CW Blog
By: Peggy Malnati 30. November 2018
Hybrid thermoplastics give load floor impact strength
Lighter, more energy-absorbing battery-electric vehicle structures
A multiyear, publicly funded research program called System integrated Multi-Material Lightweight Design for E-mobility (SMiLE) took a holistic approach to reducing mass and costs for the entire body-in-white structure (shown here) of a battery-electric vehicle by applying combinations of composites and non-ferrous metals. Some of the F-ICT members who participated in the project are (left to right): Dr.-Ing. Sebastian Baumgärtner, project leader for hybrid thermoplastic floor modules; Tobias Link, research engineer; Prof. Dr. Frank Henning, deputy head of F-ICT; and Felix Behnisch, project leader for thermoset floor modules. Source | Fraunhofer Institute for Chemical Technology.
Fig. 1 Forming-Study results for residual mold travel and filling
Extensive simulation work that was subsequently verified by small- and large-part testing was done on all major aspects of the rear floor module’s design, processability, and performance. For example, several different forming studies looked at the impact of mold travel (top) and filling (bottom). Source | Fraunhofer Institute for Chemical Technology
Fig. 2 Rear composite floor structure
The final rear floor module demonstrator featured a thin-shell, near-net-shape structure produced from UD tapes preconsolidated into a laminate (gray) as well as D-LFT ribs (green) in X-shaped lattice structures with select use of integral metallic inserts and aluminum profiles (blue) on the axial side of the part. D-LFT ribs are 2.5-3.8 cm tall. Source | Fraunhofer Institute for Chemical Technology
Fig. 3 Reduction in weight for BIW structures
At the conclusion of the SMiLE program, the total mass of the BIW for comparable vehicles was reduced 153.55 kg (42.39%) by using the holistic approach of applying composites and non-ferrous metals where each made sense. Although one project goal had been to reduce the BIW to 200 kg or less, as the project evolved, researchers desired better crash performance (adding composite structure) and needed to address costs (opting to switch from carbon fiber to glass fiber reinforcement for thermoplastic composites in the rear load floor), adding mass. Source | Audi AG
Fig. 4 Molding trials for load floor design
During the final molding trial for the rear thermoplastic composite load floor, more than 100 test parts were produced (shown here). Source | Fraunhofer Institute for Chemical Technology
Fig. 5 Combining thermoplastics and thermosets
Some of the test parts produced during the final molding trial for the rear thermoplastic composite load floor were joined with the front thermoset composite load floor and side rockers to produce demonstrator parts (shown here) for further evaluation. Source | Fraunhofer Institute for Chemical Technology
An ambitious multi-year program by Germany’s System integrated Multi-Material Lightweight Design for E-mobility (SMiLE) consortium has developed a demonstrator automotive load floor module that is part of a larger hybrid body-in-white (BIW) structure and that shows great promise for use of composites and non-ferrous metals in a medium-volume production environment. This battery-electric vehicle’s (BEV’s) rear load floor is comprised of two types of thermoplastic composite, plus metallic profiles and inserts. It functions as the floor of the trunk and rear passenger compartment. In turn, it’s adhesively and mechanically joined to a second, hybrid/thermoset composite load floor, which is resin transfer molded (RTM’d) from carbon fiber-reinforced epoxy with metallic inserts and local sandwich structures containing polyurethane-foam cores. This structure is the floor for the front half of the vehicle and holds its batteries. The complete load floor module is bonded and screwed to aluminum rockers/side rails, which are themselves bolted to crossbeams on the vehicle’s aluminum monocoque. The entire load floor module demonstrator was designed to reduce mass and provide significant crash energy absorption for a series-production vehicle with build volumes of 300 cars/day.
Consortium members who worked on the rear load floor included automakers Audi AG (Ingolstadt, Germany—also leader of the entire SMiLE program) and Audi owner Volkswagen AG (Wolfsburg, Germany); Karlsruhe Institute of Technology’s Institute of Vehicle System Technology (KIT-FAST, Karlsruhe, Germany); Fraunhofer Institute for Chemical Technology (F-ICT, Pfitztal, Germany, leader for both front and rear load floor projects), and Fraunhofer Institute for Mechanics of Materials (F-IWM, Freiburg, Germany); thermoplastic composites supplier BASF SE (Ludwigshafen, Germany); machinery OEM Dieffenbacher GmbH Maschinen- und Anlagenbau (Eppingen, Germany), and toolmaker/molder Frimo Group GmbH (Lotte, Germany).
Read MoreBy: Donna Dawson 29. November 2018
Leveraging composites for space tourism
Fig 1
The two 78-ft-long fuselages of WK2 are identical in structure: a nose cone, cabin structure, and boom section that extends to the 26-ft-high horizontal tail. The right-side cabin is pressurized for crew: two pilots and an optional seat for a flight test engineer. The left-side cabin is unpressurized and contains ballast to keep the vehicle’s center of gravity along the centerline.
