SPE Library

A unique approach to toughening thermosets has been identified by introducing small amounts of amphiphilic block copolymer. The result is a good viscosity-Tg-toughness balance. In this work the fracture behavior of these modified epoxies was carefully studied in an attempt to understand the toughening mechanisms that exist. The findings suggest that cavitation in even these nano-sized spherical micelles is the primary mechanism of toughening. These findings were also found to be a strong function of the cross-link density of the host network with higher levels of plastic deformation at the crack tip being observed in the low-cross-link density systems. Glass-fiber-reinforced composites made with epoxies modified with these toughening agents were found to have improved fatigue resistance.

In today’s environment there is an ever-increasing desire to ‘circle the square’ reaching high-performance durability light weight and manufacturing flexibility without increasing and even trying to lower overall system costs. This presentation will discuss a new enabling technology platform engineered towards these ends: cross-linked thermoset acrylics. These are non-flammable zero-emission systems that contain no volatile or hazardous components at any stage of their life cycle. They are easy to use in molding processes and ideally suited for today’s ‘greener’ lightweight automotive composites. Their application in natural fiber composites will also be outlined in the presentation.

The direct process of producing long-fiber-reinforced thermoplastics (LFT-D) is highly innovative and economical for producing semi-structural and structural components as well as cosmetic parts with grained surfaces. The advanced plastic-hybrid developments with tailored LFT and E-LFT technologies fulfill crashworthiness requirements. Similiarly the direct processing of fiber-reinforced thermosetting materials – direct strand molding compound (D-SMC) – is focused on the reproducible manufacturing of the compound resulting in a constant part production at a high level minimizing material costs and expensive post-mold operations and paint processes as well as reducing logistical costs. The high flexibility in composing the recipe in selecting the resins fillers and reinforcements result in the high degree of freedom of this process.

Joining is often one of the critical steps in the fabrication of composite products. However the low polarity and inert characteristics of polypropylene composite surfaces cause many problems in the assembly of these composites with dissimilar materials. In order to overcome the adhesion issues an epoxy-based primer was developed and the compatibility of several commercial adhesives with the primer was evaluated. Results showed very-good lap-shear strength of up to 15 MPa with substrate failure. The performance of the primer was also evaluated between -30 and 80°C and after conditioning in humidity. While lapshear strength decreased with increasing temperature it remained unchanged after conditioning. Finally different practical approaches to apply the primer film to a polypropylene continuous-fiber composite were investigated including techniques to apply the primer during and after composite consolidation.

The moulding system FIBRETEMP describes a procedure to heat moulding surfaces efficiently with a consistent distribution of temperature. The heart of this invention the use of carbon fibres to conduct electricity as well as integrating the heating element and the structure within the surface to be heated. These moulds are highly energyefficient and extraordinarily dimensionally stable while also being produced at low cost. This technology has already been proven in manufacturing composite parts and has nearly halved cycle time for some applications due to its efficient heating characteristics.

While numerous advances have been made in the manufacturing methods of long-fiber thermoplastics (LFTs) their dynamic response in terms of fatigue and vibration damping has been a subject of limited study. There is presently no standardized design information for a composites / automotive designer for use of LFTs in situations of longterm fatigue and vibration. The behavior of E-glass fiber / polypropylene LFT composites has been characterized for their fatigue behavior and vibration response in the present study. The work provides an understanding of the influence of extrusion / compression-molded long fibers and the fiber orientation that is generated during their processing. Results will be useful to designers in accounting for fatigue life and damping factors.

The deterioration of macroeconomic conditions has severely impacted automotive production and the autoplastics supply chain. Thermoplastic composites – especially long-glass-fiber versions – will benefit from these conditions via the development and implementation of new resin and compound technology as well as advances in fabrication technology adapted to the requirements of a new automotive paradigm and new applications. Our outlook is for gains in high-performance long-glass (and other fiber) reinforced-PP compounds in competition with shortglass and mineral-filled compounds.

