One of the high-temperature materials, ferritic stainless steel (FSS), was joined using laser beam welding (LBW), which reduced intermetallic phases and grain growth. The CO2 laser was effectively applied to join AISI 409 FSS tubes of wall thickness 4 mm. The power of the laser beam, which influences mechanical and metallurgical properties, varied from 2.6 kW to 3.4 kW. No defects were observed at the weld zone (WZ). However, the lowest laser power produced an undercut at the bottom of WZ. Coarsening of grains was not observed in the microstructure at HAZ. The dendritic microstructure was found in the WZ, which consists of both axial and columnar grains. A coarse dendritic structure was formed with high laser power. The delta ferrite phase was partially transformed into martensite phase at the WZ. The dislocation fields along with substructure formation were seen in TEM micrographs. The WZ was strengthened due to the phase transformation. The tensile strength of all the joints was close to the base metal (BM). More than 20% elongation was observed except for the joint at 2.6 kW. The fracture mode was observed to be ductile in all the joints.

Friction stir processing (FSP) is considered as a prolific secondary processing method to enhance the properties of aluminium matrix composites (AMCs) by altering their microstructure. AA6061/(15 wt.

Metal matrix composites (MMCs) are treated as potential engineering material for many industrial applications. The consideration given to MMCs continues to increase owing to its sound mechanical properties, such as high specific strength and excellent corrosion and wear resistance. From an industrial viewpoint, it is essential to know the capacity of MMCs to undergo secondary processing. This study elucidates the influence of cryorolling on the microstructure, mechanical properties and wear behaviour of various aluminium-based MMCs. In particular, the aluminium matrix composites (AMCs) produced through the stir casting route undergo an additional cryorolling process in order to enhance their tensile and wear resistance properties. This type of hybrid manufacturing has gained attention because of its excellent results in producing a successful structural member. This chapter deals with the fabrication of ex-situ Al-based composites produced through stir casting followed by cryorolling. Further, the influence of particle size, volume fraction of particles and the influence of the cryorolling process on microstructure, wear and tensile behaviour are emphasized. This information can be a basis to further promote the possibilities of this hybrid manufacturing and widen its potential applications.

Single-point incremental forming (SPIF) was conducted on a 1-mm-thick commercially pure titanium grade 2 (Ti-G2) sheet metal in a CNC vertical milling unit. A hardened steel ball of 12 mm diameter was used as forming tool. Frustum cups were formed with varying spindle speeds between 300, 450, and 600 RPM. Other process parameters including the vertical step down and feed rate were kept as 0.2 mm and 300 mm/min, respectively. The metallurgical and mechanical properties of the formed material were investigated by cutting samples from the frustum cup walls. Electron-backscattered diffraction (EBSD) investigation revealed limited change in grain size with an increase in spindle speed. Dislocation density was measured by x-ray diffraction peak broadening analysis. The results indicate that an increase in spindle speed resulted in an increased dislocation density. The EBSD-based textural studies revealed a strong basal texture with near P and B type orientations visible at the maximum spindle speed. The tensile tests demonstrated a proportional increase in tensile strength with an increase in spindle speed along with a significant reduction in total ductility. The enhanced dislocation density and the formation of a strong basal texture were considered as the main drivers for the improvement in the tensile strength. A maximum tensile strength of nearly 550 MPa was obtained for samples extracted from the walls of the frustum cup at the maximum spindle speed of 600 RPM. This translates to an 80% enhancement of the tensile strength when compared to the base metal .

Acoustic emission (AE) is employed in this study to understand the failure process in fiber-reinforced cellular concrete (FRCLC) subjected to direct shear load. Synthetic polyolefin fibers are used as reinforcement in FRCLC blocks, and their influence on the shear-fracture process is investigated. AE parameters are investigated to assess the effectiveness of fibers in performance improvement of shear strength and toughness of CLC. In total, 24 CLC specimens are tested under direct shear. Effect of fiber dosage and combinations of macro and microfibers are considered as study parameters. Shear crack bridging effect of fibers during the process of shear-slip is investigated. Test results indicate that AE and shear fracture energy increase with increasing fiber dosage. It is observed that discontinuous structural synthetic fibers significantly improve the ultimate shear strength, residual strength, ductility, stiffness, and toughness of CLC. Also, the structural synthetic fibers reduced the shear crack width and shear-slip of CLC. AE parameters such as counts, energy, and 3D-crack source location are presented to illustrate the role of different fiber dosages on the direct shear response. Shear crack location was found to be consistent with the observed failure planes in the specimens. AE data analysis reveals that the number of mode II type events increased with increasing fiber dosage due to increased fiber pullout. Besides, mode I type events also increased as the failure mode changed from a single split crack to distributed cracking.

