A comprehensive collection of news and information about composites.
Posted by: Ginger Gardiner4. May 2016
CIBOR performs R&D on a variety of bioscience and medical applications, including composite surgical instruments, joint implants and orthopedic implants which help stimulate bone growth.
The Center of Innovation for Biomaterials in Orthopedic Research (CIBOR) at the National Institute for Aviation Research (NIAR, Wichita, KS, US) seeks to bridge the gap between the aviation and medtech sectors, applying aerospace materials & process knowledge to the design and development of medical devices, specifically in orthopedics. CIBOR performs R&D on composite materials for a wide variety of bioscience and medical applications, including orthopedic implants and surgical instruments. Composites have benefits in medical applications which could enable significant improvements in battlefield and sports medicine, reduced cost, decreased time and invasiveness of orthopedic surgical procedures, and improved rehabilitation and long-term outcomes for orthopedic patients.
CIBOR draws upon the composites expertise of Wichita’s well-established aviation manufacturing community and NIAR to deliver global leadership in the design and fabrication of composites-based medical technology. It also works with local manufacturers seeking to diversify their composites manufacturing outside of aerospace. “CIBOR is very unique,” explains senior research engineer Kim Reuter, “we have engineers that are excellent at composite laminate design, but also have an outstanding biology team that can perform biocompatibility studies and bone growth analyses.”
CFRP's advantages in orthopedic surgical instruments include radiolucency and surfaces that do not scratch implants as readily as stainless steel. They must also be very strong to resist the forces applied during orthopedic surgeries. SOURCE: CIBOR.
Composites in sterilized surgical instruments
“The advantage of composites over stainless steel in orthopedic surgical instruments is radiolucency,” explains Kim Reuter, senior research engineer at CIBOR. “In other words, except for locating markers, they are not visible on x-ray or fluoroscopy equipment.” She notes that surgeons actually asked instrument manufacturers for this. “It is needed, for example, when an orthopedic surgeon is trying to line up a screw with a fixation device implanted within a long bone.” Stainless steel shows up as bright white on a fluoroscope (real-time x-ray), obscuring the surgeon's view. In that case, the medical team must take all of the instruments out, observe the site of interest, and then put them all back. “This is time-consuming and increases risk to the patient,” Reuter adds. Carbon fiber reinforced plastic (CFRP) instruments, however, do not show on the fluoroscope and allow for a clear view of the anatomy without removal of the instruments.
Another important driver for CFRP is for instruments that do not scratch implants. “Knee implants are designed for fatigue, and thus are highly polished,” says Reuter. “The bearing surfaces must be smooth, as they form the articulating surface of the joint. If you scratch these, you create a crack initiator.” Reuter notes that scratching these surfaces is easy to do with stainless steel instruments. And yet, these surgical tools must be very strong. “Surgeons need durable, strong instruments that can withstand the forces applied during surgery as well as the harsh sterilization environment before and after surgery.” For this reason, CIBOR looked at continuous reinforcements, mostly woven and unidirectional tape. “The composite instruments are a little thicker but almost the same dimensions as the stainless steel. The surgeons said they felt just as stiff but lighter weight.”
One further requirement, however, is that instruments must maintain their mechanical performance properties despite repeated sterilization cycles between surgical procedures. According to Andi Meyer, also a senior research engineer at CIBOR, the most common process is steam sterilization: An autoclave is filled with instruments, sealed and then filled with forced steam under high pressure to destroy microorganisms and denature enzymes and proteins. Time and temperature vary, but a one-hour cycle is common, 15 minutes of which may be at the highest pressure and temperature.
Meyer has recently completed a series of steam sterilization tests, aimed at understanding how a variety of composite materials may perform as surgical instruments after hundreds of steam sterilization cycles. Although a number of studies have reported that carbon fiber (CF) reinforced polyetheretherketone (PEEK) performs well under repeated steam sterilizations, Meyer says these mostly involved neat PEEK or chopped CF reinforced PEEK. “My results were different,” explains Meyer, “because I used stronger and stiffer materials more standard to aerospace, such as continuous carbon fiber thermoset and thermoplastic laminates, including PEEK.”
