Search

This work was aimed in the relationships investigation among the microstructure, the tensile properties and the thermo-mechanical processing of a novel Ti-25Zr-1B (wt%) alloy. The alloy was evaluated under different conditions (as-cast, hot-rolled and hot-rolled-annealed). The XRD diagrams demonstrated that all specimens were completely consisted of the α and TiB phases. The results of EDS indicated that the TiB phase dissolved a certain amount of Zr, which was in agreement with the existence of TiB peaks shifting towards lower diffraction angles. The as-cast Ti-25Zr-1B alloy microstructure and the size, the morphology, the orientation, and the distribution of the TiB particles could be significantly altered by the hot-rolling process. The hot-rolling process provided an ultimate strength increase of at least 7 pct and the elongation-to-failure increase of 135 pct relatively to the as-cast sample. In addition, the annealing heat treatment could effectively modify the mechanical properties of the hot-rolled sample. The strength decreased and the elongation-to-failure increased as the annealing temperature increased, while the temperature was below 800 °C. In contrast, as the annealing temperature increased to 900 °C, the alloy demonstrated appreciably lower elongation-to-failure and higher strength compared to the annealed form at 800 °C. The mechanical properties variation of the Ti-25Zr-1B alloy series was ascribed to the microstructure evolution of the matrix alloy as well as to the morphology and volume fraction changes of the TiB particles.

In the present study, the texture evolution and mechanical anisotropy in a typical Mg–Zn–Ca alloy through hot cross rolling (CR) and unidirectional rolling (UR) were systematically studied. The results show that the rolling path greatly affects the annealed texture. The UR develops a texture with basal poles mainly distributing along the transverse direction (TD). By contrast, an ellipse-like (0002) texture with basal pole inclining largely away from the normal direction (ND) is developed after hot cross rolling and annealing. Therefore, the CR is an effective method to tailor the texture of the experimental alloy. Unfortunately, this ellipse-like texture could not reserve during the subsequent unidirectional hot rolling and annealing. Both UR and CR plates exhibit a strong planar mechanical anisotropy compared with the traditional unidirectional rolled plate. Keywords: Mg alloys, Hot cross rolling, Texture, Mechanical anisotropy

To achieve a better balance of strength and ductility for Ti-20Zr-6.5Al-4V alloy, the fully equiaxed microstructure was obtained by post-deformation annealing process following water quench. The experimental results on microstructure evolution during the applied heat treatment routes are discussed with respect to the mechanical properties.

With the aim to develop new Zr-based alloys with excellent mechanical properties, a novel Zr-0.8B (wt%) alloy was manufactured through the following steps: casting, forging, hot-rolling and annealing treatment. The microstructure and mechanical properties of the hot-rolled and annealed Zr-0.8B alloys were investigated. The microstructure of all specimens was comprised by α and ZrB2 phases. The coarse α laths and ZrB2 whiskers were significantly refined by hot rolling. Also, a high volume of dislocations and many subgrains were formed during the hot-rolling process. A high degree of recrystallization of α phase was obtained during the annealing treatment, due to the substantially stored energy in the Zr matrix and the presence of a significant amount of subgrains. The tensile strength of the annealed Zr-0.8B alloys was decreased with the increase of annealing temperature, until 800 °C, and then increased as the heat treatment temperature was further increased to 900 °C. Many factors, such as the volume fraction of ZrB2 whiskers, grain size, dislocation density, the amount of subgrains and solution strengthening, have a significant effect on the strength. However, the elongation-to-failure showed a reverse tendency compared to the tensile strength. The reasons caused fracture of the annealed Zr-0.8B alloys are primarily attributed to dislocation pile-ups and the presence of microvoids.

We report the electronic, magnetic, and optical properties of Fe–Mn co-doped SrTiO3 using density functional theory within generalized gradient approximation. The co-doping system shows a ferrimagnetic behavior. The magnetic moments of Fe and Mn atoms are reduced by the hybridization between the O atoms and metal atoms. A half-metallic characteristic is shown in the doped system. In order to investigate the influence of the co-doping on the optical properties of SrTiO3, the extinction coefficient k(ω) and refractive index n(ω) are calculated.

