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Astrocytes are critical regulators of the immune/inflammatory response in several human central nervous system (CNS) diseases. Emerging evidence suggests that dysfunctional astrocytes are crucial players in seizures. The objective of this study was to investigate the role of transient receptor potential vanilloid 4 (TRPV4) in 4-aminopyridine (4-AP)-induced seizures and the underlying mechanism. We also provide evidence for the role of Yes-associated protein (YAP) in seizures. 4-AP was administered to mice or primary cultured astrocytes. YAP-specific small interfering RNA (siRNA) was administered to primary cultured astrocytes. Mouse brain tissue and surgical specimens from epileptic patient brains were examined, and the results showed that TRPV4 was upregulated, while astrocytes were activated and polarized to the A1 phenotype. The levels of glial fibrillary acidic protein (GFAP), cytokine production, YAP, signal transducer activator of transcription 3 (STAT3), intracellular Ca(2+)([Ca(2+)](i)) and the third component of complement (C3) were increased in 4-AP-induced mice and astrocytes. Perturbations in the immune microenvironment in the brain were balanced by TRPV4 inhibition or the manipulation of [Ca(2+)](i) in astrocytes. Knocking down YAP with siRNA significantly inhibited 4-AP-induced pathological changes in astrocytes. Our study demonstrated that astrocytic TRPV4 activation promoted neuroinflammation through the TRPV4/Ca(2+)/YAP/STAT3 signaling pathway in mice with seizures. Astrocyte TRPV4 inhibition attenuated neuroinflammation, reduced neuronal injury, and improved neurobehavioral function. Targeting astrocytic TRPV4 activation may provide a promising therapeutic approach for managing epilepsy. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13311-022-01198-8.

2.25Cr–1Mo–0.25V base metal (BM) and welded metal (WM) with different temper embrittlement states were obtained by isothermal temper embrittlement test. The ductile–brittle transition temperature and the carbide size of temper embrittled 2.25Cr–1Mo–0.25V BM and WM increased with the isothermal tempering time. The increase in temper embrittlement time leads to a decrease in yield strength (YS) and ultimate tensile strength (UTS). Hydrogen embrittlement (HE) can decrease the ductility and increase YS and UTS of the material. The hydrogen embrittlement sensitivity and microstructure analysis both show a combined effect of HE and temper embrittlement. The deeper the temper embrittlement, the more sensitive the material to HE. When the hydrogen content in the material is low, the WM is less susceptible to HE due to its welding defects.

[Purpose] This study aimed to explore whether trunk kinesiology taping (KT) can improve trunk function, mobility, and balance in post-stroke patients with hemiparesis. [Participants and Methods] We conducted a single-group pre-post design pilot feasibility study. Thirteen individuals with post-stroke hemiplegia were recruited for this study. All patients received therapeutic trunk KT on the skin, representing the direction of fibres of the trunk muscles underneath. We used the Trunk Impairment Scale (TIS) and Trunk Control Test (TCT) to measure trunk function, Fugl-Meyer assessment (FMA) for balance, limits of stability (LOS) to evaluate balance, and the modified Rivermead mobility index (MRMI) to assess mobility in post-stroke patients. All measures were assessed before and immediately after the intervention. [Results] No adverse effects were found and all patients completed the trial. Compared to the baseline, TIS scores were significantly increased after KT, whereas no changes in TCT score were detected. The directional control of LOS was significantly improved, while no significant changes were seen in the other parameters of LOS, FMA-balance, and MRMI scores. [Conclusion] The results of this investigation show that trunk KT has immediate effects that improve certain trunk functional and balance parameters in stroke patients.

In this paper, the effects of load ratio and temperature on fatigue crack growth (FCG) rates for commercial titanium alloy (CP-Ti) base metal and its weldment are investigated by experiments. Results show that the fatigue crack growth (FCG) rate of weldment is slower than that of base metal, which is mainly due to the difference of the microstructures between them. The microstructures at the weld are coarse grains and acicular martensite, which can reduce the FCG rate of weldment. The effect of load ratio on FCG rate will gradually weaken or even disappear with the increase of temperature. Also, the effect of temperature on FCG rate will gradually weaken or disappear with the increase of secondary cracks on the fracture surface. The results of finite element simulation show the FCG rate will be increased with the increase of plastic zone size and plastic strain, the increase of load ratio and temperature will reduce the FCG rate difference between weldment and base metal.

