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Thermoplastic composite materials have lately been considered increasingly for application in structural components. Especially semi-finished products with continuous fiber-reinforcement such as woven fabrics or unidirectional tapes have a high potential to increase part performance significantly. However due to their limited drapability and flowability the forming of highly complex structures such as ribs is not feesible. This paper presents an overveiw of desired features that are commonly part of complex technical applications. It shows how implementation of those can be achieved with continuous-fiber-reinforcement structures by combining them with short and long fiber-reinforcement material. The subsequent case study presents a related investigation on overmolding of unidirectional tape inserts. In conclusion an outlook is given on how these results can be transferred to more complex components.
A structural composite underbody capable of carrying crash loads has been designed fabricated assembled into a structure and tested by the Automotive Composites Consortium. The underbody is compression molded of sheet molding compound (SMC) with a vinyl ester matrix and predominately glass fabric reinforcement with some chopped glass. CAE-based design methodologies were utilized to assess the structural stiffness and impact performance of the initial composite underbody design. Weld bonding was selected as the means to join the composite underbody to the steel passenger compartment. A method for weld bonding the structural composite has been developed and tested in static and dynamic modes. The molded underbody was tested in modal bending and torsion. The underbody was assembled into a structure mimicking an automotive body-in-white and tested to simulate an offset deformable barrier crash. The Automotive Composites Consortium (ACC) is a joint program between GM Ford Chrysler and is funded in part by the United States Department of Energy.
Compression molding of fabric SMC in steel tooling is a cross between prepreg molding and regular sheet molding compound (SMC) molding. Material processing differences such as minimal material flow represent major manufacturing challenges requiring different approaches for production operations. This paper will present the observed challenges and potential approaches that will enable cost effective manufacturing scenarios. Aspects of the processing include (but are not limited to) SMC compounding charge cutting charge placement tool loading edge filling of the part wrinkles and overlaps part trimming modeling and material testing. Presented will be solutions we utilized in addition to studies and cost models used to alleviate some concerns.
Graphitic carbon nanofibers (GNFs) were first made into a “nano-nectar” which is “liquid nano-reinforcement” (LNR) with reactive nanofibers (r-GNFs). Due to the uniform dispersion of r-GNFs in the LRN simply mixing the LNR with an epoxy led to a nano-modified epoxy with uniform dispersion of nanofibers a so-called nano-epoxy. More importantly the nanofibers were involved in the cross-linking structures of the epoxy through covalent bonding between the epoxy matrix and the nanofibers. Results showed that the nano-epoxy possesses dramatically reduced viscosity and enhanced multiple mechanical and thermal performances by simply mixing two kinds of liquids: a very small amount of LNR functioning as a “nector” and a base epoxy matrix. The simplicity of the “nano-nectar” approach leading to reduced viscosity (e.g. 50% lower than the pure epoxy) can lead to faster Resin Infusion processing for automotive composite manufacturing due to reduced power requirements for flow and part consolidation.
The Automotive Composites Consortium (ACC) has selected a fabric sheet molding compound (SMC) as the main material and process system for a structural composite underbody. This Paper describes the properties of this SMC material including tensile compression and flex. Thermal properties including coefficient of linear thermal expansion and Tg temperatures were determined. The effect of two different fabric weights and several layups thicknesses and molding parameters is also reported. Overlap and butt joints within the layup were compared. The Automotive Composites Consortium is a joint program between General Motors Ford Chrysler in partnership with the United States Department of Energy.
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 model predictions and to better understand the effect of fabric draping on fiberglass fabric Sheet Molding Compound composite material properties several quasi-static structural “double dome” component tests were simulated for the purpose of test-analysis correlation and modeling methodology development.
The Automotive Composites Consortium (ACC) a partnership of Chrysler Group LLC Ford Motor Company General Motors Company and the U.S. Department of Energy conducts pre-competitive research on structural and semi-structural polymer composites to advance high strength lightweight solutions in automotive technology. An ACC focal project concerning the development of a structural composite underbody was established to provide methodologies and data for each ACC member company to implement lightweight cost-effective structural composites in high volume vehicles. This objective will be fulfilled through design analysis fabrication and testing of a structural composite underbody. A key design element required for implementation of the underbody structure is an understanding of the affects of environmental temperature and impact damage on the axial fatigue performance of the SMC composite material selected for the underbody structure fabrication. Research efforts have been made on fatigue performance of different type of composite materials (Ref. 1-5). In this study specimens were tested with no damage as well as two levels of impact damage. Environmental temperatures for the undamaged specimens were -40°C 21°C and 80°C. It was observed that fatigue life increased at low temperature conditions and decreased at high temperatures. The affect of temperature had a greater influence on fatigue life than the impact damage in this study. Temperature increases as measured at the specimen surfaces were observed as test frequency increased. Similar observations were made by Bellenger et al (Ref.6). The relationship between stress loading frequency and temperature will be investigated. Optical and scanning electron microscopy will be used to examine the crack locations and characteristics for specimens tested under different conditions.