The effects of indium on the microstructure, transformation temperature, mechanical properties, and shape memory effect of (Ti83Ta17)85−xZr15Inx alloys were investigated. The results showed that (Ti83Ta17)85−xZr15Inx (x = 1, 3, 5)(at%) alloys were all composed of orthorhombic α"-martensitic phase. The reverse martensitic transformation starting temperature (As) was 346 °C for x = 1 and increased with increasing indium content. The Young's modulus firstly decrease then increase with the addition of Indium. When the Indium content is 1 at%, the lowest strength and the largest elongation 25.8% can be obtained. The minor addition of indium can make up for the deficiency of low plasticity and retained a relatively large shape memory recovery strain. A prefect recovery strain of 4% were obtained in all (Ti83Ta17)85−xZr15Inx alloys.

The alloying effect of Zr on β (body-centred cubic)-phase stability was investigated in α (hexagonal close packed)-type Ti–Al alloys. According to calculations and experiments, adding Zr significantly modified the β-phase stability, because Zr was identified as a β-stabilising element in these Ti–Zr–Al alloys under the solution treatment. However, the water-quenched β-phase did not continue to be preserved after aging. In addition, stress-induced α″ (orthorhombic)-phase martensite transformation would occur during deformation.

To obtain excellent mechanical properties and globular microstructure in TiZr based alloys, the variation of microstructure during hot rolling at a temperature range from α region to β region has been investigated in a TiZrAl alloy for further understanding and control of processing–structure–property relationships. Experimental results showed that when hot rolling at α region, increasing rolling temperature could enhance the progress of dynamic globularization and refine the grain structure. However, coarse grain with slender α lath appeared when rolling temperature was above the α → β transus temperature. The mechanical properties of studied alloy were also investigated with the change in rolling temperature. Outstanding mechanical properties ( σ b =1564 MPa and e =10%) were obtained when rolling at 800 °C, which was found to be the optimal rolling temperature for this alloy. The high strength and good ductility of the studied alloy make it a good candidate for a wide range of applications.

The microstructure, mechanical property behavior, and fracture characteristics of Zr–χB alloys (χ=0, 0.05, 0.3, 0.8 wt%) obtained by casting and hot-rolling were investigated. Microstructural observation indicated that the dendritic equiaxed prior-β grain morphology was slightly elongated after hot-rolling treatment. The widths of the α lath of all the hot-rolled Zr–χB alloys were similar, and the length of the α lath decreased with increasing boron concentration. Tensile test results showed that the improved strength of the Zr–χB alloys can be primarily attributed to grain refinement. Strengthening the Zr–χB alloys could also be achieved by a shear-lag model mechanism because of the high strength and modulus of the ZrB2 whiskers. The refinement of the α lath and the presence of the ZrB2 whiskers were responsible for the reduced elongation-to-failure. Fractography indicated that fracture behavior strongly depends on the orientation of the ZrB2 whiskers. The effect of this orientation on the fracture mechanisms of the ZrB2 whiskers and the Zr–χB alloys was also discussed.

Traditional fiber reinforced polymer (FRP) composite that is often fabricated from single type of reinforcement has shown its ability to replace the conventional metallic material counterparts. However, due to several stringent requirements on ductility, this has affected the performance of FRP composites for the structural applications. Therefore, hybrid composites, which combine two or more fiber reinforcements, have been introduced in order to overcome the short of traditional FRP composites. This paper investigates the mechanical properties of three different arrangements of hybrid composites made from glass fiber (plain-woven and stitched bi-axial ±45˚) and plain-woven carbon fiber. Vacuum assisted resin transfer moulding method was employed to fabricate the hybrid composite panels. Mechanical properties such as tensile strength, flexural strength and volume fraction of the hybrid composites were determined per ASTM standards. Experimental results indicate that the [CWW] 6 arrangement, where C and W are weaved carbon fiber and glass fiber respectively, were superior in terms of mechanical properties.

