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Composite tension leaf springs: Available for trucks at last | CompositesWorld

Advancing through a third of the program in just three months, Archer continues to make rapid progress toward planned full wing-borne transition flight in Phase 2.

The U.S. Air Force conducted on-base and cross-country mission and performance evaluations of Beta’s composites-intensive CTOL aircraft, hitting key milestones. American Trailer 11,200 Lbs

Composite tension leaf springs: Available for trucks at last | CompositesWorld

Horizontal and vertical tail, aileron, and rudder and elevator will be developed and manufactured for the lift + cruise aircraft, scheduled to enter service in 2026.

In addition to its composite aircraft, Overair will support infrastructure, aircraft operations and training to ensure a comprehensive and sustainable AAM ecosystem.

This initial project under the Space Act Agreement is focused on studying and developing high-performance battery cells, as well as performing safety testing, to achieve purpose-built solutions for electric aircraft.  

AeroZero TPS, applicable for metals and composites, will protect critical battery housing and parts in the Lilium Jet eVTOL aircraft from burn through and risk of thermal runaway.

Through a strategic partnership, the companies introduce the FiberScanner3D module, dedicated to bringing more rapid, reliable and robust fiber structure characterization methods to lab settings.

The new alliance will broaden National Composites’ capabilities in SMC and BMC and tooling, while providing customers with comprehensive solutions, from initial design to final delivery.

A new ASTM-standardized test method established in 2022 assesses the compression-loaded damage tolerance of sandwich composites.  

Composites automation specialist increases access to next-gen technologies, including novel AFP systems and unique 3D parts using adaptive molds.

Combined LSAM and five-axis CNC milling capabilities will optimize D-Composites’ production services, flexibility and cut time and cost for composite tooling manufacture.

Evaluation of CFRTP m-pipe through Element’s U.K. facility aims to qualify the system for new operating environments.

Delivered and implemented at Toray Advanced Composites, the setup seeks to eliminate defects during hot press forming thermoplastic tapes.

ReCarbon will focus on providing a high-quality recycled carbon fiber-based product range, using Fibertech’s prepreg expertise.

Use of Envalior’s fiberglass-reinforced ForTii ACE MX53 and collaboration with its CAE department helped Koki re-adjust product design, simulation and tooling to get the best out of material performance.

Lifecycle assessment, starting at Toray’s Nijverdal site and then broadening to U.S. locations, will provide reliable emissions data to customers purchasing the range of thermoplastic composite materials.

JEC World 2024: Freudenberg Performance Materials displays innovative surface veils, flow media and spacer solutions to meet the evolving requirements of FRP parts.

Space-grade Strato panels line was incorporated into the small spacecraft platform’s solar array substrate/backup structure assemblies design, reducing costs, lead time and meeting positional tolerance without fixtures.

An independent entity, Supernova will enhance materials development and hardware industrialization for the viscous lithography manufacturing process, which can take fillers or fiber reinforcement for elevated product development.

Delivered and implemented at Toray Advanced Composites, the setup seeks to eliminate defects during hot press forming thermoplastic tapes.

HyFiVE project came to a close in 2023, providing new insight for adhesive-free joining of metal and fiber-reinforced technologies for maritime construction.

JEC World 2024: Compcut is presenting its advanced composites saw (ACS) and precision composite router (PCR), in addition to inviting attendees to bring their own materials for demonstration purposes.

GA-ASI demonstrates a path forward for the use of additive technologies for tooling, flight-qualified parts.  

JEC World 2024: Roth Composite Machinery is co-exhibiting with partner mefex GmbH to present new developments to its µRoWin software for automated filament winding.

CW explores key composite developments that have shaped how we see and think about the industry today.

Knowing the fundamentals for reading drawings — including master ply tables, ply definition diagrams and more — lays a foundation for proper composite design evaluation.

As battery electric and fuel cell electric vehicles continue to supplant internal combustion engine vehicles, composite materials are quickly finding adoption to offset a variety of challenges, particularly for battery enclosure and fuel cell development.  

Performing regular maintenance of the layup tool for successful sealing and release is required to reduce the risk of part adherence.

Increasingly, prototype and production-ready smart devices featuring thermoplastic composite cases and other components provide lightweight, optimized sustainable alternatives to metal.

