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Conference Proceedings
Lightweighting through Composites Simulations - The Composites Design and Manufacturing HUB
R. Byron Pipes, September 2013
The primary objective of the Composites Design and Manufacturing HUB (cdmHUB) is to accelerate the development of a comprehensive simulation tool set for the composites community for use in lightweighting vehicles. The cdmHUB provides a platform for the birth development refinement integration and commercialization of the simulation tools necessary to bring composites design and manufacturing simulation to a level consistent with high- performance composites simulation tools for geometric and structural modeling such as CATIA NASTRAN ABACUS and ANSYS. The cdmHUB is a cloud-based cooperative platform that can host composites design and manufacturing simulation tools that may be accessed with a web browser from the Internet.
Morphological and Mechanical Comparison of Injection and Compression Moulding In-Line Compounding of Direct Long Fibre Thermoplastics
Martin McLeod, September 2013
Long fibre thermoplastics (LFT) based on polypropylene / glass fibre (PP/GF) composites has become one of the most widely used plastics in semi-structural and structural automotive applications in both aesthetic and non-aesthetic parts. LFTs are commercially available in pre-compounded pellets for injection moulding and are developed with specific properties for targeted functions. In a rationalizing effort to reduce costs heat histories and create in-house flexibility of material blending in-line compounding (ILC) of base materials including resin additives (heat stabilizers colors coupling agents etc.) and glass roving reinforcements for direct moulding of LFT parts (D-LFT) has been developed in the last 10 years. Two major versions of D-LFT technology currently exist on the market both relying on twin-screw extrusion for ILC -- one utilizing compression moulding and the other injection moulding. These two technologies have their specific features related to fibre length orientation and resulting properties. The objective of this paper is to address some of them.
Light-Weighting with Engineered Thermoplastic Compounds Including Carbon Fiber Reinforced Polypropylene
Nolan Krause, September 2013
The automotive industry is changing. Today less means more as engineers are challenged to reduce vehicle weight to meet CAFE and emissions regulations. This presentation will highlight several high-performance solutions for mass-reducing thermoplastic compounds / composites including the strength-to-weight advantages and design considerations for: increasing performance with glass fiber reinforcement; “stiff and tough” very-long-fiber composites; going lighter by using carbon fiber compounds including carbon fiber polypropylene; and shedding weight with glass microspheres and blowing agents.
Crashworthiness Energy Absorption of Carbon Fiber Composites: Experiment and Simulation
Francesco DeLeo, September 2013
The higher mechanical characteristics and mass specific energy absorption capabilities of composite materials motivate their use in large primary structures as well as structural and crashworthy components over more traditional metallic designs. Numerical simulation has become a common tool in structural design and crashworthiness. A well-established simulation practice is needed to significantly reduce the amount of experimental testing required during product development and certification. Due to the complex mechanical behavior of advanced composite materials the capability of the existing analytical and numerical models to predict the crushing behavior is limited. The merits and weaknesses of a progressive failure material model MAT54 of a commercially available explicit finite element solver LS-DYNA are highlighted through single-element investigations. Then the suitability of MAT54 to simulate the quasi-static crushing of a composite specimen is evaluated. Through extensive calibration by trial and error the crushing behavior of a semi-circular sinusoid specimen comprised of carbon fiber/ epoxy unidirectional prepreg tape is properly simulated both in terms of the specific energy absorption and load –penetration behavior. The study is extended to five different geometries in order to evaluate the effect of geometric features on crush behavior both from an experimental and numerical standpoint. Finally an energy-absorbing composite sandwich structural concept comprised of a deep honeycomb core with carbon fiber/ epoxy facesheets subject to through-thickness crushing and penetration is considered. With the aid of the building block approach and extensive calibration of the material models and contact formulations the full-scale crush behavior is predicted.
Developing Accurate Material Models for Composites
Roger Assaker, Rani Richardson, September 2013
Modeling the behavior and failure of composite materials is challenging and requires models that take into account the material anisotropy nonlinearities and progressive damage and failure. This behavior depends on the local material composition (matrix and fibers) and underlying microstructure (fiber length content orientation) as induced by the manufacturing process. This tutorial will address the modeling of short-fiber-reinforced plastics (in Part 1) and continuous-fiber composites (in Part 2) materials and structures. Part 1 also will cover tests needed to calibrate the material model that can be used in FEA analysis taking into account the fiber orientation predicted by injection molding simulation; Part 2 also will cover the use the classical laminate theory to model the linear behavior of CFRP structures and the use of coupon test results to calibrate the nonlinear stress-strain and failure behavior of the composite.
