Long-term behaviour of binary Ni-Ti SMA wires

Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientific

Abstract

One of the main obstacles for broader utilization of SMA based actuators in industrial applications is the missing knowledge about the long-term behaviour of the SMA wires. In this work the aim is to study systematically the long-term behaviour and fatigue endurance of the binary Ni-Ti SMA wires. Study concentrates on the effects of three major design parameters on the long-term behaviour of binary Ni-Ti-based actuators: the effect of the stress level used, the effect of the temperature interval used on thermal cycling 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. The fatigue life and the evolution of transformation and plastic strains were carefully examined for the tested wires. Also the micro-scale changes and damage patterns of fractured materials were investigated. One of the major conclusions of the study is that designing and controlling long-term behaviour of binary Ni-Ti actuators is very challenging because the properties are highly sensitive to the heat-treatment state of the wires. A major effect on fatigue endurance has the temperature interval used for thermal cycling: decreasing the temperature interval used increased the fatigue life markedly. 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 the amount of plastic strain can be stated as one of the failure criteria for binary Ni-Ti wires, but that every heat-treatment state and loading level should be treated and presented separately. Fractographic analysis performed with SEM reveal similar damage patterns for fractured wires. Surface cracking and subsequent crack growth proved to be responsible for the accumulation of fatigue damage in the studied wires. The accumulated plastic strain seems to be the major factor for nucleating the surface cracking.
Original languageEnglish
Title of host publicationS(3)T 2010, School and symposium on smart structural systems technologies
Place of PublicationPorto, Portugal
Publication statusPublished - 2010
MoE publication typeB3 Non-refereed article in conference proceedings
EventSchool and symposium on smart structural systems technologies, S(3)T 2010 - Porto, Portugal
Duration: 6 Apr 20109 Apr 2010

Conference

ConferenceSchool and symposium on smart structural systems technologies, S(3)T 2010
Abbreviated titleS(3)T 2010
CountryPortugal
CityPorto
Period6/04/109/04/10

Fingerprint

Wire
Fatigue of materials
Actuators
Heat treatment
Plastic deformation
Durability
Thermal cycling
Fatigue damage
Temperature
Industrial applications
Crack propagation
Scanning electron microscopy

Keywords

  • SMA

Cite this

Karhu, M., & Lindroos, T. (2010). Long-term behaviour of binary Ni-Ti SMA wires. In S(3)T 2010, School and symposium on smart structural systems technologies [530] Porto, Portugal.
Karhu, Marjaana ; Lindroos, Tomi. / Long-term behaviour of binary Ni-Ti SMA wires. S(3)T 2010, School and symposium on smart structural systems technologies. Porto, Portugal, 2010.
@inproceedings{e865f698954745a69acf052d19a13599,
title = "Long-term behaviour of binary Ni-Ti SMA wires",
abstract = "One of the main obstacles for broader utilization of SMA based actuators in industrial applications is the missing knowledge about the long-term behaviour of the SMA wires. In this work the aim is to study systematically the long-term behaviour and fatigue endurance of the binary Ni-Ti SMA wires. Study concentrates on the effects of three major design parameters on the long-term behaviour of binary Ni-Ti-based actuators: the effect of the stress level used, the effect of the temperature interval used on thermal cycling 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. The fatigue life and the evolution of transformation and plastic strains were carefully examined for the tested wires. Also the micro-scale changes and damage patterns of fractured materials were investigated. One of the major conclusions of the study is that designing and controlling long-term behaviour of binary Ni-Ti actuators is very challenging because the properties are highly sensitive to the heat-treatment state of the wires. A major effect on fatigue endurance has the temperature interval used for thermal cycling: decreasing the temperature interval used increased the fatigue life markedly. 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 the amount of plastic strain can be stated as one of the failure criteria for binary Ni-Ti wires, but that every heat-treatment state and loading level should be treated and presented separately. Fractographic analysis performed with SEM reveal similar damage patterns for fractured wires. Surface cracking and subsequent crack growth proved to be responsible for the accumulation of fatigue damage in the studied wires. The accumulated plastic strain seems to be the major factor for nucleating the surface cracking.",
keywords = "SMA",
author = "Marjaana Karhu and Tomi Lindroos",
note = "Project code: 19567",
year = "2010",
language = "English",
isbn = "978-989-96697-0-3",
booktitle = "S(3)T 2010, School and symposium on smart structural systems technologies",

}

Karhu, M & Lindroos, T 2010, Long-term behaviour of binary Ni-Ti SMA wires. in S(3)T 2010, School and symposium on smart structural systems technologies., 530, Porto, Portugal, School and symposium on smart structural systems technologies, S(3)T 2010, Porto, Portugal, 6/04/10.

