Limitations of finite element analysis (FEA) in providing accurate localized stress and strain information in superelastic nitinol are well recognized. Understanding the parent texture and the crystallography of stress-induced martensitic transformation holds the key to bridge the gap between continuum mechanics and the microscopic stress-strain condition imposed by the phase transformation in understanding the deformation mechanism of this complex material. A scanning electron microscope equipped with an electron beam back scatter diffraction detector is a powerful tool that can extract microscopic crystallographic information from bulk specimens. The technique has been employed to study the crystallography of stress-induced martensitic transformation during tensile and bend deformations of superelastic nitinol. The results suggest that for tensile deformation, the transformation variants of stress-induced martensite (SIM) inside the Lüders band follow maximum shear stress along the martensite shape change direction. The observation also confirms that the SIM transformation is incomplete, leaving a significant amount of retained B2 parent phase inside the Lüders band. As tensile deformation proceeds, the Lüders band propagates by nucleating new martensite plates instead of by thickening of the existing martensite variants. For bend deformation, SIM appears to transform much easier in the tension side than in the compression side, confirming previous studies on the asymmetrical tension-compression property in superelastic nitinol materials. Lastly, the local stress field at the tip of martensite plate has been computed by finite element (FEA) simulation based on the observed martensite morphology. The implication on local stress field and plasticity provides a rationalization in explaining why nitinol fatigue life appears to be insensitive to the mean strain effect.
Author Information
Wu, Ming, H.
Edwards LifeSciences LLC, Irvine, CA
Gong, Xiao, -Yan
Medical Implant Mechanics LLC, Aliso Viejo, CA
Mao, Shengcheng
Beijing Univ. of Technology, Beijing, People's Republic of China
Han, Xiaodong
Beijing Univ. of Technology, Beijing, People's Republic of China
Domestic orders are delivered via United Parcel Service (UPS) or United States Postal Service (USPS). Transit
times average 3 to 5 business days. Please be aware that UPS will not deliver packages to Post Office Boxes.
International orders are delivered via courier post services which can be either a postal service, courier
service, or a combination of both. Standard Service is untraceable. Please allow 4-7 weeks for delivery.
Please be aware that carriers will not deliver packages to Post Office Boxes. Because of the variability of
customs processes and procedures in different countries, ASTM International cannot guarantee transit times to
international destinations. Customs duty and taxes are the responsibility of the consignee.
Shipping & Handling charges follow the rate schedule, below:
Order Total
Shipping & Handling Fee (US Domestic)
Up to $50.00
$18.72
$50.01 to $100.00
$20.80
$100.01 to $150.00
$29.52
$150.01 to $250.00
$39.09
$250.01 to $500.00
$56.25
$500.01 to $750.00
$76.42
$750.01 to $1000.00
$93.15
$1000.01 to $1500.00
$121.27
$1500.01 to $2500.00
$158.38
$2500.01 to $4999.00
$209.04
$5000.00 to higher
FREE
Order Total
Shipping & Handling Fee (International)
Up to $50.00
$68.72
$50.01 to $100.00
$70.80
$100.01 to $150.00
$79.52
$150.01 to $250.00
$89.09
$250.01 to $500.00
$106.25
$500.01 to $750.00
$126.42
$750.01 to $1000.00
$143.15
$1000.01 to $1500.00
$171.27
$1500.01 to $2500.00
$208.38
$2500.01 to $4999.00
$259.04
$5000.00 to higher
FREE
Shipping and Handling charges are approximate. Additional charges may be incurred if your order requires multiple shipments. This does not apply to complete sets and sections.