Stress-induced Phase Transformation Research Articles

Full-Field Deformation Study of Ti–25Nb, Ti–25Nb–0.3O and Ti–25Nb–0.7O Shape Memory Alloys During Tension Using Digital Image Correlation

AbstractA Ti–25Nb shape memory alloy (SMA) exhibits shape memory effect associated with stress-induced martensitic transformation from β to α″ phase. Addition of oxygen stabilizes the β phase and changes stress–strain response. Oxygen-added Ti–25Nb SMAs show a more distinct superelastic behavior. In this work, digital image correlation (DIC) was applied to investigate for the first time full-field deformation of Ti–25Nb, Ti–25Nb–0.3O and Ti–25Nb–0.7O (at. pct) SMAs. The specimens were subjected to loading–unloading tensile tests to study local and global mechanical characteristics related to activity of particular deformation mechanisms of the SMAs. Strain and strain rate fields were quantitatively compared at selected stages of each SMA’s deformation. It was found that the Ti–25Nb SMA exhibits a macroscopically localized Lüders-type deformation associated with the stress-induced phase transformation, whereas Ti–25Nb–0.3O and Ti–25Nb–0.7O SMAs show more discrete types of deformation related to activity of interstitial oxygen atoms. As a consequence, at particular stages of deformation, local values of strain rate of Ti–25Nb SMA were significantly higher than those of average strain rate. The results obtained in this paper provide a better understanding of the deformation mechanism in the oxygen-added Ti–25Nb based SMAs.

Laser powder bed fusion of a β titanium alloy: Microstructural development, post-processing, and mechanical behaviour

β-Titanium alloys demonstrate unique properties, especially their low elastic modulus, good balance of strength and ductility, and strong heat treatment response. In this study, pre-alloyed powder of a β-Ti-alloy Ti–34Nb–13Ta–5Zr-0.3O (TNTZO) was processed using Laser Powder Bed Fusion (LPBF). Dense builds that demonstrate a full β microstructure with limited texture were achieved following process optimisation, with an elastic modulus of 56.5 GPa, tensile strength of 756 MPa, elongation-to-failure of 20 %, and recoverable strain of 1.3 %. Due to the high oxygen content, the β→α′′ deformation induced transformation was supressed, which resulted in a typical elastic-plastic stress-strain behaviour unlike the double-yielding behaviour typically experienced in superelastic Ti-alloys. The alloy was particularly sensitive to ageing heat treatments that resulted in needle α-precipitation, with tensile strengths exceeding 950 MPa, elastic modulus of ∼80 GPa, and recoverable strain of 1.5 %, yet at the expense of a reduced elongation-to-failure of 9 %. Transmission electron microscopy and electron backscattered diffraction investigations revealed the deformation mechanism was slip-dominated with no trace of twinning or stress induced phase transformation.

A three-dimensional phase-field model for studying the orientation-dependent interface evolution in stress-induced martensitic phase transformation

In this study, we address the challenging task of predicting the motion of interfaces in stress-driven martensitic phase transformations within shape memory alloys. The novelty of our approach lies in the introduction of a monolithically solved thermodynamic-based phase-field method, specifically tailored for large strain conditions at the nanoscale for three-dimensional problems. To achieve this, we have developed a custom finite element software seamlessly integrated into the FEniCS open-source framework, providing a sophisticated and efficient tool for the examination of nanostructure evolution. Our investigation delves into five distinct and complex scenarios under diverse loading conditions for two– and three-dimensional problems, each presenting unique challenges: (i) a straightforward uniaxial tension scenario featuring a square domain with a pre-existing martensitic nucleus; (ii) the evolution of interfaces in a square sample incorporating a circular central nanovoid under biaxial tensile stress; (iii) the analysis of a rectangular beam subjected to horizontal and vertical compressive loads; (iv) the assessment of an initially voided rectangular beam experiencing mixed loading conditions; and (v) the three-dimensional simulations of cubic-to-tetragonal phase transformation using various orientation of the habit plane. In contrast to prior studies, our analysis not only explores the standard factors of habit plane reorientation and strain transformation values but also delves into the impact of nanovoids on austenite–martensite interface evolution.

