Large Elongation Research Articles

Digital Image Correlation and Finite Element Computation to Reveal Mechanical Anisotropy in 3D Printing of Polymers

In this study, we propose to revisit the mechanical anisotropy inferred to printed ABS polymers using fused deposition modelling by combining digital image correlation (DIC), mechanical testing and finite element computation. Tensile specimens are printed using different design orientations and raster angles. Monitoring of deformed samples is performed, and strain fields are derived for each configuration. Finite element modelling of the 3D-printed material behaviour is considered to shed more light on deformation mechanisms. Experimental results show that a heterogeneous strain field develops, leading to more significant strain localisation for samples printed with the main dimension aligned with the building direction. The optimal printing angle allowing the filament to be crossed at -45°/+45° shows the best behaviour with even larger elongation at break compared to the raw material. However, digital image correlation based on optical imaging shows that a limiting scale exists for revealing the effect of filament orientation on strain localisation. Finite element results reveal the nature of the strain localisation as related presence of porosity close to the frame and the development of asymmetrical filling within the printed structure.

Digital image correlation to reveal mechanical anisotropy in 3D printing of polymers

ABSTRACT In this work, we propose to study the mechanical anisotropy inferred in printed acrylonitrile butadiene styrene polymer using fused deposition modelling by combining digital image correlation and mechanical testing. Tensile specimens are printed utilising different design orientations and raster angles. Monitoring of deformed samples is performed and strain fields are derived for each configuration. The results show that a heterogeneous strain field develops leading to a more significant strain localisation for samples printed with the dimensions mainly aligned with the building direction. An optimal printing angle allowing the filament to be crossed at −45°/+45° shows the best behaviour even with a larger elongation at fracture compared to the raw material. The digital image correlation based on optical imaging indicates, however, scaling limits to reveal the effect of the filament orientation on strain localisation.

Multifunctional MXene sediment-based composite film for electromagnetic interference shielding and joule heating

Owing to outstanding conductivity, hydrophilicity and large specific surface area, MXenes are widely applied for energy storage, electromagnetic interference shielding, sensors, and biomedicine. However, the exfoliation and delamination process to prepare single-layer MXenes is apparently low-efficiency, remaining a great amount of abandoned MXene sediment (MS) wastes. Herein, considering the appreciable electrical conductivity of MS, a flexible composite film was fabricated by integrating MS and waterborne polyurethane (PU). The as-synthesized MS-PU films exhibit maximum tensile strength of 25.4 MPa and large elongation of 51.4%, which subsequently leads to high toughness of 10.9 MJ m−3. Furthermore, the MS-PU films with small thickness (<50 μm) present good EMI shielding efficiency (∼30 dB) and fast Joule heating performance (thermal response <20 s). This work explores the practical application of MXene sediments for EMI shielding and Joule heating, thus promotes the full utilization of the whole MXene industry.

Enhancing strength and ductility in a near medium Mn austenitic steel via multiple deformation mechanisms through nanoprecipitation

High-Mn austenitic steels, usually deformed via the TWIP (twinning induced plasticity) mechanism, suffer high cost and other technical issues (e.g., hot-dip galvanizing, welding, etc.) from the high Mn content. Nevertheless, decreasing the Mn content would result in a shift of deformation mechanisms from TWIP to TRIP (transformation induced plasticity), usually causing quasi-cleavage brittle fracture. Herein, we report that by massive nanoprecipitation of coherent disordered particles, the grain sizes of a near medium Mn austenitic steel are successfully refined to 0.9 ± 0.4 μm, leading to a significant stacking fault energy increment of 6.4–7.9 mJ m–2 and accordingly, the transition of deformation mechanism from TRIP to multiple deformation mechanisms, namely, stacking faults, dislocation slip, nanotwinning and ԑ-martensite transformation. Moreover, the high-density of coherent nanoprecipitates effectively refines ԑ martensite and nanotwins from 20–500 nm and 10–50 nm to a few atomic columns and 1–15 nm, respectively. More importantly, these deformation mechanisms were sequentially activated at different deformation stages, resulting in a consistently high work hardening rate. Based on the synergistic refinement effects of grains, twins and martensite and the transition of deformation mechanism, a near medium Mn ultrafine-grained (UFG) austenitic steel with 15 wt.% Mn is developed, which shows a unique combination of high tensile strength (1210 ± 19 MPa) and large elongation (72 ± 6 %). These findings provide a new route to addressing the trade-off between the Mn content and mechanical performance of high-Mn austenitic steels which could facilitate their widespread applications.

