Carbon Fiber Reinforced Polymers (CFRP) vs ALLVAR: Near Zero Thermal Expansion Materials

Carbon Fiber Reinforced Polymers (CFRP) vs ALLVAR: Near Zero Thermal Expansion Materials Blogpost written as the title. There are two sets of tubes with a vs in between. The first is CFRP tubes and the second are ALLVAR tubes.

Carbon Fiber Bar and Tube vs ALLVAR Alloys Bar and Tube

In the realm of advanced materials for precision structures, carbon fiber reinforced polymers like Toray M55J have often been seen as a benchmark for space-grade low or near-zero thermal expansion components with high stiffness. But what if you need a material that goes beyond simply minimizing thermal expansion? ALLVAR Alloys, featuring negative coefficients of thermal expansion (CTE), are introducing an entirely new approach to solving thermal expansion challenges—one that tackles the complexities of moisture, temperature extremes, corrosion, and more. The comparison is no coincidence. M55J carbon fibers excel where traditional metals fall short with slightly negative CTE, but ALLVAR Alloy 30 goes even further by exhibiting a highly negative, CTE in a titanium-based alloy system.

 

A Brief Look at Carbon Fiber Reinforced Polymers

Carbon fiber reinforced polymers have been developed for decades, driven by aerospace and high-performance industries looking for strength, stiffness, and low weight. Among these, Toray M55J layups with cyanate ester polymers stand out for their high elastic modulus and low thermal expansion characteristics. Unlike many conventional materials, a well-designed M55J laminate can achieve near-zero CTE, making it a popular choice for components like struts, precision optical benches, and telescope structures.

However, it is crucial to note that carbon fiber composites, including M55J and cyanate ester layups, often have an anisotropic coefficient of thermal expansion—typically negative in the fiber direction but significantly different in the transverse and out-of-plane directions. Moreover, a phenomenon known as the coefficient of moisture expansion (CME), while smaller in cyanate esters compared to conventional matrix materials, can affect dimensional stability when humidity fluctuates, especially in high-precision assemblies. These factors can lead to internal stress and potential microcracking, delamination, or catastrophic failure over time if not carefully accounted for in design.

Another issue with carbon fiber reinforced polymers is their inherent variability from layup to layup. Slight variations in fiber orientation can produce large differences in stiffness and CTE. This results in a large amount of yield loss. The more demanding the application the tighter the CTE tolerance required. The tighter the CTE tolerance required, the greater the yield loss. For example, it is estimated that less than 10% of the carbon fiber composite structures used on the Jame Webb Space Telescope would meet CTE requirements on the Habitable Worlds Telescope, NASA’s next flagship space-based telescope mission.

Since their original discovery in 2011, ALLVAR Alloys have been developed to offer a new and more versatile way to control thermal expansion. ALLVAR Alloy 30 was specifically designed with a targeted -30 ppm/°C along its length, allowing engineers to compensate for traditional materials and even for the thermal expansion variability present in M55J layups. By carefully selecting the geometry and orientation of an ALLVAR Alloy component, designers can cancel out or tune the overall structure’s expansion to an unprecedented degree. This has the potential to give telescope designers unprecedented control over thermal expansion.

Thermal Expansion Tunability

Carbon Fiber Reinforced Polymer’s achieve dimensional stability by carefully arranging multiple CFC composite layers with offsetting thermal expansions. The resulting stack-up yields a tuned coefficient of thermal expansion material that is often near zero. Choosing specific reinforcement materials also add variability to the stackups total CTE.

ALLVAR Alloys can help offset discrepancies in the expected CFRP’s coefficient of thermal expansion (CTE). When thermomechanical stability is critical, small shims of ALLVAR Alloy 30 can be used to tune the CTE of individual components.

