Effect of the in-situ post weld heat treatment (PWHT) was investigated on the flash profile, austenite/ferrite phase balance and mechanical properties of the upset resistance dissimilar weld between the Fe-Cr-Ni and Fe-Cr stainless steels rods. In order to explore the effect of the heat treatment on the joint strength, two as-welded samples with the low strength (116 MPa) and high strength (372 MPa) were used. The results showed that in-situ PWHT was beneficial for both welded samples, though in different ways. For the weld with the low strength, PWHT improved the joint strength (∼ 130% in the optimum condition compared to the as-welded sample) due to the increase in the size of the flash and the related bonded area at the joint interface. However, ferrite percent in the weld zone increased from ∼ 50% up to ∼70%. For the sample with the high strength, ferrite/austenite phase balance was restored at an optimum condition of PWHT. However, the joint strength decreased slightly (less than 5%) due to the grain growth in the Fe-Cr rod, i.e. the fracture location. Fracture analysis was used for justification of the variations in the joint strength. For both of the Fe-Cr-Ni side and Fe-Cr side of the welds, in-situ PWHT generally reduced the hardness. This observation was discussed at the light of the simultaneous effects of the grain growth and formation of little martensite.

Metals such as Cu, Al, Ni, Ta, and stainless steels, despite their softness and ductility, are considered difficult to machine. This is due to large cutting forces and corresponding formation of a very thick chip during cutting, and hence, these metals are referred to as “gummy.” Their poor machinability of these materials arises because of an unsteady and highly redundant mode of plastic deformation referred to as sinuous flow. The prevailing plastic deformation mode during machining can be overcome by the application of certain coatings and chemical media on the undeformed free surface of the workpiece ahead of the cutting process. Using in situ imaging and concurrent force measurements, we present two different mechanochemical routes through which these media can improve machinability. The first route, which requires chemicals that adhere to the metal surface, such as glues and inks, improves cutting by inducing a change in the local plastic deformation mode—from sinuous flow to one characterized by periodic fracture or segmented flow. The second route, which requires chemicals that can react with the workpiece to form a low-friction layer, changes the sinuous flow mode to a smooth, laminar one. Both routes decrease cutting forces by more than 50% with order of magnitude improvement in surface texture as characterized by measured roughness and defect density. The results suggest a broad range of opportunities for improving the performance of machining processes for many difficult-to-cut gummy metals.

Advanced high strength steels (AHSS) and ultra-high strength steels (UHSS) have been increasingly implemented by the automotive industry for better crashworthiness and fuel economy. However, these steels are often sensitive to the trimmed edge cracking. The objective of the present paper is to study the sheared edge of ultra-high strength dual-phase steel, DP980, in mechanical trimming and hole punching by sheared edge quality assessment, stretchability, and hole expansion tests as well as finite element analysis. Furthermore, the mechanism of fracture propagation in trimming and hole punching processes of DP980 was discussed. Rather a unique fracture mechanism was observed for trimming of DP980 steel leading to the burr removal at the final stage of the trimming process. Finite element analysis revealed that, under very large clearances, a secondary crack initiates from the edge of the lower tool, and the primary propagated crack turns toward it simultaneously. Intersecting of these two cracks leads to the total separation and leaves the edge of the trimmed part with a broken burr. Fracture observation of trimmed specimens revealed that crack initiation sites under tension moved from the middle of the trimmed surface toward the burr tip with increasing the clearance. This study demonstrates the importance of stretchability tests for designing the stamping dies as well as a reliable finite element simulation for characterizing the material behavior during the shearing process.

The synergistic effect of combining different modification methods was investigated in this study to improve the interlaminar toughness and delamination resistance of fiber reinforced polymers (FRP). Epoxy-compatible polysulfone (PSU) was end-capped with epoxide group through functionalization, and the fiber surface was chemically grafted with an amino functional group to form a micron-size rough surface. Consequently, the long chain of PSU entangles into cross-linked thermoset epoxy network, additionally, epoxide group on PSU further improves the bonding through chemical connection to the epoxy network and amino group on the fiber surface. The combined modification methods can generate both strong physical and chemical bonding. The feasibility of using this method in vacuum-assisted resin transfer molding was determined by rheometer. The impact of formed chemical bonds on the cross-linking density was examined through glass transition temperatures. The chemical modifications were characterized by Raman spectroscopy to determine the chemical structures. Synergistic effect of the modification was established by mode I and mode II fracture tests, which quantify the improvement on composites delamination resistance and toughness. The mechanism of synergy was explained based on the fracture mode and interaction between the modification methods. Finally, numerical simulation was used to compare samples with and without modifications. The experiment results showed that synergy is achieved at low concentration of modified PSU because the formed chemical bonds compensate the effect of low cross-linking density and interact with the modified fiber.

