior. The representation of a cure and time-dependent viscoelastic model is possible due to the thermorheologically simple nature of the thermosetting resins. Here, a shift factor is applied to obtain stress relaxation times that change with the temperature and the degree of cure of the material. To produce the stochastic behavior of the materials, random fields were created by implementing the Karhunen-Loève Expansion method with a Monte Carlo simulation. The manufacturing method consisted of a vacuum-assisted transfer molding (VARTM) with a post-curing treatment. To emulate this process, the mechanical and thermal boundary conditions are divided into four stages. The first one refers to the curing stage. Here, the plate is constrained in the mold and subjected to thermal conduction in the surfaces. The second stage is when the plate is released from the mold and left to cool down to room temperature by natural convection. The third stage consists of placing the cooled plate into an oven (forced thermal convection). Finally, the plate is left to cool down as in the second stage. The stress and distortions that result from this manufacturing process were analyzed in six plates with different ply configurations. The results showed that the quasi-isotropic laminate [−60/−30/0/30/60/90] undergoes the highest interlaminar stresses and distortions, followed by the asymmetric cross-ply laminate[903/03] . tt also revealed that the post-curing process increases the interlaminar residual stresses in most of the laminates, especially in the case of the antisymmetric angle ply laminate. The effect of the cure dependent viscoelastic model is then compared to a basic linear elastic material response. Revealing that a viscoelastic model predicts higher stresses during the curing stage (in-mold plates) but lower stresses once the plates are released from the molds. Finally, the effects of taking into account the random nature of the curing kinetics parameters were observed in the curing stage of a cross-ply laminate. This analysis revealed that the stresses can be 23.86% higher than the values predicted from a viscoelastic model that ignores this effect. Demonstrating the importance of considering the random nature of the properties involved in the curing process.복합 재료는 매트릭스(matrix)의 경화 속도에 관련된 수축 과정을 거친다. 재료 열팽창에 더해지는 이러한 수축 효과는 재료의 기계적 성능에 부정적인 영향을 미치는 기하학적 비틀림과 잔류 층간 응력을 초래한다. 본 연구는 항공 우주 구조물에 사용되는 탄소 섬유 강화 복합재료 라미네이트(laminate)에 제조 공정이 미치는 영향을 분석한다. 여기서, 경화 정도 및 시간 의존적 특성을 갖는 점탄성 재료를 모델링하는 컴퓨터 시뮬레이션 툴이 구현된다. 또한, 결과의 신뢰성을 높이기 위해 경화 동역학 파라미터의 랜덤 특성을 고려하는 확률론적 모델이 구현된다. 이 모델은 열화학 및 기계 공정을 결합하는 다중 물리 시스템으로 구성된다. 먼저, 열전달 해석은 FourierFourier의 열전도 지배 방정식과 Kamal의 경화 동역학 모델을 통해 수행된다. 그런 다음 점탄성 거동을 나타내기 위해 아홉개의 요소(9-element)로 일반화 된 Maxwell 모델이 구현된다. 재료모델이 경화 모델과 점탄성 모델 만으로 표현될 수 있는 이유는 열경화성 수지가 열/유동학적으로 간단한 성질을 가지기 때문이다. 여기서, 재료의 온도 및 경화 정도에 따라 변화하는 응력 완화 시간을 얻기 위해 환산 인자(shift factor)가 적용된다. 재료의 확률론적 거동을 나타내는 랜덤 필드(random field)는 Monte Carlo 시뮬레이션으로 Karhunen-Loève Expansion 방법을 구현하여 만들어진다. 이번 연구에서 모델링하는 제조 공정은 진공 레진 전달 몰딩(vacuumvacuum--assisted transfer molding, assisted transfer molding, VARTM)과 그 후처리 과정으로 구성되었다. 이 공정을 모방하기 위한 열기계적 경계 조건은 4 단계로 나뉜다. 첫 번째는 경화 단계이다. 