Prof.Yiu-Wing Mai has made many significant and sustained contributions pushing the boundaries of science and engineering of advanced materials,especially nanomaterials and nanocomposites in recent two decades.This Festschrift on “Trends in Nanomaterials and Nanocomposites:Fundamentals,Modelling and Applications” is dedicated to his 75th birthday in recognition of his influential research on nanomaterials and nanocomposites.The range of topics covered represents a cross-section of the scientific interests of Prof.Mai and his collaborators.We would like to thank Prof.Jian Lu,Editor-in-Chief ofNano Materials Science,for publishing this special issue.

Yiu-Wing Mai (米耀榮),Professor/University Chair in Mechanical Engineering at the University of Sydney,is a 27th generation descendant of Mi Fu(米芾),the great calligrapher and painter of the Northern Song Dynasty (960–1127).He received his BSc (Eng) &Williamson Prize in 1969,PhD in 1972 and DSc in 1999 from the University of Hong Kong.His PhD project was supervised by Prof.Charles Gurney on a thesis:On the rate of slow cracking of materials.From 1974 to 1976,he did postdoctoral research on interface design of boron fiber-epoxy composites with Prof.Tony Atkins at the University of Michigan–Ann Arbor and on fracture mechanics of polymers with Prof.Gordon Williams at Imperial College London.Mai took up a short-term lectureship at the University of Sydney in December 1976 but never left.He was promoted to a Personal Chair in 1987 and a University Chair in 2004.He also spent time in Hong Kong University of Science and Technology (1993–1995) and City University of Hong Kong(2000–2002).

Professor Yiu-Wing Mai AM FRS FREng FAA FTSE ForMem CAE(中國工程院外籍院士)

In Sydney,Prof.Mai has made many outstanding contributions on two research areas,fracture mechanics of materials and advanced composites,in which he collaborated closely with Prof.Brian Cotterell(who moved to NUS,Singapore in 1991)and Prof.Lin Ye(who came to Sydney in 1992).He is a firm believer of the Griffith/Gurney energy approach to analyze the fracture and mechanical behaviors of materials.A most important contribution is the development of the Essential Work of Fracture(EWF)concept and methodology in 1980s to obtain the fracture toughness of ductile polymers[1],their blends and nanocomposites with high (toughness/yield strength) ratio by separating the essential work from the total fracture work in experiments on selected specimen geometries [2].The EWF method has created considerable interest in the research and engineering communities.The energy approach to fracture mechanics was presented in a monograph:Elastic and Plastic Fracture:metals,polymers,ceramics,composites,biological materials,Ellis Horwood,Chichester 1985 and John Wiley,New York 1987,which Prof.Mai co-authored with Prof.Tony Atkins.

Prof.Mai is always conscious that good research should have good socio-economic benefits.The common use of asbestos cements in house constructions in 1950s in Australia is well-known to cause mesothelioma and lung cancer.From late 1970s to mid-1980s,he undertook a R&D project funded by James Hardie Coy&Ltd.to develop and ascertain the mechanical reliability of wood fiber cements which ultimately replaced asbestos cements.He soon realized that in these fiber cements,like other quasi-brittle materials,e.g.,coarse-grained ceramics [3a,b],there is a predominant size effect on fracture caused by the large crack-wake fracture process zone which must be adequately incorporated in the analytical models.In this context,he and Prof.Brian Cotterell developed a fracture mechanics framework to characterize the material and structural failure behaviors of cementitious matrices and fiber cements in one of the first books on this subject:Fracture Mechanics of Cementitious Materials,Blackie A&P/Chapman&Hall,Glasgow,1996.

Throughout the 1990s,strongly supported by the Cooperative Research Centre for Advanced Composite Structures,Prof.Mai worked on carbon fiber composites for aerospace,civil and marine structures.The main objective was to improve composites manufacturing processes.In these areas,Mai and his colleagues contributed much original work on stitching and z-pinning,thermoforming and pultrusion of composites.Especially,their fracture mechanics models on mode I and mode II stitching [4a,b] and z-pinning [5a,b] of laminated composites have become classics in this field and remain highly cited to-date.