In this work, fatigue crack growth behavior of commercial pure titanium (CP-Ti) under different load levels is carried out considering the degree of plastic deformation of crack tip. Results show that there are great differences in the stage of crack stable growth in different loading conditions. In the same crack growth rate, strain energy and plastic zone in high load ratio are much higher than those in low load ratio, when crack growth rate is low. However, when crack growth rate is high, the differences of strain energy and plastic zone between these two loading conditions are much smaller. More plastic strain energy will be consumed and a wider range of plastic deformation in crack tip will be required in the high load amplitude. It seems that ΔK and ΔJ cannot describe these phenomena, while ΔJac and Δ J ac ′ proposed in this paper may be more suitable to describe these phenomena in the fracture surface. In different loading conditions, at the late stage of crack growth, the fracture morphologies are all dimples. The data in all the conditions obey the Paris’ law mode, with the same coefficient and index in the rapid growth stage using the parameter Δ J ac ′ .

The tensile properties and creep behaviours of a pure titanium (TA2) welded joint are discussed based on the digital image correlation technique. The mechanical properties of welded, heat-affected, and base metals were evaluated separately and demonstrated significant differences. The global creep constitutive models for a TA2 welded joint were determined considering the influence of stress and the threshold stress of local regions. Subsequently, the full-field creep strain of the welded joint is described using a partition method. A modified power law constitutive model for full-field creep, related to creep stress and distance from the welding centreline, is proposed to predict the creep strain with high precision at any local position. The tensile and creep tests prove that the global deformation and mechanical properties of the TA2 welded joint are significantly different from those of TA2 and the local region. To design welded components, the effects of the difference between local properties and global properties, as well as the global response of the welded joint, must be considered.

At present the orthotropic pressurized metal structure is generally used as the isotropic one, ignoring the anisotropic characteristics of material caused during rolling process. At the same time, the elastic stress analysis design method is commonly used in pressure vessel, and the load capacity coming from plasticity of material has not been utilized. Therefore, elastic-plastic analysis of orthotropic pressurized structure is of great theoretical significance and engineering value. In present paper the limit load of orthotropic titanium cylindrical shell under internal pressure was studied. By finite element method with twice elastic slope criterion the variations of limit load for orthotropic and isotropic titanium cylindrical shells under different diameter-thickness ratios were investigated. The effect of orthotropic mechanical property on limit load of titanium cylindrical shell was discussed. At the same time, the difference of limit loads between orthotropic and isotropic titanium cylindrical shells was compared. The calculation results show that the limit loads of orthotropic and isotropic titanium cylindrical shell increase with the diameter-thickness ratio, and the limit load of orthotropic titanium cylindrical shell increases more obviously. Additionally, if the yield strength of isotropic cylindrical shell is the same as or close to the yield strength of circumferential direction for orthotropic titanium cylindrical shell, the difference of limit load is smaller. While the yield strength of isotropic cylindrical shell is much different from the yield strength of circumferential direction for orthotropic titanium cylindrical shell, the difference of the limit load is higher.

Low cycle fatigue (LCF) behavior of CP-Ti along transverse direction under symmetrical strain and stress-controlled modes was compared systematically. For the strain-controlled tests, tension-compression asymmetry (TCA) has little effect on LCF behavior due to the negligible compressive mean stress. For the stress-controlled tests, TCA is detrimental to LCF resistance. The microstructure evolution during cycling deformation was characterized by EBSD and TEM to identify different deformation mechanisms. It was found that strain cycling deformation was dominated by dislocation slip and exhibited the transition from planar slip to wavy slip with the increase of strain amplitude. For the stress-controlled tests, tensile twinning together with dislocation slip accommodated the increased ratcheting deformation. The strain-life curve under stress-controlled tests is lower than that at strain-controlled tests due to the heterogeneous plastic deformation caused by ratcheting deformation. In order to obtain a unified fatigue life prediction model for different control modes, a novel effective strain range related model was proposed by introducing the TCA factor into the original Manson–Coffin relation. Furthermore, the application of this effective strain range related model was extended to the condition of asymmetrical stress cycling by correcting fatigue ductility coefficient and exponent.

