Maraging steel (M250) is extensively used in aerospace industries for the fabrication of solid propellant tanks in the welded and repair welded condition. The purpose of the investigation is to study the effect of multiple weld repairs on the microstructure and mechanical behavior of the alloy. The microstructure of the alloy in the as-welded condition contains two distinct heat-affected zones (HAZ) with different contents of reverted austenite. The results indicate that increased weld repair reduced the weld strength from 1722 to 1405 MPa whereas elongation increased from 5.8 to 6.1

This work presents the experimental investigation of the impact of hydrogen on the microstructural and mechanical characteristics of fastener steels using the electrochemical hydrogen charging technique. The accumulation and diffusion of hydrogen in high-strength fastener steels were reported to affect the durability of the components. Considering the failures of fasteners due to hydrogen embrittlement, it was essential to understand the effect of hydrogen content on high-strength fastener steels to find the threshold hydrogen content that can lead to hydrogen embrittlement. In this study, the behavior of 35NCD16 steel was investigated when atomic hydrogen is introduced into the crystal lattice. The effect is simulated using mechanical testing of the specimens, which have been supersaturated with hydrogen by electrolytic charging. The hydrogen contents are evaluated for specimens exposed to nascent hydrogen for different time intervals. As the primary step, the torque testing of hydrogen-charged fasteners was carried out. Further, a slow strain rate notch tensile and smooth tensile behaviors of hydrogen-charged specimens and the fractographic characteristics of the broken specimens were evaluated. A correlation between microstructure, mechanical property, and hydrogen content was established.

Abstract This article aims to summarize the work on cryogenic strength and toughness and to present the fractography of aluminum alloys. It presents case studies on the importance of understanding the fractography of aluminum alloys and the role of microstructure in the appearance of fractographic features, with variables comprised of in-plane/through-thickness anisotropy, test temperature, heat treatment condition, and the effect of welding.

Background: The dorsal venous arch (DVA) is a superficial venous network of the hand. It is formed by the union of four dorsal metacarpal veins in the middle of the dorsum of the hand. Medially and laterally the dorsal venous arch continues as basilic and cephalic veins respectively. Commonly, these veins are chosen for intravenous procedures, the most prominent being the dorsal metacarpal veins. The present study aims to study the different types of formation of dorsal venous arch in both the sexes. Methods: 100 hands of voluntary participants were studied (50 male hands, 50 female hands) in St Peter’s Medical College, Hospital and Research Institute, Hosur, Tamil Nadu. The rubber tourniquet was tied 1 hand breadth above the wrist to make the veins prominent and observed the pattern of formation of DVA with laterality and sex being noted. Results: In the present study, the formation of dorsal venous arch, commonly type 2 pattern in males and type 1 pattern in females were observed. The prominent venous pattern was observed in males and on the lateral side of the dorsal metacarpal veins. Conclusions: The present study carried out to enlighten the vascular surgeons, postgraduates, interns, paramedics and nurses regarding the knowledge of different types of the formation of dorsal venous arch of hand, so that hassle free procedures can be carried out on these superficial veins of hands at the time of routine and emergency situations.

The effects of hot rolling temperature and subsequent cooling at different cooling rates on the microstructure, texture, and mechanical properties of α + β titanium alloy Ti-6Al-4V were studied using a battery of structural and mechanical characterization tools. To this end, Ti-6Al-4V samples were subjected to a rolling reduction of 50 % below the β-transus (750°C and 850°C) and near the β-transus (950°C) temperature followed by water quenching and air cooling. Detailed electron back scatter diffraction provided information on the fraction, morphology, and orientation of the alpha and β-phases for different processing conditions and bulk texture analysis provided information on the orientation relationship at the macroscale. Mechanical properties, like hardness and modulus, were determined at different length scales using the Vickers microhardness experiment, instrumented microindentation, and nanoindentation. Hot rolling at sub β-transus temperatures (750°C and 850°C) leads to the equiaxed morphology of the α-phase and the absence of a Burgers orientation relationship (BOR) with the β-phase, whereas near the β-transus, hot rolling leads to the multi-variant lamellar morphology of the α-phase and a strong BOR with the β-phase for both the cooling conditions. Hot rolling at 850°C followed by water quenching showed an optimum combination of indentation hardness and modulus. This has been primarily attributed to the relatively low kernel average misorientation of the basal-prism-oriented grains compared with the prism-pyramidal oriented grains after indentation. The basal oriented grains are both elastically and plastically harder compared with the prism-oriented grains that are elastically soft but plastically hard. The orientation specific indentation hardness property is reflected in the microhardness property for sub β-transus deformed samples. A clear processing-microstructure-texture-mechanical property paradigm in the context of variant selection and distinct cooling rates for hot rolling of Ti-6Al-4V is established.