Status of the Composite Underbody Component & Assembly Structural Test-Analysis Correlation
Hannes Fuchs, September 2013
Computer aided engineering-based design methodologies have been utilized throughout the Automotive Composites Consortium Focal Project 4 to assess the vehicle level structural stiffness and impact performance of the composite underbody design proposals and to estimate the potential mass reduction for several candidate material scenarios. To increase confidence in the vehicle level CAE model predictions and to better understand the effect of material and manufacturing variability prototype molded underbody components were fabricated and subsequently built into underbody assemblies to assess their structural performance. Non-destructive component and assembly tests were devised to assess the general static and modal performance of the underbody component and a quasi-static destructive test of a built-up underbody assembly was developed to simulate the deformation and loading observed in the worst case vehicle impact design load case. The paper will discuss the preparation and fabrication of the built-up test assemblies the structural stiffness and modal performance testing of trimmed underbody molded components and assemblies and the destructive testing of assemblies. The predicted performance was investigated for two composite thickness assumptions to account for the additional thickness observed in the prototype components. Predictions were then compared to the measured test results to understand the status of correlation between the response of idealized components and the as-molded prototype test components. A comparison of the non-destructive stiffness and modal test results to the predictions indicated that the stiffness and modal response were reasonable. The destructive underbody test was developed to better represent the physical composite and metallic components. The destructive underbody test was limited by buckling of the longitudinal rail. The results correlated well with predictions up until rail buckling occurred after which significant local damage was
Simulation of Folgar Tucker Orientation Model with a Semi-Circular Advancing Front Geometry
Syed Mazahir, September 2013
Folgar Tucker model has been in use in commercial software for predicting fiber orientation for fiber/polymer suspensions. One of the major challenges in modeling injection molding processes is the complex flow in the frontal region. However the standard method of using the model with Hele Shaw approximation limits its capability as a prediction tool especially near the advancing front region and in the outer layers of the molded part. In this work the effects of the fountain flow region were assessed by including a simplified semi-circular cap to the finite element mesh. Simulations were performed with a fixed mesh and a full 2-D velocity field was solved using Navier Stokes equation for steady state and the orientation equations were decoupled from momentum equations. We looked at combinations of inlet conditions for orientation and the model parameters to determine which are most compatible with the geometrical simplification used to describe the front. All combinations of model parameters and initial conditions considered in this work qualitatively reproduce the measured orientation profile. However large discrepancies between predicted and experimental orientation near the walls suggest the need for a robust approach to handle the effects of the advancing front on fiber orientation.
Effect of the Adhesive Joint Cross-Section Parameters on the Bond-Line Read-Through Severity in Composite Automotive Body Panels Bonded at Elevated Temperature
Hannes Fuchs, September 2013
The Automotive Composites Consortium (ACC) is conducting a multi-year project to develop a better understanding of the root causes of the visual surface distortion effect known as bond-line read-through (BLRT). Initial studies using a finite-element analysis (FEA) based approach showed good agreement with experimental observations and highlighted the importance of accounting for viscoelastic adhesive material properties. A parametric FEA-based study of a small laboratory scale coupon was conducted to examine the effect of the adhesive joint cross-section geometry and adhesive type on the predicted peak curvature resulting from an elevated temperature adhesive cure. The parameters evaluated in this study were uniform and non-uniform adhesive thickness SMC substrate thickness adhesive bead width and adhesive type.
Bulk Molding Compound Use in Automotive Fuel Cell Applications
Cedric Ball, September 2013
Hydrogen fuel cell-driven electric cars continue on a slow but steady progression toward commercial viability. Dismissed by many as being too expensive fuel cells are within range of the cost of other vehicle propulsion systems due to advancements in design and manufacturing that have taken place in recent years. Composites have been an integral part of the success of proton exchange membrane (PEM) fuel cells. Bipolar plates made from conductive bulk molding compound have proven to be effective durable and low cost in comparison to other materials. This presentation documents properties recent developments and successful commercialization of thermoset bulk molding compound for transportation fuel cell applications.