Source | TSC
Fig 2 A
VMS Eve (WK2) and VSS Unity (SS2) all-composite structures being prepared for flight. WK2 has a 140-ft wing span, providing space for carrying an SS2 to launch position. Shown here, SS2 moves into position to lock into WK2 release mechanism.
Source | TSC
Fig 2 B
WK2 and SS2 in flight. WK2 is designed to carry SS2 to an altitude of about 9 miles, at which point SS2 detaches for the final flight to the edge of the Earth’s atmosphere.
Source | TSC
Fig 3
Installation of Pratt & Whitney engine into composite cowlings and high-temperature composite inlet duct and exhaust nozzle. Source | TSC
Fig 4
TSC graphics illustrate dimensions and configuration of SS2: Schematic diagram includes illustration of the unique feather system that facilitates re-entry into Earth’s atmosphere and its non-powered glide toward the ground. Source | TSC
Fig 5
SS2 feather function is tested in TSC facility. The carbon fiber composite feather is folded up 90° to increase drag and reduce speed as SS2 prepares to re-enter Earth’s atmosphere. Source | TSC
Fig 6 A
Extensive testing has been conducted on rocket technology to ensure performance of SS2 in its drive to suborbital space. The rocket has now been qualified for human-rated service. Shown here, a rocket moved into position for testing. Source | TSC
Fig 6 B
Fuel ignited for hot fire test. Source | TSC
Step 1
Tooling is prepared for carbon composite layup of new SpaceShip fuselage sections SS2-003 and SS2-004. Tooling preparations include waxing, and application of an appropriate mold release and primer. Source | TSC
Step 2 A
Solvay MTM45-1 prepreg fabric is precision cut by automated ply cutter or hand cut by skilled technicians. Shown here, a Gerbercutter from Gerber Technology (Tolland, CT) performs automated ply cutting.
Step 2 B
TSC technician hand cuts prepreg to small shapes for custom layup.
Source | TSC
Step 3
In general terms, composite manufacturers build sandwich structures in one of two ways: One is a multiple stage system where plies of prepreg fabric are laid up for the outside skin in the designated fiber architecture to meet specified loads and conditions — with appropriate sacrificial films and layers. The layup is vacuum bagged, debulked and cured. The film adhesive and core are then arranged over the skin laminate. The inside skin and film adhesive can then be similarly laid up and cured.
Other manufacturers use a single stage system where the entire structure is laid up, vacuum bagged, debulked and cured in a single operation.
Source | TSC
Step 4
An SS2 fuselage skin panel is subjected to a thorough debulking process to force out any air trapped between the prepreg plies. Entrapped air can lead to porosity or other flaws in the final cured product. Typical debulking includes pulling a vacuum on the layup before cure.
Source | TSC
Step 5
Parts are typically oven-cured at the recommended resin time and temperature for OoA cure. After cure, parts are de-molded and prepared for assembly. Photo shows upper half of SS2-003 cabin ready for assembly, with windows and emergency egress ports cut out. The crew and passenger cabin is 2.3m outside diameter (OD), by 3.7m long. (A) Side windows are 43cm OD; (B) top windows 33 cm; (C) crew station windows 53 cm. (D) Emergency egress. Source | TSC
Step 6
Finished parts are assembled primarily by bonding, with addition of metal fasteners as needed. Photo shows assembly of SS2 fuselage and wing. The leading edges of the wing and the horizontal stabilizer are faced with a thermal protection system derived from NASA’s Space Shuttle program’s thermal insulation systems. Source | TSC
It all started with the Ansari XPrize. Wealthy space enthusiasts Anousheh and Amir Ansari offered $10 million to the first private enterprise, worldwide, “to build a reliable, reusable, privately financed, manned spaceship capable of carrying three people to 100 km [62 miles] above the Earth’s surface twice within two weeks,” says the Ansari XPrize website.
The award, given in 2004, went to Mojave Aerospace Ventures (MAV, Mojave, CA, US), owned and funded by Microsoft co-founder Paul Allen for spaceship technology engineered by Burt Rutan and his Scaled Composites team at the Mojave Spaceport. The spaceship that reached the goal was an all-carbon fiber composite structure named SpaceShipOne. In one of the many departures from the ordinary in this venture, the spaceship did not launch from Earth’s surface, but was delivered part of the way to its destination by the (also) carbon fiber composite WhiteKnight. Dubbed the mothership, WhiteKnight was designed to replace the first stage of a traditional rocket used to launch a craft from Earth’s surface. When WhiteKnight reached its target altitude, SpaceShipOne was released from its mothership and a dedicated rocket on SpaceShipOne provided the second-stage boost, driving the spaceship up to its suborbital goal.
Read MoreBy: Scott Francis 28. November 2018
IACMI Scale-Up Research Facility to host Compression Molding Workshop
Source | IACMI
The Institute for Advanced Composites Manufacturing Innovation’s (IACMI, Knoxville, TN, US) and CompositesWorld will host a Compression Molding Workshop on January 17, 2019. The limited seating workshop will take place at IACMI’s Scale-Up Research Facility (SURF, Detroit, MI, US) and offers OEMs and composites fabricators an opportunity to learn about two existing technologies:
The workshop aims to enable OEMs and fabricators seeking to expand composites penetration in automotive and other end markets.
