Long-term behaviour of binary Ti-49.7Ni (at.%) SMA actuators - The fatigue lives and evolution of strains on thermal cycling

    Research output: Contribution to journalArticleScientificpeer-review

    11 Citations (Scopus)

    Abstract

    Long-term behaviour and fatigue endurance are the key issues in the utilization of SMA actuators, but systematic research work is still needed in this field. This study concentrates on the effects of three major design parameters on the long-term behaviour of binary Ti-49.7Ni-based actuators: the effect of the temperature interval used in thermal cycling, the effect of the stress level used and the effect of the heat-treatment state of the wire used. The long-term behaviour of the wires was studied in a custom-built fatigue test frame in which the wires were thermally cycled under a constant stress level. The fatigue lives of tested specimens and the evolution of transformation and plastic strains on thermal cycling were recorded. Before the fatigue testing, a series of heat treatments was carried out to generate optimal actuator properties for the wires. One of the major conclusions of the study is that the temperature interval used for thermal cycling has a major effect on fatigue endurance: decreasing the temperature interval used for thermal cycling increased the fatigue life markedly. When the transformation is complete, a 20 ?C increase of the final temperature reduced the fatigue lives at the most by half for the studied Ti-49.7Ni wires. With partial transformations the effect is more distinct: even the 5 ?C increase in the final temperature reduced the fatigue life by half. The stress level and heat-treatment state used had a marked effect on the actuator properties of the wires, but the effects on fatigue endurance were minor. The fatigue test results reveal that designing and controlling long-term behaviour of binary Ti-49.7Ni actuators is very challenging because the properties are highly sensitive to the heat-treatment state of the wires. Even 5 min longer heat-treatment time could generate, at the most, double plastic strain values and 30% lower stabilized transformation strain values. The amount of plastic strain can be stated as one of the failure criteria for binary Ti-49.7Ni, but that every heat-treatment state and loading level should be treated and presented separately with its own design relations.

    Original languageEnglish
    Article number115019
    JournalSmart Materials and Structures
    Volume19
    Issue number11
    DOIs
    Publication statusPublished - 1 Nov 2010
    MoE publication typeA1 Journal article-refereed

    Fingerprint

    spectral mixture analysis
    fatigue life
    Thermal cycling
    Actuators
    actuators
    Fatigue of materials
    wire
    cycles
    heat treatment
    Wire
    Heat treatment
    endurance
    plastics
    fatigue tests
    Plastic deformation
    Durability
    intervals
    temperature
    Temperature
    Fatigue testing

    Cite this

    @article{45af577af48e446f9e5c35c0d04f2653,
    title = "Long-term behaviour of binary Ti-49.7Ni (at.{\%}) SMA actuators - The fatigue lives and evolution of strains on thermal cycling",
    abstract = "Long-term behaviour and fatigue endurance are the key issues in the utilization of SMA actuators, but systematic research work is still needed in this field. This study concentrates on the effects of three major design parameters on the long-term behaviour of binary Ti-49.7Ni-based actuators: the effect of the temperature interval used in thermal cycling, the effect of the stress level used and the effect of the heat-treatment state of the wire used. The long-term behaviour of the wires was studied in a custom-built fatigue test frame in which the wires were thermally cycled under a constant stress level. The fatigue lives of tested specimens and the evolution of transformation and plastic strains on thermal cycling were recorded. Before the fatigue testing, a series of heat treatments was carried out to generate optimal actuator properties for the wires. One of the major conclusions of the study is that the temperature interval used for thermal cycling has a major effect on fatigue endurance: decreasing the temperature interval used for thermal cycling increased the fatigue life markedly. When the transformation is complete, a 20 ?C increase of the final temperature reduced the fatigue lives at the most by half for the studied Ti-49.7Ni wires. With partial transformations the effect is more distinct: even the 5 ?C increase in the final temperature reduced the fatigue life by half. The stress level and heat-treatment state used had a marked effect on the actuator properties of the wires, but the effects on fatigue endurance were minor. The fatigue test results reveal that designing and controlling long-term behaviour of binary Ti-49.7Ni actuators is very challenging because the properties are highly sensitive to the heat-treatment state of the wires. Even 5 min longer heat-treatment time could generate, at the most, double plastic strain values and 30{\%} lower stabilized transformation strain values. The amount of plastic strain can be stated as one of the failure criteria for binary Ti-49.7Ni, but that every heat-treatment state and loading level should be treated and presented separately with its own design relations.",
    author = "Marjaana Karhu and Tomi Lindroos",
    note = "Project code: 19567",
    year = "2010",
    month = "11",
    day = "1",
    doi = "10.1088/0964-1726/19/11/115019",
    language = "English",
    volume = "19",
    journal = "Smart Materials and Structures",
    issn = "0964-1726",
    publisher = "Institute of Physics IOP",
    number = "11",

    }

    Long-term behaviour of binary Ti-49.7Ni (at.%) SMA actuators - The fatigue lives and evolution of strains on thermal cycling. / Karhu, Marjaana; Lindroos, Tomi.