Meyer tested their properties, pre-sterilization, and again, after 200, 400, 600, 800 and 1,000 steam sterilization cycles. Meyer explains, "the best material for an instrument depends on what the primary driver is — e.g., is the main goal a cheap instrument or a very long-lasting one? — and also on the manufacturer. For example, PEEK is expensive and many of our local manufacturers prefer not to work with it.” She says that CF/epoxy tested after 1,000 steam sterilization cycles showed 84% of original strength, while CF/PEEK showed only 54%. However, the appearance of the CF/epoxy was significantly more degraded than the CF/PEEK. "This study had surprising results that discourages generalization of material properties," says Meyer. "It showcases the need for experienced composite engineers to design medical products appropriately."
She notes that, "Not all CFRP can handle the hot-wet environment of steam sterilization. Designing for high strength applications and testing materials in harsh environments is second nature for composite experts in the aerospace industry, but unfortunately, some composite medical devices are being introduced into the market without evaluating all operational conditions." Meyers asserts that improperly designed composites are creating a negative impression, "which adds to the challenge of bringing composites into the medical industry."
Carbon fiber/PEEK hip implants (left) are being developed with the goal to reduce the need for revision surgery (repeat hip joint replacement) in 15 years or less due to complications from bearing surface wear. SOURCE: (left) Composites in daily life, composites.ugent.be, (right) “A PEEK into the Future of Hip Implant Bearing Surfaces,” QMED.com.
Revision-free implants require new materials and test methods
This CIBOR research was sponsored by an orthopedic manufacturer who wanted to research CFRP in hip and knee implants. Though used in spinal implants for over two decades, and gaining acceptance in plates and nails for fracture fixation, this composite material is still in exploratory stages for total joint replacements like knees and hips.
Past CIBOR chief scientific officer, Dr. Paul Wooley, reported that although hip and knee implants are designed to have an estimated 15-year lifespan, they often fail quite short of that. He adds that now 30% of patients in their 50s and 55% of patients younger than 50 will require revision surgery — replacement of the implant with another implant — before the 15-year lifecycle expires. Revisions are also expensive, costing 41% more than the primary surgery, with a hospital stay that is typically 2 days longer, a slower recovery and a 32% higher rate of complications. Patients are also receiving implants at a younger age and demanding higher performance. Thus, a longer-lasting, durable hip or knee implant that does not require revision procedures is indeed a Holy Grail.
CIBOR senior research engineer Andi Meyer explains that there is significant mechanical stress during implant service life. Bearing surface wear and resulting debris are widely regarded as primary culprits for issues such as osteolysis (bone tissue destruction), loosening leading to implant failure.
CFRP reportedly offers potential for joint replacements that last longer than 15 years. “Strong and stiff implants made of traditional metals shield the bone from stress, whereas CFRP materials can be tailored to match stiffness of the bone" says Meyer, "this allows the bone to be subjected to stress so it does not become weak and start to atrophy.” The latter happens with metal implants, which means revision surgery. “Since you lose bone stock with each revision,” she says, “eventually, revision becomes impossible.” (This is why joint replacements are typically avoided for young people.)
Aesculap, a division of healthcare supplier B. Braun Melsungen, is using CF/PEEK in its FDA-approved EnduRo knee implant. Aesculap worked with Invibio Biomaterial Solutions, which was formed in 2011 as a wholly owned subsidiary of Victrex plc to focus exclusively on the medical device market. SOURCE: Plastics Today and Aesculap.
According to Meyer, a composite implant can be designed to flex more and share the load with surrounding bone so there is less bone loss. “The problem,” says Meyer, “is the ASTM test methods for these implants were not designed for this different type of load-sharing performance offered by composite materials.” In fact, CFRP’s improved flexibility actually precluded it from passing the legacy performance tests, because the standards used to evaluate implants were written for metal.
