An anisotropic elasto-plastic material model for injection-molded long fiber-reinforced thermoplastics accounting for local fiber orientation distributions

Abstract

This paper presents an anisotropic elasto-plastic material model for injection-molded long fiber-reinforced thermoplastics. It considers local heterogeneities which are attributed to process-induced variations of fiber orientation distributions and fiber volume fractions. These inhomogeneities have an effect on the mechanical properties and need to be considered in structural computations. In the material model, this is realized through a two-step homogenization procedure. First, an anisotropic stiffness tensor is approximated using mean field homogenization. Second, the plastic behavior is described using Hillâs transversely isotropic yield criterion averaged over the three principal directions of the fiber orientation. The advantage in combining these two approaches is a micro-mechanically based, yet fast numerical calculation of the composite material behavior within an explicit finite element code. The anisotropic material model is calibrated by simulating tensile tests on specimens taken in different directions from an injection-molded plate of fiber reinforced thermoplastic. The spatial variation of fiber orientation distribution and fiber volume fraction throughout the plate is determined from numerical mold filling simulations and is compared with computer tomography scans at different positions. A validation of the model is performed through simulating position-dependent tensile tests on smooth and notched specimens as well as a punch test which is well reproduced

Measures describing curvilinear short fiber distributions

“…are defined, see Eqs. (18) and (24). In this sense, the two angles (27) can be chosen for a mean orientation,…”

“…Furthermore, it is known, see, for example [14], that a fiber reinforced specimen has different material properties over its thickness, which is caused-apart from the melt flow behavior of the thermoplastic-by the spatial distribution of the fiber orientation. Applications from glass fiber reinforced plastic, where the short fibers are straight lines, are discussed in a number of publications, see, for example [7,8,13,18]. In these publications, the fiber orientation of glass fiber reinforced samples has already been extensively investigated.…”

Comparison of Real and Simulated Fiber Orientations in Injection Molded Short Glass Fiber Reinforced Polyamide by X-ray Microtomography

“…These result from different flow directions during mold filling and process-related velocity and shear rate distribution over the component thickness. Generally, these layers can be subdivided into the three main layers of the skin, shear, and core layer, equivalent to the shear rate curve [ 18 , 19 , 20 , 21 ].…”

“…For the evaluation of fiber orientation with µCT measurements, the tensor representation is often used for SGFRP. For this purpose, the tensor components a 11 , a 22, and a 33 are plotted over the thickness of the specimen in a 3 × 3 matrix [ 20 , 21 , 23 ]. If the value for one of the components , or is “1” during the evaluation, it means that the fibers are oriented in the direction of the corresponding axis [ 14 , 17 ] (see Figure 1 ).…”

Caracterización de las propiedades tensiles de un material compuesto laminado Epoxi-Carbono empleado en la fabricación de un monoplaza tipo Fórmula SAE

“…Por otra parte, la principal desventaja de los materiales compuestos reforzados con fibra continua suele ser su elevada anisotropía, lo que dificulta el estudio analítico y el diseño de componentes. Sin embargo, al realizar pruebas estandarizadas es posible determinar el comportamiento del material y con una caracterización mecánica adecuada es posible entender el comportamiento mecánico del material que permita realizar diseños adecuados (Al-Mosawi, 2014;Liu et al, 2017;Schulenberg, Seelig, Andrieux, y Sun, 2017;Viscardi, Arena, Barra, y Guadagno, 2016;Yaqiang, Xin, y Zhishen, 2017). Utilizar materiales compuestos mediante técnicas de laminado es muy práctico, ya que permite el uso de estructuras de paredes finas a partir del uso de pre-impregnados (Elkington, Bloom, Ward, Chatzimichali, y Potter, 2015).…”