This study investigates the effect of a brazing thermal cycle on the microstructure and mechanical properties of Fe–Cr–Mn–Ni–C stainless steel using microstructural examination, X-ray diffraction, ferrite content, hardness, impact, and tensile testing. Stainless steel was exposed to a high-temperature brazing thermal cycle of 1180 °C for 20 min, followed by different cooling practices, including furnace, air, and water quenching. The microstructure of the as-received steel mainly comprised austenite, ferrite, sigma phase, and carbides. Air and furnace cooling resulted in the formation of a sigma phase by decomposition of the ferrite phase. The amount of sigma phase varied depending on the cooling rate, which in turn influenced the mechanical properties. Water-quenched specimens were free from the sigma phase, while furnace-cooled specimens had a sigma phase of 9

In this study, the effect of uniaxial pre-strain in the range of 1-9%, has been studied on room temperature tensile and creep behavior of aluminum alloy AA2219-T87. Tensile properties of pre-strained specimens showed an increase in yield strength up to 3% pre-strain, beyond which ductility in terms of percentage elongation was below the specification limit of 6%. Room temperature creep test results indicated that as the applied stress increases, the creep rate increases and time to failure decreases, in a linear manner. Fracture toughness of AA2219-T87 calculated based on an empirical relationship showed a decreasing trend with increasing pre-strain. Based on extensive experimental results, it is recommended to limit the amount of pre-strain to 3% during the fabrication of hardware to meet the material specifications.

The present study proposes a novel method to predict the size dependent creep behavior of bi-material joints formed by constraining a creep compliant metal, such as Sn, having varied thickness ranging from 1.4 mm to 170 µm, between stiff elastic substrates, such as Cu. A dramatic reduction in the secondary or minimum creep rate was observed with decrease in joint thickness. Finite element (FE) analysis using continuum formulations attributed this strengthening to the geometric constraints imposed by Cu, which increases the triaxiality in the joints and hence reduces the effective stress. While FE results were in close agreement with experiment in thick joints, it significantly overpredicted the creep rate of miniature joints. Further, orientation imaging revealed that microstructure varied with length scale, from bulk Sn with multiple grains to miniature joints having a few grains. The additional strengthening was captured using dislocation-based crystal plasticity (CP) creep modeling of Sn-Cu joints by incorporating this microstructural length scale, in addition to the geometric constraints. CP simulations revealed that orientation anisotropy of Sn and the constraints imposed by substrates on dislocation motion lead to higher strength in the miniature joints. Using the insights from FE and CP modeling a unified length scale sensitive model, incorporating both geometric or continuum and microstructural factors, was developed that can accurately predict the creep response of the joints of macro and meso length scale.

Extra low interstitial (ELI) grade of titanium alloy Ti6Al4V is used for the fabrication of components operating at cryogenic temperatures in satellite launch vehicles, given its excellent combination of strength and toughness up to 90 K. In the present study, test coupons required for strength and toughness evaluation were 3D printed in X, Y, Z, and 45°(along the direction of a body diagonal of an imaginary cubic build volume) orientations through laser powder bed fusion (LPBF) process and were vacuum stress relieved. Mechanical properties at room temperature met the minimum specified values against ASTM-F3001 standard in all orientations and were consistent within each orientation. However, the highest strength (~ 1080 MPa) and toughness were observed in the 45° orientation. The impact strength was in the range of 333–363 kJ/m2, and plane strain fracture toughness (KIc) values in X, Y, and 45° orientations were > 60 MPa√m. In the Z orientation, a marginally lower KIc value (58 MPa√m) was observed and is attributed to the higher probability of easier propagation of cracks in between the 3D printed layers. Microstructure in all the four orientations revealed a mixture of fine alpha (α) laths and acicular alpha prime (α′) in the transformed beta (β) matrix. Higher strength in the samples representative of Z and 45° orientations is attributed to higher dislocation density and higher grain boundary length. Higher fracture toughness observed in specimen representative of 45° orientation is attributed to the higher grain orientation spread (GOS) and lower volume fraction of pores, which results in a more tortuous crack propagation path. Fractography in all orientations showed typical ductile failure with the presence of dimples. Finally, based on the strength and toughness in different orientations, it can be concluded that LPBF processed Ti6Al4V-ELI components can be used in stress relieved condition for fracture critical aerospace applications at room temperature.