The composite pressure vessel market is fast-growing and now dominated by demand for hydrogen storage.

The burgeoning advanced air mobility (AAM) market promises to introduce a new mode of transport for urban and intercity travelers — particularly those who wish to bypass the traffic congestion endemic to the world’s largest cities. The electric vertical take-off and landing (eVTOL) aircraft serving this market, because they depend on battery-powered propulsion, also depend on high-strength, high-performance composite structures produced at volumes heretofore unseen in the aerospace composites industry. This CW Tech Days will feature subject matter experts exploring the materials, tooling and manufacturing challenges of ramping up composites fabrication operations to efficiently meet the demands of a challenging and promising new marketplace.

Manufacturers often struggle with production anomalies that can be traced back to material deviations. These can cause fluctuations in material flow, cooling, and cure according to environmental influences and/or batch-to-batch variations. Today’s competitive environment demands cost-efficient, error-free production using automated production and stable processes. As industries advance new bio-based, faster reacting and increased recycled content materials and faster processes, how can manufacturers quickly establish and maintain quality control? In-mold dielectric sensors paired with data analytics technology enable manufacturers to: Determine glass transition temperature in real time Monitor material deviations such as resin mix ratio, aging, and batch-to-batch variations throughout the process Predict the influence of deviations or material defects during the process See the progression of curing and demold the part when the desired degree of cure, Tg or crystallinity is achieved Document resin mix ratios using snap-cure resins for qualification and certification of RTM parts Successful case histories with real parts illustrate how sensXPERT sensors, machine learning, and material models monitor, predict, and optimize production to compensate for deviations. This Digital Mold technology has enabled manufacturers to reduce scrap by up to 50% and generated energy savings of up to 23%. Agenda: Dealing with the challenge of material deviations and production anomalies How dielectric sensors work with different composite resins, fibers and processes What is required for installation Case histories of in-mold dielectric sensors and data analytics used to monitor resin mixing ratios and predict potential material deviations How this Digital Mold technology has enabled manufacturers to optimize production, and improve quality and reliability

SolvaLite is a family of new fast cure epoxy systems that — combined with Solvay's proprietary Double Diaphragm Forming technology — allows short cycle times and reproducibility. Agenda:  Application Development Center and capabilities Solutions for high-rate manufacturing for automotive Application examples: battery enclosures and body panels

OEMs around the world are looking for smarter materials to forward-think their products by combining high mechanical performance with lightweight design and long-lasting durability. In this webinar, composite experts from Exel Composites explain the benefits of a unique continuous manufacturing process for composites profiles and tubes called pull-winding. Pull-winding makes it possible to manufacture strong, lightweight and extremely thin-walled composite tubes and profiles that meet both demanding mechanical specifications and aesthetic needs. The possibilities for customizing the profile’s features are almost limitless — and because pull-winding is a continuous process, it is well suited for high volume production with consistent quality. Join the webinar to learn why you should consider pull-wound composites for your product. Agenda: Introducing pull-winding, and how it compares to other composite manufacturing technologies like filament winding or pultrusion What are the benefits of pull-winding and how can it achieve thin-walled profiles? Practical examples of product challenges solved by pull-winding

Composite systems consist of two sub-constituents: woven fibers as the reinforcement element and resin as the matrix. The most commonly used fibers are glass and carbon, which can be processed in plane or satin structures to form woven fabrics. Carbon fibers, in particular, are known for their high strength/weight properties. Thermoset resins, such as epoxies and polyurethanes, are used in more demanding applications due to their high physical-mechanical properties. However, composites manufacturers still face the challenge of designing the right cure cycles and repairing out-of-shelf-life parts. To address these issues, Alpha Technologies proposes using the encapsulated sample rheometer (premier ESR) to determine the viscoelastic properties of thermosets. Premier ESR generates repeatable and reproducible analytical data and can measure a broad range of viscosity values, making it ideal for resins such as low viscous uncured prepreg or neat resins as well as highly viscous cured prepregs. During testing, before cure, cure and after cure properties can be detected without removing the material from the test chamber. Moreover, ESR can run a broad range of tests, from isothermal and non-isothermal cures to advanced techniques such as large amplitude oscillatory shear tests. During this webinar, Alpha Technologies will be presenting some of the selected studies that were completed on epoxy prepreg systems utilizing ESR and how it solves many issues in a fast and effective way. It will highlight the advantages of this technique that were proven with the work of several researchers. Moreover, Alpha Technologies will display part of these interesting findings using the correlations between the viscoelastic properties such as G’ and mechanical properties such as short beam shear strength (SBS).