In order to understand the effects of cyclic asymmetry and control mode on low cycle fatigue (LCF) behavior of CP-Ti along rolling direction (RD), symmetrical strain and stress-controlled fatigue tests were conducted in this paper. LCF behavior of CP-Ti along RD under different control modes was systematically compared from the aspects of cyclic response, microstructure evolution and fatigue life with the technique of electron backscatter diffraction (EBSD) and scanning electron microscope (SEM). It was found that cyclic softening resulted by dislocation slip dominates strain-controlled fatigue. On the contrary, cyclic hardening dominates stress-controlled fatigue at high stress amplitude, leading to a higher cyclic stress-strain curve. Owing to asymmetrical hysteresis loop, compressive ratcheting strain is accumulated in stress-controlled LCF test despite of the fully reversed stress cycling. EBSD results show there is a transition of deformation mechanism from dislocation slip to dislocation slip and twinning dominated cyclic deformation with the increase of compressive ratcheting strain. Meanwhile, GOS analysis and SEM observation indicate that the appearance of massive twins results in the heterogeneous plastic deformation and micro-cracks are favorable to be initiated in the twin abundant area. Besides, compressive ratcheting strain has significant effects on fatigue crack growth as the fracture surface presents the serious abrasion of cleavage facets and fatigue striations. Finally, strain-life curves under different control modes are identical, indicating that fatigue life along RD is insensitive to compressive ratcheting strain under the interaction of these factors.

The anisotropic tensile mechanical properties of pure titanium (TA2) tubes were studied by means of theoretical analysis, finite element simulation and tensile tests. Based on the stress analysis of circumferential tensile of TA2 tube, an equation for calculating the tangential force of circumferential tensile specimen was established, and the relationship among tangential force, friction and position of ring specimen was analyzed. The finite element simulation analysis of circumferential tensile process of TA2 ring specimen was carried out, which verified the tangential force equation derived from theoretical analysis. The effect of gauge length and friction on necking and tensile load was analyzed, and the optimal gauge length was selected for the ring hoop tensile test. Finally, the axial and circumferential tensile digital image correlation experiments were carried out to verify the theoretical and finite element simulation results. The friction coefficient between TA2 tube and D-blocks (using Teflon lubricant) was determined by the inverse finite element method and the friction experiment, and the true stress–strain curve of TA2 tube was obtained. The results show that the axial and circumferential mechanical behaviors of TA2 tubes are significantly different and anisotropic.

Based on the Hill yield criterion, considering three directional stress (r, θ, z) of pressure pipe, the analytical solution for limit load of orthotropic pressure pipe with constant-depth internal circumferential crack under combined pressure, axial force and bending has been derived. The effect of crack size, anisotropy of pipe material, load (pressure, moment), and pipe size on the limit load of orthotropic pressure pipe is discussed. The results show that it is necessary to consider three directional stress for thick-walled pipe, and the influence of radial stress on the limit load cannot be ignored for thick-walled pipe. The limit load of pipe with constant-depth internal circumferential crack decreases with crack size. The limit load of pipe under pure bending is only related to axial yield strength. The limit load of pipe under pure internal pressure is mainly determined by circumferential yield strength.