Inhomogeneity of microstructure and mechanical properties in compression-type bulk formed specimens

The effect of elongation and spreading in a material on strain and microstructure inhomogeneity during compression-type bulk forming processes was investigated to improve the strain homogeneity of the materials. For systematic investigation, four different compression-type forming processes, namely wire flat rolling, plate flat rolling, wire caliber rolling, and uniaxial compression, were compared. Strain inhomogeneity and macroscopic shear bands (MSBs) were clearly observed during the compression-type bulk forming processes based on a comparative study on the shape change, effective strain and hardness distributions, and microstructural evolution in twinning-induced plasticity steel. The flat-rolled wire had the largest strain inhomogeneity, followed by the caliber-rolled wire, compressed specimen, and flat-rolled plate in the listed order. The inhomogeneity of the strain distribution along the horizontal direction tended to increase with the pure spreading during the forming process. Meanwhile, the inhomogeneity of the strain distribution along the vertical direction increased with decreasing elongation during the process. Therefore, a small pure spreading and large elongation of the specimen result in more homogeneous and higher quality products in the compression-type bulk forming process. For instance, the flat-rolled plate exhibited weak MSBs and low strain inhomogeneity because of the small pure spreading and large elongation during the forming process.

Novel Species and Records of Dictyosporiaceae from Freshwater Habitats in China and Thailand.

China and Thailand are rich in fungal diversity with abundant freshwater resources that are favorable for numerous fungal encounters. Resulting from this, the majority of the Dictyosporiaceae species reported were from these two countries. During the investigation on the diversity of lignicolous freshwater fungi in the Greater Mekong Subregion, eleven collections of cheirosporous species on submerged wood were collected from lentic and lotic habitats in China and Thailand. Phylogenetic analysis that combined nuclear small-subunit ribosomal RNA (SSU), internal transcribed spacer region (ITS), nuclear large subunit ribosomal RNA (LSU) and translation elongation factor 1α (tef 1-α) loci revealed six new species: Dictyocheirospora chiangmaiensis, D. multiappendiculata, D. suae, Digitodesmium aquaticum, Vikalpa grandispora and V. sphaerica. In addition, four known species were also identified and reported based on morphological and phylogenetic evidence. The detailed descriptions and illustrations of these taxa are provided with an updated phylogenetic tree of Dictyosporiaceae.

Multistimuli-Responsive PNIPAM-Based Double Cross-Linked Conductive Hydrogel with Self-Recovery Ability for Ionic Skin and Smart Sensor.

Multistimuli-responsive conductive hydrogels have been appealing candidates for multifunctional ionic skin. However, the fabrication of the multistimuli-responsive conductive hydrogels with satisfactory mechanical property to meet the practical applications is still a great challenge. In this study, a novel poly(N-isopropylacrylamide-co-sodium acrylate)/alginate/hectorite clay Laponite XLS (PNIPAM-SA/ALG/XLS) double cross-linked hydrogel with excellent mechanical property, self-recovery ability, temperature/pH-responsive ability, and strain/temperature-sensitive conductivity was fabricated. The PNSAX hydrogel possessed a moderate tensile strength of 290 kPa at a large elongation rate of 1120% and an excellent compression strength of 2.72 MPa at 90%. The hydrogel also possessed excellent mechanical repeatability and self-recovery ability. Thus, the hydrogel could withstand repetitive deformations for long time periods. Additionally, the hydrogel could change its transparency and volume once at a temperature of 44 °C and change its volume at different pHs. Thus, the visual temperature/pH-responsive ability allowed the hydrogel to qualitatively harvest environmental information. Moreover, the hydrogel possessed an excellent conductivity of 0.43 S/m, and the hydrogel could transform large/subtle deformation and temperature information into electrical signal change. Thus, the ultrafast strain/temperature-sensitive conductivity allowed the hydrogel to quantitatively detect large/small-scale human motions as well as environmental temperature. A cytotoxicity test confirmed the good cytocompatibility. Taken together, the hydrogel was suitable for human motion detecting and environmental information harvesting for long time periods. Therefore, the hydrogel has a great application potential as a multifunctional ionic skin and smart sensor.