In the current phase of the Automotive Composites Consortium structural composite underbody project a draping analysis of a full underbody made of woven glass-fabric sheet molding compound (SMC) was used to identify changes in local mechanical properties due to fabric shearing during compression molding. As a laboratory-scale effort woven glass-fabric SMC was compression molded into double-dome shapes and flat plaque configurations of three separate 4-ply layups. Double domes underwent static crush impact and mechanical testing; mechanical properties were further compared to corresponding flat plaque properties. All data was used to broaden the material property database and validate model predictions of strand orientations in a molded part.
Weight reduction of components is becoming increasingly important for example in automotive applications where significant fuel savings and CO 2 emission reduction can be made. In many cases metal load - bearin g parts can be replaced by short or long fib er reinforced thermoplastics. These composites have become an integral part of industrial large scale production especially due to their economical processability and increased functionality. The limited mechanic al properties such as stiffness and impact strength prohibit the use of injection moulded parts in higher load - bearing applications. Furthermore the viscoelastic behavior of the matrix at high temperature or at permanent load is a disadvantage (tendency to creep). Local continuous fib er reinforcement can overcome these disadvantages by increasing the properties and reducing tendency to creep. The technology of continuous fiber reinforcement with thermoplastic materials includes in principal all pre - impreg nated fiber structures like woven and non - woven fabrics UD - strands tape layups or winded geometries. To characterize the effect of unidirectional fiber reinforcement in this research work a single pre - impregnated fiber strand was chosen. These strands we re then being manufactured to generic specimens in a specialized mould for insert technology with a standard injection moulding process a s one of the most important processing technology for thermoplastic polymers . The mechanical behavior of the parts acco rding to the variation of material and process parameters were analyzed with a static tensile test and a dynamic - mechanical analysis (DMA).
Different compatibilization strategies from master batch mixing using a twin-screw extruder with various coupling agents were investigated to improve the stiffness of nanocomposites based on a high impact TPO (n-Izod > 600 J/m) with 2% and 4% of organoclay content. Three coupling agents based on grafted maleic anhydride polymers (gMA) were used to tailor the compatibility of the organoclays to either or both the rubbery domains and the polyolefin matrix. A detailed microstructural of the different nanocomposites revealed the preferential presence of organoclays in the rubbery domains the matrix or both depending on the masterbatch sequential compounding strategy i.e. the type of coupling agent(s) mixed with the type of organoclay. As anticipated the presence of organoclays in both the matrix for improved tensile properties (Young’s modulus and stress and strain at yield) and in the rubbery domains for higher impact resistance (n-Izod at 0 and 23°C and flat sheet impact at -40°C). A control experiment on a blend of PP and an ethylene-propylene copolymer with a PPgMA coupling agent and organoclay compounded in a similar fashion led to the usually improved tensile properties but reduced impact resistance. In this case the organoclay was found present in the matrix only as the coupling agent used could not compatibilize the organoclay to the copolymer phase. It is concluded that organoclays act on the rubbery phase to increase its toughening effect in the TPO presumably by increasing the cavitation stress of the TPO.
The objective of this research is to investigate the potential of using exfoliated graphene nanoplatelets (GNP) as the conductive filler to construct highly conductive polymeric nanocomposites to substitute for conventional metallic and graphite bipolar plates in the polymer electrolyte membrane (PEM) fuel cells. High density polyethylene (HDPE) was selected as the polymer matrix and solid state ball milling (SSBM) followed by compression molding was applied to fabricate HDPE/GNP nanocomposites. Results showed that HDPE/GNP nanocomposites made by this method exhibited excellent flexural properties and low gas permeability with GNP loadings up to 60wt% which successfully meet the DOE requirements for bipolar plates. However it was found that using GNP alone as a single conductive filler was insufficient to achieve the required electrical conductivity (>100 S/cm). Combining GNP with a minor second conductive filler such as carbon black (CB) and carbon nano-tubes(CNT) could substantially enhance the electrical conductivity of the resulting nanocomposites. At the same time the processing time of SSBM is considered as a crucial parameter in optimizing the various properties of the final nanocomposites. It is believed that the bipolar plates made from HDPE/GNP nanocomposites will allow lighter weight of PEM fuel cells with enhanced performance which is particularly suited for automotive applications.