In this paper, the effects of pre-strain on fatigue crack growth rate are investigated considering wide ranges of load amplitudes and load ratios for commercial titanium alloy (CP-Ti). Considering the influences of load ratio and load amplitude, the effect of pre-strain on the strain energy and crack tip plastic zone size, and on the fatigue fracture mechanism have been clearly demonstrated. Besides these, how the pre-strain affects fatigue crack propagation, and therefore affects whole fatigue life have also been clearly stated. Results demonstrate that pre-strain may be more sensitive to the enhancement of fatigue crack growth resistance under high load ratio and high peak load conditions. Fatigue lives increase with increasing in the pre-strain level. With the increase of load ratio and load amplitude, pre-strain has more and more significant influence on the plastic strain energy of specimen. A high pre-strain level of 8% and a high load ratio of R = 0.8 are more sensitive to the fatigue life. Static load or static damage has the most significant contribution to the crack tip plastic deformation than fatigue load. The production of twin crystal and dislocation structure after pre-strain process will greatly ensure the enhancement of fatigue crack resistance under all loading conditions. This research will provide support to the insight of pre-strain effect on fatigue crack growth behavior of CP-Ti.

Experimental and numerical investigations are both performed to study the fracture behavior of CTS specimen of CP-Ti under I-II mixed mode loading. The results show that crack growth path and loading capability of CTS specimen are dependent on both loading angle and crack length. Or rather, crack length effect of CTS specimen on the loading capability and crack growth path (except for pure mode I) becomes more remarkable, as the component of mode I increases. Opening stress from mode I loading is the main reason, the applied mode (tensile and bending opening stress) of which is associated with the crack length of CTS specimen. It is due to the opening stress applied on the specimen, crack length effects on the transition from ductile to brittle fracture and plastic zone (except for pure mode I) ahead of crack tip are more obvious when the component of mode I is dominant, which also explain the results of loading capability and crack growth path (except for pure mode I) respectively. In addition, critical J-integrals Jc are analyzed, the results show that constraint effect on Jc of mode I dominant crack is much more remarkable than that of mode II dominant crack, which is also because of the applied style of opening stress on the specimen.

The aim of the present work is to contribute to the characterization of the biaxial tensile behavior of commercially pure titanium, under various in-plane loading conditions at room temperature, by a non-contact digital image correlation system. Several loading conditions, with load ratio ranging from 4:0 to 0:4 and displacement rate ranging from 0.001 to 0.1 mm/s, are examined. It is found that the yield strength and ultimate tensile strength of biaxial sample are greater than that of uniaxial sample, where the equi-biaxial sample shows the highest strength. It is also observed that increase in strain rate leads to remarkable improvement of tensile strength. Fractographic analysis indicates that the shape and size of dimples are load ratio and strain rate dependent. Additionally, a modified Johnson&ndash, Cook constitutive model was proposed to account for the effect of strain rate on biaxial tensile deformation. The experimental results are in good agreement with the simulated results, indicating that the proposed model is reliable to predict biaxial tensile deformation of commercially pure titanium at different strain rates.

Crack sizes, geometrical configurations of specimens and structures, as well as loading conditions have significant effect on in-plane and out-of-plane constraint effects. Safety assessment with constraint effects can effectively improve the accuracy. There are prominent discrepancies between compressive fracture and tensile fracture. Most of engineering structures are usually under biaxial loading conditions, so that the influence of biaxial compressive loading on fracture analysis with constraint effects is worth paying attention. The size effect factor (relative crack length a/W, thickness to width ratio t/W and crack inclination angle β) and load factor (lateral pressure coefficient λ) of central cracked plate (CCP) specimens with I-II mixed mode crack on constraint effects under biaxial compressive loading have been investigated through theoretical analysis and finite element analysis. In-plane non-singular T-stress (T11) and its components (Tx, Ty, and Txy), out-of-plane non-singular T-stress (T33), out-of-plane constraint parameter Tz and stress triaxiality factor h have been adopted to quantify constraint effects. It demonstrates that λ has remarkable influence on SIF, T11 and T33 under biaxial compressive loading. The effect of higher a/W (long cracks) on B11 is more noticeable when I-II mixed mode crack is closer to pure mode II crack or pure mode I crack. The proportion of shear fracture increases under biaxial compression with λ. With the increase of β, B33 decreases sharply and then increases rapidly with higher λ. Tz can directly reflect stress states and adequately describe the loss of out-of-plane constraint. The stress state of crack tip is more likely to asymptotic plane-strain condition ahead of crack tip under compression. There are crucial differences in variation range and tendency of Tz subjected to biaxial tensile and biaxial compressive loading. Moreover, Tz is insensitive to λ. Stress triaxiality factor h can illustrate in-plane and out-of-plane constraint effects including size effect and load factor (sensitive to a/W, t/W, β and λ), especially can be adopted as a unified constraint parameter for long cracks under biaxial compressive loading. The in-plane T-stress components can be directly calculated by T11 under biaxial compression. The empirical equations of KII and T11 containing size effect and load factor simultaneously are effective and convenient for applications.