“We have recommended that the industry consensus test standards be rewritten to define thresholds required for using CFRP or other materials not currently used in replacement devices,” says Meyer. “However, when we went to the orthopedics capital — Warsaw, Indiana — and talked to the major players, we discovered a lack of interest in collaboration on this topic. To our knowledge, no progress has been made on revising the test standards.”
Even so, carbon fiber composite implants are proceeding into the market. A 2012 report in Plastics Today touted CF/PEEK’s successful performance in a total knee arthroplasty (TKA) and a 2014 research article looked at 62 TKA patients receiving this device, showing successful results, though early still, and for a relatively small cohort. A 2015 literature review also showed CF/PEEK to have potential wide-scale success in joint and other implants, though it admitted its span of 24 articles was limited.
CIBOR has also made significant progress in testing carbon foam materials as aids in bone growth and regeneration. Be sure to read about it in our upcoming June issue’s feature article.
Posted by: Jeff Sloan29. April 2016
CTE of polybenzoxazine compared to epoxy, epoxy/phenolic and phenolic. These data, provided by
Dr. Hatsuro Ishida at Case Western Reserve University, come from the US Federal Aviation Administration (FAA).
Dr. Hatsuro Ishida, professor at Case Western Reserve Univeristy (Cleveland, OH, US), has been at the forefront of benzoxazine research and development and formulation since the polymer was adopted by the composites industry in the early 1990s. He has continued this work and reported, at the SPE Thermoset Topcon (April 19-20), on his latest development.
Ishida says the latest benzoxazine resins to come out of his lab represent the fourth generation of this versatile matrix resin and signals a step-change in physical and mechanical properties. Polybenzoxazine is formulated by the synthesis of a benzoxazine monomer that is synthesized from phenol, formaldehyde and a primary amine.
The list of properties available with polybenzoxazine, says Ishida, are considerable:
Polybenzoxazine's flammability characteristics appear to make it a strong
candidate for aerocomposites applications.
In testing, Ishida reports, polybenzoxazine showed mechanical properties and shrinkage better than epoxy, fire performance second only to phenolic, use temperature comparable to or better than BMI, and cost on par with epoxy. It also features a dielectric constant better than epoxy, a CTE of 41 ppm/°C, a peak heat release in flammability tests of <50 W/g, and a flex strength much higher than the corresponding epoxy or phenolic composites.
Benzoxazines currently on the market in the composites industry are supplied by Henkel Corp. (Rocky Hill, CT, US), Huntsman Advanced Materials (The Woodlands, TX, US), and Shikoku Chemicals (Kagawa, Japan). The resin’s high-temperature and flammability performance, high strength, thermal stability and nearly unrestricted outtime, have made it attractive in applications — particularly in aerospace — where BMI traditionally has been favored.
Ishida says that neither he nor Case Western Reserve University are equipped to commercialize his formulations, but he is very open about his lab’s benzoxazines chemistries and encourages resin suppliers to adopt them. Ishida can be reached at firstname.lastname@example.org.
Posted by: Jeff Sloan28. April 2016
ZeMC2, Zeon Technologies and Asbury Carbons worked together to develop 3858A, a carbon fiber/ceramic bulk molding compound (BMC) that is conductive and uncommonly wear-resistant.
ZeMC2 reports that it was approached by a manufacturer of centrifugal pumps who was looking for a new bushing material capable of outperforming the typical metal or plastic industry standards. Centrifugal pumps can range in size from a few gallons per minute to more than 10,000 gpm, and can be found in a range of applications including irrigation, flood water evacuation, water circulation, refinery “offsite” loading and transfer, chemical transfers, and more.