Achieving high strength and large elongation in a strip casting microalloyed steel by ageing treatment

The microstructure and mechanical properties of a Nb–V microalloyed steel produced by strip casting in as-coiled and aged conditions were investigated using scanning electron microscopy, electron backscatter diffraction, X-ray diffraction, transmission electron microscopy, atom probe tomography and tensile tests. Tensile test results show that, after ageing at 650 °C for 5 min, accompanying an increase of yield strength from 698 ± 3.6 MPa to 758 ± 7.9 MPa, the elongation increases from 7.1 ± 0.4% to 12.6 ± 0.4% simultaneously. Microstructural analysis shows that both the as-coiled and aged specimens possess a microstructure predominantly comprising a mixture of acicular ferrite and bainitic ferrite. Hardness tests for specimens aged at different temperatures show very similar peak hardness values but higher ageing temperature requires less time for peak ageing. Ageing treatment leads to a decrease of dislocation density, which is responsible for the enhancement of elongation for aged specimens, while Nb–N-rich and Nb–V–N-rich clusters develop successively during ageing, which contributes to the increase of yielding strength after ageing. The strengthening contributions from solid solution, dislocations, grain boundaries and clusters were calculated, and the results indicated that dislocations and grain boundaries are the dominant strengthening mechanisms for the current strip casting steels.

Spatially heterogeneous microstructure in in-situ TiO-reinforced Ti6Al4V/316L functionally graded material fabricated via directed energy deposition

The strength–ductility trade-off is challenging for metal materials fabricated using conventional techniques. Directed energy deposition (DED), which can manufacture functionally graded materials (FGMs) with spatially heterogeneous microstructure, offers a potential solution to this problem. Here, a spatially heterogeneous microstructure which consisted of equiaxed, irregular, and columnar grains from top to bottom regions was realized in a DED-fabricated Ti6Al4V/316 L FGM. In building direction, the steep temperature gradient in the bottom region promoted the epitaxial growth of columnar grains. The columnar grains in the middle and top regions were restrained by the heterogeneous nucleation of in-situ formed TiO particles and the increasing constitutional supercooling, ultimately inducing the irregular and equiaxed grains. The equiaxed grains in the top region contributed to superior strength and wear resistance, while the irregular and columnar grains in the middle and bottom regions correlated with large elongation. Hence, FGM integrates the high strength, superior ductility, and excellent wear resistance. Furthermore, the strength–ductility synergistic mechanism and heterogeneous microstructure formation mechanism, including heterogeneous nucleation of the in-situ formed TiO particles and columnar-to-equiaxed transition, were unveiled. • Spatially heterogeneous microstructure was obtained in Ti6Al4V/316 L FGM. • The TiO particles for heterogeneous microstructure formation were in-situ formed. • Ti6Al4V/316 L FGM shows the trade-off between strength and ductility. • The refined grains in the middle region contribute to the sustained good ductility.