This paper deals with the detailed analysis of the lateral process forces in rolling-cut shearing of heavy steel plates and their impact on edge defects. Rolling-cut shearing is still the most common method of heavy-plate side trimming. However, this method can entail edge defects like uneven longitudinal shape as well as burr and fractures in the area of the cut-changeover (beginning and end of the periodical cuts). In the existing literature, neither the root cause of these edge defects nor their nexus with the upper blade trajectory (blade drive-kinematics) has been analyzed in detail. In this work, these issues will be explored based on the finite element method (FEM) simulations and measurements from an industrial plant. The complex interrelation between drive-kinematics, varying lateral force, unintended lateral motion of the upper blade, unintended variation of the blade clearance, and quality defects is analyzed. The variation of the lateral force is identified as the root cause of such quality defects and a physical explanation for variations of the lateral force is given. The detailed understanding of the shearing process serves as a solid basis for an optimization and re-design of the drive-kinematics in a future work. Measurements from an industrial plant and simulation results show good agreement and thus confirm the theory. The results are transferable to other rolling-cut trimming shears.

During the micromachining processes of particle-reinforced metal matrix composites (PMMCs), matrix-particle interface failure plays an important role in the cutting mechanism. This paper presents a novel analytical model to predict the cutting forces in micromilling of this material considering particle debonding caused by interface failure. The particle debonding is observed not only in the processed surface but also in the chip. A new algorithm is proposed to estimate the particles debonding force caused by interface failure with the aid of Nardin–Schultz model. Then, several aspects of the cutting force generation mechanism are considered in this paper, including particles debonding force in the shear zone and build-up region, particles cracking force in the build-up region, shearing and ploughing forces of metal matrix, and varying sliding friction coefficients due to the reinforced particles in the chip-tool interface. The micro-slot milling experiments are carried out on a self-made three-axis high-precision machine tool, and the comparison between the predicted cutting forces and measured values shows that the proposed model can provide accurate prediction. Finally, the effects of interface failure, reinforced particles, and tool edge radius on cutting forces are investigated by the proposed model and some conclusions are given as follows: the particles debonding force caused by interface failure is significant and takes averagely about 23% of the cutting forces under the given cutting conditions; reinforced particles and edge radius can greatly affect the micromilling process of PMMCs.

The manufacturing of low-density paper such as tissue and towel typically involves a key operation called creping. In this process, the wet web is continuously pressed onto the hot surface of a rotating cylinder sprayed with adhesive chemicals, dried in place, and then scraped off by a doctor blade. The scraping process produces periodic microfolds in the web, which enhance the bulk, softness, and absorbency of the final tissue products. Various parameters affect the creping process and finding the optimal combination is currently limited to costly full-scale experiments. In this paper, we apply a one-dimensional (1D) particle dynamics model to systematically study creping. The web is modeled as a series of discrete particles connected by viscoelastic elements. A mixed-mode discrete cohesive zone model (CZM) is embedded to describe the failure of the adhesive layer. Self-contact of the web is incorporated in the model using a penalty method. Our simulation results delineate three typical stages during the formation of a microfold: interfacial delamination, web buckling, and post-buckling deformation. The effects of key control parameters on creping are then studied. The creping angle and the web thickness are found to have the highest impact on creping. An analytical solution for the maximum creping force applied by the blade is derived and is found to be consistent with the simulation. The proposed model is shown to be able to capture the mechanism of crepe formation in the creping process and may provide useful insights into the manufacturing of tissue paper.

Aluminum alloys have been increasingly adopted in the fabrication of automotive body structures as an integral component of mass savings strategy. However, mixed use of dissimilar aluminum alloys, such as sheet metals, castings, and extrusions, poses significant challenges to the existing joining technologies, especially in regard to single-sided joint access. To address this issue, the current study applied the friction stir blind riveting (FSBR) process to join 1.2 mm-thick AA6022-T4 aluminum alloy to 3 mm-thick Aural-2 cast aluminum. A newly developed, robot mounted, servo-driven, FSBR equipment and the procedure using it to make FSBR joints were introduced systematically. The effect of rivet feed rate and spindle speed on joint formation and cross section geometry was investigated, and it was found that a high spindle speed and a low rivet feed rate, i.e., high heat input, are prone to produce good joints, and that low heat input can cause severe problems related to insufficient softening of the sheets. The rivet deformation, especially the notch location on the mandrel relative to the shank has significant influence on lap-shear strength and fracture mode of the final joints. A rivet pull-out fracture mode was observed at higher rivet feed rates and lower spindle speeds and exhibited significantly improved energy absorption capability, i.e., 62% higher compared to traditional blind riveted (BR) joints.