Introduction: Pregnancy-induced hypertension (PIH) is one of the risk factor in pregnancy leading to placental insufficiency which in turn is responsible for maternal and foetal morbidity and mortality. PIH causes morphological changes in placenta. Decreased placental surface area and variation in the attachment of umbilical cord on placenta are more commonly noted in PIH which hampers the uteroplacental perfusion resulting in foetal mortality and morbidity. Hence afforts were made to study the incidence of reduced placental surface area and mode of cord attachment on placenta. Materials and methods: The study was conducted in the Department of Anatomy, Sri Siddhartha medical college and Hospital, Tumakuru, Karnataka. A total of 100 (50 normal and 50 PIH) human placentae were studied. Placental surface area and mode of attachment of umbilical cord in normal and PIH pregnancy were measured and noted. This study was analysed statistically by using Unpaired t-test and Chi-square test. Results: The study revealed significantly decrease in placental surface area and also there is increased incidence of central and marginal attachment of umbilical cord in PIH cases. Conclusion: Study reveals, PIH cause morphological changes in placenta, it decreasing the uteroplacental blood flow which reduces foetal nutrition ultimately decreasing the neonatal weight. KEY WORDS: PIH, uteroplacental blood flow, neonatal weight, placental surface area and Umbilical cord.

Purpose This study aims to develop indium-based solders for cryogenic applications. Design/methodology/approach This paper aims to investigate mechanical properties of indium-based solder formulations at room temperature (RT, 27 °C) as well as at cryogenic temperature (CT, −196 °C) and subsequently to find out their suitability for cryogenic applications. After developing these alloys, mechanical properties such as tensile and impact strength were measured as per American Society for Testing and Materials standards at RT and at CT. Charpy impact test results were used to find out ductile to brittle transition temperature (DBTT). These properties were also evaluated after thermal cycling (TC) to find out effect of thermal stress. Scanning electron microscope analysis was performed to understand fracture mechanism. Results indicate that amongst the solder alloys that have been studied in this work, In-34Bi solder alloy has the best all-round mechanical properties at RT, CT and after TC. Findings It can be concluded from the results of this work that In-34Bi solder alloy has best all-round mechanical properties at RT, CT and after TC and therefore is the most appropriate solder alloy amongst the alloys that have been studied in this work for cryogenic applications Originality/value DBTT of indium-based solder alloys has not been found out in the work done so far in this category. DBTT is necessary to decide safe working temperature range of the alloy. Also the effect of TC, which is one of the major reasons of failure, was not studied so far. These parameters are studied in this work.

Aluminum alloy AA2219-T852 tubular specimens were subjected to biaxial testing. The specimens were tested under tensile as well as internal pressure simultaneously to create biaxial loading conditions with stress ratios ( λ ) of 0.33, 0.5, 1, 2 and 3. Uniaxial and biaxial tensile test results showed that biaxial yield stress (YS) increased from 4 to 15% depending upon the value of λ . Increase in YS was observed at lower λ, whereas lowest increase was observed in equi-biaxial tests compared with uniaxial YS. Theoretical yield criteria of von-Mises and Tresca were compared with experimental data and it was found that the von-Mises yield criterion was closely matching with experimental data, with less than 5% error. Based on the results obtained from the present study, components subjected to biaxial stress condition can be optimally designed.

This study investigates the effect of the joint length scale on the creep behavior of Pb-free Sn-rich Sn-3.0 wt.% Ag-0.5 wt.%Cu (SAC 305) solder-Cu joints. SAC 305-Cu solder joints having SAC solder layers of different thickness ranging from 1 mm to 50 μm were fabricated by diffusion bonding and examined using a scanning electron microscope to ascertain the role of length scale on the microstructure of the joints. Subsequently, tensile creep tests were performed at 85°C. At given nominal stress, a systematic reduction in the creep rate occurred with a reduction in joint thickness, which can be expressed by a power law. A comparison of the creep stress exponent of bulk SAC solder and the solder-Cu joints revealed that the creep mechanism was dislocation climb-controlled by core or pipe diffusion in both types of samples. The overall size-dependent creep strengthening of SAC 305-Cu joints can be attributed to the geometrical effects, which affect the macroscopic stress state, and the microstructural effect arising due to a change in the statistical distribution of Sn grains in the solder and the constraints on dislocation motion due to elastic Cu substrates. The additional strengthening imparted by precipitates in SAC solder was delineated by comparing the creep behavior of Sn-Cu joints with the SAC-Cu joints.