Purpose: Diffuse large B cell lymphoma (DLBCL) with MYC rearrangement or double expression of MYC and BCL-2 (DE DLBCL) has a relatively poor prognosis and does not respond well to standard R-CHOP. In the current study, we aimed to investigate the efficacy and safety of R-split-EPOCH plus high dose methotrexate (HD-MTX) in the particular patient population. Methods: A total of 28 patients diagnosed with DE DLBCL or DLBCL with MYC rearrangement between January 2015 and December 2018 were included and retrospectively analyzed. All the participants underwent R-split-EPOCH plus HD-MTX as introduction therapy, with split infusion of etoposide, doxorubicin, and vincristine for 48 hours on D1-2 and D10-11, respectively. Results: The overall objective response (ORR) rate was 100%, with 24 (85.7%) complete response (CR) and 4 (14.3%) partial response (PR). The CR rate was 76.9% and 93.3% for DLBCL patients with MYC rearrangement and DE DLBCL patients, respectively. The 1- and 3-year PFS rate was 100% and 74.9%, respectively. The 1- and 3-year OS rate was 100% and 92.9%, respectively. Grade 3/4 non-hematological toxicity and grade 3/4 hematological toxicity occurred in 50% and 85.7% of patients, respectively. No treatment-related death was reported. Conclusions: R-split-EPOCH plus HD-MTX regimen is an effective and feasible treatment option for DE DLBCL and DLBCL with MYC rearrangement.

In engineering, many pressure pipes are made of steels with good plasticity, which are subject to internal pressure, axial force, shear force, bending moment, torsion moment or their combined loads. The plastic limit load is an important indicator of the load capacity of pressure pipe. According to Hill yield function, the theoretical solutions of limit load of orthotropic cylindrical pipe under various combined loads under internal pressure, axial force, shear force, torsion moment, and bending moment have been derived on the basis of elastic perfectly plastic constitutive model. The effects of radial stress on different combined limit loads of cylindrical pipe are explored and these results show that the radial stress should be considered about the limit load calculation especially for thick-walled cylindrical pipe. The interactions of various load combination are analyzed in detail and drawn with the interaction curves. For isotropic cylindrical pipe, the limit load increases with the yield strength. For the orthotropic cylindrical pipe, the limit loads of cylindrical pipe under axial force, bending moment, shear force, and torsion moment without internal pressure are only related to the axial yield strength. The limit bending moment is mainly dependent on the axial yield strength when internal pressure is lower, while the impact of the circumferential yield strength of orthotropic cylindrical pipe is obvious when internal pressure is some higher. When the axial yield strength of orthotropic cylindrical pipe is the same, the circumferential yield strength can enhance the limit axial load, limit torsion moment, and limit shear load. Under the different load conditions including internal pressure, bending moment, axial force, shear force, and torsion moment or their combined loads, the relation of limit bending moment with yield strength ratio is diverse, which is decide by the load combination, the circumferential yield strength, and the axial yield strength.

In this paper, the effect of the cold creep on fatigue crack growth rate are investigated by experiment considering wide ranges of load amplitudes and load ratios with or without certain degrees of dwell time. To further illustrate the cold creep influence, a series of finite element results are carried out. Finally fracture morphology analyses are also made to explain related crack growth behavior. Results show that fatigue crack growth rate either increases or decreases with certain degrees of hold load and dwell time imposed, depending on the values of the load amplitude and load ratio. This finding is the same as that in the fatigue life. Discussion shows that the effect of creep on fatigue crack growth can be attributed to the competition of the creep stress relaxation and creep strain. A process of inhibiting and promoting crack growth is performed. The fatigue-creep interaction diagram based on the analyses is depicted, by which the interaction between cold creep and fatigue can be well understood. Finally further studies and discussion are carried out by fracture morphology analyses from the dislocation pile-ups, which is in accordance with the finite element results from local creep behavior. This research will provide support to the clear understanding of the cold creep effects on the fatigue crack growth behavior.