For over 50 years the auto industry has been gradually replacing steel with plastics and molded composites. Substantial progress has been made particularly in applications where significant parts consolidation is possible using composites. The need is greater than ever for further substitution of composites for steel but large performance gaps between steel and composites limit the rate of progress. Current gap factors include: stiffness and strength molding thickness process cycle time ability to weld to steel and cost. This presentation will address approaches for eliminating each of these gap elements for non-appearance parts using a systems approach based on new thermoplastic composite technologies.

Composite parts made from long-fibre-reinforced thermoplastic (LFT) material systems are known for their high impact and tensile strength. And due to the benefits of the outstanding price to performance relationship of the in-line compounded (ILC) direct-LFT (LFT-D) technology used for production of composites based on the use of polypropylene and glass fibres it has achieved consistently more applications in the automotive industry. But LFT-based automotive applications are mainly used for parts with large surfaces which can contribute significantly to the total amount of VOCs and odor inside a car. The current work explains a feasible approach of using commercial additives – provided as a complete system – in combination with VOC- and odor-reducing additives to further enhance the mechanical and outgasing properties of the PP / GF composites produced by LFT-D / ILC technology.

Fast and cost-efficient design of higher quality lighter and more energy efficient vehicles is one of the key success factors for today’s automotive industry. Predictive CAE and the use of composites materials offering good weight to mechanical-performance ratio are two ingredients that will help the industry moving forward profitably. We will introduce the DIGIMAT nonlinear micromechanical-modeling technology which can be used to predict the nonlinear behavior and failure of multi-phase materials based on their underlying microstructure (e.g. fiber content fiber orientation fiber length etc.). The multi-scale material-modeling process used to model the reinforced plastic part will then be presented.

An integrated approach linking process to structural modeling has been developed to predict the nonlinear stress-strain responses and damage accumulations in injection-molded long-fiber thermoplastics (LFTs). The approach uses Autodesk® Moldflow® Plastics Insight’s fiber orientation results predicted by a new fiber-orientation model developed for LFTs and maps these results to an ABAQUS® finite-element mesh for damage analyses using a new damage model for LFTs. The damage model which has been implemented in ABAQUS via user-subroutines combines micromechanical modeling with a continuum damagemechanics description to predict the nonlinear behavior of LFTs due to plasticity coupled with damage. Experimental characterization and mechanical testing were performed to provide input data to support and validate both process modeling and damage analyses.

Dielectric cure monitoring has been used in thermoset laboratories for decades to characterize materials. Historically attempts to take the technology to the production floor where the benefits can be maximized in production tools have failed due to shortcomings in sensor durability and system reliability. Breakthroughs in dielectric sensor design have resulted in the development of durable in-mold sensors that can operate on the production floor. Thermoset molders can now “see” changes in flow and cure inside their production tools allowing automatic “real-time” adjustments for process variation and enabling significant gains in productivity and quality. Benefits to compression and injection molders include: 10-25% reductions in cycle time improvements in quality and reduction of scrap and a better understanding of flow and cure rates inside the mold.

Often times a composite component can be used to replace a metallic component providing a significant reduction in weight while providing little or no loss in strength or stiffness. For automotive engineers to further utilize composites in new applications it is important to understand the mechanical behavior of the material in all the critical loading directions. This paper focuses on the relevant tests necessary to characterize the mechanical properties of a pultruded carbon fiber composite material. The mechanical properties evaluated include tension compression interlaminar shear and fatigue testing in the fiber direction. Included is a discussion on key aspects of the testing in order to ensure reliable results. Also a set of design criteria is developed for the use of the material according to the measured properties.