Atomistic Simulation of the Effect of H-Phase Precipitate on the Transformation Temperatures and Stress-Induced Phase Transformation in Ni-Rich NiTiHf

AbstractPrecipitation hardening is considered the most feasible method for strengthening NiTiHf alloys. In order to design the optimum aging treatment to form precipitates, it is crucial to understand the effect of precipitates on the thermomechanical behavior of these alloys. In this research, the effect of H-phase precipitates was studied on the martensitic and superelastic behavior of Ni-rich NiTiHf. Using atomistic simulations, two scenarios for formation of precipitates, resembling the short and long aging time of the alloy, were considered. In the first case a single and large precipitate was embedded into the center of NiTiHf matrix, and in the second case eight fine precipitates were inserted into the model. Upon the calculation of the transformation temperatures, the models with precipitates showed higher austenite start and finish temperatures. Moreover, by simulating the stress-induced phase transformation, it was found that the presence of fine precipitates inhibits the formation of different martensite variants leading to smaller transformation strains.

Nondissipative Martensitic Phase Transformation after Multimillion Superelastic Cycles.

Superelastic alloys used for stents, biomedical implants, and solid-state cooling devices rely on their reversible stress-induced martensitic transformations. These applications require the alloy to sustain high deformability over millions of cycles without failure. Here, we report an alloy capable of enduring 10×10^{7} tensile stress-induced phase transformations while still exhibiting over 2% recoverable elastic strains. After millions of cycles, the alloy is highly reversible with zero stress hysteresis. We show that the major martensite variant is reversible even after multimillions of cycles under tensile loadings with a highly coherent (11[over ¯]0)_{A} interface. This discovery provides new insights into martensitic transformation, and may guide the development of superelastic alloys for multimillion cycling applications.

On the superelastic behavior during spherical nanoindentation of a Ni-Ti shape memory alloy

Nanoindentation, the most widely-used probe for small-scall mechanical property evaluation, has been increasingly adopted for exploring the local behavior of shape memory alloys (SMAs). Herein, we explore the influence of the testing parameters (i.e., peak load, indenter radius, loading/unloading rate, and cyclic loading) on the superelastic behavior of a Ni-Ti SMA at room temperature, at which it is in the austenitic state, during spherical nanoindentation. The possible underlying mechanisms for measured response due to each of the testing parameters are discussed in terms of the roles of forward/reverse stress-induced phase transformations, dislocation activity, latent heat evolution, and geometric compatibility of the interfaces during the post-yield deformation.

A deep-neural network potential to study transformation-induced plasticity in zirconia

Zirconia (ZrO2) ceramics uniquely exhibit transformation-induced plasticity, allowing plastic deformation prior to failure, setting them apart from most other ceramics. However, our understanding of ZrO2 plasticity is hindered by the challenge of simulating stress-induced atomic-scale phase transformations, owing to lack of an efficient interatomic potential accurately representing polymorphism and phase changes in ZrO2. In this work, we introduce a novel deep neural network interatomic potential, DP-ZrO2, constructed using a concurrent-learning approach. DP-ZrO2 reproduces properties of various ZrO2 phases, matching their phase diagrams as well as transformation pathways with accuracy comparable to ab initio density functional theory. Leveraging DP-ZrO2, we conducted molecular dynamics simulations of temperature-induced interphase boundary migration and nanocompression. These simulations demonstrate the potential’s efficiency and applicability in studying deformation microstructures involving phase transformations in ZrO2. Our approach opens the door to large-scale simulations under complex loading conditions, which will shed light on the conditions favouring ZrO2 transformation-induced plasticity.

Imparting high elastocaloric cooling potential to NiTi alloy by two-step enhancements

The large adiabatic temperature change during the stress-induced phase transformation in the superelastic NiTi alloy makes it a leading candidate material for solid-state elastocaloric cooling applications. However, NiTi with a uniform grain structure generally offers either large cooling capacity or low energy dissipation, but not both. In an earlier study, we demonstrated that the alloy with graded grain sizes, obtained using differential annealing of heavily cold-worked sheets, can overcome this intrinsic limitation. However, non-transformable components (residual martensite and amorphous phases), which are introduced into the microstructure during cold rolling, impair the full exploitation of the cooling potential of the graded NiTi. Here, we introduce an intermediate processing step, namely post-deformation annealing, which eliminates the undesirable phases while maintaining nanocrystallinity, before imparting a microstructural gradient. Results show that the synergy between various microstructural elements results in a significant enhancement in the cooling capacity while keeping the energy dissipation low. Moreover, the functional fatigue performance of the graded alloy is also preferable to that of the conventional coarse-grained NiTi. The micromechanical reasons behind these improvements are elucidated by recourse to detailed experiments.