Development of high strength potato starch nanocomposite films with excellent UV-blocking performance: Effect of heat moisture treatment synergistic with ligninsulfonic acid

The preparation biodegradable polymeric materials with both high strength and toughness remain elusive. In this thesis, potato starch (PS) nanocomposite films were fabricated through heat moisture treatment (HMT) synergistic with lignosulfonic acid (LA) nanoparticles (HMT-PS/LA). The results of mechanical properties indicated the optimal heat moisture treatment conditions and LA content were 110 ℃, 25% and 7 wt%, respectively. The fabricated HMT-PS/LA nanocomposite films exhibited a high tensile strength (TS) of 53.6 ± 1.6 MPa and a large elongation at break (E%) of 80.25 ± 2.9%, respectively, which were 1478% and 43.6% higher than those of PS film. In addition, the water content (WC) and water vapor permeability (WVP) of the HMT-PS/LA film decreased by 28% and 47.23%, respectively. Moreover, the HMT-PS/LA film presented superior UV-blocking performance and good biodegradability in four normal environments. Thus, this paper provided an innovative design strategy to obtain an outstanding polymer material with integrated strength and toughness.

A pendulum actuator for environmental vibration isolation based on magnetostrictive composite material

In precision optical experiments, optical devices are usually suspended by pendulum systems to isolate environmental vibration. However, a traditional pendulum vibration isolator only isolates the horizontal vibration. Here, a new type of pendulum actuator, which bases on giant magnetostrictive composite material, is proposed to achieve environmental vibration isolation. The core element in actuator is a flexible wire, which is made of a thin quartz fiber embedded in epoxy resin-bonded magnetostrictive composite material with Terfenol-D particles. The designed flexible wire is deformable in vertical direction and capable to isolate the vertical vibration. The experiments are performed to verify the performance of the actuator. The response of the actuator shows great linearity with a sensitivity of 0.78 μm/A to the driving current. It also shows a large elongation range up to 5.9 μm in the linear area. Furthermore, performance of actuator on environmental vibration isolation is tested. The peak-to-peak value of vibration along vertical direction can be reduced by 17.5 dB with no negative impact on vibration along horizontal direction, which corroborates the capability of the novel pendulum actuator to isolate the environmental vibration in precision measurement.

First report of Leaf Spot Caused by Paramyrothecium foliicola on Tomato (Solanum lycopersicum) in China.

Tomato (Solanum lycopersicum) is a staple vegetable across the world. In October 2019, leaf spots were observed on tomato (cv. Tianmi) in a greenhouse in JiZhou District Tianjin, China(117°10 'E; 39°55 'N). Symptoms initially appeared as small brown spots, which gradually expanded and turned into circular, oval or irregular spots (some spots with distinct concentric zones). In severe cases, some spots coalesced and eventually covered the whole leaf. Disease incidence ranged between 12 and 18%. Twenty symptomatic leaves from five plants were collected and cut into small pieces, surface disinfested in 2% NaClO for 60 s, rinsed three times in sterile water, and subsequently plated on potato dextrose agar (PDA). Plates were incubated at 25°C in the dark for 7 days. A total of 102 isolates were obtained and 92 isolates had the same morphology. Colonies were initially white with abundant aerial mycelia and formed sporodochia with conidial masses in olivaceous green concentric rings. All isolates formed single-celled, hyaline, and rod-shaped conidia were 4.91 to 7.43 (avg. 6.53±0.72) × 1.41 to 2.45 （avg. 2.11±0.30）μm with rounded ends (n=50). Conidiophores were highly branched. These characteristics resembled a Paramyrothecium-like fungus (Lombard et al. 2016). The genomic DNA of three representative single-spored isolates TJJXPF1-3 were extracted and the internal transcribed spacer (ITS) region, β-tubulin (tub2), large subunit ribosomal RNA (LSU), calmodulin (cmdA) and translation elongation factor 1-alpha (tef1) genes were amplified and sequenced using the primer pairs ITS4/ITS5 (White et al. 1990), Bt2a/Bt2b (Glass and Donaldson 1995), LR0R/LR5 (Rehner and Samuels 1995; Vilgalys and Hester 1990), CAL-228F/CAL2Rd (Carbone and Kohn 1999; Groenewald et al. 2013) and EF1-728F/EF2 (O'Donnell et al. 1998), respectively. All sequences were deposited in GenBank (ITS: MW463444, OM368178, OM368179; tub2: MW269542，OM714930，OM714931; LSU: OM349050, OM397398, OM390582; cmdA: MW280443, OM350474, OM350476; tef1: MW560083, OM350475, OM350477). BLASTN analysis showed 99.3-100% similarity with reference isolate QB1 of P. foliicola (MK335967, MT415353, MT415362, MT415356 and MT415359). Multilocus phylogenetic analysis showed that TJJXPF1-3 best grouped with the P. foliicola clade, which was identified by morphological characteristics and phylogenetic analysis. To fulfill Koch's postulates, pathogenicity tests were conducted by spray-inoculation with a conidial suspension of isolate TJJXPF1 prepared with distilled water (1×105 conidia/mL) on five 45-day old tomato plants. Three healthy plants were sprayed with sterile water as control. All treatments were incubated in an artificial climate chamber (25°C, 80% RH, 12h light/12h dark ). After two weeks, leaf spots were observed on all inoculated plants, which were similar to those in the greenhouse of JiZhou District, while control plants remained asymptomatic. Additionally, the pathogens were reisolated from symptomatic leaves and three representative isolates TJJXPF4-6 were identified as P. foliicola. The pathogenicity tests were repeated thrice. To our knowledge, this is the first report of leaf spot caused by P. foliicola on tomato in China. This disease could be a serious threat to tomato production in the future. Our findings will help to differentiate this disease from other leaf spot-like diseases and develop disease control strategies.