For those looking to go even further, ALLVAR Alloys is introducing a tailorable thermal expansion alloy separate from ALLVAR Alloy 30. This new alloy system will allow designers to specify the target thermal expansion needed for their project. Whether you want to target to match to dissimilar glass indices of refraction or transform an assembly of dissimilar materials from a thermometer to an ultra-stable structure, ALLVAR has you covered. Specify the CTE needed, and ALLVAR Alloys can provide an alloy custom-suited for your project. Stay tuned for more information or reach out if you need this today.

Carbon Fiber Reinforced Polymer versus ALLVAR: Material Properties

PropertyUnits

ALLVAR Alloy 30

M55J-CE*

CTE Range @25°C(ppm/°C)-30-0.5 to -1.1 ppm/°C
Max Operating Temperature(°C)100200°C
UTS(MPa)6501550
Elastic Modulus(GPa)55320
Tensile Modulus(GPa)283
Density(g/cc)5.081.191
Thermal Conductivity(W/m·K)8.88~1

*Please note that the material properties depend on the reinforcement material chosen. We chose a M55J/cyanete ester system because of its attractive properties for CFRP space applications.

Machinability, Cryo Damage, and Yield Loss

One common drawback of carbon fiber composites is their machinability. Drilling or cutting carbon fiber layers can lead to delamination or micro-cracking, compromising the structural integrity of M55J layups. Special tooling is also required to handle the abrasive nature of carbon fiber and to manage fine dust, which can be hazardous. M55J composites perform exceptionally well in high-stiffness applications, but repairs or complex machining can significantly increase manufacturing challenges and costs.

ALLVAR Alloys, on the other hand, machine more like a beta-titanium alloy. With proper coolant, speeds, and feeds, ALLVAR Alloy 30 can be turned, milled, or drilled. Also, because it is a titanium-based system, ALLVAR Alloy 30 is less likely to suffer from the same temperature-induced damage that might occur in composite matrix materials at cryogenic temperatures.

Corrosion Resistance and Galvanic Considerations

Carbon fiber composites themselves don’t corrode in the same way metals do, but they can cause galvanic corrosion when in contact with certain metals. A prime example is the combination of carbon fiber with aluminum structures, which can lead to corrosion damage over time. M55J composites often require careful selection of inserts and fasteners that electrically isolate them from metal structures to avoid this effect. 

ALLVAR Alloys, being titanium-based, also do not induce galvanic corrosion when paired with carbon fiber or other metals. Titanium’s excellent corrosion resistance makes it well-suited for harsh corrosive environments..

Should You Use A Carbon Fiber Composites like M55J or ALLVAR Alloys?

It depends on your application! If you need ultrahigh stiffness and near-zero thermal expansion in one direction, and you have a manufacturing process that can accommodate specialized tooling and potential CME effects, M55J carbon fiber and cyanate ester composites are an outstanding choice. Their legacy of use in aerospace and high-end structural components speaks for itself. But if your goal is to achieve a highly negative or specifically tailored CTE while ensuring corrosion resistance, easier machining, and minimal galvanic concerns, consider using ALLVAR Alloy 30.

Still unsure if M55J carbon fiber composites or ALLVAR Alloys are better for your project? We’re a team of materials scientists at heart. Whether it’s the negative CTE of ALLVAR Alloys or the familiar performance of carbon fiber, we’d be happy to help you navigate the tradeoffs and select the right material for your next project. Please contact us by clicking the orange button below—your success is our top priority.

We can also provide spec-sheets of M55J carbon fiber properties alongside example CTE data for ALLVAR Alloys across a wide range of temperatures. Our experimental ALLVAR Alloys with a wide range of tuned thermal expansion properties are also in the works, so stay tuned for future breakthroughs.

Want to learn more? ALLVAR has plenty of content ready to help you choose if it is right for you. Check out our post Matching ZERODUR®’s CTE – ALLVAR Alloy 30 enabled near zero CTE struts – ALLVAR Alloys for more information on the tuning of ALLVAR Alloy 30 with other materials to create custom CTE components. Ready to design your own optics with ALLVAR Alloys? Reach out to us today

Contact Us Today to Revolutionize Your Thermal Performance

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