The development and implementation of lightweight materials using fiber composites made by injection molding represents an engineering challenge due to the inability to control the fiber orientation in the required direction of mechanical demand. This paper presents progress in developing the capability of predicting fiber orientation in simple and complex flow geometries for highly concentrated short-glass-fiber suspensions and the extension of this approach to long-glass-fiber suspensions. Three important aspects included in the approach are the implementation of new theories to model fiber orientation the evaluation of model parameters from rheological experiments and the use of stable numerical methods based on discontinuous Galerkin finite-element method.

The Automotive Composites Consortium (ACC) is conducting a multiyear project to develop a better understanding of the root causes of the visual surface deformation effect known as bond-line read-through (BLRT). BLRT is associated with bonded automotive Class A exterior panels and produces out-of-plane deformations on the order of 0.010- 0.050 mm. The ACC is studying the relationship between material and process factors and BLRT severity. The majority of the investigations have focused on SMC composite panels bonded with urethane and epoxy adhesives under elevated-temperature cure conditions and subsequently primed and topcoat painted. An investigation was conducted to see if analytical tools could predict the BLRT effect observed in the physical experiments. The present work describes the initial effort to model the BLRT effect using a finite-element analysis (FEA)-based approach. As part of this effort detailed threedimensional FEA solid models were developed for two idealized panel configurations: (a) an outer panel with an adhesive bead and drops and (b) a bonded outer/inner panel assembly. Results were predicted for the case of an idealized elevated-temperature adhesive cure condition using a steady-state thermo-elastic analysis. The predicted surface curvature results indicated a good qualitative agreement to available measurement data with the analysis over-predicting the BLRT severity.

Design engineers working with composite materials typically use a linear finite-element-analysis (FEA) solution and a failure-index calculation based on the current state of stress in the model. However this type of analysis can only provide accurate results up to first-ply failure because of the linear assumption. This presentation will show how nonlinear progressive-ply failure analysis can go beyond first-ply failure and simulate subsequent damage propagation through a structure. This allows engineers to make a better assessment of conditions for ultimate failure so they can optimize their designs and also provide guidance on the most appropriate physical-test program.

Increased use of polymer matrix composites depend on having a deeper understanding of their mechanical response under varying strain rates. In this study the mechanical behavior of thermoplastic woven composites was investigated under varying strain rates between 5.0 x 10-5 s-1 and 5.0 x 102 s-1 using a screw-driven universal testing machine and an impact testing and imaging apparatus. Results yielded stress vs. strain curves over the full range of loading rates highlighting the strain-rate sensitivity exhibited by the thermoplastic composites. In addition the non-contact strain-measurement system revealed the effect of woven architecture on the mechanical behavior of thermoplastic woven composites.

Thermoformed polyethylene terephthalate (PET) produce trays (clamshells) produced by a large retail supplier using virgin resin were compared to PET clamshells containing 30, 70, or 100% recycled-PET (RPET). Comparisons were made of functional groups, ultravioletvisible (UV-Vis) light absorption, and thermal properties. An increase in the crystallization temperature was observed as RPET increased when compared to virgin PET. This suggests that the crystallization temperature (Tc) may be used as a quantitative indicator for determining the amount of RPET in a plastic composite.

This paper examines the effect that blending two biodegradable polymers has on the thermal properties and morphology of the resultant foams blown with carbon dioxide (CO2). Polylactic acid (PLA) Polyhydroxybutyrate-co-valerate (PHBV) and blends of both were foamed and characterized in terms of thermal characteristics relative density cell size and foam morphology. The results indicate that although PLA and PHBV are immiscible the presence of small quantities of PHBV could lead to low density foams with finer more uniform cells.

Plug-assist thermoforming is a well known technique in polymer processing due to its interesting features. The dynamic value of driving-force for the stretching process is determined based on equilibrium equation. This amount of force is required for applying to a plug in order to stretch a sheet. It is used for calculation of the required theoretical work, and power of a plug-assist thermoforming process. By using a non-linear viscoelastic rheological model in the proposed mathematical model, its validity was examined by performing experimental tests on ABS sheets.