Cellular lightweight concrete (CLC) is increasingly used for low strength non-structural and structural applications. The effects of synthetic fiber reinforcement on the fracture behavior of CLC is investigated. In particular, acoustic emission (AE) technique is employed to study the influence of macro (structural), micro polyolefin synthetic fibers and their combinations on the fracture behavior of CLC beams. Notched fiber reinforced CLC beams were tested to study the crack initiation and propagation characteristics using AE sensors. Different AE parameters are correlated with the crack growth and damage accumulation. An attempt has been made to correlate the crack mouth opening displacement (CMOD) with the number of AE hits. The variation of cumulative acoustic energy release of the cracks is studied with respect to applied load and CMOD. Three dimensional source location of cracks is carried out based on the AE events picked by the sensors bonded to the CLC specimens. The analysis of AE results indicates that the crack source location identification from AE is consistent with the actual crack development. Analysis of AE signals reveal that the CLC matrix cracking produces signals with less number of hits that lie in the notched plane in bending. Moreover, the signals from the post peak regime correspond to more number of hits which tend to be scattered around the plane of notch due to the fiber pull out.

Synergistic effect of different fibers on the improvement of fracture behavior of concrete is a widely accepted phenomenon. However, the fracture mechanisms behind their improvement need to be clearly understood for optimizing the fiber dosage. In this work, the fracture behavior of synthetic fiber-reinforced concrete (SynFRC), steel fiber reinforced concrete (SFRC) and hybrid fiber reinforced concrete (HFRC) under flexural loading is studied using acoustic emission (AE) technique. Three different fiber dosages, by volume of concrete, of 0.50%, 0.75% and 1.0% and their hybrid combinations were considered as study parameters. Test results show that it is possible to retain sufficient workability in the fresh state and obtain good fracture resistance through a hybrid combination of hooked end steel fibers and macro- synthetic polyolefin fibers. AE parameters were investigated to acknowledge the efficiency of the fibers in improving the fracture behavior and toughness of SynFRC, SFRC, and HFRC. AE parameters such as hits, events, AE energy, and 3D-crack source locations were presented to illustrate the role of different fiber dosages on the Mode-I fracture response. The source locations of AE event above the artificial notches created at the mid-span of specimens were investigated and classified into tensile or shear cracks. AE and fracture energy increased with fiber dosage. SFRC demonstrated higher energy dissipation capacity followed by HFRC and SynFRC.

This paper presents the stress-strain behavior of structural synthetic fiber-reinforced cellular lightweight concrete (CLC) stack-bonded prisms under axial compression. Masonry compressive strength is typically obtained by testing stack-bonded prisms under compression normal to its bed joint. CLC prisms with cross-sectional dimensions of 200 x 150 mm (7.87 x 5.90 in.) with an overall height of 470 mm (1.54 ft) were cast with and without different dosages of synthetic fiber reinforcement. Polyolefin was used as a structural fiber reinforcement at different volume fractions (v(f)) of 0.22, 0.33, 0.44, and 0.55% with and without microfiber dosage of 0.02%. Experimental results indicate that the presence of fibers helps in the improvement of strength, stiffness, and ductility of CLC stack-bonded prisms under compression. Test results also signify that the hybrid fiber reinforcement provides better crack bridging mechanism both at micro and macro levels when compared to only macrofibers. Simple analytical models were developed for stress-strain behavior of CLC blocks and stack-bonded CLC prisms based on the experimental results with and without fibers under compression.

This paper investigates the effect of hybrid-synthetic fiber reinforcement on uniaxial tension behavior of low strength cellular lightweight concrete (CLC). Low strength CLC material is increasingly used for structural and non-structural masonry applications. These masonry units of low compressive strength typically offer little resistance to tensile stresses under lateral loading resulting in the collapse of CLC walls. A unique experimental setup was developed to test CLC under uni-axial tension. Dog-bone CLC specimens of length 600 mm and 150 mm x 100 mm cross section (test region) were cast with different synthetic fiber dosages and tested under uni-axial tension. Digital Image Correlation (DIC) technique was used to understand the crack-bridging mechanisms of the fibers. Experimental surface strains and crack openings were inferred using DIC technique. Presence of fibers prevented the premature fracture and led to improved post-cracking stiffness and ductility. Restricted crack localization and improved ductility were also observed due to addition of fiber reinforcement. Analytical models were used to predict the behavior of fiber reinforced cellular lightweight concrete (FRCLC) in tension based on the matrix and fiber parameters. The predictions had a good correlation with the experimental results. (C) 2017 Elsevier Ltd. All rights reserved.

Cellular light weight concrete (CLC) masonry has gained tremendous popularity in recent decades owing to its sustainability, density, low thermal conductivity and use of less mortar joints. The objective of this study is to develop a high performance fiber reinforced cellular concrete to provide a better alternative than aerated autoclaved concrete blocks for structural applications of masonry. Use of micro-fibers (fibrillated) enhances pre-cracking behavior of masonry by arresting cracks at micro-scale, while macro (structural) fibers induce ductile behavior in post-peak region by arresting the crack propagation soon after the crack initiation. In particular, the mechanical behavior of CLC cylinders under pure compression and CLC blocks under flexure with and without polyolefin structural fiber reinforcement as well as hybrid fiber reinforcement is investigated. Test results indicate that the addition of structural fibers improved the compressive strength up to 66.8% for 0.55% volume fraction. Post-peak ductility improved up to a factor of nine in case of compression for 0.55% volume fraction. Similarly, it resulted in 15.31% increase of post-peak flexural ductility by a hybrid addition of 0.44% and 0.02% volume fraction of macro and micro fibers respectively. Hybrid fiber reinforcement enhanced the peak strength and ductility which indicated better crack bridging both at micro and macro levels. (C) 2015 Elsevier Ltd. All rights reserved.