A series of Zr50–Ti50 (at%) alloy specimens with different treatments was prepared. Tensile test, X-ray diffraction (XRD), optical microstructure, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses were performed to investigate alloy tensile properties and microstructure. Hot-rolling process was found to have a remarkable strengthening effect. The tensile strength of hot-rolled specimens had an increase of 37% compared with solution-treated specimen (undeformed). All specimens exhibited α′-Zr structures and similar microstructures. However, a significant plasticity difference was observed in the Zr50–Ti50 hot-rolled specimens with different cooling rates. Detailed TEM microstructural analysis showed that the morphology of twins in the hot-rolled specimens was different. Most of the twins were nano-twins. It was found that the twins had effective on Zr50–Ti50 alloy plasticity, in the meantime significant effects on tensile properties due to the complicated interactions between twin boundaries and dislocations. All these findings in this work may provide a new strengthening mechanism for Zirconium-based alloys.

Abstruct The microstructure evolution and mechanical properties response of a TZAV alloy during combined thermomechanical treatments containing hot rolling, cold rolling and subsequent annealing processes are investigated. Stress induced martensitic transformation presents after cold rolling and results in transformation from β to α ″ phase. Few peaks of ω phase were observed in specimens annealed below 650 °C. The microstructure of cold rolled and low temperature annealed specimens are characterized by stretched β grains and fibrous structures. While annealed at 700 °C, the specimen has most of approximate granular α grains. The average aspect ratio of α grains increases as the annealing temperature increases. After annealing at 800 °C, the stretched β grains recrystallize into approximate equiaxed grains. Tensile testing results showed that the deformed specimens have lower strength than annealed specimens. Hardness results showed the similar trend with strength. Otherwise, the relationships between microstructural parameters and mechanical properties are also discussed in this work. Results show that the strength is greatly dependent on thickness of α grains and content of β phase but has little to do with shape parameters of α grians, conversely, the ductility is related to shape parameters but independent of thickness and content.

The joining of titanium alloy to conventional structural steel has many industrial applications. However, it is difficult to join titanium alloys to steel due to great differences in thermal, physical, and chemical properties. Among these properties, the expansion coefficient is an important physical parameter. In this study, the expansion coefficient and mechanical properties of Ti–8Cu–5.7Al–3.8Zr (wt.%) alloy were studied. According to the experimental results, the eutectoid structure, which was composed of Ti 2 Cu and α phase, was observed in both air cooled and furnace cooled TiCuAlZr alloy after annealing at 800 °C. And the furnace cooled specimen revealed a more evident eutectoid structure. The results also showed that the difference of the average thermal expansion coefficients (−60 to 80 °C) between TiCuAlZr alloy and 9Cr18 martensitic stainless-steel were only 4%, which was beneficial to join titanium alloys to stainless steel. In addition, the air cooled specimen exhibited relatively good mechanical properties. The strength and the elongation were 1050 MPa and 8.5%, respectively.

The existing forms and effects of carbon on the surface structure and hardness of ZrTiAlV alloys with various Zr contents were investigated in this study. Each sample of ZrTiAlV–C alloys with Zr content below 17.3 at.% is composed of (TiZr)C compound, a few β phases, and matrix α phase. The Zr content in the compound increases with increased Zr content in alloys. At 17.3 at.% Zr content, both ZrC and (TiZr)C compounds are simultaneously observed. Only ZrC compound in addition to solid solutions is observed when the Zr content exceeds 17.3 at.%. Comparison of the XRD results of ZrTiAlV–C alloys with those of ZrTiAlV alloys shows that the addition of carbon to ZrTiAlV alloys can restrain the precipitation of Zr–Al compound. Microstructures show that the grain size of carbide in ZrTiAlV–C alloys decreases with increased Zr content. Hardness tests show that addition of carbon markedly affects the mechanical properties of ZrTiAlV alloys as the Zr content changes. The hardness of ZrTiAlV alloys with Zr content below 17.3 at.% gradually increases. However, a rapid decrease is observed when the Zr content is 25.95 at.%. Then, a plateau is observed when the Zr content ranges from 25.95 at.% to 60.55 at.%, and a rapid increase is observed when the Zr content is 69.2 at.%. However, the curve of hardness vs. Zr content of ZrTiAlV–C alloys is characterized as a parabola. The maximum hardness of ZrTiAlV–C alloys is 53.9 HRC when the Zr content is 43.25%. The maximum hardness increases by about 11% compared with the maximum hardness of ZrTiAlV alloys with various Zr contents. Otherwise, hardness tests also indicate that the strengthening effect of carbide on the β phase is better than that on the α phase.