This study investigates the effect of length scale on the tertiary creep behavior of elastically constrained ductile metal joints. Creep tests were performed in tension on Sn-Cu joints of thicknesses ranging from 1.4 mm to 170 mu m. Sn being more creep compliant as compared to Cu undergoes creep deformation, whereas Cu remains in the elastic state. The overall creep rate and the amount of strain accumulated during the tertiary creep decreased with reduction in joint thickness. This was accompanied by a reduction in the extent of lateral contraction, especially near the fracture surfaces of the joints. Fractographs revealed a transition in the mode of creep failure from pure necking in thick joints to cavitation along with constrained necking in thin joints. A joint size dependent tertiary creep model incorporating necking and cavitation was developed to explain the observed transition in tertiary creep behavior and final failure. The model captures the effects of both joint size dependent triaxial stress state and a decrease in the size of the necking ligament with reduction in joint size. Overall, the decrease in strain accumulated during tertiary creep is attributed to smaller size of the neck and higher triaxiality in thin joints, which enhances the strain due to cavity growth and reduces that due to necking as the joint thickness reduces.

In this work, different indium solder alloys were developed and characterized for their shear properties to find out their suitability for cryogenic applications. Microstructures were investigated by backscattered scanning electron microscopy; phases were identified by energy dispersive x-ray spectroscopy and confirmed by x-ray diffraction. Solder joints were prepared using copper substrates, and shear strength of substrate/solder/substrate joints was measured at room temperature (+27 °C), cryogenic temperature (–196 °C) and after 10 thermal cycles. Highest shear strength of 47.2 and 32.5 MPa was obtained in Cu/In-32Bi-20Sn/Cu joint at room temperature as well as after thermal cycling, respectively, but at cryogenic temperature, the shear strength (67.5 MPa) of Cu/In-3Ag/Cu joint was found to be the highest.

Monel (R) 400 alloy is widely used in marine and chemical industries due to its moderate strength and high resistance to corrosive environments. In the present work, hot workability of Monel (R) 400 alloy in as-cast condition was studied using the processing maps approach. Hot-compression tests were performed in a Gleeble thermo-mechanical simulator in the temperature, T, range of 900-1200 degrees C and strain rate, epsilon, of 10-2 - 10+1 s-1. The data obtained from the tests was used to construct processing map at a true strain, epsilon, of 0.5 utilizing the modified dynamic material model (DMM) proposed by Murty and Rao. Processing map identified three stable domains for possible hot working occurring in the following T and epsilon range - Domain-1: T = 900-1200 degrees C and epsilon = 10- 2-10- 1.75 s- 1; Domain-2: T = 1150-1200 degrees C and epsilon = 10- 1.75- 10-1 s- 1; and Domain-3: T = 1100-1200 degrees C and epsilon = 10+0 - 10+1 s-1. A broad flow instability regime in the form of flow localization was also identified at all temperatures and intermediate strain rates (epsilon = 10- 1.5 - 10+0 s- 1). Complete recrystallized microstructure with discontinuous dynamic recrystallization (DDRX) as the dominating deformation mechanism was observed in Domain-3 (occurring at higher epsilon). In contrast, microstructural analysis of the deformed specimens in Domain-1 and Domain-2 occurring at lower epsilon showed limited DRX at the serrated grain boundaries with dynamic recovery (DRV) and continuous DRX (CDRX) as the operating deformation mechanisms. With the aid of the processing map along with evolved microstructures of the deformed specimens, Domain-3 was identified as the optimum "safe" regime for thermo-mechanical processing. Results obtained from the processing map are then successfully validated through industrial trial forgings performed in the T range 950-1200 degrees C. The forging process was also simulated in identical process parameters using finite element method (FEM) software DEFORM (R)-3D to study the flow behavior and effective stress and strain distribution in the forged billets.

3D printing is an advanced manufacturing technology, enabling production of complex shapes by adding material layer-upon-layer. A fuel injection system component designed with Inconel-718 nickel-based superalloy for an advanced rocket propulsion system was realized through Laser Powder Bed Fusion method. 3D printing allowed realizing the complex component having interconnected channels and having minute openings, which are impossible to manufacture by conventional manufacturing methods such as CNC machining. Detailed metallurgical characterization and mechanical property evaluation were performed to qualify the component for space application. The process helped in avoiding multiple piece assemblies for the fuel injection system and developing an integrated component within a short turnaround time. Microstructure evaluation revealed absence of any defects such as porosity, lack of fusion and microcracks. The mechanical properties were evaluated on 3D-printed test coupons in four different orientations along with the component. The fractographs in STA condition in four different orientations revealed a typical ductile fracture with the presence of dimples. Computed tomography of component was carried out and it was concluded that defects > 139 μm were not present, which is the limitation for the thickness of Inconel-718 component scanned. The formation of fine, complex channels and absence of defects > 139 μm as observed in CT, makes the component suitable for complex fuel injection operation for high-temperature space application.