Interrelationships of stress-induced martensitic phase transformation and pitting corrosion in iron-based shape memory alloys

Orientation dependence of stress-induced martensitic transformation under compression and the influence of a corrosion attack on superelastic properties were investigated for Fe42.7Mn34.7Al13.4Ni7.7Cr1.5 (at.−%) single crystals. The results of incremental strain tests show that the crystallographic orientation has a considerable impact on the superelastic performance, eventually resulting from the formation of twinned or detwinned martensite to accommodate strain as well martensite variant interaction. In order to investigate the effect of a corrosive environment on the mechanical performance and martensitic transformation, compression specimens were immersed in a 5.0 wt.−% NaCl solution for 24 h before tested in incremental strain tests. The immersion of the compression specimens revealed a partial surface corrosion attack including localized pitting corrosion. The localized corrosion attack increased the number of active martensite plates, most probably due to an induced multiaxial stress state. Further investigations on specimens subjected to −6% compressive strain revealed that areas with retransformed martensite serve as nucleation zones for corrosion damage. Stress-induced corrosion cracks developed, which eventually deteriorate functional response.

Studying the effects of Nb on high-temperature deformation in TiAl alloys using atomistic simulations

Intermetallic γ(TiAl)-based alloys find their application as high-temperature materials for aero engine and automotive components. Microstructure optimization and microalloying play key roles in optimizing these alloys. Several pioneering experimental works showed improved mechanical properties of γ(TiAl)-based alloys containing Niobium (Nb). Despite Nb being a key alloying element, its contribution remains debated, if not least understood, due to the TiAl microstructure's complexity with hierarchical interfaces. This work examines the effects of Nb on the high-temperature deformation behavior of TiAl alloys using atomistic simulations. These revealed that Nb alloying retarded the stress-induced phase transformation of γ → α2, favoring a refined microstructure with the dislocation sources from microstructure boundaries and interfaces at high temperature and improving thus the ductility. Our microstructure-informed atomistic models reveal a comprehensive picture of the underlying nanomechanical events.

Achieving prominent high-temperature mechanical properties in a dual-phase high-entropy alloy: A synergy of deformation-induced twinning and martensite transformation

Dual-phase high-entropy alloys are renowned for their favorable balance of strength and ductility at ambient conditions. However, their mechanical properties, especially the associated deformation mechanisms at elevated temperatures, remain less explored. In this study, the AlCoCrFeTi0.5Ni2.5 HEA consisting of FCC (i.e., L12) and BCC (i.e., B2 + A2) phases was subjected to compressive test at elevated temperatures ranging from 500 to 800 °C. The results demonstrate that this HEA exhibits excellent high-temperature mechanical properties up to 700 °C, superior to most refractory HEAs and Inconel 718 superalloy. Notably, its yield strength surpasses 1000 MPa, with pronounced strain-hardening evident at 600 °C. Upon reaching 700 °C, despite strain-softening occurring at the late deformation stage, the yield strength remains above 900 MPa. Microstructural analysis of the sample deformed at 600 °C indicates increased stacking faults and deformation twins in the FCC phase. Additionally, the BCC phase displays a high density of dislocation entanglements and nanoscale martensite lathes. It is revealed that the high-temperature twins in the FCC phase are triggered by the pre-existing local chemical ordered domains, while the martensitic laths in the BCC phase are activated via stress-induced phase transformation driven by stress concentration at the B2/A2 interface. The synergistic effect of multiple deformation mechanisms operating in both the FCC and BCC phases significantly enhances the strain-hardening capability, contributing to the remarkable mechanical properties at elevated temperatures. These findings provide valuable insights for developing dual-phase HEAs with outstanding mechanical properties over an extensive range of temperatures.