A Heusler Ni 50 Mn 30 Ga 1 Cu 4 alloy with the highest compressive strength has been obtained by substituting 4 at% Cu for Ga in a ternary Ni 50 Mn 30 Ga 20 ferromagnetic shape memory alloy. It is shown that the highest compressive strength of 3178.9 MPa with a fracture strain up to 13.6% can be achieved at room temperature. To date, this is the highest compressive strength reported in the Ni–Mn–Ga alloy system. The martensitic structure changes from 7M with 0 at% Cu to non-modulated T martensite with 4 at% Cu . In addition, the Cu doping markedly increases the martensitic transformation temperature from 82.1 °C to 136.6 °C. At the same time, the Curie temperature and saturation magnetization for the Ni 50 Mn 30 Ga 16 Cu 4 alloy slowly decrease due to the 4 at% Cu addition.

The effect of partial substitution of Cu for Ga on the microstructure, martensitic transformation and mechanical properties of Ni 50 Mn 30 Ga 20− x Cu x alloys was investigated by optical microscope (OM), different scanning calorimetry (DSC) and X-ray diffraction (XRD). The results show that the Ni 50 Mn 30 Ga 20− x Cu x alloys exhibit thermoelastic martensitic transformation. The martensitic transformation temperatures of the Ni 50 Mn 30 Ga 20− x Cu x sample increase remarkably with increase of Cu content, while the martensite structure of these alloys changes from 7 M to non-modulated T martensite at room temperature. In addition, the compressive strength and fracture strain of alloys are clearly enhanced with increase of Cu content, which can be attributed to the strengthening of solution.

The structural evolution and mechanical properties of Zr–45Ti–5Al–3V alloy during heat treatment are investigated. X-ray diffraction (XRD) is used to analyze the alloy phase composition. The ω phase is detected after normalizing at 773 K and 873 K. The β-phase content increases with increasing holding temperature from 773 K to 973 K. The transmission electron microscopy (TEM) images of the microstructure shows that the thickness of the secondary αs phase is remarkably dependent on the cooling rate. The phase transformation is controlled by nucleation rate during cooling from low temperature 773 K and by growth velocity when cooled from high temperatures 973 K and 1073 K. The growth of the αs phase is very slow or stops when the temperature is cooled to 939.6 K. The thickness b of the αs phase of the Zr–45Ti–5Al–3V alloy relies on the onset transition temperature during cooling T0, and cooling rate υ has been deduced as b ( T 0 , υ ) = 0.019 ( T 0 − 939.6 ) / υ based on diffusion controlled growth mechanism. Tensile test results indicate that the strength of heat-treated Zr–45Ti–5Al–3V alloy is very sensitive to cooling rate.

Deformation of the bulk metallic glasses (BMGs) and the creation and propagation of the shear bands are closely interconnected. Shearing force was loaded on Zr41.2Ti13.8Cu12.5Ni10.0Be22.5(Vit.1) BMGs by cutting during the turning of the BMG rod. The temperature rise of alloy on the shear bands was calculated and the result showed that it could reach the temperature of the super-cooled liquid zone or exceed the melting point. The temperature rise caused viscous fluid flow and brought about the deformation of BMGs. This suggested that the deformation of BMGs was derived, at least to some extent, from the adiabatic shear temperature rise.

The effects of aging on magnetic properties and phase transformation were investigated for Ni 53 Mn 23.5 Ga 23 Ti 0.5 shape memory alloy. The results show that the amount and size of Ni 3 Ti particles firstly increase and then amount of second phase decreases with the increasing aging temperature. Moreover, the transformation temperatures gradually decrease; Curie temperatures slightly decrease first and reach their minimum values at 973 K then increase with the increasing aging temperature. The saturation magnetizations firstly remain almost unchanged and then slightly decrease when aging temperature is above 973 K.

The effect of Fe elements on the total energy of Ni 2 MnGa ferromagnetic shape memory alloy was investigated. It is shown that Fe addition has little effect on the majority-spin density of state (DOS), but changes minority-spin DOS significantly. Substituting Fe for Mn decreases the total DOS of the parent phase, leading to the increase in parent phase stability. When Fe content is higher than 12.5at%, the increasing of martensitic transformation is related to the precipitation of γ phase.