Both experimental and numerical investigations are performed to study the fracture behaviors of I-II mixed mode crack for commercially pure Titanium (CP-Ti). Three different types of specimens are considered in this paper, including Compact tension shear specimen (CTS specimen), Four point bending specimen (FPB specimen) and Cracked central plate (CCP). Results show that there exist two fracture modes of these specimens, including tensile-type fracture mode and shear-type fracture mode. For single edge notched specimen, the failure mode is determined by plastic mixity parameter Mp, and the critical values of Mp distinguishing the fracture modes are dependent on the specimen geometry (CTS or FPB specimen). For central cracked plate, specimens are all in a tensile-type fracture mode. Furthermore, specimen in a shear-type fracture mode has a higher loading capability than that in a tensile-type fracture mode. And the loading capability of specimen in tensile-type fracture decreases almost linearly with Mp. Finally, constraints of these specimens are analyzed. Discrepancies of constraint between specimens increase with the component of mode I increasing. And the difference of constraint resulted from specimen type is much greater than that from crack length.

Multiple cracks have been widely observed in pressure vessels and structure components. When multiple cracks approach each other, the interaction between them could affect the stress field around the cracks. So multiple cracks should be taken into account simultaneously because the interaction could change the stress intensity factor (SIF) of the cracks. In ASME Boiler and Pressure Vessel Code Section XI, a flaw combination criterion is provided for interacting parallel surface cracks. However, the criterion for the offset distance does not consider the influence of crack size on the magnitude of the interaction and is only given by an absolute value. In present paper, firstly, SIF for parallel surface cracks is evaluated as a function of the crack front position, relative position, aspect ratio and relative size by numerical analysis based on M-integral. And the influence of the interaction on SIF is quantified. It is shown that the crack front position, relative position between two cracks, aspect ratio and relative size are important parameters to determine the interaction between parallel surface cracks. Secondly, the new combination criteria for the offset distance are proposed for the fracture evaluation based on analysis results.

This paper presents the results of mode-I and mixed-mode I/II delamination of Zirconium-Titanium-Steel clad plate by experiment and CZM (cohesive zone model) method. DIC (Digital Image Correlation) method was also used to make comparisons with CZM method in characterizing the strain field on specimen surface. Systematic parametric studies were carried out to investigate the efforts of various material and geometrical parameters. It is founded that the results of strain by DIC and CZM simulations show the same trend, but the value by DIC is sometimes lower or higher than the numerically obtained one. The results show that under different loading conditions, the interfacial resistance of the metal clad plate is of great difference, the interface loading capacity of mode-I is much smaller than that of mixed-mode I/II and Tn (strength perpendicular to the interface) of mode-I is much lower than that of mixed-mode I/II in cohesive model. The different parameters of the CZM affect the trend of the load-displacement curve at different stages for two modes. Fractographic examination shows that the shear force acts vertical to the direction of the wave, and the main morphologies of interfacial fracture are characterized by partial slip bands and dimples, which is attributed to the wave bonding characteristics of the interface of the metal clad plate. The work provides a fundamental mechanistic understanding of the fracture mechanisms in Zirconium-Titanium-Steel clad plate.