Long-term behaviour of binary Ni-Ti SMA wires. / Karhu, Marjaana; Lindroos, Tomi.

S(3)T 2010, School and symposium on smart structural systems technologies. Porto, Portugal, 2010. 530.

Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientific

TY - GEN

T1 - Long-term behaviour of binary Ni-Ti SMA wires

AU - Karhu, Marjaana

AU - Lindroos, Tomi

N1 - Project code: 19567

PY - 2010

Y1 - 2010

N2 - One of the main obstacles for broader utilization of SMA based actuators in industrial applications is the missing knowledge about the long-term behaviour of the SMA wires. In this work the aim is to study systematically the long-term behaviour and fatigue endurance of the binary Ni-Ti SMA wires. Study concentrates on the effects of three major design parameters on the long-term behaviour of binary Ni-Ti-based actuators: the effect of the stress level used, the effect of the temperature interval used on thermal cycling 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. The fatigue life and the evolution of transformation and plastic strains were carefully examined for the tested wires. Also the micro-scale changes and damage patterns of fractured materials were investigated. One of the major conclusions of the study is that designing and controlling long-term behaviour of binary Ni-Ti actuators is very challenging because the properties are highly sensitive to the heat-treatment state of the wires. A major effect on fatigue endurance has the temperature interval used for thermal cycling: decreasing the temperature interval used increased the fatigue life markedly. 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 the amount of plastic strain can be stated as one of the failure criteria for binary Ni-Ti wires, but that every heat-treatment state and loading level should be treated and presented separately. Fractographic analysis performed with SEM reveal similar damage patterns for fractured wires. Surface cracking and subsequent crack growth proved to be responsible for the accumulation of fatigue damage in the studied wires. The accumulated plastic strain seems to be the major factor for nucleating the surface cracking.

AB - One of the main obstacles for broader utilization of SMA based actuators in industrial applications is the missing knowledge about the long-term behaviour of the SMA wires. In this work the aim is to study systematically the long-term behaviour and fatigue endurance of the binary Ni-Ti SMA wires. Study concentrates on the effects of three major design parameters on the long-term behaviour of binary Ni-Ti-based actuators: the effect of the stress level used, the effect of the temperature interval used on thermal cycling 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. The fatigue life and the evolution of transformation and plastic strains were carefully examined for the tested wires. Also the micro-scale changes and damage patterns of fractured materials were investigated. One of the major conclusions of the study is that designing and controlling long-term behaviour of binary Ni-Ti actuators is very challenging because the properties are highly sensitive to the heat-treatment state of the wires. A major effect on fatigue endurance has the temperature interval used for thermal cycling: decreasing the temperature interval used increased the fatigue life markedly. 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 the amount of plastic strain can be stated as one of the failure criteria for binary Ni-Ti wires, but that every heat-treatment state and loading level should be treated and presented separately. Fractographic analysis performed with SEM reveal similar damage patterns for fractured wires. Surface cracking and subsequent crack growth proved to be responsible for the accumulation of fatigue damage in the studied wires. The accumulated plastic strain seems to be the major factor for nucleating the surface cracking.

KW - SMA

M3 - Conference article in proceedings

SN - 978-989-96697-0-3

BT - S(3)T 2010, School and symposium on smart structural systems technologies

CY - Porto, Portugal

ER -

Karhu M, Lindroos T. Long-term behaviour of binary Ni-Ti SMA wires. In S(3)T 2010, School and symposium on smart structural systems technologies. Porto, Portugal. 2010. 530