Ultrasonic welding is a well-known technique for joining thermoplastics and has recently been introduced to joining carbon fiber-reinforced composites (CFRC). However, suitable models for predicting joint performance have not yet been established. At present, most failure models for bonded composites are built based on uniform adhesive joints, which assume constant joint properties. Nevertheless, the joint properties of ultrasonic spot welds for CFRC are variable, which depend on the input welding parameters. In this paper, the effect of welding energy, which is the most important welding parameter, on the joint properties is investigated. Then, a surface-based cohesive performance model based on mode-II (in-plane) shear loading is developed to predict the joint performance, wherein the critical fracture parameters in the model are described via the functions of welding energy. After comparing the simulated results with experiments, the model is proven feasible in predicting the joint properties of the ultrasonic spot welds under shear loading condition, and hence, a mix-mode cohesive-zone model is practical to predict the joint performance under any loading conditions with the predicted fracture parameters.

This paper presents a comprehensive experimental study in exploring the influence of key printing parameters on mechanical properties and failure mechanisms of acrylonitrile butadiene styrene (ABS) material. Three parameters with three levels—layer thickness (0.09 mm, 0.19 mm, and 0.39 mm), printing plane (XY, YZ, and ZX), and printing orientation (horizontal, diagonal, and vertical)—are considered, which form an L 27 experimental design. Following L 27 , tensile and compressive specimens are fabricated and tested. Young's modulus, yield strength, failure strength, and strain of specimens are measured, evaluated, and compared with their injection-molded counterparts. Experimental results indicate that tensile specimens with a layer thickness of 0.09 mm and printing plane orientation of YZ-H reveal the highest stiffness and failure strength. While injection-molded specimen shows the highest yield strength, ductility of printed specimens is 1.45 times larger than that of injection-molded part. YZ along with XY specimens shows a neat and clean standard fracture failure at 45 deg, where the layers reorient themselves followed by stretching before fracture failure, thus providing sufficient ductility as opposed to ZX specimens, which fail along the direction perpendicular to the loading. Compressive XY-H and XY-D specimens have the highest stiffness and yield strength, and failure mechanisms involve initial compression followed by squeezing of layers leading to compactness followed by breakage due to tearing off or fracture of layers. The findings imply that anisotropy of fused deposition modeling (FDM) parts cannot be avoided and hence the appropriate parameters must be chosen, which satisfy the intended properties of the material subject to specific loading scenario.

Unlike ferrous materials, where the cementite (Fe 3 C) phase acts as an abrasive that contributes to flank wear on the cutting tool, most titanium (Ti) alloys possesses no significant hard phase. Thus, the origin of flank wear is unclear in machining Ti alloys. To address this question, a Ti-6Al-4V bar was turned under various conditions with uncoated carbide and polycrystalline diamond (PCD) inserts, most commonly used tool materials for machining Ti alloys. These inserts were retrieved sporadically while tuning to examine the wear patterns using a confocal microscope. To correlate the patterns with the microstructure of the original bar, the microstructure was carefully characterized using Orientation Image Microscopy ™ (OIM) with electron-backscattered diffraction (EBSD). From the wear patterns, two distinct types of damage were identified: (a) microscopic and macroscopic fractures on the cutting edges and (b) scoring marks on flank faces. This paper demonstrates that both types of damage were caused primarily by the heterogeneity in hardness in the α -crystals, where the plane perpendicular to the c-axis in an α -crystal is substantially harder than any other direction in the α -crystal as well as the isotropic β -crystal. In addition to such heterogeneities, adhesion layer, ubiquitous to machining Ti alloys, detaches small fragments of the tool, which resulted in microscopic and macroscopic fractures observed on flank wear.

Delamination as the main defect created during drilling of composite laminate is principally a crack nucleation and propagation phenomenon. The fracture-based investigation is performed to identify the significance of different modes involving in this process. The sensitivity analysis is implemented to evaluate magnitude and importance of each mode. As a result, mode I is a dominant mode while drill point removes the material; however, the crack continues to propagate under pure mode III for a while after drilling due to contact of flutes with spalls. This paper investigates the crack formation process for wide variety of drilling conditions and tool geometries. It is demonstrated that although mode III contributes, its minor effect might be neglected if comparing with fracture mode I. Therefore, it may be vanished as a tool design strategy. It is indicated that chisel edge plays a great role in crack propagation under major mode I; therefore, any further design approach which limits or eliminates opening action of chisel edge decreases delamination significantly. Material removal starting from hole perimeter as well as implementing small predrilled holes (such as action of primary cutting lips in step drill) are examined as solutions based on this approach.