여기서 플레이트는 몰드(mold)에 구속되고 몰드 표면에서 열 전도가 일어난다. 두 번째 단계는 플레이트가 몰드에서 분리되어 대류에 의해 상온으로 냉각되는 상태이다. 세 번째 단계는 냉각된 플레이트를 오븐(강제 열 대류)에 넣는 것이다. 마지막으로, 플레이트는 두 번째 단계에서와 같이 냉각되도록 방치된다. 이 제조 공정에서 발생하는 응력과 비틀림은 플라이 구성이 다른 6 개의 플레이트에 대해 분석되었다. 시뮬레이션 결과 준 등방성 라미네이트 [-60 / -30 / 0 / 30 / 60 / 90]가 가장 높은 층간 응력과 비틀림을 겪었고 그 다음으로는 비대칭 크로스-플라이(cross-ply) 라미네이트[903/03] 가 높은 층간 응력과 비틀림을 기록했다. 또한, 후처리 공정은 대부분의 비대칭 앵글 플라이(angle ply) 라미네이트에서 층간 잔류 응력을 증가시키는 것으로 밝혀졌다. 경화 의존 점탄성 모델의 타당성은 선형 탄성 재료모델과의 비교를 통해 검증된다. 점탄성 모델은 선형 탄성 모델에 비해 경화 단계에서는 더 높은 응력을 예측하지만 플레이트가 몰드에서 분리되면 더 낮은 응력을 보여준다. 마지막으로, 경화 동역학 파라미터의 랜덤 특성을 고려함에 따른 효과는 크로스-플라이 라미네이트의 경화 단계에서 관찰되었다. 랜덤 특성을 고려한 모델은 이 효과를 고려하지 않은 모델에 비해서 최대 23.86% 더 높은 응력을 가질 수 있음이 관측되었다. 이는 경화 공정과 관련된 랜덤 특성을 고려하는 것이 복합재료 경화 공정을 해석하는 데에 매우 중요 함을 보여준다.Chapter 1. Introduction 1 1.1 Aerospace Industry Materials 2 1.2 Composite Materials 4 1.3 Manufacture of Composite Materials 6 1.4 Previous Research 9 1.5 Thesis Structure 10 Chapter 2. Literature Review 11 2.1 Thermochemical Model 11 2.2 Viscoelastic Model 14 2.2.1 Analog Mechanical Models 15 2.2.2 Multiple Element Models 20 2.2.3 Generalized Kelvin Model 21 2.2.4 Generalized Maxwell Model 22 2.3 Cure and temperature dependence 24 2.4 Random Field Modeling 28 2.4.1 Orthogonal Series Expansion 29 2.4.2 Karhunen-Loève Expansion 31 2.4.3 Parameters to be randomized 33 2.5 Classical Lamination Theory 34 Chapter 3. Materials and Methodology 36 3.1 Materials 36 3.2 Methodology 40 3.3 Experimental Setup 44 Chapter 4. Model Verification 46 Chapter 5. Results 50 5.1 Residual stress comparison 50 5.2 Cure-induced distortion 53 5.3 Curing-induced distortions coupling effects 58 5.4 Post curing-induced stress and distortion 64 5.5 Viscoelasticity Effects 66 5.6 Random Field Distribution 68 5.7 Experimental Results 73 6. Conclusions 78 Bibliography 81 Appendix 91 Appendix A. Laminate Stiffness Matrix 91 Appendix B. Thermochemical analysis code 93Maste

Fiber-dependent injection molding simulation of discontinuous reinforced polymers

Diese Arbeit präsentiert neuartige Simulationstechniken für Spritzgusssimulationen mit faserverstärkten Polymeren (FRPs). Spritzguss ist einer der meistverbreiteten Prozesse zur Massenproduktion von diskontinuierlich faserverstärkten Polymerbauteilen. Die Prozessparameter (Füllrate, Temperatur, etc.) beeinflussen die Bauteileigenschaften signifikant. Für eine adäquate Vorhersage der finalen Bauteileigenschaften muss eine Simulation alle Prozessschritte (Formfüllung, Nachdruck, Abkühl-/Aushärtungsphase, Abkühlung außerhalb des Werkzeuges) beinhalten. Während der Formfüllung hat die Strömungsmodellierung oberste Priorität. Das komplexe Matrixverhalten muss unter Beachtung von Scherrate, Temperatur und, falls vorhanden, chemischer Reaktion modelliert werden. Die sich ausprägende Faserorientierung, die von Strömungsfeld, Faserlänge und Volumengehalt abhängt, sollte aus zwei Gründen berechnet werden. Einer ist das Ausprägen von anisotropen Material- und somit auch Bauteileigenschaften aufgrund der Fasern. Zudem rufen die Fasern auch während der Formfüllung anisotropes Verhalten im flüssigen Material hervor. Auch die Faserlänge beeinflusst das mechanische und Fließverhalten des Materials und wird