Molecularly Engineered Unparalleled Strength and Supertoughness of Poly(urea-urethane) with Shape Memory and Clusterization-Triggered Emission.

To address the challenge of realizing multifunctional polymers simultaneously exhibiting high strength and high toughness through molecular engineering, ultrastrong and supertough shape-memory poly(urea-urethane) (PUU) is fabricated by regulating: i) the reversible cross-links composed of rigid units and multiple hydrogen bonds, and ii) the molecular weight of soft segments. The optimal material exhibits an unparalleled strength of 84.2MPa at a large elongation at a break of 925.6%, a superior toughness of 322.8MJm-3 , and remarkable fatigue resistance without fracture. The repeated stretching of this material induces an irreversible deformation, which, however, can be rapidly recovered by heating. Moreover, all samples are capable of temporary shape fixation at -40°C (recovering the original shape at 30°C) and exhibit blue fluorescence when excited at the optimum wavelength, which is ascribed to clusterization-triggered emission (CTE) due to the formation of microphase-separation structures. Thus, the adopted approach provides a solution to a long-standing problem and paves the way to the realization of intrinsically luminescent shape-memory materials exhibiting both ultrahigh strength and ultrahigh toughness.

Achieving high ductility in a 1.4 GPa grade medium Mn lightweight TRIP/TWIP steel with hierarchical lamellar structure

The present work reports a tri–phase hierarchical lamellar structure to tailor the ultra–high yield strength and high ductility balance in a novel Si–Al added medium Mn lightweight TRIP/TWIP steel. The warm–rolled sample was subjected to small cold rolling and low–temperature tempering to obtain the nano–scale twins and martensitic laths in the austenitic matrix, together with the hard δ–ferrite with nano–precipitates. The yield strength of 1403 MPa was obtained in the tempered sample, which is 370 MPa higher than the warm–rolled counterpart. Interestingly, the hard zone (δ–ferrite) confined the propagation of the plastic strain, leading to an intrinsic hetero–deformation induced (HDI) strengthening effect. The large ductility of 30% was ascribed to the large yield point elongation and the enhanced strain hardening after the Lüders strain, which is closely associated with HDI hardening and extra TRIP/TWIP effects.