    In: Smart Materials and Structures, Vol. 19, No. 11, 115019, 01.11.2010.

    Research output: Contribution to journalArticleScientificpeer-review

    TY - JOUR

    T1 - Long-term behaviour of binary Ti-49.7Ni (at.%) SMA actuators - The fatigue lives and evolution of strains on thermal cycling

    AU - Karhu, Marjaana

    AU - Lindroos, Tomi

    N1 - Project code: 19567

    PY - 2010/11/1

    Y1 - 2010/11/1

    N2 - Long-term behaviour and fatigue endurance are the key issues in the utilization of SMA actuators, but systematic research work is still needed in this field. This study concentrates on the effects of three major design parameters on the long-term behaviour of binary Ti-49.7Ni-based actuators: the effect of the temperature interval used in thermal cycling, the effect of the stress level used and the effect of the heat-treatment state of the wire used. The long-term behaviour of the wires was studied in a custom-built fatigue test frame in which the wires were thermally cycled under a constant stress level. The fatigue lives of tested specimens and the evolution of transformation and plastic strains on thermal cycling were recorded. Before the fatigue testing, a series of heat treatments was carried out to generate optimal actuator properties for the wires. One of the major conclusions of the study is that the temperature interval used for thermal cycling has a major effect on fatigue endurance: decreasing the temperature interval used for thermal cycling increased the fatigue life markedly. When the transformation is complete, a 20 ?C increase of the final temperature reduced the fatigue lives at the most by half for the studied Ti-49.7Ni wires. With partial transformations the effect is more distinct: even the 5 ?C increase in the final temperature reduced the fatigue life by half. The stress level and heat-treatment state used had a marked effect on the actuator properties of the wires, but the effects on fatigue endurance were minor. The fatigue test results reveal that designing and controlling long-term behaviour of binary Ti-49.7Ni actuators is very challenging because the properties are highly sensitive to the heat-treatment state of the wires. Even 5 min longer heat-treatment time could generate, at the most, double plastic strain values and 30% lower stabilized transformation strain values. The amount of plastic strain can be stated as one of the failure criteria for binary Ti-49.7Ni, but that every heat-treatment state and loading level should be treated and presented separately with its own design relations.

    AB - Long-term behaviour and fatigue endurance are the key issues in the utilization of SMA actuators, but systematic research work is still needed in this field. This study concentrates on the effects of three major design parameters on the long-term behaviour of binary Ti-49.7Ni-based actuators: the effect of the temperature interval used in thermal cycling, the effect of the stress level used and the effect of the heat-treatment state of the wire used. The long-term behaviour of the wires was studied in a custom-built fatigue test frame in which the wires were thermally cycled under a constant stress level. The fatigue lives of tested specimens and the evolution of transformation and plastic strains on thermal cycling were recorded. Before the fatigue testing, a series of heat treatments was carried out to generate optimal actuator properties for the wires. One of the major conclusions of the study is that the temperature interval used for thermal cycling has a major effect on fatigue endurance: decreasing the temperature interval used for thermal cycling increased the fatigue life markedly. When the transformation is complete, a 20 ?C increase of the final temperature reduced the fatigue lives at the most by half for the studied Ti-49.7Ni wires. With partial transformations the effect is more distinct: even the 5 ?C increase in the final temperature reduced the fatigue life by half. The stress level and heat-treatment state used had a marked effect on the actuator properties of the wires, but the effects on fatigue endurance were minor. The fatigue test results reveal that designing and controlling long-term behaviour of binary Ti-49.7Ni actuators is very challenging because the properties are highly sensitive to the heat-treatment state of the wires. Even 5 min longer heat-treatment time could generate, at the most, double plastic strain values and 30% lower stabilized transformation strain values. The amount of plastic strain can be stated as one of the failure criteria for binary Ti-49.7Ni, but that every heat-treatment state and loading level should be treated and presented separately with its own design relations.

    UR - http://www.scopus.com/inward/record.url?scp=78649416293&partnerID=8YFLogxK

    U2 - 10.1088/0964-1726/19/11/115019

    DO - 10.1088/0964-1726/19/11/115019

    M3 - Article

    AN - SCOPUS:78649416293

    VL - 19

    JO - Smart Materials and Structures

    JF - Smart Materials and Structures

    SN - 0964-1726

    IS - 11

    M1 - 115019

    ER -