CAE Simulation Catalyzes Composites Growth: Material Modeling & Optimization
Giuseppe Resta, September 2013
Automakers have developed successful computer simulation processes to meet the most stringent crash noise/vibration/ harshness (NVH) and aerodynamic and vehicle dynamics requirements making computer-aided engineering (CAE) an established component in today vehicle-design process. Engineers and management are comfortable with CAE deliverables for traditional metal-based vehicle design and now require reliable simulation technologies and methods to integrate engineered plastic such as carbon fiber laminates in their standardized and automated simulation procedures. This presentation will discuss the challenges of composite material calibration how CAE simulation can be used to aid material characterization the unique modeling and visualization requirement for composites and how optimization simplifies the design of laminate composite structures tailoring the material itself to the loading requirements and avoiding overdesign of part.
Modelling and Optimisation of a Multiaxial Fabric
Tom James, September 2013
The primary aims of the project were to determine the suitability of ESI PAMFORM with regards to modelling a multiaxial fabric and to assess how a manual forming process could be simulated. Material models for multiaxial fabrics were developed through physical testing. Four different simulation methods were investigated and compared in terms of ease of set up processing time and results. An optimisation process was developed using batched input files in order to examine the optimum fabric property for a given component. This process is now used to assist in the selection of a fabric in the early stages of any new component design. A UK government-funded Knowledge Transfer Partnership (KTP) with Nottingham University was started in January 2013 with the aim to create a validated materials database for use with this simulation.
Light Weight Class A" SMC Body Panels-TCA Lite®"
Mike Siwajek, September 2013
Currently the automotive industry is making a major push toward vehicle weight reduction. While traditional SMC provides several advantages over other materials for use on Class “A” body panels weight reduction is not necessarily one of them. The invention of a lower density Class “A” SMC allows the material to maintain its traditional advantages while also competing with other lightweight alternatives. Unreinforced panels (e.g. fenders roof panels etc.) molded with the material can reduce weight by up to 20%. Closure panels (e.g. hoods decklids etc.) when bonded to low-density inner panels can provide up to 30% weight savings over a traditional SMC assembly. This paper will summarize the development of the material as well as present manufacturing trial and part performance data. Initial evaluations at OEM facilities will also be discussed.
Constituitive Property Estimation of Stitched Composites for Engineering Applications—A Hybrid Approach
Siddharth Ram Athreya, September 2013
Fiber-reinforced polymer composites are finding new applications in aerospace high-performance as well as medium build-volume alternate powertrain automobiles civil infrastructure sports equipment and emerging alternate energy industries due to their high stiffness-to-weight ratio. Laminated structures are among the most common forms of structural fiber-reinforced polymer composites. Fiber orientation in each lamina and the stacking sequence of the laminated structures can be chosen to tune the desired strength and stiffness. For enhancing the predictive modeling capability of composite structural performance an accurate computation of the effective material properties of composite materials is of special interest to engineers. This paper discusses the prediction of the effective mechanical properties of glass fiber-reinforced epoxy composites (fabricated using an infusion process) utilizing both classical laminate theory as well as a finite element-based micromechanics approach and compares the results against experimental findings. The results from the physical tests exhibit good correlation with the predicted mechanical properties.
Experimental Evaluation of the Orientation of Long Semi-Flexible Glass Fibers in Complex 3-Dimensional Flow
John T. Hofmann, September 2013
The experimental orientation of long semi-flexible glass fibers has been evaluated in complex 3-dimensional flow. Preliminary experimental values of long-fiber orientation were obtained within injection-molded end-gated plaques at multiple percentages of plaque length and width including in the areas of complex flow near the mold side walls. Additionally experimental values of orientation were obtained within the sprue and gate region of the injection molded parts. Modification of the experimental method for measuring fiber orientation in these regions due to the increased length and flexibility of long fibers is included.
A Method for Characterizing Fiber Length Distribution in Random Fiber Composites
Tim Latimer, September 2013
It is well known that retained fiber length in random fiber composite materials relates directly to the mechanical properties. Longer fibers lead to higher aspect ratios that increase stiffness and strength as well as enhance the creep and fatigue properties. Direct compounding of thermoplastics promotes fiber length retention by the use of continuous glass fiber in the compounding process. In the same way pre-compounded long fiber pellets provide increased fiber length relative to traditional short fiber injection molding compounds but perhaps not to the extent of direct compounded methods. Despite the known fiber length retention characteristics of these various materials and processes via qualitative analysis and examination of resultant mechanical performance a rapid and robust quantitative fiber length characterization method seems to have eluded the industry to date. Time consuming counting of individual fibers randomly selected from samples seems to be the norm. Based upon these limitations and needs a method to rapidly characterize the fiber length distribution in random fiber composites was investigated. The experimental procedure is discussed and the results to date are presented.