The high-temperature high-mechanical performance end of the composite materials spectrum–so-called advanced composites–has long been dominated by thermoset matrices primarily epoxy and urethane chemistries with carbon or aramid continuous-strand unidirectional fiber or fabric weave reinforcements. However that is starting to change as thermoplastic resin suppliers begin to investigate and more aggressively position their own high-temperature offsets in this segment–not just as lower cost lower weight faster processing replacement for thermosets but as direct metal replacements themselves. By offering molders and OEMs the option to produce performance parts with higher productivity thermoplastic matrices that do not need to be polymerized in the tool numerous benefits are gained including reducing cycle times volatile-organic compound (VOC) emissions energy consumption spoilage and finishing steps–all of which help drive down costs and make advanced composites more affordable for higher volume applications than metals. This can be particularly attractive for processors without autoclaves or without sufficient auto clave resources to process traditional high-performance thermoset composite matrices or where producing parts via these or other traditional thermoset processes are difficult and/or costly. This paper will provide an overview of current market pressures supporting the growth of high-performance thermoplastics and then will review various processing options for both thermoset and thermoplastic high-performance composites. Next several short case histories involving conversions to thermoplastic matrices directly from metals will be presented. Lastfuture trends that could impact this segment will also be considered.
Hybrid materials featuring thermoplastic polymer composites in conjunction with metals can be used as structural materials in commercial tr ansport and military vehicles and for protection of buildings and infrastructure. C onstituent thermoplastics and metals have distinct advantages as protective materials however metals on their ow n are heavy hence hybrid materials offer option as lighter materials. This study focuses on the effect of surface treatments to improve adhesion between dissimilar materials such organic polymers with metal reinforcement materials. Surface energy was found to possess a direct relationship with the amount of polar groups on the surface of a modified polymer and free radicals on the metal surface. Higher surface energy correlates with superior interface adhesi on. This work establishes the ba sis that polar groups and free radicals improve adhesion between polymeric (thermoplastics) and metallic surfaces.
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 model predictions and to better understand the effect of temperature on hybrid composite-to-metal joint performance quasi-static structural joint coupon tests were simulated for the purpose of test analysis correlation and modeling methodology development.
Rheology is the science of material flow behavior, which is a very complex and multi-dimensional science. Even though it is complex, it also is quintessential to understand in order to optimize the processing of polymers. Knowing the difference between amorphous and crystalline polymers, what Melt Index really tells, and the effects of melt temperature on melt fracture are all important elements in the understanding of rheology. A simple understanding of what polymer rheology is and how shear and temperature can affect the flow characteristic of a polymer may make a big difference in the P & L of a company.
Daniel Watt, Stephanie Masse, Bobbye Baylis, May 2011
The present study examines the effects of bounded voids of different sizes and shapes on the strength and leakage of contour welds. Bounded voids are holes that are situated on the laser beam path, but whose melt flow is constrained from leaving the faying surface. The most significant result is that divot clusters can lead to quite high porosity in the interface, but even with that porosity, both high hydraulic burst test strengths and hermetic seals can be achieved.
A new class of cationic initiators, lanthanide triflates, has been studied in the cationic curing of DGEBA/PA mixtures. The reaction mechanism of the cationic curing of DGEBA/PA mixtures has been studied. The kinetics of this process has been evaluated by the Differential Scanning Calorimentry (DSC).The crosslinking degree is predicted from time and temperature of curing via the Gel-curve.
As new state-of-the-art flexible packaging technology is installed in its target markets and with processing costs under pressure to enable these technologies to ramp-up in 2011, surface pre-treatment technologies must become a key enabler relative to higher processing speed, wider widths, and requirements on inks and coatings to transfer and adhere to substrates at these speeds and widths. This paper presents evidence of new flexible packaging print performance opportunities using a new, revolutionary atmospheric plasma treatment (APT) technology.
Sandwich composites are being aggressively pursued as structural materials by various defense and commercial industries. These
include navy, air force, army, automotive and sporting industries to name a few. The present work describes the compression and release response of a glass-fiber-reinforced polyester composite (GRP) under
shock loading to 20 GPa. Shock experiments in GRP were performed at Sandia National Laboratories and the US Army Research
Laboratory. GRP is a heterogeneous material.
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