Strength-ductility synergy of an additively manufactured metastable high-entropy alloy achieved by transformation-induced plasticity strengthening

This study investigated the microstructures and mechanical properties of a metastable high-entropy alloy (HEA) Fe34Co34Cr20Mn6Ni6 produced by laser powder bed fusion (LPBF) and compared them with those of an as-cast one. The LPBF-processed HEA exhibited a face-centered cubic (FCC) structure due to the high cooling rate of the laser-induced melt pools. In contrast, the as-cast HEA featured a mass of hexagonal close-packed (HCP) phase within the FCC matrix due to the elemental segregation resulting from low cooling rates. The LPBF-processed HEA exhibited superior strength-ductility synergy when compared to its as-cast counterpart. The yield strength, ultimate strength, and plasticity of the LPBF-processed HEA were 305 MPa, 808 MPa, and 18.9 %, respectively, which were much higher than those of the as-cast HEA (171 MPa, 463 MPa, and 7.3 %). This strength-ductility synergy was attributed to the in-situ formation of a fine HCP phase through the stress-induced phase transformation (TRIP) effect. The fine HCP phase provided abundant FCC/HCP interfaces, thus enhancing strong back stress hardening and facilitating the deformation uniformity. In contrast, the as-cast HEA displayed coarse and straight FCC/HCP interfaces that hindered back stress hardening. Moreover, the interaction between the pre-existing HCP phase and the stress-induced HCP phase in the as-cast HEA tended to cause stress concentration and subsequent crack initiation, leading to reduced ductility in the as-cast HEA. These findings are expected to provide valuable insights for a better understanding of additively manufactured TRIP-assisted HEAs.

Synergistic toughening effect of SiC whiskers and particles in ZrO2–Al2O3–SiC ceramics

Zirconia ceramics have a good application prospect in the high-tech fields, whereas their potential utilization is highly limited by their mechanical properties. To fabricate zirconia based ceramics with superior mechanical properties, SiC whiskers (SiCw) and SiC particles (SiCp) were selected as the toughening phases for the preparation of ZrO2–Al2O3–SiC ceramics, and an advanced sintering technique called as oscillatory pressure sintering (OPS) was applied in the present work. The mechanical properties of such ceramics with 5 vol% SiCw and 10 vol% SiCp were significantly improved. The Vickers hardness increased to 15.26 GPa while the bending strength reached 917 MPa, and the fracture toughness rose to 6.83 MPa·m1/2. The toughness of the ceramics was improved by synergistic toughening effects including whisker toughening, stress-induced phase transformation toughening and particle dispersion toughening. Furthermore, SiCp and ZrO2, Al2O3 and SiCp, ZrO2 and SiCw as well as Al2O3 and SiCw formed a well-matched coherent phase boundary. The semi-coherent relationship was also generated at the phase boundary of SiCp and SiCw.

Cryogenic temperature deformation behavior and shape memory mechanism of NiTiFe alloy

The excellent shape memory properties of NiTiFe alloys make them a popular choice for tube connection components and actuators in the aerospace industry. However, in order to obtain these properties, the alloy must undergo pre-deformation at specific cryogenic temperatures to induce the martensitic phase transformation. Despite their widespread use, the deformation behavior and shape memory mechanism of NiTiFe alloys at cryogenic temperatures remain unclear. To address this, we conducted a study investigating the deformation behavior and shape memory mechanism of Ni47Ti50Fe3 alloy at temperatures ranging from −190 °C to 150 °C using tensile tests, free recovery tests, and EBSD analysis. Our findings suggest that the deformation behavior of NiTiFe alloy can be classified into four classes corresponding to different deformation mechanisms. At temperatures above the Md (−15 to −30 °C), dislocation slip and {114}B2 deformation twinning occur without reversible strain. However, reversible and irreversible strains occur simultaneously at temperatures between −50 to −90 °C. At temperatures ranging from −110 to −150 °C, the reorientation/detwinning of the R-phase, stress-induced martensitic phase transformation, and yield stage of martensite occur in sequence. When the deformation temperature is within the range of −165–190 °C, the reorientation/detwinning of martensite occurs during the stress platform stage, and irreversible strain occurs during the yield stage of martensite. The best shape memory effect of the NiTiFe alloy is observed at deformation temperatures near Mf (−180 °C). Moreover, the reverse phase transformation temperatures increase with the increasing deformation amounts, even without plastic deformation. The temperature-dependent deformation map of NiTiFe alloy was obtained based on the tests conducted in this study, from which the influence of deformation temperatures on the different critical stresses and the deformation mechanism under different temperature conditions can be determined.