Molecular dynamics simulation was employed to study the tensile behavior of single crystal titanium nanowires (NWs) with [ 11 2 ¯ 0 ] , [ 1 ¯ 100 ] and [0001] orientations at different strain rates from 10 8 s −1 to 10 11 s −1 . When strain rates are above 10 10 s −1 , the state transformation from HCP structure to amorphous state leads to super plasticity of Ti NWs, which is similar to FCC NWs. When strain rates are below 10 10 s −1 , deformation mechanisms of Ti NWs show strong dependence on orientation. For [ 11 2 ¯ 0 ] orientated NW, { 10 1 ¯ 1 } compression twins (CTs) and the frequently activated transformation between CTs and deformation faults lead to higher plasticity than the other two orientated NWs. Besides, tensile deformation process along [ 11 2 ¯ 0 ] orientation is insensitive to strain rate. For [ 1 ¯ 100 ] orientated NW, prismatic a > slip is the main deformation mode at 10 8 s −1 . As the strain rate increases, more types of dislocations are activated during plastic deformation process. For [ 0001 ] orientated NW, { 10 1 ¯ 2 } extension twinning is the main deformation mechanism, inducing the yield stress of [0001] orientated NW, which has the highest strain rate sensitivity. The number of initial nucleated twins increases while the saturation twin volume fraction decreases nonlinearly with increasing strain rate.

Molecular dynamics was used to simulate tensile behavior of nanocrystalline titanium with ultra-small grain size ranging from 2.8 nm to 10.2 nm at the strain rate ranging from 10 8 s −1 to 10 10 s −1 . Three dimensional samples with random oriented grains containing no textures were developed by Voronoi tessellation. For all the samples, the yielding is solely controlled by GB mediated process. The inverse Hall-Petch relation between grain size and flow stress was found. The strain rate sensitivity shows increase with the decrease of grain size due to the enhancement of grain boundary (GB) mediated process. Meanwhile, it increases with the applied strain rate due to the local disorder around GBs. Remakeable grain coarsening observed in the 2.8 nm sample causes the slight increase of flow stress. Both GB mediated process and partial dislocation slips play an important role in the plastic deformation of nanocrystalline Ti. With the increase of grain size, rare twins initiated from GBs can be observed. From the size dependent dislocation density analysis, it is concluded that with the increase of grain size, dislocation related deformation contributes more to the plastic strain.

Tensile deformation of single crystal titanium nanowires (NWs) with size ranging from 3 nm to 20 nm along [0001] orientation is investigated by molecular dynamics (MD) simulations. For all NWs, the initial yielding at different strain rates is induced by the nucleation of 101¯2 twinning. Following the saturation of twin volume fraction, the size dependent transition of deformation mechanisms in twinned regions is observed. At the strain rate from 108 s−1 to 109 s−1, following the deformation twinning, the phase transformation from HCP to FCC dominates the plastic deformation of Ti NWs. By increasing sample size to 20 nm, phase transformation can be replaced by prismatic dislocation slip. At the strain rate from 109 s−1 to 1010 s−1, the critical size for the transition from phase transformation to full dislocation slip decreases with the applied strain rate. With further increasing sample size, after the saturation of 101¯2 twins, the initial single crystal NW transforms to nanocrystalline NW. Subsequent plastic deformation mechanism in the nanocrystalline Ti NW with large size is transferred from grain boundary dominate deformation to the cooperation of grain boundary deformation and dislocation activity. Furthermore, deformation mechanism map is proposed to provide a deep understanding of the plastic deformation of Ti NWs. Keywords: Molecular dynamics simulation, Titanium nanowire, Size effect, Tensile deformation mechanism

The crack tip constraint effect should be considered in the fracture assessment of structures with cracks, and the in-plane constraint and out-of-plane constraint should be illustrated simultaneously for the three-dimensional cracks in practical engineering structures. The constraint effect of central cracked plate (CCP) specimens with I-II mixed mode crack under uniaxial compression has been investigated quantitatively in present work. The relationship between T-stress components (Tx, Ty, Txy) and in-plane constraint parameter T11 has been established. The effects of a wide range of in-plane and out-of-plane geometrical configurations (including relative crack length a/W and thickness to width ratio t/W), material parameters (including elastic modulus E and Poisson's ratio ν), crack inclination angle β and friction coefficient μ corresponding to stress intensity factors (K), in-plane constraint parameter T11 and out-of-plane constraint parameters T33 and Tz at the crack tip have been calculated and discussed theoretically and numerically. It demonstrates that the constraint parameters can effectively express the stress-strain field at the crack tip. The relative crack length a/W has an influence on the in-plane and out-of-plane constraint parameters, and the thickness to width ratio t/W mainly affects the out-of-plane constraint parameters T33 and Tz. The out-of-plane constraint parameters should be considered for long cracks. There is a loss of out-of-plane constraint under compression when t/W less than or equal to 0.9, which can be much more directly and evidently investigated through the analysis of Tz than T33. The empirical equations for KII, T11 and Tz have been obtained according to theoretical analysis and simulation results, which are convenient and effective for application.