im Umkehrschluss durch das Strömungsfeld während der Formfüllung beeinflusst. Die Faserlänge hat großen Einfluss auf die Schlagzähigkeit des Bauteils, aber auch auf die effektive Viskosität in Faserrichtung im flüssigen Material. Umgekehrt erzeugt das Strömungsfeld aber auch Kräfte auf die Fasern, die diese zum Brechen bringen können. Stand der Technik Simulationen beachten den Einfluss der Faserorientierung und -länge auf das Strömungsfeld nicht. Diese Arbeit präsentiert einen neuartigen Ansatz, in welchem Viskosität, Faserorientierung, Faserlänge und Geschwindigkeit gekoppelt sind. Zur Berücksichtigung der Fasereigenschaften in der Viskositätsmodellierung und somit auch in der Geschwindigkeit wird die Viskosität als Tensor vierter Stufe, der als Funktion von Matrixviskosität, Faserorientierung, -länge und -volumengehalt definiert ist, modelliert. Der Viskositätstensor wird für eine homogenisierte Matrix-Faser-Suspension auf Basis von mikromechanischen Modellen berechnet. Für die Modellierung des Faserbruchs werden die hydrodynamischen Schlepp- und Auftriebskräfte beachtet. Zusätzlich werden makroskopische Ansätze zur Berechnung der Faser-Faser Interaktionskräfte (Schmier- und Reibkraft) gezeigt und verifiziert. Neben der Formfüllung beeinflussen die weiteren Prozessschritte Nachdruck, Abkühl-/Aushärtungsphase und Abkühlung außerhalb des Werkzeuges ebenfalls die Bauteileigenschaften. Durch das anisotrop visko-elastische Verhalten können Verzug und Eigenspannungen aufkommen. Stand der Technik Software simuliert diese Phänomene in der Regel anisotrop mit linear elastischen Modellen. Diese Arbeit präsentiert einen Ansatz zur Berechnung von Verzug und Eigenspannungen für FRPs mit duromerer Matrix und thermo-visko-elastischen Modellen. Relevante Prozessdaten wie Faserorientierung, Temperatur und Aushärtungsgrad werden übertragen um diese in der Verzugssimulation mit zu betrachten. Faser- und Matrixeigenschaften werden zur Homogenisierung verwendet und unter Beachtung der Faserorientierung wird ein orthotropes Material definiert. Das Matrixverhalten wird als Funktion von Aushärtungsgrad und der Temperatur modelliert. Zusätzlich werden thermische und chemische Schwindung beachtet. Die vorgestellten Methoden sind für Formfüllsimulationen in der open-source, finite Volumen basierten Software OpenFOAM und für die Verzugsanalyse in die kommerziellen finiten Elemente basierten Software Simulia Abaqus implementiert. Numerische Studien verifizieren die Implementierung und Methoden. Die Formfüllsimulationen zeigen eine gute Übereinstimmung mit experimentellen Ergebnissen, was die neu entwickelten Ansätze validiert

Fiber-dependent injection molding simulation of discontinuous reinforced polymers

This work presents novel simulation techniques for injection molding of fiber reinforced polymers. These include approaches for anisotropic flow modeling, hydrodynamic forces from fluid on fibers, contact forces between fibers, a novel fiber breakage modeling approach and anisotropic warpage analysis. Due to the coupling of fiber breakage and anisotropic flow modeling, the fiber breakage directly influences the modeled cavity pressure, which is validated with experimental data