The Ni53Mn23.5Ga18.5Ti5 ferromagnetic shape memory alloy has been aged under 2% constant-strain at various temperatures for 3 h, and the microstructure and martensitic transformation behaviors have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). It was found that after constant-strain aging, the amount of the Ni-rich precipitates with lenticular morphology is higher and the size of the second-phase particle is smaller when compared to that of the conventional aged samples. The martensitic transformation temperatures first decrease remarkably with the increase of aging temperature, and then increase when the aging temperature exceeds 973 K, which can be attributed to the change of the Ni-content in the matrix as well as the strengthening effect by fine Ni3Ti precipitates.

This paper presents a theoretical model to explain the quasi-supercontinuum interband emission from InGaAs/GaAs self-assembled semiconductor quantum dot lasers by accounting for both inhomogeneous and homogeneous optical gain broadening. The experimental and theoretical agreement of a room temperature (293 K) broadband laser emission confirms the presence of multiple-state lasing actions in highly inhomogeneous dot ensembles. The corresponding full-width half-maximum of the photoluminescence is 76 meV as opposed to those wideband lasing coverage at only low temperature (~60 K) from typical quantum dot lasers. A newly proposed change of homogeneous broadening with injection that occurs only in highly inhomogeneous quantum dot system is critical to account for the continuous wideband lasing but not the conventional ideas of carrier dynamics in semiconductor lasers. In addition, the analysis of threshold conditions reveals that broadband lasing only occurs when the energy spacing between quantized energy states is comparable to the inhomogeneous broadening of quantum-dot nanostructures. The study is important in providing a picture of this novel device and realization of broad lasing coverage for diverse applications, especially in the research field of short-pulse generation and ultra-fast phenomena in semiconductor quantum-dot laser.

We report on the development of InAs/InGaAlAs quantum-dash-in-well structure on InP substrate for wideband emitter applications. A spectral width as broad as 58 meV observed from both photoluminescence and surface photovoltage spectroscopy on the sample indicating the formation of highly inhomogeneous InAs-dash structure that results from the quasi-continuous interband transition. The two-section superluminescent diodes (SLDs), with integrated photon absorber slab as lasing suppression section, fabricated on the InAs dash-in-well structure exhibits the close-to-Gaussian emission with a bandwidth (full-width at half-maximum) of up to 140 nm at ~ 1.6 mum peak wavelength. The SLD produces a low spectrum ripple of 0.3 dB and an integrated power of ~ 2 mW measured at 20degC under 8 kA/cm2. The oxide stripe laser exhibits wide lasing wavelength coverage of up to 76 nm at ~ 1.64 mum center wavelength and an output optical power of ~ 400 mW from simultaneous multiple confined states lasing at room temperature. This rule changing broadband lasing signature, different from the conventional interband diode laser, is achieved from the quasi-continuous interband transition formed by the inhomogeneous quantum-dash nanostructure.

The temporal coherence functions of InGaAs-GaAs quantum-dot (QD) and InAs-InGaAlAs quantum-dash (Qdash) superluminescent diodes (SLDs) and broadband laser diodes (BLDs) are reported. Using an optical fiber-based spectral interferometer, the fabricated devices were shown to yield low coherence lengths of 4.00-12.29 mum and 33.48-74.56 mum for SLD and BLD devices, respectively. In addition, there were negligible secondary coherencies indicating that these devices have the potential for use in low coherent interferometric systems.

We demonstrate the effect of nonequilibrium carrier distribution in a self-assembled InAs-InAlGaAs quantum-dash-in-well semiconductor lasers on InP substrate. The progressive changes of electroluminescence spectrum with increasing injections show the presence of localized photon reabsorption and lasing action from different dash ensembles at room temperature as opposed to that obtained in typical self-assembled quantum-dot lasers only at low temperature below 100 K.