Surface preparation is a critical step in composite structure bonding and plays a major role in determining the final bonding performance. Solvay has developed FusePly, a breakthrough technology that offers the potential to build reliable and robust bonded composite parts through the creation of covalently-bonded structures at bondline interface. FusePly technology meets the manufacturing challenges faced by aircraft builders and industrial bonding users looking for improved performance, buildrates and lightweighting. In this webinar, you will discover FusePly's key benefits as well as processing and data. Agenda: Surface preparation challenges for composite bonding FusePly technology overview Properties and performance data

The EPTA – European Pultrusion Technology Association in cooperation with the American Composites Manufacturers Association (ACMA) invites you to the 17th World Pultrusion Conference which takes place on 29 February – 1 March 2024 in Hamburg, Germany. Visit the most important event in Europe in the market for pultruded fiber reinforced materials  This conference takes place every two years and is the meeting point of the European and worldwide Pultrusion Industry. More than 25 international speakers from Finland, Belgium, Germany, France, Spain, The Netherlands, Turkey, UK, USA, Canada and others will present practical presentations about innovative applications, technologies and processes. Equally current market trends and developments are on the agenda. This World Pultrusion Conference takes place again in the week before the JEC World Composites Show (5-7 March 2024, Paris). The presentation language will be English. Please finde here the full program and booking opportunities. We appreciate very much welcoming you in Hamburg! Inquiries should be requested by email: info@pultruders.com

The Program of this Summit consists of a range of 12 high-level lectures by 14 invited speakers only. Topics are composite related innovations in Automotive & Transport, Space & Aerospace, Advanced Materials, and Process Engineering, as well as Challenging Applications in other markets like Architecture, Construction, Sports, Energy, Marine & more.

JEC World in Paris is the only trade show that unites the global composite industry: an indication of the industry’s commitment to an international platform where users can find a full spectrum of processes, new materials, and composite solutions.

Charting the Skies of Tomorrow: The Sustainable Aviation Revolution Welcome to a new era of air travel where innovation meets sustainability. Electric, hybrid-electric and hydrogen-powered aircraft represent a promising path to reach climate neutrality goals, with the aviation industry and governments jointly pushing boundaries to bring disruptive aircraft into service by 2035. From cutting-edge technologies to revamped regulations and greener airports, the pursuit of sustainable aviation requires unparalleled collaboration throughout the whole aviation value chain and ecosystem. Join us at the Clean Aviation Annual Forum from 5 until 6 March 2024, as we navigate towards cleaner skies together.

Composites 2024 is an international conference that focuses on advanced technology and development of composite materials. It brings together participants from academia and industry who share an interest in Composite Materials. It is a unique opportunity for composite specialists and newcomers alike and has long been a venue where researchers and industrialists network and share with colleagues from around the world and establish long term partnership. The conference includes plenary talks, keynote and oral presentations as well as posters sessions, an exhibit area for industry partners and sponsors, and an entertaining social program.

The European polyamide market is going through unprecedented times as it grapples with rising energy and feedstock prices, as well as declining consumption levels with lower demand from almost all application segments (including automotive, construction, fibres and E&E). Coupled with the growing emphasis on sustainability, recycling and the circular economy, this is a challenging period for the polyamide market in Europe. Is 2024 the year that the polyamide segment looks to emerge from the crisis tunnel? The industry needs to adapt to the new market reality, to innovate and invest in new technologies and processes to meet the new market demands and requirements with regards to economic sustainability and a circular economy. The Wood Mackenzie European Polyamide Conference takes place at the Kap Europa Congress Center in Frankfurt, Germany on 13-14 March 2024, combining integrated analysis across the polyamide value chain with sessions focused on feedstocks, polymers, and key application markets, deep dives into emerging trends and technologies. Themes for 2024 include: Is there any hope for the European polyamide industry? Is the polyamide profitability gone? What can we expect in the coming years? Will China's importation threat permanently change the European polyamide market? What are the future polyamide price trends and forecasts? Who will be the winners and losers of the current situation Is the circular economy a threat or an opportunity for the polyamide industry?

