From Aerospace to In-Home Applications, Advanced Auxetic Gauges Primed for Widespread Use

Auxetic materials differ from classical materials in that they exhibit negative Poisson’s ratios. In other words, under the tensile force applied in the longitudinal direction, auxetics expand in the perpendicular transverse direction. 

Scientists continue to look for auxetic properties in materials. Recently, Noah Stocek, a PhD student collaborating with Western physicist Giovanni Fanchini, has developed one such nanomaterial. 

Two Dimensional Auxetic Nanosheets

Both scientists worked at Interface Science Western to develop 2-D nanosheets of tungsten semi-carbide, also known as W2C. These are chemical compounds containing equal parts of tungsten and carbon atoms. Adhering to the properties of auxetic materials, these nanomaterials expand perpendicular to the applied force when stretched in one direction. 

The development is significant because it is only the second material to expand substantially in a way that is opposite to classical materials. Prior to this, there was only one reported material that could expand by 10 percent per unit length counterintuitively. The present nanomaterial, the tungsten semi-carbide nanosheet, can expand by 40 percent. It is a new world record. While explaining the achievement of this development, Stoeck said: 

“In 2018, theorists predicted that it might exhibit this behavior to an excellent level, but nobody had been able to develop it, despite extensive attempts by research groups all over the world.”

To explain in more detail what Stoeck and Fanchini developed, they scientifically and experimentally reported on an ad hoc designed dual-zone remote plasma deposition system that could grow tungsten carbides out of thermodynamic equilibrium with well-tuned ratios of W and C precursors. The research highlighted the specific conditions under which this system allowed for the synthesis of flakes of few-layer tungsten semicarbide (FL-W2C). These flakes were two-dimensional in nature, for they could retain their periodicity at the mesoscopic level in a Stranski–Krastanov growth process.

A Novel Shift from Chemical Means to Plasma Physics

The developer-duo had identified at a very early stage of their process that it was impossible to construct a new tungsten semi-carbide nanomaterial using chemical means. As a result, they switched to plasma physics, with the aim of forming layers of single atoms. 

To carry out the development of the nanomaterial by leveraging plasma methods, the developer duo moved away from the conventional route of having special furnaces where gasses could be heated at a high temperature to chemically react and form the substance. They designed a new customized instrument system for producing plasma, which contains electrically charged particles. 

Applications of the Newly Developed Nanomaterial

One of the most useful potential applications of these nanosheets could be a radically new type of strain gauge. These gauges could measure expansion in a very effective way and stretch in everything, from the wings of airplanes to household plumbing.

Since these materials are more electrically conductive, they can be used in sensors or devices to detect changes and shifts in the environment. Not only could they detect these materials, but owing to their ‘sensor’ capabilities, they could also send information to other electronics. 

While elaborating on one of the possible applications, Stoeck said:

“Imagine if you want to know if a pipe in your house is deforming and risks bursting at some point. You can stick a sensor on the pipe made from this two-dimensional nanomaterial and then use a computer to monitor the current passing through it. If the current rises, it means the pipe is expanding and risks bursting.” 

In the future, more development on the auxetic properties of a material will definitely lead to new solutions. For now, companies like Michigan Scientific Corporation and Omega are deep into strain gauge manufacturing and development. These companies could start leveraging this development and the nanomaterial produced as an outcome to advance their product/solution portfolio. 

#1. Omega

Omega, a DwyerOmega brand, can leverage the nanomaterial to further augment its robust and diverse strain gauge product line. Its diaphragm strain gauges can measure strain and stress in a variety of applications, including pressure, force, displacement, and strain in metals, plastics, and composites. The dual parallel strain gauge product line helps reliably measure bending stress in a variety of applications. 

Omega also has torsion and shear strain gauges, linear strain gauges, t-rosette strain gauges, and rosette strain gauges. With tight tolerances for easier alignment, Omega’s gauges offer reliable performance and long-term stability. Its Full Bridge and Half Bridge Strain Gauges demonstrate excellent linearity over compatibility with a wide temperature range. 

Its T-Rosette strain gauges can measure the effects of temperature, load, and vibration on components. They are particularly useful in measuring biaxial stresses with known principal directions.

The company is perfectly placed to either develop a new product line based on auxetic gauges or expand its existing product line with auxetic properties. 

DwyerOmega emerged as a brand after Dwyer Instruments, Inc. agreed to acquire OMEGA Engineering, Inc. from Spectris plc (LSE:SXS) for approximately $530 million on April 19, 2022. Dwyer paid US$525 million at a valuation of approximately 20.4x Omega’s 2021 adjusted EBITDA. For the 2021 financial year, Omega generated sales of £129 million ($168 million) and adjusted EBITDA of £19.7 million ($25.7 million).

#2. Michigan Scientific Corporation

Michigan Scientific Corporation, a privately held company based out of Charlevoix, Michigan, United States, is known for offering a range of engineering services, products, and solutions. One area where this company could brilliantly leverage this development is its strain gauge services. 

The company is a specialist in designing and creating custom strain gauge transducers, which could be used in a range of cases, including measuring vehicle suspension forces, powertrain torques, steering component forces, engine and motor loads, and braking torques on vehicles in the field. 