In this paper, the interaction between two identical, non-coplanar, semi-elliptical surface cracks is investigated. The interacting cracks are assumed to be in an infinite plate subjected to remote tension or to pure bending loads. The stress intensity factors (SIFs) for these cracks are calculated using three-dimensional linear finite element analysis. A parametric study involving the relative horizontal and vertical separation distance between the two surface cracks is carried out for a specific crack shape and crack depth to plate thickness ratios of 0.3 and 0.2, respectively. An empirical formula is derived that relates the effects of the relative positions of these cracks to their SIFs.

Gain and alpha factors were measured on InAs-InAlGaAs quantum-dash lasers with their heterostructures intermixed by either a dielectric-capping or ion-implantation technique. The laser intermixed by the dielectric-capping technique exhibits a blue shift as much as 93 nm without degrading the laser quality. In comparison, the laser intermixed by the ion-implantation technique has a larger shift but lower differential gain and higher alpha factor. The result implies that quantum-dash lasers of different wavelengths can be effectively integrated on the same chip by the dielectric-capping intermixing technique.

In this paper, the boundary element method (BEM) for two-dimensional contact mechanics analysis is employed to obtain the elastic stresses in a straight-shank symmetric attachment lug subjected to single pin-loading in the direction of 0°, 22.5° and 45° from the symmetric lug axis. Several lug geometries are considered and the effects of friction and the different conditions of fit between the pin and the lug are investigated. Some results for the contact stress distribution around the periphery of the pin-hole are presented, as are numerical values for the stress concentration factor obtained for the cases considered. Where possible, the BEM results are compared with those available in the open literature and the agreement between them is excellent. The BEM study shows that for a given lug configuration and direction of loading, the normalized stresses, and hence the stress concentration factor, depend only on the friction condition and the extent of the contact area between the lug and the pin. It is shown further that if this contact area is also fixed, the stress concentration factor varies linearly with the coefficient of friction for the range of values considered.

The authors report on the nanowires-like and nanodots-like lasing behaviors in addition to multiple-wavelength interband transitions from InAs/InAlGaAs quantum dash (Qdash) lasers in the range of ~1550 nm. The presence of lasing actions simultaneously from two different dash ensembles, after postgrowth intermixing for crystalline quality improvement, indicate the absence of optical phonon emission due to the small variation in quantized interband transition energies. This effect is reproducible and shows different lasing characteristics from its quantum dot and quantum wire laser counterparts. Furthermore, the small energy spacing of only 25 nm (at center lasing wavelength of ~1550 nm) and the subsequent quenching of higher energy transition states at higher bias level in Qdash lasers suggest the absence of excited-state transition in highly inhomogeneous self-assembled Qdash structures. However, the appearance of a second lasing line in a certain range of high injection level, which is due to the presence of different sizes of dash assembles, corresponds to the transition from smaller size of Qdash ensembles in different planar active medium. This unique transition mechanism will affect the carrier dynamics, relaxation process in particular and further indicates localized finite carrier lifetime in all sizes of Qdash ensembles. These phenomena will lead to important consequences for the ground-state lasing efficiency and frequency modulation response of Qdash devices. In addition, these imply that proper manipulation of the Qdash ensembles will potentially result in localized nanolasers from individual ensemble and thus contributing towards enormously large envelope lasing coverage from semiconductor devices.

We demonstrate the importance of multi active layer stacking in realizing a semiconductor broadband quantum-dash-in-well laser. The photoluminescence measurements show the negligible factor of largely localized inhomogeneous quantum-dash ensembles in producing ultra-wide envelope of emission.

Ni-Mn-Ga alloys possess thermoelastic martensitic transformation and ferromagnetic transition. Despite the giant magnetic-field-induced strain and stress-induced martensitic transformation developed in Ni-Mn-Ga alloys, however, little information is obtained about optical properties of Ni-Mn-Ga alloys as candidate materials in digital information storage. In this study, the optical reflectivity of Ni-Mn-Ga alloys in martensite and austenite phases has been investigated. The results reveal that the maximum reflectivity difference between the martensite and austenite phases is about 24%, indicating the promising application in phase-transition information storage. The calculated DOS shows that the effect of martensitic transformation on optical properties is attributed to the change of Ni 3 d partial DOS between the austenite and martensite phases.