The typical design of centrifugal pumps locates a bushing (or sets of bushings) around the outside of a spinning shaft to provide mechanical stabilization to the shaft while rotating at high RPM. These bushings are typically made out of a metal or plastic material and have a life span of one to two years. Primary modes of failure of typical bushings are related to the high stress — thermal and mechanical stress — developed during operation. Mechanical wear, chemical erosion and debris impact are also well-known failure modes.
In the particular application studied, the pump design required a start up and dry run for 1 hour, generating extremely high temperatures and associated stresses on the bushing materials. Clearance tolerances for the shaft bearings ranged from 1/1000-1/20,000 of an inch. The pump manufacturer was looking for a thermally stable, conductive and lubricious material. Traditional wear bushings would expand, melt, or bind in the application as they lacked the necessary properties, ultimately resulting in a variety of failure modes including:
ZeMC2 and Zeon Technologies developed a proprietary resin that was combined with Asbury’s novel carbon fiber materials, and ceramic, to create a new BMC with outstanding performance capabilities. The BMC is called 3858A and supplied by ZeMC2. It exhibits significantly improved thermal stability through a range of operating temperatures, as well as improved strength and toughness made possible by Asbury’s graphite and carbon fiber material solutions. 3858A can be machined and press fit, is chemically inert and conductive, and can be manufactured in virtually any bulk feedstock size.
After four years of service in a cetrifugal pump, bushings fabricated with 3858A BMC, featuring a proprietary thermoset resin, showed no change in inside or outside dimension. Similar tests with polyphenelene sulfide (PPS), polyamide-imide (PAI) and polyimide showed dimensional degradation.
After 2,000 operating hours in extreme application conditions (dry run, high/low temperatures), 3858A samples were analyzed and benchmarked against competitive materials. In short: 3858A significantly outperformed other competitive materials (PPS, PAI, PI), showing no sign of degradation. After four years in the field, the companies says, bushings show no measurable or visible wear.
Mechanical properties of 3858A:
Posted by: Ginger Gardiner28. April 2016
GE is a leader in developing the Industrial Internet, aiming to dramatically improve manufacturing and industrial efficiency. SOURCE: slideshare presentations from (left) GE, (right) National Instruments.
I’m going to start this blog with some background and definitions. I will get to composites, but I think it’s important to understand the basic vocabulary first. So bear with me.
The Industrial Internet — referring to the Industrial Internet of Things (IoT) — is a term reportedly coined by General Electric (GE, previously Fairfield, CT and now Boston, MA, US) to describe the integration of complex physical machinery with networked sensors and software. GE has actually been building an Industrial Internet platform since at least 2011, with some nascent movements as early as 2008. Though GE is not the only company developing technologies for the industrial internet — Siemens is another player — it is a leader and heavily invested.
At the center of GE's transformation is Predix. Originally developed by GE to connect its own people, data and machines, Predix is now opened to outside companies. What is Predix? It is a technology platform that helps developers quickly build apps for the industrial internet. It has access to big data repositories (“data lakes”) and can be deployed in the cloud for more widespread access. Perhaps most importantly, it enables users to run analytics on big data, remotely monitor machines — e.g., jet engines, wind turbines, etc. — and even have machines talk to each other.
One of the big picture goals of Predix is being able to combine operational technology (OT) with information technology (IT). Bringing OT and IT together allows engineers and companies to see what’s going on in a machine, for example, whether something is wrong, and what can be done about it before it affects customers. Like doctors, the analytics can be used to predict when the machines might have problems in the future.
One example is in jet engines. These are currently outfitted with numerous sensors that provide data on various operational parameters, but that “just tells you there’s a problem,” says Bill Ruh, CEO of GE Digital. Analyzing these parameters for multitudes of engines, however, and combining with fleet analytics provides new insights and capabilities. As explained in Laura Winnig’s article, “GE’s Big Bet on Data and Analytics” in MIT Sloan Management Review:
The company learned that the hot and harsh environments in places like the Middle East and China clogged engines, causing them to heat up and lose efficiency, thus driving the need for more maintenance. GE learned that if it washed the engines more frequently, they stayed much healthier. “We’re increasing the lifetime of the engine, which now requires less maintenance, and we think we can save a customer an average of $7 million of fuel annually because the engine’s more efficient,” Ruh explains. “And all of that was done because we could use data across every GE engine, across the world and cluster fleet data.”