Thousands of people visit our Supplier Guide every day to source equipment and materials. Get in front of them with a free company profile.

Jetcam’s latest white paper explores the critical aspects of nesting in composites manufacturing, and strategies to balance material efficiency and kitting speed.

Arris presents mechanical testing results of an Arris-designed natural fiber thermoplastic composite in comparison to similarly produced glass and carbon fiber-based materials.

Cevotec, a tank manufacturer, Roth Composite Machinery and Cikoni, have undertaken a comprehensive project to explore and demonstrate the impact of dome reinforcements using FPP technology for composite tanks.   

Initial demonstration in furniture shows properties two to nine times higher than plywood, OOA molding for uniquely shaped components.

The composite tubes white paper explores some of the considerations for specifying composite tubes, such as mechanical properties, maintenance requirements and more.

Foundational research discusses the current carbon fiber recycling landscape in Utah, and evaluates potential strategies and policies that could enhance this sustainable practice in the region.

CW Top Shops honoree Sargo Oy shares its successes in upgrading operations from hand layup to infusion, employing low-waste manufacturing practices, research in large-format 3D printing for mold production and more.

CompositesWorld discusses recent changes, upcoming events and strategies for the upcoming year. 

Projects use Duplicor prepreg panels with highest Euroclass B fire performance without fire retardants for reduced weight, CO2 footprint in sustainable yet affordable roofs, high-rise façades and modular housing.

Automated fiber placement develops into more compact, flexible, modular and digitized systems with multi-material and process capabilities.

Switching from prepreg to RTM led to significant time and cost savings for the manufacture of fiberglass struts and complex carbon fiber composite foils that power ORPC’s RivGen systems.

Sara Black’s 2015 report on the development of snap-cure epoxies for automotive manufacturing still resonates today. 

Projects use Duplicor prepreg panels with highest Euroclass B fire performance without fire retardants for reduced weight, CO2 footprint in sustainable yet affordable roofs, high-rise façades and modular housing.

To incorporate more environmentally conscious practices into its manufacturing processes, VSC is working with Carbon Conversions to reclaim, recycle and reuse its carbon fiber materials.

As the marine market corrects after the COVID-19 upswing, the emphasis is on decarbonization and sustainability, automation and new forms of mobility offering opportunity for composites.

Novel material to combine Ohoskin’s leather alternative made from orange and cactus byproducts with ReCarbon’s recycled carbon fiber.

The three-year strategic collaboration will help boost the company’s growth, reinforce its commitments to become carbon neutral by 2040 and innovate more circular chemicals and materials.

Oak Ridge National Laboratory's Sustainable Manufacturing Technologies Group helps industrial partners tackle the sustainability challenges presented by fiber-reinforced composite materials.

The composites industry is increasingly recognizing the imperative of sustainability in its operations. As demand for lightweight and durable materials rises across various sectors, such as automotive, aerospace, and construction, there is a growing awareness of the environmental impact associated with traditional composite manufacturing processes.

This CW Tech Days event will explore the technologies, materials, and strategies that can help composites manufacturers become more sustainable.

Closed mold processes offer many advantages over open molding. This knowledge center details the basics of closed mold methods and the products and tools essential to producing a part correctly.

During CW Tech Days: Thermoplastics for Large Structures, experts explored the materials and processing technologies that are enabling the transition to large-part manufacturing.

Explore the cutting-edge composites industry, as experts delve into the materials, tooling, and manufacturing hurdles of meeting the demands of the promising advanced air mobility (AAM) market. Join us at CW Tech Days to unlock the future of efficient composites fabrication operations.

In the Automated Composites Knowledge Center, CGTech brings you vital information about all things automated composites.

CW’s editors are tracking the latest trends and developments in tooling, from the basics to new developments. This collection, presented by Composites One, features four recent CW stories that detail a range of tooling technologies, processes and materials.

