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5 Shape-memory (alloys) smart materials

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Smart Materials
This chapter is in the book Smart Materials
5 Shape-memory (alloys) smart materials5.1 IntroductionShape-memory alloys (SMAs) are advanced smart materials with the unique capabil-ity to revert to a predetermined shape after being deformed, triggered by changes intemperature or stress [34]. This behavior arises from a reversible phase transforma-tion between two crystalline phases: martensite (low-temperature phase) and austen-ite (high-temperature phase). When cooled, SMAs enter the martensitic phase, allow-ing them to be easily deformed. Upon heating, the alloy transitions to the austeniticphase, causing it to return to its original shape–a phenomenon known as the shape-memory effect (SME) [35].In addition to SME, SMAs also exhibit superelasticity (or pseudoelasticity), wherethe material can undergo large strains when stressed and recover its original shapeimmediately upon unloading, without needing a temperature change. This occurs dueto stress-induced phase transformation between the austenite and martensite phases.Common SMAs include nickel–titanium (NiTi) alloys, also known as nitinol, whichare widely used in medical devices such as stents and orthodontic wires, as well as inactuators, sensors, and robotics. The unique properties of SMAs make them ideal forapplications requiring precise actuation, adaptive structures, and energy absorption[5]. Their ability to adapt to environmental changes and recover from deformationgives SMAs a prominent role in the development of intelligent systems, enabling inno-vation in fields such as aerospace, automotive, and biomedical engineering.5.2 Background on shape-memory alloys (SMA)SMAs have their roots in the discovery of SME in the early twentieth century. The phe-nomenon was first observed in 1932 in a gold–cadmium alloy, but it was not until the1960s that SMAs gained significant attention with the discovery of the nickel–titaniumalloy (nitinol) by the Naval Ordnance Laboratory in the United States. Nitinol, whichstands for nickel–titanium, displayed both shape memory and superelastic properties,sparking interest in its potential applications.The development of SMAs was driven by the need for materials that could per-form specific functions autonomously without requiring complex mechanical systems.Over time, SMAs have evolved from being a scientific curiosity to becoming integralin diverse fields such as aerospace, biomedical engineering, and robotics.The underlying mechanism of SMAs is the reversible phase transformation be-tween martensite (low-temperature phase) and austenite (high-temperature phase).https://doi.org/10.1515/9783111379623-005
© 2025 Walter de Gruyter GmbH, Berlin/Boston

5 Shape-memory (alloys) smart materials5.1 IntroductionShape-memory alloys (SMAs) are advanced smart materials with the unique capabil-ity to revert to a predetermined shape after being deformed, triggered by changes intemperature or stress [34]. This behavior arises from a reversible phase transforma-tion between two crystalline phases: martensite (low-temperature phase) and austen-ite (high-temperature phase). When cooled, SMAs enter the martensitic phase, allow-ing them to be easily deformed. Upon heating, the alloy transitions to the austeniticphase, causing it to return to its original shape–a phenomenon known as the shape-memory effect (SME) [35].In addition to SME, SMAs also exhibit superelasticity (or pseudoelasticity), wherethe material can undergo large strains when stressed and recover its original shapeimmediately upon unloading, without needing a temperature change. This occurs dueto stress-induced phase transformation between the austenite and martensite phases.Common SMAs include nickel–titanium (NiTi) alloys, also known as nitinol, whichare widely used in medical devices such as stents and orthodontic wires, as well as inactuators, sensors, and robotics. The unique properties of SMAs make them ideal forapplications requiring precise actuation, adaptive structures, and energy absorption[5]. Their ability to adapt to environmental changes and recover from deformationgives SMAs a prominent role in the development of intelligent systems, enabling inno-vation in fields such as aerospace, automotive, and biomedical engineering.5.2 Background on shape-memory alloys (SMA)SMAs have their roots in the discovery of SME in the early twentieth century. The phe-nomenon was first observed in 1932 in a gold–cadmium alloy, but it was not until the1960s that SMAs gained significant attention with the discovery of the nickel–titaniumalloy (nitinol) by the Naval Ordnance Laboratory in the United States. Nitinol, whichstands for nickel–titanium, displayed both shape memory and superelastic properties,sparking interest in its potential applications.The development of SMAs was driven by the need for materials that could per-form specific functions autonomously without requiring complex mechanical systems.Over time, SMAs have evolved from being a scientific curiosity to becoming integralin diverse fields such as aerospace, biomedical engineering, and robotics.The underlying mechanism of SMAs is the reversible phase transformation be-tween martensite (low-temperature phase) and austenite (high-temperature phase).https://doi.org/10.1515/9783111379623-005
© 2025 Walter de Gruyter GmbH, Berlin/Boston

Chapters in this book

  1. Frontmatter I
  2. Preface V
  3. Acknowledgments IX
  4. Contents XI
  5. 1 Introduction and historical perspective 1
  6. 2 Smart materials and structural systems 56
  7. 3 Electrorheological (fluids) smart materials 77
  8. 4 Piezoelectric smart materials 96
  9. 5 Shape-memory (alloys) smart materials 121
  10. Authors’ bibliography 149
  11. Bibliography 151
  12. Index 155
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https://doi.org/10.1515/9783111379623-005

Chapters in this book

  1. Frontmatter I
  2. Preface V
  3. Acknowledgments IX
  4. Contents XI
  5. 1 Introduction and historical perspective 1
  6. 2 Smart materials and structural systems 56
  7. 3 Electrorheological (fluids) smart materials 77
  8. 4 Piezoelectric smart materials 96
  9. 5 Shape-memory (alloys) smart materials 121
  10. Authors’ bibliography 149
  11. Bibliography 151
  12. Index 155
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