High-strain-rate deformation: Stress-induced phase transformation and nanostructures in a titanium alloy

Microstructural evolution in adiabatic shear bands of a Ti-10V-2Fe-3Al (wt.%) alloy subjected to high strain-rate dynamic loading was investigated in detail via high-resolution transmission electron microscopy (HRTEM), focusing on the underlying plastic deformation mechanisms. The alloy after solution treatment consisted of a coarse body-centered cubic β single-phase microstructure, which exhibited double-yield and stress-collapse characteristics. The former was a result of stress-induced martensite transformation accompanied by the formation of nanotwins in the martensite, and the latter was caused by thermal softening stemming from dynamic recovery. Substantial grain refinement with three orders of magnitude grain size reduction occurred in the center of adiabatic shear bands due to severe plastic deformation along with dynamic recovery. Multiple deformation mechanisms in the adiabatic shear bands were identified, including the formation of face-centered orthorhombic α″ martensite, {111}α″ type I nanotwins, and hexagonal close-packed α phase, where distinctive nano-twinned structures and phase transformation from α″ to α with an orientation relationship of {1¯11}α″//{1¯101}α were observed. The transition area of the adiabatic shear bands contained mainly high-density dislocation regions and plate-like structures with relatively fewer nanoscale grains, where the transition from nanokinks to nanotwins along with phase transformation was also revealed, corroborating that kink bands served as nanotwin nucleation sites. The mechanisms of the microstructural evolution in relation to the mechanical response during the high strain-rate dynamic loading were discussed.

Development of modulation, pairing mechanism, and slip system with optimum vanadium substitution at Bi-sites in Bi-2212 ceramic structure

Present study focuses extensively on the change in electrical, superconducting and microhardness parameters with partial substitution of trivalent V+3 impurities replacing Bi+3 ions in Bi-2212 ceramic compound with the aid of dc electrical resistivity and microhardness test measurements. Experimental findings, calculation results, and phenomenological discussions provide that the optimum vanadium substitution level is found to be x = 0.01 in the Bi2.0-xVxSr2.0Ca1.1Cu2.0Oy (Bi-2212) ceramic system for the highest conductivity, crystallinity quality, superconducting, and mechanical performance features depending on the decreased microscopic structural problems. All the findings are wholly verified by scanning electron microscopy (SEM) and X-Ray diffraction (XRD) analyses. The dc electrical measurements indicate that the optimum vanadium ions support the pairing mechanism for the formation of new polaronic states in the clusters of microdomains, and hence expand superconducting energy gap due to the enhancement of amplitude part of pair wave function in the spin-density wave systems. The excess vanadium content degrades all the basic thermodynamics and quantum mechanical quantities mentioned due to the stress-induced phase transformation. Numerically, the Bi-2212 advanced ceramic matrix prepared by the optimum vanadium impurity is noticed to present the smallest residual resistivity value of 0.08 mΩ cm, room temperature resistivity value of 8.84 mΩ cm, and broadening degree of 0.36 K. Similarly, the ceramic material is found to possess the highest residual resistivity ratio of 3.05, carrier concentration number of 0.153041, critical transition offset and onset value of 84.66 K and 85.02 K, respectively. Besides, the microhardness findings reveal that the same compound with the least sensitivity to the applied test loads exhibits the largest Hv value of 4.799 GPa, Young's moduli of 393.303 GPa, yield strength of (0.969 GPa), and elastic stiffness coefficient of 15.5574 (GPa)7/4 under the applied test load of 0.245 N. The XRD investigations show that the presence of optimum vanadium impurity supports the formation of a high superconducting phase, c-axis length, and average crystallite size. All the findings are morphologically confirmed by the SEM images. It is found that the crystallographically best crystallinity quality and view of surface morphology is observed for the optimum vanadium substitution level. All in all, new higher properties for the conductivity, crystallinity quality, surface morphology, superconducting, and microhardness parameters based on the optimum vanadium replacement encourage the Bi-2212 crystal system to use in much more application places.

Residual stress distributions around indentations and crack in 3Y-TZP ceramics measured using piezo spectroscopy

The residual stress state around indentation and crack in 3Y-TZP ceramics is studied by piezo spectroscopy. The use priority of A1 (≈468 cm−1) peak position is determined by comparing the offset of A1 peak position and A2 (≈648 cm−1) peak position under low pressure and high pressure. The plastic deformation zone is successfully peeled off through the widening of half height width under stress, and the residual stress in the elastic deformation zone around the indentation and crack is predicted more accurately using the Yoffe model. The results show that there is no T-M transformation in the low-pressure zone, so the residual stress distribution is consistent with the Yoffe model results. The residual stress around the crack in the high-pressure zone is completely contrary to the prediction of Yoffe model, because the stress induced phase transformation mechanism causes the residual compressive stress of the highest 8 GPa and 80 vol% of the phase variable at the crack tip.