CompositesWorld’s CW Tech Days: Infrastructure event offers a series of expert presentations on composite materials, processes and applications that should and will be considered for use in the infrastructure and construction markets.

CompositesWorld’s CW Tech Days: Infrastructure event offers a series of expert presentations on composite materials, processes and applications that should and will be considered for use in the infrastructure and construction markets.

Explore the cutting-edge composites industry, as experts delve into the materials, tooling, and manufacturing hurdles of meeting the demands of the promising advanced air mobility (AAM) market. Join us at CW Tech Days to unlock the future of efficient composites fabrication operations.

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Tension leaf springs with progressive spring rates meet the demanding needs of truck suspensions.  

BrightDrop electric delivery vans (above) as well as Chevrolet Silverado/GMC Sierra pickups from General Motors Co. feature North America’s first composite tension leaf springs (TLS) with progressive spring rates on rear axles for better ride and lighter vehicles. Photo Credit: General Motors Co. (above) and SPE Automotive Div. (image at top, in line with title)

Last year, some versions of 2022 model year Chevrolet Silverado and GMC Sierra full-size, half-ton pickups and all BrightDrop electric delivery vans from General Motors Co. (GM, Detroit, Mich., U.S.) debuted with North America’s first tension leaf springs (TLS) featured on the rear axles. Compared to a steel leaf spring (SLS), the composite TLS reduces mass significantly for these light- and medium-duty truck programs while improving durability, ride, noise/vibration/harshness (NVH) and more. The road to developing this technology was neither straightforward nor easy.

Leaf springs are an important element of vehicle suspension systems, which themselves are a series of linkages, springs and shock absorbers that connect vehicle wheels and body, enabling both to move relative to each other while permitting control of steering and braking.

They are designed to spring/flex vertically in response to irregular road surfaces and as weight is added to or removed from the vehicle. As such, leaf springs serve multiple functions, such as improving ride smoothness, locating the axle to facilitate turning, controlling vehicle height, protecting cargo from damage and keeping tires aligned on the road.

Leaf springs have been used to improve vehicle ride for hundreds of years, starting with horse-drawn carts and carriages, and were widely used on nearly all motorized vehicles until the 1930s when GM introduced helical coil springs as part of its independent front suspension offerings.

With some exceptions, today SLS are mostly used on commercial vehicles designed to carry heavier loads, including larger trucks, buses, delivery vans and pickups, because their high spring rates and high load capacity make them cost effective versus other suspension options.

There are numerous mono- and multi-leaf spring designs and mounting options, but all essentially feature a relatively thin, curved/bowed plate called a leaf (initially wood and currently metal or composite) or a stack of (usually) progressively shorter leaves joined to each other in a pack via a central bolt and additional external clips.

Lateral/longitudinal leaf springs are oriented parallel to the vehicle’s main axis (front to back) and perpendicular to the axles; transverse leaf springs run parallel to the axles (left to right) and perpendicular to the main axis of the vehicle. With longitudinal leaf springs, which are typically used on the rear suspension, the pack’s center is connected to the axle, its front is connected directly to the frame and its rear is connected to the frame via a shackle (short swing arm) that pivots to compensate as the leaf spring lengthens/shortens in response to the addition/removal of weight, or as the suspension moves up/down in response to a bumpy road.

Most leaf springs are still steel, although that wasn’t always the case. The first composite leaf spring — a filament-wound, compression-molded transverse rear mono-leaf — debuted in 1981 on GM’s C3 (third-generation) Chevrolet Corvette sports car. The new design was lighter, quieter, corrosion-resistant and improved ride. Three years later, the C4 Corvette sported front and rear transverse composite mono-leaf springs (CMLS), a change that enabled the hood line to be lowered. By 1985, GM minivans were equipped with CMLS, and in 1986, luxury cars followed. For the next decade or so, millions of midsize cars used CMLS technology.

In Europe, the Mercedes-Benz Sprinter commercial van from Mercedes-Benz Group AG (Stuttgart, Germany) has sported transverse CMLS in the front for 16 years, and in the rear starting in 2016. However, CMLS technology never took off on North American light-duty or commercial trucks, despite numerous attempts. This is likely due to the linear spring rate characteristic of composite and steel mono-leaf designs and the stepped but still linear rates of steel multi-leaf designs (see sidebar below).