Semiconductor broadband light sources are greatly in demand for highly-sensitive sensing, spectroscopy, optical telecommunications, eye-safe low-speckle sources for flash lidar and high resolution bio-imaging particularly optical coherence tomography (OCT). In this paper, we report on the observation of broadband lasing action from the InAs/InAlGaAs quantum dash (Qdash) structure. This novel device exhibits lasing action with emission wavelength coverage over 60nm at the center wavelength around ∼1.60 µm. By applying the quantum-dash intermixing (QDI) technique to the same material structure, we have successfully tuned the center lasing wavelength of the Qdash broadband laser to 1.54 µm and broadened its emission coverage over 80 nm, making it an attractive source for many novel applications in optical communications. The intrinsic response of Qdash lasers under optical modulation has been studied.

This paper reports on the measurement and analysis of the coherence function for broadband emitters such as superluminescent diodes (SLDs) and novel broadband laser diodes (BLDs) from self-assembled InGaAs/GaAs quantumdot (QD) and InAs/InP quantum-dash (Qdash) structures that emit at center wavelengths of 1150nm and 1650nm, respectively. Using the fiber-based spectral interferometry system, coherence lengths in fiber of 23 µm and 48 µm have been measured from the QD and Qdash BLDs. Larger spectral bandwidth of 137 nm and 78 nm have been measured from the QD and Qdash SLDs that yield coherence lengths in fiber of 3 µm and 10 µm, respectively. The coherence function of both BLDs and SLD reveals negligible secondary coherence subpeaks and sidelobes indicating the possibility of using these broadband sources to produce low artifacts optical coherence tomography (OCT) images.

The broadest bandwidth (80 nm) superluminescent diode (SLD) with center wavelength at 850 nm fabricated on GaAs/AlGaAs double quantum-well structure is characterized and analyzed. The broadband flat-top like spectrum and a 0.3 dB spectral modulation enable this device to produce an axial resolution of 4 mum in optical coherence tomography systems.

Authors demonstrate the generation of broadband stimulated emission in the postgrowth wavelength tuned InAs/InAlGaAs quantum-dash (Qdash) laser grown on InP substrate. The laser exhibits room temperature lasing wavelength coverage of up to 50 nm at center wavelength of ~1.57 mum. Despite the bandgap blue-shift of ~70 nm after Qdash intermixing process, the laser exhibits a broadband signature of lasing linewidth, which is comparable to the as-grown laser. The integrity of the material is retained after intermixing, suggesting its potential application in the fabrication of monolitically-integrated ultra-broadband semiconductor Qdash laser.

We study the optical gain and alpha factor of InAs/InAlGaAs quantum-dash lasers on InP substrate after being subjected to the postgrowth intermixing process. The intermixing was achieved using dielectric capping process that involves the deposition of dielectric film and subsequent rapid thermal annealing. Compared to the un-intermixed laser, we found that the intermixed lasers with a 93 nm bandgap blue-shift exhibit good material quality with improved differential gain and comparable alpha factor.

We demonstrate the effect of nonequilibrium carrier distribution in a highly inhomogeneous quantum-dash-in-well laser. The electroluminescence spectra show the presence of localized photon reabsorption and lasing action from different quantum-dash ensembles at room temperature.

We demonstrate a widened ultrabroad-stimulated emission in InAs/InAlGaAs quantum-dash laser using the postgrowth lattice-intermixing technique. The 100 nm wavelength blue-shifted device exhibits larger lasing bandwidth (~41 nm) than as-grown laser (~25 nm) with a spectral ripple of

We report on the growth of InAs quantum-dash in InGaAlAs quantum-well structure on InP substrate using molecular beam epitaxy. The influence of different growth parameters such as InAs layer thickness, quantum barrier growth temperature, and number of stacking layers on the morphology and optical properties of dash structures were studied. The results serve as useful references for improved epitaxial growth control of InAs/InGaAlAs/InP system for optical device applications.