As three-dimensional (3D) atomistic simulations require much higher computational costs, two-dimensional (2D) atomistic simulations under plane strain condition are widely used to study dislocation emission from the crack tip. In order to study the difference of crack tip behavior in 2D and 3D simulations, both 2D and 3D atomistic simulations of the anisotropic crack tip response in hcp titanium were performed, as well as the comparison of simulation results with linear elastic fracture mechanics (LEFM) predictions. The comparing results find significant discrepancies of the near tip stress fields, incipient crack tip deformation and critical stress intensity factor in 2D and 3D simulations. In consistent with the theoretical predictions, crack tip plasticity is solely contributed by the inclined slip mode with a lower critical stress intensity factor than that for cleavage, otherwise an artificial cleavage behavior may be observed in 2D simulations. In contrast to this, the lower stress triaxiality near the free surface leads to an easier dislocation nucleation in free 3D simulations. Besides, the participation of the oblique slip mode improves crack tip plasticity and facilitates the activation of the inclined slip mode that cannot be activated in 2D simulations. In general, the incipient crack tip behavior observed in 3D simulations shows more consistency with experimental results.

〈 1 2 - 1 0 〉 and 〈 1 0 1 - 0 〉 oriented twin boundaries (TBs) have important roles in the modification of strength and ductility of HCP metallic materials. As microcracks may be prone to initiated from TBs, their intrinsic brittleness and ductility need to be studied. Combing atomistic simulations and theoretical calculations, it is demonstrated that the incipient crack propagation behavior along most of the two sets of TBs in HCP titanium is dominated by brittle mode at very low temperature. Nevertheless, significant dislocation activities in the later stage can hinder the crack propagation along 〈 1 2 - 1 0 〉 oriented TBs. Consequently, the ductility of 〈 1 2 - 1 0 〉 oriented TBs is generally superior to that of 〈 1 0 1 - 0 〉 oriented TBs. Furthermore, brittle-ductile transition occurs with the increase of strain rate and temperature due to dislocations emitted from the crack tip and TB site.

The effect of bend angle on plastic limit loads of pipe bends under different load conditions is presented using three-dimensional non-linear finite element analyses. Based on finite element analysis, the characteristics of deformation, stress and strain were studied and effect of bend angle on the limit load was discussed. The results show that the effect of bend angle on limit load is great both at 0°∼120° range under internal pressure, torsion moment and in-plane bending moment and at 0°∼90° under out-of-plane moment. Then existing expressions of limit load and the finite element results were compared, and the solutions of limit load under single load condition were made. The proposed unified load solutions were obtained by fitting the finite element data under internal pressure, in-plane bending moment, out-of-plane bending moment and torsion moment. The results show that the proposed unified load solutions are consistent and in good agreement with the current finite element results.

Due to the non-negligible role of T-stress on fracture parameter, T-stresses of three typical specimens, including central cracked plate (CCP), compact tension specimen (CTS) and four point bending specimen (FPB), are calculated using 3D finite element method. From the results, the tensile dominant specimen like CCP is in a lower-constraint state when the component of mode I is significant, and in a higher-constraint state when the component of mode II is significant, compared with bending dominant specimen like CTS and FPB specimens. Further, the crack initiation angles and plastic zones are assessed for the three specimens based on modified maximum tangential stress (MMTS) and modified R-criterion (MR). From the comparison, the effect of T-stresses or constraints induced by specimen geometries and loading modes play a significant role on crack initiation angle and plastic zone around the crack tip, which in turn can affect the fracture of specimen.