Consequently, most truck suspensions have continued to use multi-leaf SLS or metallic coil springs. Notable exceptions are GM’s 2019 Silverado/Sierra 1500 pickups and 2021 Ford F-150 pickups from Ford Motor Co. (Detroit, Mich., U.S.), which feature the first hybrid multi-leaf spring on rear axles. That system combined a high-strength steel main pack/leaf with a high-pressure resin transfer molded (HP-RTM) fiberglass-reinforced epoxy helper pack (second leaf). The resulting dual spring rate reportedly provided the same stiffness and durability as a multi-leaf SLS at 30% lower mass, while increasing payload capability, reducing part count, decreasing interleaf friction and noise and providing smoother engagement.

Traditional steel or composite mono-leaf springs have linear spring rates regardless of how much weight the vehicle is carrying. Multi-leaf SLS systems offer multiple spring rates. As load is applied to the first bowed leaf spring, it bends/is displaced via suspension travel. Partway through that deflection, the first spring contacts the next leaf spring, which begins to bend, contributing a second spring rate. Hence, a vehicle with a multi-leaf spring will have multiple spring rates, but they are stepped so the transition between rates is not smooth, as shown for the multi-leaf SLS at 30 millimeters’ displacement in the graph below.

This makes a multi-leaf spring more effective at providing a smoother ride than a mono-leaf spring for a vehicle whose load changes regularly as cargo (or occupants/gear) is added/removed and/or as the vehicle travels rougher roads or offroad. However, it won’t create the smoothest ride because of those transitions between one spring rate to the next.

Compared to a steel multi-leaf spring, with linear/stepped spring rates, a tension leaf spring, which offers a progressive spring rate, provides a smoother ride both unloaded (curb weight load) and fully loaded. Photo Credit: Muhr und Bender KG

A better option to ensure a more homogeneous ride regardless of load status or road condition would be to design a leaf spring with a progressive spring rate offering smoother transitions at increasing load and displacement (tension leaf spring curve above). Some metal coil springs do provide progressive spring rates via coil-to-coil or coil-to-seat contact. However, coil springs are less desirable on rear axles (under the cargo-carrying rear box) as they are less efficient at carrying heavy loads. They also are prone to rust, NVH issues and sagging as they age.

Creating an SLS with a progressive spring rate has proven very challenging. To permit a practical amount of suspension travel (the spring’s response to higher loading), the induced strains would be so high that they would lead to severe plastic deformation or outright failure of steel leaves or to severely curtailed suspension travel (with concurrent restrictions in load-carrying capacity) — poor options for commercial vehicles. However, because composites generally offer better fatigue properties than steel and can repeatedly handle high induced strains without permanent deformation or failure, efforts have been focused on composite materials for nearly 15 years.

The ability to incorporate a progressive spring rate into a composite mono-leaf spring was finally solved by Tier 1 Muhr und Bender KG (Mubea, Attendorn, Germany) in 2018. Previously, no leaf spring (regardless of material) offered an infinitely progressive spring rate (see sidebar for more on spring rates). Even then, it took a full decade of R&D effort for Mubea — which has deep experience designing and building suspension systems for passenger and commercial vehicles — to find the right combination of design and materials to prove out the concept and to build a production facility to service the first commercial TLS program in Europe.

Geometry of conventional steel multi-leaf spring (top) versus composite tension leaf spring (bottom, with front of spring on the left and rear of spring on right) — both shown from the side. Photo Credit: Muhr und Bender KG

In terms of geometry, the TLS looks different than typical C-shape mono- or multi-leaf springs. While the front half does curve upward, there is an extra S-curve (elbow) at the rear instead of a shackle that is key to providing a progressive spring rate while still maintaining a reasonable amount of suspension travel. Without a shackle, length compensation occurs via tensile loading in the spring rather than shackle rotation. This induced tensile load adds to the spring rate progressively as spring displacement increases. 