Michigan’s solutions include shaft torque transducers, crankshaft transducers, shear pin transducers, and products for half-shaft strain gauging, driveshaft strain gauging, axial force gauging, and more. 

These solutions’ instrumentation applications include circuit board instrumentation for monitoring stress, thermal chamber door panels monitored for deformation during manufacturing, and fully instrumented industrial-sized drive shafts.These solutions also collect and analyze data obtained from the projects in which they’re deployed. 

We have already seen that the ‘sensor’ capabilities of newly developed strain gauges add to their value. This would be a value addition for Morgan Scientific Corporation as well, which is in the business of installing strain gauges on-site at customer locations to instrument the customer’s components and record data to support a range of test and development activities. 

Other Significant Recent Advances in Auxetics

Auxetics in Civil Construction

According to reports published in the International Journal of Protective Structures, auxetic materials are finding increasing use in fields related to civil engineering. They could be combined with cementitious material in a variety of forms, including foam-mortar composite, fabric-mortar composite, and fiber-reinforced cement composite. 

Auxetic foam layers, for instance, prove useful in retrofitting brittle masonry walls under compression. They significantly increase the post-yield strain hardening effect in the cementitious composite.

Auxetic fabrics offer higher shear stiffness and notable fracture toughness. Resultantly, these composites are useful in overcoming the challenges posed by the low compressive strength of Auxetic Foam Mortar (AFM), which has a porous structure and low density.

The Auxetic fiber-reinforced cement composite solves many of the conventional cementitious material’s drawbacks, including poor ductility, insufficient tensile strength, and low fracture toughness.

Auxetics in Fibre

Auxetic fibers can be used in a range of areas, including composite materials, personal protective clothing, upholstery, ropes, cords, fishnets, and much more. The properties that auxetic fibers empower these application areas include fiber pull-out resistance, fiber fracture toughness, energy absorption, densification and indentation resistance, impact resistance, and more.

Auxetics in Biomedical 

Auxetics can contribute significantly to the biomedical subsegments of prosthetics, surgical implants, suture/muscle/ligament anchors, and even dilators that help open up blood vessels during heart surgery. 

Auxetics in Enhancing the Quality of Piezoelectrics

Electrodes can be built of auxetic metals. These electrodes could work by sandwiching a piezoelectric polymer or embedding piezoelectric ceramic rods in an auxetic polymer matrix. They have significant enhancement capacity for piezoelectric performance and can increase device sensitivity by at least a factor of two and by a multiple of as high as a hundred.

Use of Auxetic in Filters

Cleaning fouled filters is feasible using auxetic foam and honeycomb filters. Specifically, the auxetic inclusions help adjust the filter pores to an effective size and shape. They also compensate for the effects of pressure build-up in a fouled filter. An auxetic filter can open up the pores in both directions—along and transverse to the direction of the tensile load.

Designing On-Demand Auxetic Materials

As the segments above demonstrate, the use of advanced auxetics is expanding rapidly and spreading daily to new application areas. To address this demand, researchers have already conducted valuable studies on designing auxetic materials on demand.

In 2022, a research titled ‘A three step recipe for designing auxetic materials on demand‘ came into publication where the researchers established a unified framework to describe bidimensional perfect auxetics with potential use in the design of new materials. 

The research drew heavily on the natural connection between rotating rigid units and antiferromagnetic spin systems. The researchers also elaborated on the conditions that facilitate the emergence of a non-trivial floppy mode that causes the auxetic behavior. 

The research pointed toward three designs for new auxetics: an exotic crystal, a Penrose quasicrystal, and a long-desired isotropic auxetic. The research claimed that the auxeticity of these designs could remain robust under small structural disturbances, validated by experiments and numerical simulations. 

The research theory represented each design by a minimal model. These models were based on polygons and springs that could capture these models’ essential collective response to external loads. 

The researchers were hopeful that these models could be simulated directly to test materials’ properties while ignoring bending forces. Another significant achievement of the research results was in the form of its ability to generalize the behavior of auxetic domain walls and natural textures these systems have owing to their analogy with magnetic systems.

Finally, those involved in the research claimed it to be groundbreaking in that it could establish the ground rules for creating never-seen-before isotropic perfect auxetics. They were also hopeful that the research could find application in producing 3D polyhedral materials.

Click here to learn about the potential of nanoscale 3D printing.

The Road Ahead for Advanced Auxetics

It is now proven beyond doubt that auxetic structures have moved beyond the phase of a single design to customized solutions that can serve a range of functions. Its evolution has seen variant elemental 2D patterns, hybrid structures, and innovative performance-oriented dimensional upgrades. The evolution has also witnessed an expansion in the list of materials that may have auxetic features embedded in them. The list of compatible materials now includes polymers, ceramics, metals, biomaterials, cement, textiles, and cementitious compounds.

Diversified structural models and generalized fabrication models – both have seen improvements, resulting in the auxetic behavior of materials with high rigidity. Researchers and technologists are also looking into the stress-redistributing properties of auxetic materials. 

However, for auxetics to become more advanced, some challenges have to be overcome. For instance, performance under high-velocity impact and the mechanisms of deformation and failure require more scrutiny. More work is required on impact resistance implementation. Adequate attention to these aspects could make auxetics a scientific and technological feature with immense value in everyday life.

Click here for the list of five companies leading the development of nanotechnology.