Improvement of high-temperature strength of 6061 Al matrix composite reinforced by dual-phased nano-AlN and submicron-Al2O3 particles

Nano-AlN and submicron-Al2O3 particles were simultaneously utilized in a 6061 Al matrix composite to improve the high-temperature strength. According to the SEM and TEM characterization, nano-AlN and submicron- Al2O3 particles are uniformly distributed in the Al matrix. Brinell hardness results indicate that different from the traditional 6061 Al matrix alloy, the aging kinetics of the composite is obviously accelerated by the reinforcement particles. The T6-treated composite exhibits excellent tensile properties at both room temperature and elevated temperature. Especially at 350 °C, the T6-treated composite not only has a high yield strength of 121 MPa and ultimate tensile strength of 128 MPa, but also exhibits a large elongation of 11.6%. Different strengthening mechanisms of nano-AlN and submicron-Al2O3 particles were also discussed in detail.

Ultrahigh yield strength and large uniform elongation achieved in ultrafine-grained titanium containing nitrogen

In this study, we systematically investigated the influences of nitrogen content and grain size on the tensile properties and deformation behaviors of titanium at room temperature. By high-pressure torsion and annealing, we obtained ultrafine-grained (UFG) Ti-0.3 wt%N alloy with a fully recrystallized microstructure, which combined an unprecedented synergy of ultrahigh yield strength (1.04 GPa) and large uniform elongation (10%). The hardening and strain-hardening mechanisms of Ti-0.3 wt%N alloy were comprehensively studied via deformation substructure observation and first-principles calculations. It is revealed that the contributions of nitrogen to the excellent strength/ductility balance in UFG Ti-0.3 wt%N were twofold. On one hand, nitrogen atoms inside the grains strongly impeded the motion of <a> dislocations on prismatic plane due to the shuffling of nitrogen from octahedral to hexahedral site, giving rise to a six-fold increase in the friction stress relative to pure Ti. Moreover, the greatly reduced stacking fault energy difference between prismatic and pyramidal planes in Ti-0.3 wt%N alloy facilitated an easier activation of <c+a> dislocations, which contributed to an enhanced strain-hardening rate. On the other hand, some nitrogen atoms segregated near the grain boundaries, a phenomenon discovered in α-titanium for the first time. These segregated nitrogen atoms served as an additional contributor to the high yield strength of UFG Ti-0.3 wt%N, by raising the barrier against dislocation slip transfer between grains. Our experimental and theoretical calculation work provide insights for the design of affordable high strength titanium without a large sacrifice of ductility, shedding lights on a more widespread use of this high strength to weight ratio material.

Application of a sparse mixed regression method to design the optimal composition and heat treatment conditions for transformation-induced plasticity steel with high strength and large elongation

The chemical compositions and heat treatment conditions for obtaining low-alloyed transformation-induced plasticity (TRIP) steel were designed using a sparse mixed regression method (SMRM) that automatically and spontaneously selected several regression models. The input data concerning the elemental compositions (Fe, C, Si, Mn, Cr, Ni) and austempering conditions were collected from published reports. The SMRM-based analysis of these data established three models, which each proposed conditions for the alloy and process for obtaining high strength and large elongation. Experimental results confirmed that all three sets of conditions provided bainite with retained austenite, which was necessary for the low-alloyed TRIP steel. The tensile tests revealed that all three cases exhibited strengths >1.6 GPa and elongations >11%. Evaluating the metallurgical parameters highlighted two different design concepts, in one of which key factor is to reduce the Mn content, which is different from most of the conventional approach for preparing low-alloyed TRIP steel.

