Successful ‘smart materials’ needs a different mindset

The laser was once defined as a solution in search of a problem. It is a definition that could equally apply to smart materials. Successful users have to be able to integrate an aspect of this wide versatility, back in the product design or redesign phase. A reason to suspect that smart materials are in fact spreading quietly into industry and consumer worlds comes not from success stories, but because those using materials successfully are selling a more effective product. This offers customers a genuinely cost effective approach to whatever application seek. The presence of smart materials themselves, is of no more significance to a user than knowing the precise types and grade of plastic making up a component. It's the real and perceived benefits that matter.     

Towards sensor array materials: can failure be delayed?

Further to prior development in enhancing structural health using smart materials, an innovative class of materials characterized by the ability to feel senses like humans, i.e. ‘nervous materials’, is discussed. Designed at all scales, these materials will enhance personnel and public safety, and secure greater reliability of products. Materials may fail suddenly, but any system wishes that failure is known in good time and delayed until safe conditions are reached. Nervous materials are expected to be the solution to this statement. This new class of materials is based on the novel concept of materials capable of feeling multiple structural and external stimuli, e.g. stress, force, pressure and temperature, while feeding information back to a controller for appropriate real-time action. The strain–stress state is developed in real time with the identified and characterized source of stimulus, with optimized time response to retrieve initial specified conditions, e.g. shape and strength. Sensors are volumetrically embedded and distributed, emulating the human nervous system. Immediate applications are in aircraft, cars, nuclear energy and robotics. Such materials will reduce maintenance costs, detect initial failures and delay them with self-healing. This article reviews the common aspects and challenges surrounding this new class of materials with types of sensors to be embedded seamlessly or inherently, including appropriate embedding manufacturing techniques with modeling and simulation methods.     

Towards sensor array materials: can failure be delayed?

Abstract

Further to prior development in enhancing structural health using smart materials, an innovative class of materials characterized by the ability to feel senses like humans, i.e. ‘nervous materials’, is discussed. Designed at all scales, these materials will enhance personnel and public safety, and secure greater reliability of products. Materials may fail suddenly, but any system wishes that failure is known in good time and delayed until safe conditions are reached. Nervous materials are expected to be the solution to this statement. This new class of materials is based on the novel concept of materials capable of feeling multiple structural and external stimuli, e.g. stress, force, pressure and temperature, while feeding information back to a controller for appropriate real-time action. The strain–stress state is developed in real time with the identified and characterized source of stimulus, with optimized time response to retrieve initial specified conditions, e.g. shape and strength. Sensors are volumetrically embedded and distributed, emulating the human nervous system. Immediate applications are in aircraft, cars, nuclear energy and robotics. Such materials will reduce maintenance costs, detect initial failures and delay them with self-healing. This article reviews the common aspects and challenges surrounding this new class of materials with types of sensors to be embedded seamlessly or inherently, including appropriate embedding manufacturing techniques with modeling and simulation methods.     

‘WFD’ – What is it and what’s ‘LOV’ got to do with it?

Fatigue cracking of any kind can significantly reduce the load carrying capability of a structure. Because of this it is considered to be a major threat to structural integrity. Chapter 14 of the Code of Federal Regulations (14 CFR) includes specific requirements intended to preclude catastrophic failures due to fatigue. Fatigue cracking may be symptomatic or incidental, localized or at multiple locations. The 14 CFR requirements make no distinction. They are intended to mitigate the strength reducing effects of fatigue regardless of why or how it manifests itself. The Aloha Airlines incident of 1988 was caused by fatigue cracking at multiple locations that could be considered symptomatic. This incident precipitated an avalanche of activities related to symptomatic fatigue cracking at multiple locations. This included research, development and even new rulemaking. In many respects, this cracking was treated like a new phenomena. For many it was seen as a new and singular threat that needed special attention. Consistent with this a new term, “widespread fatigue damage” (WFD), was coined. Is WFD really something new? Does it need special treatment and maybe even its own rule? These questions are considered and it is concluded that WFD is not something new. It is also argued that WFD is and always has been within the scope of existing rules. However, one thing that is missing in the rules is the concept of a “limit of validity” (LOV) of an airplane’s fatigue management program (FMP). The LOV is the cumulative amount of operation beyond which it has not been validated that the FMP will keep the threat of catastrophic failure due to fatigue sufficiently low. The LOV is very much dependent on the fatigue knowledge base that has been acquired at any given time. The lack of an LOV is a deficiency relative to fatigue management in general and not just for what has been labeled WFD. It is concluded that rulemaking is needed to require the establishment of an LOV for certain existing airplane models and future certified ones. Additionally, the existing requirement to provide full-scale fatigue test evidence should not be limited to addressing the threat of WFD but should be required to characterize the fatigue performance of all primary structure in support of establishing an LOV for the FMP.     

When should we change the definition of the second?