Note, this same goal is being pursued via structural health monitoring (SHM) systems. Changing operations from human-based decisions to analytics-based decisions is still new and often untrusted. Still, GE has set high goals, envisioning Predix as the iOS or Android of the machine world.
GE's vision of industrial internet solutions comprises Predix, apps and digital twins of physical machines like power turbines. SOURCE: GE.
A key concept within GE’s vision for the Industrial Internet is the digital twin, which is a virtual model of each physical production asset — i.e., each jet engine or wind turbine. As explained in The Economist article, “The digital twin”:
“The ultimate vision for the digital twin is to create, test and build our equipment in a virtual environment. Only when we get it to where it performs to our requirements do we physically manufacture it. We then want that physical build to tie back to its digital twin through sensors so that the digital twin contains all the information that we could have by inspecting the physical build,” says John Vickers, NASA’s leading manufacturing expert and manager of NASA’s National Center for Advanced Manufacturing.
Digital twins comprise elements like 3D CAD models, manufacturing simulations and real-time data feeds from sensors in the physical operating environment. The article goes on to assert that the real benefit of digital twins are actualized when all aspects, from design to real-time data feed, are brought together to optimize the asset over its lifetime. The goal is not to just cut prototyping or construction costs, but to predict failure more easily and accurately as real-time data is fed into the model, and thus reduce both maintenance costs and downtime.
Two GE application examples of digital twins:
GE Aviation and jet engines (left) and GE Power & Water and digital wind farms (right).
An example of how digital twins will improve industrial performance is GE’s pilot “digital wind farm” concept. The digital wind farm design informs the configuration of each wind turbine prior to procurement and construction. Once the farm is built, each virtual turbine receives data from its physical twin. Software and the digital twins are then used to optimize power production of the wind farm by adjusting specific parameters in each physical turbine, like the torque of the generator or speed of the blades. GE hopes to achieve a 20% gain in efficiency.
According to the Economist article, “For every physical asset in the world, we have a virtual copy running in the cloud that gets richer with every second of operational data,” says Ganesh Bell, chief digital officer and general manager of Software & Analytics at GE Power & Water. “The Digital Twin is not a generic model. It’s a collection of actual physics-based models reflecting the exact operating conditions, such as lifing, performance and failure modes, in the real world.”
The GE Digital Thread. SOURCE: GE, slide 6 from slideshare presentation “GE’s Digital Manufacturing Transformation”.
One last definition before we discuss composites. Christine Furstoss, global technology director for GE Global Research, has described how GE sees the digital thread in the manufacturing.cioreview.com article “Digital Thread: Creating a Self-improving, Brilliant Factory”. She notes that Henry Ford perfected the assembly line and Toyota introduced “Lean Manufacturing”. GE has begun using sensors and big data analytics to improve both the speed and efficiency of manufacturing. It sees a self-improving, agile and connected supply chain communicating and operating through a digital thread in real time.
This thread begins when a new product designer creates a CAD model of the part or product to be made. Once optimized, the design is transmitted digitally to manufacturing engineering, where processes are modeled and simulated. Here, too, factory flow and layout, robots and manufacturing controls will be simulated and optimized. Once the design and processes are virtually validated, the data is transmitted to the brilliant factory, where intelligent machines will translate the data to manufacture the part or product. This factory is digitally connected real-time to its suppliers for optimal production control and logistics.
Here, GE really can’t claim pioneer status. Lockheed Martin has been talking about “digital tapestry” for years. In fact, Lockheed has put it into action as the leader of the Defense Advanced Research Projects Agency (DARPA, Arlington, VA, US) Transition Reliable Unitized STructure (TRUST) project. TRUST is pursuing certification of unitized bonded composite primary structures without redundant fasteners by using big data to achieve the manufacturing process control required for reliability. Similar to how GE’s digital twin gets better with every second of operational data, TRUST’s bayesian process control gets smarter with every part made.