For a long time,Mai has been a leading contributor on the fracture mechanics characterization of composite interfaces.In particular,he demonstrated that high-toughness and high-strength composites could be simultaneously achieved by suitably controlling the interfacial bonding at the fiber-matrix interface.Furthermore,he and his colleagues published a seminal paper using fracture mechanics to describe the single fiber pullout problem as a progressively debonding interface crack which included the fiber Poisson contraction and the non-uniform friction at the debonded fiber-matrix interface.This rigorous analysis allowed the interface fracture energy,the residual fiber clamping stress and the friction stress to be evaluated [6].The model was later extended to include the effects of finite embedded length,constraints due to neighboring fibers and fiber surface roughness.These papers and the research monograph he co-authored with Prof.Jang-Kyo Kim (Hong Kong University of Science&Technology):Engineered Interfaces in Fiber Reinforced Composites,Elsevier,Oxford,1998,have been,and will continue to be,standard references for researchers working on composite interfaces.

From 2000 to 2002,Prof.Mai was working on superhard nanocomposite coatings(H ＞40 GPa)by PVD for cutting tools funded by the Hong Kong Innovation &Technology Commission and General Motors China with exciting results at the City University of Hong Kong.However,the award of an inaugural research-only Federation Fellowship(2002–2007) lured him back to Sydney.For this gave him too good an opportunity to establish a research team focusing on an exciting class of new materials,polymer nanocomposites,in which nano-sized particles(＜100 nm) are incorporated into polymer matrices as we enter into the 21st century.During the past two decades,in collaboration with colleagues in Australia,Hong Kong,Taiwan and China,he and his team have made important continuing contributions on the basic understanding of the deformation,failure and toughening mechanisms of polymers containing 0D,1D and 2D nano-fillers and 3D nano-foams;novel syntheses and new fabrication methods of multi-scale hierarchical reinforcements;and multifunctional applications,such as permeability [7],optical transparency[8-9],fire retardancy [10],electrical/thermal conductivities [11],cathodes/anodes [12] in batteries,interleaf toughening,strain/damage sensing[13],and friction/wear[14].Many of these results are given in a monograph which he co-authored with Assoc.Prof.Aravind Dasari(NTU,Singapore) and Prof.Zhong-Zhen Yu (BUCT,China):Polymer Nanocomposites-Towards Multi-Functionality,Springer-Verlag,London,2016.

Short-fiber reinforced polymers (SFRPs) have been extensively used in automobiles,sporting goods,dental,electronic and electrical industries owing to their low-cost and easy processing.It is a composites area of great practical importance and in which one of us,Prof.Shao-Yun Fu,and Prof.Mai had made significant contributions.To bring their research results and those scattered in the published literature to the wider composites community,with Dr.Bernd Lauke(Leibniz Institute of Polymer Research Dresden),they wrote a comprehensive monograph:Science and Engineering of Short Fiber Reinforced Polymer Composites,1st edition,2009,Woodhead Publishing,Cambridge and 2nd edition 2019,Elsevier,London.

Prof.Mai's wide interests on solid and fracture mechanics led him to electromagnetic materials and microelectronic assemblies.These are evidenced by two research monographs:Fracture Mechanics of Electromagnetic Materials:Nonlinear field theory and applications”,Imperial College Press,London,2013 which he co-authored with Dr.Xiaohong Chen(Pratt &Whitney,CT,USA);andRobust Design of Microelectronics Assemblies against Mechanical Shock,Temperature and Moisture”,Woodhead Publishing,Cambridge,2015 which he wrote with Dr.Ee Hua Wong(University of Canterbury,NZ).