The microwave caesium (Cs) atomic clock has formed an enduring basis for the second in the International System of Units (SI) over the last few decades. The advent of laser cooling has underpinned the development of cold Cs fountain clocks, which now achieve frequency uncertainties of approximately 5×10(-16). Since 2000, optical atomic clock research has quickened considerably, and now challenges Cs fountain clock performance. This has been suitably shown by recent results for the aluminium Al(+) quantum logic clock, where a fractional frequency inaccuracy below 10(-17) has been reported. A number of optical clock systems now achieve or exceed the performance of the Cs fountain primary standards used to realize the SI second, raising the issues of whether, how and when to redefine it. Optical clocks comprise frequency-stabilized lasers probing very weak absorptions either in a single cold ion confined in an electromagnetic trap or in an ensemble of cold atoms trapped within an optical lattice. In both cases, different species are under consideration as possible redefinition candidates. In this paper, I consider options for redefinition, contrast the performance of various trapped ion and optical lattice systems, and point to potential limiting environmental factors, such as magnetic, electric and light fields, collisions and gravity, together with the challenge of making remote comparisons of optical frequencies between standards laboratories worldwide.     

Can nanotechnology be ‘green’? Comparing efficacy of nano and microparticles in cementitious materials

The use of nano-sized particles in cementitious materials introduces a myriad of potential innovations from new functionality to enhanced mechanical performance, but such materials can be energy-intensive to manufacture. With increasing emphasis on sustainable development, it is important to investigate and understand benefits and costs of using nanomaterials compared to relatively less energy-intensive microparticles. The current research investigates the effect of chemically inert nano and microparticles (i.e., titanium dioxide (TiO₂) and calcium carbonate (limestone)) on early age properties and behavior of cement-based materials. Results indicate that the early age hydration rates, shrinkage, and pore structure of cement-based materials can be modified and optimized by tailoring the size of fillers. Life cycle analysis indicates that photocatalytic reactivity of TiO₂ could offset initial higher environmental impacts. Thus, optimally sized nanoparticles could revolutionize the construction industry by allowing tailoring of structure and properties of cement-based composites, with environmental sustainability preserved through the selection of lower embodied-energy particles.     

Self‐healing materials: what can nature teach us?

Natural materials such as bone and insect cuticle are capable of self‐repair, a facility that greatly increases their durability and safe working stress. Some engineering materials have also been designed to be self‐healing, although currently they cannot match the performance of natural materials as regards the efficiency and longevity of the healing process. In this paper, we review the state of the art regarding these two types of materials. We discuss the role of fracture mechanics in the development of theoretical models of self‐healing; we identify certain crucial parameters that make natural materials successful and discuss how these lessons can be applied to improve the performance of self‐healing materials for engineering applications.     

Bicycle helmet legislation: can we reach a consensus?

Debate continues over bicycle helmet laws. Proponents argue that case-control studies of voluntary wearing show helmets reduce head injuries. Opponents argue, even when legislation substantially increased percent helmet wearing, there was no obvious response in percentages of cyclist hospital admissions with head injury-trends for cyclists were virtually identical to those of other road users. Moreover, enforced laws discourage cycling, increasing the costs to society of obesity and lack of exercise and reducing overall safety of cycling through reduced safety in numbers. Countries with low helmet wearing have more cyclists and lower fatality rates per kilometre. Cost-benefit analyses are a useful tool to determine if interventions are worthwhile. The two published cost-benefit analyses of helmet law data found that the cost of buying helmets to satisfy legislation probably exceeded any savings in reduced head injuries. Analyses of other road safety measures, e.g. reducing speeding and drink-driving or treating accident blackspots, often show that benefits are significantly greater than costs. Assuming all parties agree that helmet laws should not be implemented unless benefits exceed costs, agreement is needed on how to derive monetary values for the consequences of helmet laws, including changes in injury rates, cycle-use and enjoyment of cycling. Suggestions are made concerning the data and methodology needed to help clarify the issue, e.g. relating pre- and post-law surveys of cycle use to numbers with head and other injuries and ensuring that trends are not confused with effects of increased helmet wearing.     

Absence of ‘fragility’ and mechanical response of jammed granular materials

We perform molecular dynamic simulations of frictional non-thermal particles driven by an externally applied shear stress. After the system jams following a transient flow, we probe its mechanical response in order to clarify whether the resulting solid is ‘fragile’. We find the system to respond elastically and isotropically to small perturbations of the shear stress, suggesting absence of fragility. These results are interpreted in terms of the energy landscape of dissipative systems. For the same values of the control parameters, we check the behaviour of the system during a stress cycle. Increasing the maximum stress value, a crossover from a visco-elastic to a plastic regime is observed.     

What can cities do to increase resilience?

This paper examines climate change mitigation and adaptation from an insurance industry perspective, with particular reference to London and the USA. It illustrates how British insurers are increasingly shaping public policy and using new technology to manage the risks from climate change impacts and makes a plea for society to make more use of insurance expertise in future decision making. In particular, more dialogue is needed between architects, planners and insurers to adapt our buildings and cities for climate change impacts. The paper is an abbreviated and updated version of the paper presented by the author in Houston, Texas, in 2005.