The boundary element method (BEM) for two-dimensional numerical stress analysis is employed to investigate crack-face bridging of cracked fibre-metal laminates (FML) with cut-outs in this study. The fracture mechanics prediction of crack growth in these perforated laminates involves the interaction of the geometry and crack size, the delamination between the pre-peg and metal layers, and the extent of fibre-bridging of the crack flanks with the stress field caused by the cut-out. The present work investigates the effects of a stress concentration on the fibre-bridging stress and the stress intensity factor of a bridged crack in fibre-metal laminates. A number of cracked configurations are analyzed and the FML, ARALL2, is considered. The bridging stresses on the crack flanks are modeled in the 2-D analysis using power-law expressions and with the mechanical properties of the laminate homogenized through the thickness. An iterative scheme is employed to solve for the bridging stresses as they are not known a priori. Three dimensional finite element method (FEM) analyses are also carried out to confirm the validity of the 2-D BEM models. FML's with circular cut-outs will contain high bridging stresses near the cut-out resulting in fibre failure there, causing a reduction of the extent of fibre bridging of the crack. Results of the study show a likelihood of fibre failure near the edge of the cut-out and this could lead to a reduction of the bridging length. Comparison of the BEM with the FEM stress intensity factors for the range of problems analyzed reveals that the percentage difference is generally less than about 6%, except for a few cases when the power-law index of 0.5 is assumed. The BEM results indicate an increasing bridging stress and stress intensity factor with decreasing bridging length and the benefits of the fibre bridging of the crack are clearly demonstrated. This numerical study confirms that the 2-D BEM models employed can indeed be used to provide a quick and reasonable estimate of the stress intensity factor for a bridged crack in a FML with a circular cut-out.

The authors report the demonstration of the bandgap-tuned InAs quantum dash broadband laser with widened laser emission linewidth at room temperature using postgrowth intermixing technique. The 100 nm wavelength blueshifted, as-cleaved laser exhibits ultrabroad lasing spectral coverage of ∼85 nm at a center wavelength of 1.54 μm with a total emission power of ∼1 W per device. Compared to the as-grown laser, this laser shows broader lasing bandwidth (∼41 nm) with improved spectral ripple (

The authors demonstrate the generation of ultrabroadband stimulated emission in the quasi-zero-dimensional InAs∕InAlGaAs quantum-dash laser grown on InP substrate. The laser exhibits lasing wavelength coverage of up to 76nm at ∼1.64μm from simultaneous multiple confined states lasing at room temperature. Unlike the conventional interband diode laser, the rule changing broadband lasing signature is achieved from the quasicontinuous interband transition formed by the inhomogeneous quantum-dash nanostructure.

Stress intensity factors for semi-elliptical surface cracks in internally pressurised thick-walled cylinders of radius ratio 3 are presented for a wide range of crack sizes. These solutions were obtained using the boundary integral equation method for three-dimensional stress analysis. Only one crack shape is considered—a semi-ellipse with the length of its semi-minor axis equal to 0·6 times the length of its semi-major axis —but the ratio of crack depth to wall thickness ranged from 0·2 to 0·8. Hoop strain distributions at the outer circumference of the cylinder are also presented for the different crack sizes analysed; the results are useful for experimentally monitoring crack growth.

Using the numerical boundary integral equation (BIE) method for two-dimensional elasto-plasticity based on the quadratic isoparametric formulation, solutions for the deformations and stresses in two 2024-T81 aluminum sheets with pressurized circular holes are obtained. Results are presented showing the plastic zone developments in these structures, the variations of the stresses when subjected to the applied radial pressures at the hole peripheries, as well as the residual stress distributions when the loads are completely removed. Where appropriate, the computed solutions are compared with those obtained analytically for a similar problem.

Using the boundary integral equation method for three-dimensional elastostatics, stress intensity factor influence coefficients for a wide range of internal semi-elliptical surface cracks in cylinders with radius ratios 2·0 and 2·5 are obtained. Only one crack shape is considered, namely, a semi-ellipse with ellipse aspect ratio 0·8, but the crack depths treated range from 20% to 80% of the wall thickness. The influence coefficients obtained correspond to the stress intensity factor, K I , solutions for the cracks subjected to four different stress distributions—uniform, linear, quadratic and cubic pressure variations—on the crack faces. They can be superposed to obtain K I solutions for other stress distributions, such as those caused by internal pressure, thermal gradients and autofrettage. Numerical results are presented for all these load situations. In the case of autofrettage, the effects on K I for a wide range of overstrain conditions are considered.