Mai is a prolific researcher and has published more than 850 SCI papers with over 36,000 non-self cites and an h-index of 89 according to the Web of Science.Corresponding metrics are h=110 and ＞61,000 times cited based on Google Scholar.For his various achievements,Mai has been recognized,inside and outside Australia,through many prizes and medals:RILEM Award &Robert L'Hermite Medal (1981),AFG Inc.Achievement Award (2000),ICF Honorary Fellow (2001),Gruppo Italiano Fracttura Honorary Member (2002),Centenary Medal (2003),ICF Takeo Yokobori Gold Medal (2013),ICCM Scala Award and World Fellow(2015),IOM3 Griffith Medal and Prize(2016),and AGM Michell Medal (2016) among others.He was elected to several prestigious national academies:Australian Academy of Technological Sciences and Engineering(1992),Australian Academy of Science (2001),Royal Society of London(2008),Royal Academy of Engineering(2011)and Chinese Academy of Engineering (2017).For his service to engineering,particularly in the fields of advanced fiber composites and fracture research,he was appointed a Member of the Order of Australia (2010) by the Australian Government;and in recognition of his scholarly contributions to scientific research and society,he was conferred an honorary Doctor of Science(honoris causa)degree by his alma mater,the University of Hong Kong(2013).

Prof.Mai is enthusiastic and engaging with the fracture mechanics and advanced composites professions.He served as President of the AFG Inc.(1996–1998) and the ICF (2002–2005).In particular,he was the Founding President of the Asian-Australasian Association for Composite Materials(1997–1998),and he played a critical role in promoting R&D in composite materials in this region and initiated a very successful biannual conference series:Asian-Australasian Conference on Composite Materials(ACCM)since ACCM-1 held in Osaka,1998.Now,ACCM with ICCM and ECCM are the three major meetings for the composites community.

The Centre for Advanced Materials Technology(CAMT)was launched in 1989 by Prof.Mai and it has since provided an excellent training ground for generations of research fellows and graduate students in fracture mechanics,composites science and engineering,and nanotechnology.In the last 40 years,Prof.Mai successfully supervised and co-supervised over 60 PhDs and 16 Masters,and advised more than 70 postdocs and research fellows.He mentored and inspired many to successful careers in academia,business and industry across the world.He genuinely cares for those under his tutelage and sticks by them.For this is the only way he learned from his mentors,Charles Gurney,Tony Atkins and Gordon Williams,who shaped his own career.He was deeply moved by so many alumni who attended a re-union Workshop celebrating the 30thAnniversary of the CAMT at Tongji University in Shanghai,China,in 2019(See photo below).

We have always been impressed by Prof.Mai's scholarship,dedication,drive and energy,touching and impacting so many young people who studied and worked in the CAMT.Indeed,he has helped develop our academic careers,as he has for other CAMT alumni.He is our role model.We treasure our friendship with him and his lovely wife,Louisa,over many years.We wish them good health and look forward to many more years of exciting research from Mai.

Contributions to this Festschrift to honor Prof.Mai's 75th birthday were invited from his friends,colleagues and students within the nanomaterials and nanocomposites research community.The response was overwhelming.Considering the topics of the contributed papers,the Special Issue was divided into two parts:Part I -Mechanical behaviors and modeling,and Part II -Functionalities and applications.In the first part,the mechanical behaviors and modeling of nanomaterials,nanothreads,nanocomposite hydrogels,bulk polymer nanocomposites and fiber-reinforced composites,were introduced and discussed in detail.In the second part,various fabrication strategies of advanced functional nanomaterials and nanocomposites were developed and reviewed for superhydrophobic,flame-retardant,thermally conductive,energy harvesting,smart strain sensing,anti-corrosion and electromagnetic interference shielding applications.We thank all the authors,reviewers and editorial staff for maintaining the high qualities of the papers in the Special Issue worthy of the scientists they are honoring.We hope you enjoy reading them.

Declaration of competing interest

The authors declare no conflict of interest.