Background: In cervical vertebrae, the costal and transverse elements are connected to each other around the foramen transversarium of the transverse process. The adult cervical vertebrae are characterized by the presence of Foramen Transversarium (FT) in transverse process. These transverse foramina are found to have variations in size, shape and numbers and may be absent, incomplete or duplicate, which may lead to various symptoms. Aim: To study the anatomical variations of cervical vertebrae. Materials and methods: The present observational study was performed on 182 dry human cervical vertebrae of unknown sex and age. Intact cervical vertebrae without any degenerative or traumatic disorders were included in this study. Deformed and damaged vertebrae were excluded from the study Results: Out of these 364 foramen transversarium, 98 (27%) foramen transversarium were of type-I. Type -I was the most common presentation in the present study. Type -II foramen transversarium were seen in 33 (09%) foramen transversarium. Out of 364 foramen transversarium 88 (24%) foramen transversarium were of type-III. Type-IV foramen transversarium were seen in 62 (17%) foramen transversarium. Type-V foramen transversarium were seen on 83 (23%) foramen transversarium. Out of 182 vertebrae 40 (22%) showed complete double foramen transversarium. Incomplete double foramen transversarium were seen in 24 (13%) of vertebrae. One side complete & other side incomplete foramen transversarium were seen in 04 (02%) vertebrae. Conclusion: Knowledge of such variations is important for Physicians, Neurologists Otorhinolaryngologists, radiologists and Orthopedicians. Presence of accessory foramen transversarium especially of incomplete variety, the second part of vertebral artery may be dislodged and prone to get damaged easily during posterior cervical injuries. It helps in radiological imaging, neurological diagnosis and complex surgical procedures in the cervical area. KEY WORDS: Cervical Vertebrae, Foramen transversarium, Accessory Foramen Transversarium.

Extra-low interstitial (ELI) grade of Titanium Alloy Ti6Al4V is used for the structural applications in cryogenic stages of launch vehicles due to its high strength-to-weight ratio and ability to maintain ductility and fracture toughness at cryogenic temperatures up to 77 K. Conventional manufacturing through melting–forging–machining route results in a lot of material wastage and is also time-consuming. 3D printing by Laser Powder Bed Fusion (LPBF) route was used to replace conventionally processed Ti6Al4V-ELI structural members for the launch vehicle inter-stages experiencing cryogenic temperature of 77 K. Detailed metallurgical characterization was performed on the parts to ascertain their suitability to replace conventional forged route parts for the intended application. Microstructure evaluation confirmed that no significant defects, such as porosity, micro-cracks and lack of fusion are present. The 3D printed test coupons in 4 different orientations printed along with the components were subjected to mechanical property evaluation and are meeting the specification. Fractographs of the tensile-tested specimens in the different directions exhibited typical ductile failure features of dimples. 3D printed components were subjected to computed tomography and found to be free from internal defects above acceptable limits. The results are also compared with the conventional manufacturing route in this paper.

The high-temperature deformation behavior of nickel-base superalloy IN718 was investigated in the solution-treated (ST) condition. High-temperature tensile tests were performed between 600 °C and 850 °C at strain rates of 1 × 10−3, 1 × 10−2, and 1 × 10−1 s−1. The deformation behavior of this material was analyzed using optical microscopy, scanning electron microscopy, and transmission electron microscopy. In the investigated temperature–strain rate regime, material undergoes partial precipitation, serrated yielding, and embrittlement. Serrated yielding was observed at 600 °C, 650 °C, and 700 °C and is attributed to dynamic strain aging. The appearance of serrated flow at high temperatures up to 700 °C in the ST condition can be attributed to the availability of excess Nb in the matrix. Beyond 700 °C, Nb concentration significantly decreases in the matrix due to the formation of Ni3Nb precipitate. Nb is responsible for the appearance and disappearance of serrations at high temperature. The alloy exhibits embrittlement phenomenon in the range of 750 °C to 850 °C when thermally exposed in air. The alloy shows a ductile mode of fracture when tested at 600 °C and 700 °C, whereas completely brittle fracture was observed at the 800 °C test temperature. Formation of brittle oxides at grain boundaries in the presence of atmospheric oxygen resulted in the embrittlement of the alloy at 750 °C to 850 °C. An oxidation-assisted intergranular cracking mechanism is responsible for embrittlement of this alloy, which was proved by scanning transmission electron microscopy-energy dispersive spectroscopy.