Application to Composites
“We’ve actually implemented the Industrial Internet into composites manufacturing already,” says Avner Ben-Bassat, president of Plataine Technologies (Waltham, MA, US and Tel Aviv, Israel). (See “Applying the Industrial Internet to composites production” and “Optimizing composites aerostructures production”.) “We see an advancement and merging of traditional design tools and product lifecycle management (PLM) tools with data storage in the cloud and algorithms enabling intelligent manufacturing systems and anomaly detection.” What does this mean exactly?
“Say you have a part that fails a quality control check,” explains Ben-Bassat. “We can track that part’s digital thread back to the details of its tooling, layup and material lot numbers. If the issue stems from a mold that needs maintenance or a materials issue,we can immediately access the thread of every other part using those materials and pull them from the line. We can even pull them from customer sites before there is an operational problem.” But this is only possible with digital technology, Ben-Bassat notes. “With traditional methods, you’d be lost in paperwork for weeks.”
The software not only finds potential issues and correlations, but also makes decisions. “If parts are pulled from the production line,” notes Ben-Bassat, “then the system automatically triggers new production to meet schedule and any new input demand. In other cases, if a batch of pre-preg is disqualified, the system will automatically reassign future jobs to alternative rolls."
Plataine has already begun working with GE, adapting its current Total Production Optimization (TPO) products to the Predix platform, but is also developing new applications. Ben-Bassat says the functions he is describing here are already offered today, and Plataine is filing patents for many new extensions of these capabilities.
One example is real-time, digital feedback loops between engineering, manufacturing and service. Ben-Bassat explains, “So with your digital tools in place, your part quality is consistent, but as you collect data you see that the part was designed to cost $1,000 but is actually exceeding $1,500 per unit. The digital systems we are putting in place actually provide the data feedback to engineering to address this cost overrun. It allows for better and more accurate identification of issues throughout the product life cycle and continuous improvement.” This enhanced business analysis is extended into in-service use as well. “Perhaps you achieved cost reduction and it now costs 50% less to make the part, but once it gets into service, repairs cost 75% more. We can identify that and feed the data back for improvement in design and manufacturing.”
Ben-Bassat says as aerospace OEMs continue to use Tier 1 and 2 facilities around the world to manufacturer components and sub-systems, it becomes critical to better manage quality control. “Right now, you have globally shared CAD systems which control part designs and drawings, but how do you transfer best practices for efficiency and quality in manufacturing?” He asserts that with sensors and the type of Industrial Internet applications Plataine is developing, “you know what each supplier is doing because you’re collecting all of the process parameter data real-time.” He adds that many companies have worked with Plataine in the past to pursue optimization of process control, “but now there is a dramatic increase in the data at our disposal, so we can achieve improvements much more quickly and drive increased value.”
Just as Lockheed Martin and DARPA identified in the TRUST program, there is now an opportunity to identify non-conforming parts before the end of the process chain and bring them back into acceptable limits, which saves both time and cost.
With Industrial Internet solutions and sensors collecting data throughout processing, it is now possible to identify non-conforming parts before the end of the process chain and provide feedback throughout the digital thread. SOURCE: Plataine.
Plataine has made several announcements recently, partnering with companies like Siemens PLM (Waltham, MA, US), Argosy International (New York, NY, US) and Airbus’ Composite Technology Center (CTC, Stade, Germany). “By integrating our manufacturing automation and optimization solutions into their processes, we add more capabilities to the digital thread."