“The ratio between tensile strength and [tensile] modulus is key to making this concept work,” explains Jared Heitsch, Mubea engineering manager – chassis composites. “While our tensile strength is similar to that of steel, our modulus is about one-fifth that of steel. Composite’s lower modulus allows us to induce a high amount of tensile loading in the spring, enabling our progressive [spring] rate while maintaining wheel travel. This concept does not work in steel while still permitting good suspension travel owing to the lower elastic elongation that steel can withstand before yielding.”

Finding the right type of continuous fiber reinforcement for the application proved important. Initial work ruled out carbon fiber because slightly better weight savings came at higher cost. Also, carbon fiber’s higher strength and modulus and penchant for brittleness would have led to the same kinds of restrictions seen in SLS (restricted travel or restricted load-carrying capacity) or would have required modifications to the geometry that would have caused other vehicle-level performance issues, adds Heitsch. As the longitudinally mounted TLS deforms due to displacement, fibers orient to carry high tensile loads in combination with the bending mode of the spring, which progressively resists further deflection. Interaction between both forces provides the progressive spring rate.

In its final form, Mubea’s composite TLS is produced by robotically laying up as many as 60 plies of continuous fiberglass-reinforced epoxy prepreg/tapes (all at zero-degree orientation) and compression molding the stack. The fully automated process offers high repeatability and reproducibility (R&R) and is fast enough to supply high-volume automotive programs like GM’s pickups.

As Mubea’s concept for the TLS evolved, the company talked with automakers in Europe and North America to assess interest. The first customer was Mercedes Benz’s Sprinter van, which switched to a composite TLS on the rear axle in 2018. Meanwhile, Mubea had also been working with GM to prove out the technology on the automaker’s light-duty pickups since 2015. Significant virtual prototyping was done, followed by physical prototyping and small- then large-scale physical testing, including significant on-vehicle testing at GM’s Canadian Technical Centre in Oshawa, Ontario, Canada. Design and testing work was iterative, and each round led to further modifications of the concept and design. Once the technology was proven in GM engineering, the TLS was launched on 2022 Sierra/Silverado pickups.

In a parallel program, work was underway to adapt the technology to GM’s new BrightDrop electric delivery van, which is a larger vehicle designed to carry heavier payloads than either the pickups or the Sprinter van. Being an electric vehicle (EV), weight savings would be more impactful in terms of distance traveled/charge. Although the basic TLS design is the same for both platforms, BrightDrop’s spring is longer and thicker to accommodate that vehicle’s heavier loads. Interestingly, the technology passed all the automaker’s requirements while eliminating the need for shackles, shackle bushings and helper leaves.

Weight savings is a major benefit of the technology change. On Silverados/Sierras, the TLS saved 32 kilograms per vehicle (75% mass reduction) versus SLS and was 58% lighter than the hybrid system on 2019 models. On the BrightDrop Zevo 600, 52 kilograms were saved versus comparable SLS. Lighter leaf springs increased payload capacity while reducing CO2 emissions. This helps the pickups avoid greenhouse gas penalties, which makes the technology lower on a net cost basis.

The TLS also eliminates corrosion and is projected to double the durability/lifespan of SLS while improving ride, thanks to the progressive rate curve, reduction in unsprung mass and elimination of interleaf friction and self-generated noises, which have historically been a major warranty issue with SLS systems. The progressive spring rate also reduces impact loads on the jounce bumpers.

Not only does the tension leaf spring look different than a conventional SLS, but it also performs differently and offers a greater range of benefits. Photo Credit: Muhr und Bender KG

Additional benefits include more flexible design parameters, thanks to the more forgiving production process. For example, lateral stiffness can be improved without degrading ride quality; wind-up/wind-down stiffness is improved and slip-yoke travel is reduced versus SLS, further improving NVH. Wheel recession can be tuned for desired steering characteristics, and the tuning range for suspension damping also is improved thanks to reduced interleaf friction.

“The TLS represents the next evolution in leaf springs and suspension components for light- and medium-duty trucks,” explains Leandro Castro, GM design release engineer. “As such, our peers in industry have recognized its significance with important industry honors, including the 2020 Altair Enlighten Award and the 2022 SPE Automotive Innovation Grand Award.”

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Respondents that complete the survey by April 30, 2024, have the chance to be recognized as an honoree.

Composite tension leaf springs: Available for trucks at last | CompositesWorld

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