An interatomic potential for ternary NiTiHf shape memory alloys based on modified embedded atom method

NiTi-based high temperature shape memory alloys (HTSMAs) can operate in high temperature applications, where binary NiTi cannot function. NiTiHf is among the most popular HTSMAs due to its lower preparation cost and good thermal stability. Various aspects of material properties of NiTiHf and the effect of different factors, such as composition, heat treatment and precipitates, on its behavior is yet to be understood. Molecular dynamics (MD) simulations can provide insights to acquire such an understanding. However, MD simulations of NiTiHf have not been possible due to the absence of a reliable interatomic potential, which is a necessary tool for such simulations. In this study, density functional theory (DFT) simulations were employed and a ternary Second Nearest Neighbor Modified Embedded Atom Method (2NN MEAM) potential was calibrated for NiTiHf. To perform this study, the related unary and binary potentials were calibrated by fitting the values of their reproduced physical properties to the DFT results. The final ternary MEAM potential was checked for reliability and transferability by performing MD simulations. The results showed that the developed potential can appropriately capture the temperature-induced and stress-induced martensitic phase transformations in NiTiHf.

Stressed during cycling: Electrochemically induced mechanical deformation in Ni-rich cathode materials

The polycrystalline architecture of Ni-rich cathode materials faces complex stresses during electrochemical cycling. Recently in Matter, Wang et al. discussed different modalities of the O3-O1 phase transformation due to electrochemically induced mechanical deformation using aberration-corrected scanning transmission electron microscopy and applying an artificial-intelligence-assisted super-resolution algorithm. The polycrystalline architecture of Ni-rich cathode materials faces complex stresses during electrochemical cycling. Recently in Matter, Wang et al. discussed different modalities of the O3-O1 phase transformation due to electrochemically induced mechanical deformation using aberration-corrected scanning transmission electron microscopy and applying an artificial-intelligence-assisted super-resolution algorithm. Direct observation of chemomechanical stress-induced phase transformation in high-Ni layered cathodes for lithium-ion batteriesWang et al.MatterFebruary 27, 2023In BriefMechanical degradation and phase transformation are two main causes of the failure of battery cathodes. Aided by deep-learning-aided super-resolution imaging, we discover that severe chemomechanical deformation during battery operation triggers phase transformation and the formation of bending bands and kinks in layered oxide cathodes. The failure mechanism uncovers the connection between mechanical degradation and phase transformation in layered oxides, and it provides useful guidance for the development of advanced layered cathodes for next-generation lithium-ion batteries. Full-Text PDF

On the nonlinear analysis of pre-strained shape memory alloy beams

We present a theoretical and numerical investigation of the transverse dynamic response of monolithic Shape Memory Alloy (SMA) beams under the effect of axial pre-strains. The SMA beam is taken as benchmark structure to evaluate the effect of (axial) pre-strain on either the free or the forced dynamics. The combination of the static stress, produced by the pre-loading conditions, with the dynamic stress, associated with the vibratory response, affects the occurrence of the stress-induced SMA phase transformation hence providing a mechanism to passively tune the dynamic response. Particular attention is given to the effect that different pre-strain levels have on the overall ability to dissipate mechanical energy, that is on the effective damping. The numerical model of the SMA beam accounts for both material and geometric nonlinear behaviors. The nonlinear material behavior is due to the SMA phase-transformation and it is modeled via the one-dimensional improved Brinson’s model (including tension–compression asymmetry), while the geometric nonlinear behavior is due to large displacements occurring during the phase transformation and it is accounted for via von Kármán assumptions. The resulting model is solved numerically via the finite element method and used to evaluate both the free and the forced response of the beam. The free response analysis suggests the existence of optimal pre-strain levels to achieve maximum damping capacity, while the forced response highlights the occurrence of nonlinear dynamic features, such as bifurcation. In both cases, it is found that the level of pre-strain can significantly affect the dynamic response as well as the effective damping. The results presented in this work provide useful guidelines to understand the dynamics of continuous SMA structures under pre-strain and the ability to tune either their resulting dynamics or dissipation properties.