But isn’t all of this software and optimization expensive? “The prices of sensors have come down and continue to do so,” says Ben-Bassat. “You can set up RFID antennae for freezer tracking of prepreg for as little as $5,000 to 10,000.” He concedes that some of the big OEMs have invested over $100,000 in integrated digital systems, but there are also low-cost lab-scale systems for research organizations. The tracking and optimization software is offered on a subscription basis, minimizing the need for any further capital expenditure. “From Day One, we developed our software to be scalable up and down the digital thread,” says Ben-Bassat. He adds that the future being offered with Predix is looking more to modular, collaborative solutions based on applications, like those commonly developed for iPhones and iPads. “What we are offering can start as local applications but then be distributed across operations, and also start as relatively simple feedback loops but over time integrate more algorithms to increase functions, ability to respond to alarms and decision-making intelligence (Artificial Intelligence).”
I’m going to visit CTC in June and will hopefully be able to give more details on the vision it sees for composites using the Industrial Internet. Stay tuned for an update.
Posted by: Jeff Sloan27. April 2016
Ashland, to assess the performance of its new 1.2 specific gravity Arotran 771 SMC, fabricated an automotive panel to Ford Motor Co. specifications and then tested it for E-coat tolerance. The material showed no blistering, which is seen as key to winning a place on production cars and trucks.
Michael J. Sumner, group leader – gelcoat, SMC, marine resin, Ashland Performance Materials (Columbus, OH, US), reported at SPE’s Thermoset Topcon (April 19-20) on the development of Arotran 771, the company’s newest sheet molding compound (SMC), designed specifically for use in automotive applications. Prompted by customer demand for a tough, low-density, E-coat-capable, cost-effective SMC, Arotran 771 offers a specific gravity of 1.2, along with some impressive physical and mechanical properties.
Sumner walked attendees through the SMC’s development, with particular emphasis on the evaluation of resin performance. Ashland looked at various combinations of vinyl ester and unsaturated polyester resin (UPR), testing for finished part surface quality, mechanical performance, Tg and E-coat tolerance.
Tg of Ashland's new Arotran 771 SMC (50:50 blend, with 5 wt% resin toughener in legend). The material offers a specific gravity of 1.2, with good strength and toughness, along with the ability to tolerate the E-coat process.
Initial tests of surface quality, as measured by advanced laser surface analyzer (ALSA), showed that a 50:50 blend of vinyl ester and UPR was optimal, with an ALSA value of 64. Ashland added a 5 wt% reactive toughener to the mix and got very good mechanical values: tensile strength 85 MPa, tensile modulus 8,600 MPa, flex strength 182 MPa, flex modulus 8200 MPa and elongation 1.41%. Drop dart impact resistance is 3.1J.
Further testing, Sumner says, revealed that the selection of initiator system and mold temperature can influence part quality. Ashland conducted a series of tests, combining different initiators with mold temperatures of 121°C or 150°C and evaluated surface quality and mechanical properties. The best-performing combination included the reactive toughener and a mold temperature in the 121-150°C range (see table).
Mechanical properties of Arotran 771 SMC (50:50 blend with toughener) compared to
non-toughener and standard SMC at two mold temperatures, with different initiators.
To assess E-coat performance, Sumner says Ashland fabricated several SMC panels to a Ford Motor Co. specification and ran them through the Ford E-coat test protocol, involving exposure to 38°C/100°F and 100% humidity for 10 days, followed by short-term exposure to 200°C/392°F heat. The panels showed absorption of 2.25% with no blistering, the latter of which is required to pass the test.
Arotran 771 represents a substantial increase in SMC performance, comparable to the TCA Ultra Lite brand SMC — also 1.2 specific gravity — introduced in 2015 by Continental Structural Plastics (CSP, Auburn Hills, MI, US). Sumner says Ashland is trialing Arotran 771 with several customers involved in the automotive supply chain.
In the meantime, Ashland is not standing pat. Sumner reports that the company is already working on chemistries to help push SMC specific gravity down to 1.1 and, eventually, 1.0. And those products could come on the market relatively soon. “If we can get to 1.0,” Sumner asserts. “We can effectively compete with aluminum.”