On the Wake Dynamics of an Oscillating Cylinder via Proper Orthogonal Decomposition

The coherent structures and wake dynamics of a two-degree-of-freedom vibrating cylinder with a low mass ratio at Re=5300 are investigated by means of proper orthogonal decomposition (POD) of a numerical database generated using large-eddy simulations. Two different reduced velocities of U*=3.0 and U*=5.5, which correspond with the initial and super-upper branches, are considered. This is the first time that this kind of analysis is performed in this kind of system in order to understand the role of large coherent motions on the amplification of the forces. In both branches of response, almost 1000 non-correlated in-time velocity fields have been decomposed using the snapshot method. It is seen that a large number of modes is required to represent 95% of the turbulent kinetic energy of the flow, but the first two modes contain a large percentage of the energy as they represent the wake large-scale vortex tubes. The energy dispersion of the high-order modes is attributed to the cylinder movement in the inline and cross-stream directions. Substantially different POD modes have been found in the two branches. While the first six modes resemble those observed in the static cylinder or in the initial branch of a one-degree of freedom cylinder in the initial branch, the modes not only contain information about the wake vortexes in the super-upper branch but also about the formation of the 2T vortex pattern and the Taylor–Görtler structures. It is shown that the 2T vortex pattern is formed by the interplay between the Taylor–Görtler stream-wise vortical structures and the cylinder movement and is responsible for the increase in the lift force and larger elongation in the super-upper branch.

Mechanical properties of toughened windmill palm fibre with different chemical compositions

Windmill palm fibres are well-known plant fibres exhibiting the largest elongation at break. In this study, lignin or hemicellulose was removed from windmill palm fibres in a targeted manner to prepare materials with different chemical compositions. The structure and mechanical properties of the windmill palm fibres were analysed using in situ scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetry, X-ray diffraction analysis and tensile testing. The large elongation at break was attributed to the unwinding of the single fibre, the micro cracks and the small degree of orientation (<62 %). On a microscopic scale, the lumen shape of fibre cross section influences the local stress distribution. The hemicellulose-removed fibres exhibited a high breaking strength of 236 MPa with deterioration of the thermal property. The binding force between single fibres is the weakest after lignin removal. The removal of hard lignin softens the fibres and increases the elongation at break to >30 %.

Development of Ti-Mo-Fe alloys combining different plastic deformation mechanisms for improved strength-ductility trade-off and high work hardening rate

Titanium-based biomaterials are the gold standard for orthopedic implants; however, they are not generally suitable for the manufacture of intravascular stents. Their low strength-ductility trade-off and low work hardening rate are their main limitations. However, Ni-free alloys are desirable for such application in order to avoid allergic reactions caused by the high Ni-content materials currently applied. Therefore, in this study, three alloys of the Ti-Mo-Fe system (Ti-8Mo-2Fe, Ti-9Mo-1Fe and Ti-10.5Mo-1Fe) were designed to present high strength-ductility compromise and high work hardening rate. Their microstructures, mechanical properties and plastic deformation mechanism were investigated. Athermal ω precipitates were observed in the β matrix of all solution-treated alloys. In the solution-treated β matrix of the Ti-9Mo-1Fe alloy, additional nanometer-sized α" particles were detected by transmission electron microscopy (TEM). Although the combined TWIP/TRIP effects were expected by the design method on the Ti-8Mo-2Fe and Ti-9Mo-1Fe alloys, no TRIP effect was actually observed. In fact, stress-induced martensitic (SIM) transformation occurred mainly at the {332}<113> twins/matrix interfaces for all the strained microstructures and acted as a localized stress-relaxation mechanism, delaying the fracture. Based on the electron backscatter diffraction (EBSD) analyses, in the Ti-8Mo-2Fe and Ti-10.5Mo-1Fe alloys, the formation of a dense network of {332}<113> twins was responsible for their high and steady work hardening rates (1370 and 1120 MPa) and large uniform elongations (22% and 34%). The absence of SIM α" as the primary mechanism of plastic deformation and solid solution hardening of Fe resulted in their high strengths (yield strength of 772 and 523 MPa). In Ti-9Mo-1Fe, the formation of mechanical twinning was hindered, resulting in limited strain-hardening capability and low uniform elongation (6%). The nanometer-sized α" particles in its β matrix along with the athermal ω precipitates are thought to impair the mechanical twinning and the ductility of this alloy.