Read MoreBy: Ginger Gardiner 28. November 2018
Measuring temperature inside composites and bondlines
Wireless, remote in situ temperature monitoring
AvPro’s ThermoPulse system is being tested at Abaris Training and three other sites for statistical validation of its ability to measure temperature within a composite bondline during composite repair. Though the antenna (orange block) interrogating the microwire sensors is shown here taped to the test panel, AvPro is developing the ability for the antenna to read from overhead stations and robotic arms. Source | Abaris Training and AvPro Inc.
Fig. 1 Embedded sensors, antenna and temperature control
ThermoPulse microwire sensors are much smaller than thermocouples (center and right, respectively, top left photo) currently used to measure temperature. These microsensors remain embedded in bondlines and parts without causing defects and are interrogated using a magnetic antenna (top right) which plugs into a hot bonder (left) for data logging and analysis, temperature readout and control of heat blanket, autoclave, oven or other temperature/curing device. Source | AvPro Inc.
ThermoPulse microwire sensors remain embedded in bondlines and parts without causing defects and are interrogated using a magnetic antenna (shown here) which plugs into a hot bonder (next image) for data logging and analysis, temperature readout and control of heat blanket, autoclave, oven or other temperature/curing device. Source | AvPro Inc.
ThermoPulse microwire sensors remain embedded in composite bondlines and parts without causing defects and are interrogated using a magnetic antenna (previous image) which plugs into a hot bonder (shown here) for data logging and analysis, temperature readout and control of heat blanket, autoclave, oven or other temperature/curing device. Source | AvPro Inc.
Fig. 2 Three microwires, one calibrated sensor
ThermoPulse sensors comprise a reference wire, a measurement (sensing) wire and an autocalibration wire. When interrogated with an electromagnetic field from the ThermoPulse antenna, each wire generates a voltage pulse that changes with temperature. The area under this voltage response is the temperature at a given time. Each microwire has a designed optimal range (highest sensitivity) starting at 100°F below its Curie Temperature (TCurie). TCurie is the temperature at which the voltage pulse will disappear, and is a magnetic, physical property of each wire’s tailored metal alloy. The autocalibration wire’s TCurie is set well below the composite/adhesive cure temp. and once its voltage pulse disappears, the system is calibrated. The TCurie of the sensing wire is set to 100°F above the desired cure temp while the reference wire’s TCurie is set several hundred degrees above cure and provides a stable pulse for reference. Source | AvPro Inc.
Having full visibility into a composite and/or adhesive bondline during cure has been an issue for decades. Current temperature sensors — thermocouples — are too large to be embedded without causing a defect in the part. Thus, it is now only possible to read temperature at the surface and perimeter of parts and bonded repairs. It is difficult to know the temperature of an adhesive at the bottom of a repair patch, inside a thick fuselage or wing skin laminate or between those skins and thick stringers. Yet, that temperature is crucial for proper resin flow, wetting and cure.
Currently, the composites industry compensates for this shortcoming by spending months and millions of dollars testing to ensure that estimated time and temperature recipes do indeed complete cure and produce the necessary properties. Despite this, suppliers still spend many man-hours and dollars each year reviewing and certifying parts where thermocouples fail or where leading/lagging thermocouples are sufficiently outside of prescribed boundaries to cast doubt on properties and in-flight performance.
Read MoreBy: Sara Black 27. November 2018
Basalt fiber gives prosthetics more “give”
Prosthetics and orthotics often take advantage of composite materials’ strength and durability. One application in particular that benefits from composites are sockets, custom-shaped, hollow forms into which an amputee’s stump fits; sockets also include hardware that accepts limb or hand/foot attachments. Manufacturer Coyote Design (Boise, ID, US) is well known for its composite “definitive sockets” (as distinguished from temporary, typically plastic, test sockets, for fit testing). To produce a socket, a hollow cast is made of the patient’s stump and is then filled with plaster to create a positive shape. That plaster shape, fitted with a hollow pipe for handling inserted in the center, becomes the mold for the composite socket layup. The layup is wet-out with resin with the help of a vacuum (via the hollow pipe) and cured at room temperature, often with the help of a heat blanket, says Coyote Design’s Rod Smith, director of marketing.
Dale Perkins, Coyote Design’s cofounder, was an early adopter of composites and was not afraid to try new or exotic composite reinforcements. For example, one amputee patient and avid outdoor enthusiast (and who later summitted Mt. Everest) suggested using aramid for a tough prosthetic. However, several sockets made with that fiber failed, due to a lack of adhesion to the polyester resin Perkins was using at the time. Materials improved with the advent of carbon fiber braided tubes, or “socks,” wet out with epoxy resin or acrylic-modified epoxy. Carbon fiber prosthetic sockets exhibited good mechanical performance, but the material’s brittleness caused a high rate of cracking failure, and patients often reported uncomfortable stiffness. In addition, manufacturing with carbon fiber required masks, protective gear and dust collection systems for health and safety.
Read More