Improvement in Orientation Measurement for Short and Long Fiber Injection Molded Composites
Gregorio Vélez-García, September 2013
Short-fiber-reinforced thermoplastics are a feasible alternative to develop lightweight materials for semi-structural applications. These materials present a layered structure showing a complex fiber orientation distribution along the molding. The details of fiber orientation in a center-gated disk with diameters of 1.38 and 2.05 mm were obtained in several regions including the gate and advancing front. Several modifications were introduced in the method of ellipses to obtain unambiguous orientation measured over small sampling area. Two fiber suspensions (30 % short glass-fiber PBT and PP) with different rheological characteristics were used in these experiments. The results showed an asymmetric distribution of fiber orientation that gradually washs out as the flow progress. In addition the initial orientation measured at the gate presented a fiber distribution different from the random orientation that is assumed in literature for a center-gated disk.
Multi-Scale Modeling of High Cycle Fatigue of Chopped and Continuous Fiber Composites
Kurt Danielson, September 2013
Two micro-mechanically based composite fatigue models are introduced in this presentation. The focus is on the high- cycle fatigue model implemented specifically for chopped- fiber-reinforced plastics. Its application for a Toyota Motor Europe automotive oil-cooler bracket made of a nylon 6/6 material reinforced by short-glass fibers will be presented. Through this case study the presentation aims to show how the use of proper fatigue-modeling tools developed specifically for composites can increase the accuracy of simulation in the field of durability and pave the way for new simulation standards towards the desired lightweight reductions.
Evolution of an Excellent Lightweighting Tool – PUR Sandwich Composites
Mike Super, September 2013
This presentation details how polyurethane spray sandwich technology originally developed for sunshades has been improved for use in more demanding applications such as load floors and parcel shelves. Polyurethane sandwich construction combines the low weight of a honeycomb core with the high strength of a fiber-reinforced polyurethane skin to produce load-bearing parts with very-high flexural stiffness and excellent thermal properties making it an attractive lighter weight alternative to ABS polypropylene sheet-molding compound (SMC) and wood products. Information on the deflection performance of different constructions with different systems including some with natural and some with glass mats will be given to guide manufacturers on the best ways to hit specific targets such as cost thickness or weight. Newer formulations enable productivity improvements including longer open times and shorter demolding times which facilitate production of larger parts and reduced scrap as well as feature higher bio-renewable content than previous versions.
Three Dimensional Predictions of Fiber Orientation for Injection Molding of Long Fiber Reinforced Thermoplastics
Ken (KC) Cheng, September 2013
Long fiber-reinforced thermoplastic (FRT) composites in automotive industrial fabrication are of critical requirement -- more so than short FRTs. The FRT products’ mechanical properties and warpage are dominated by fiber orientation within the part. This presentation will discuss a recently proposed new fiber orientation model for improving the prior developed models with regard to interaction and diffusion of the fibers immersed in a matrix namely iARD- RPR (Improved Anisotropic Rotary Diffusion model combined with Retarding Principal Rate model). The iARD-RPR model has been demonstrated to describe changes in fiber orientations well whether treating short fibers or long fibers. In this study 40 wt% glass-fiber immersed in polypropylene matrix was injection molded in a center gated disk and then predicted fiber orientation distribution pass the thickness was compared with measured results. Good agreement with experimental observations was achieved.
A Method for Developing Composite Beam Structures that are Optimized for Energy Management using Non-Linear Topology Optimization
Ram Iyer, September 2013
A methodology utilizing a non-linear topology-optimization technique was applied to develop designs of mass- efficient composite beam structures. The traditional linear optimization technique is shown as suitable to develop designs that are maximized only for part stiffness. Non- linear effects like plasticity and material failure are not taken into consideration using linear techniques and hence the suitability of the linear-optimization technique can prove to be inadequate for applications that require energy management. Non-linear topology optimization using the software tool LS-Tasc from LSTC uses fully non- linear LS-Dyna simulations to arrive at the optimized design shape. Plasticity material damage and failure and load path variation on account of contact are taken into consideration as is typical with non-linear LS-Dyna simulations. The optimization process tracks the contribution of each element in the finite-element model of the design space to the stated objective and performance constraints to determine the ideal load path and hence the part shape. Development of the beam structure designs using this methodology results in design shapes that can be optimized for energy management rather than stiffness.


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