Ultrasonic metal welding has been used to join multiple layers of battery tabs with the bus bar in lithium-ion battery assembly operations. This paper describes joint performance models for ultrasonic metal welds of multiple layers of dissimilar battery tab materials, i.e., aluminum and copper. Finite element (FE) models are developed to predict the mechanical performance of the ultrasonically welded joints. The models predict peak shear load, energy absorption capability, and failure modes, which are necessary for modeling product performance and defining process requirements for the welds. The models can be adjusted to represent different quality of welds created in conditions of underweld (UW), normal-weld (NW), or overweld (OW) using physical attributes observed through microscopic analysis. The models are validated through lap shear tests, which demonstrate excellent agreement for the maximum force in the NW condition and good agreement for the UW and OW conditions. The models provide in-depth understanding of the relationship among welding process parameters, physical weld attributes, and the weld performance. The models also provide significant insight for further development of ultrasonic welding process for battery tabs and help optimize welding process for more than four-layered joints.

Stress corrosion cracking is a phenomenon that can lead to sudden failure of metallic components. Here, we use laser shock peening (LSP) as a surface treatment for mitigation of stress corrosion cracking (SCC), and explore how the material differences of 304 stainless steel, 4140 high strength steel, and 260 brass affect their mitigation. Cathodic charging of the samples in 1 M sulfuric acid was performed to accelerate hydrogen uptake. Nontreated stainless steel samples underwent hardness increases of 28%, but LSP treated samples only increased in the range of 0–8%, indicative that LSP keeps hydrogen from permeating into the metal. Similarly for the high strength steel, LSP treating limited the hardness changes from hydrogen to less than 5%. Mechanical U-bends subjected to Mattsson's solution, NaCl, and MgCl 2 environments are analyzed, to determine changes in fracture morphology. LSP treating increased the time to failure by 65% for the stainless steel, and by 40% for the high strength steel. LSP treating of the brass showed no improvement in U-bend tests. Surface chemical effects are addressed via Kelvin Probe Force Microscopy, and a finite element model comparing induced stresses is developed. Detection of any deformation induced martensite phases, which may be detrimental, is performed using X-ray diffraction. We find LSP to be beneficial for stainless and high strength steels but does not improve brass's SCC resistance. With our analysis methods, we provide a description accounting for differences between the materials, and subsequently highlight important processing considerations for implementation of the process.

7075-T6 aluminum suffers from limited elongation during tensile forming; electrically assisted forming (EAF), which uses direct current to improve formability, is a viable candidate process to improve this effect. In past electrical tension testing by various authors, two types of waveforms have been examined: continuous current and square waveforms. For tension, it was shown that the applying current using square waveforms was able to extend formability beyond what continuous current could do, due to reducing the overheating in the necking region. The goal of this paper is to model the temperature and flow stress effects of saw tooth waves by modifying an existing square wave temperature prediction model and combining it with a theoretical flow stress model. Nondecaying and linearly globally decaying saw tooth waveforms are used in an attempt to control the temperature of the necking zone to allow for increased strain at fracture. Comparisons between saw tooth waveforms and square waveforms are exhibited, and it is found that the saw tooth waveforms are inferior to square waves for increasing strain at fracture for 7075-T6.

Deformation of a direct quenched type of ultra-high strength steel (UHSS) with low-carbon content is studied in this work. Although this material, as manufactured, combines high strength and good ductility, it is highly sensitive to the workshop fabrication processes used. The presence of stress concentration due to structural discontinuity or notch effects can accentuate the effect of fabrication processes on the deformation capacity of the material. To evaluate the influence of fabrication methods on deformation capacity, a series of tensile tests are done on both pure base material (BM) and after the steel has been subjected to heat input (HI) or cold forming (CF). To study the effect of HI due to welding or other heat-based workshop fabrication processes, the surface of the material was dressed by laser beam at controlled speed and laser intensity. CF effects were studied by bending the specimens to a predetermined angle prior to subjecting the steel to tensile testing. Experimental results were compared with numerical simulation using ls-dyna simulation software. The generated results show acceptable agreement between experimental and numerical simulation outcomes.

In order to evaluate the shearing quality, the material inhomogeneity through thickness after shearing is introduced by the authors. This study investigates the shearing and local formability of hot-rolled high-strength steel (HSS) plate, which is generally exploited for the manufacturing of the beam of heavy trucks. Various kinds of plates with different thicknesses and strengths are used to figure out the effect of material properties on the shearing quality. Both the shear surface morphology and microhardness distribution of the sheared edge are considered for evaluating the influence of the sheared-edge quality on local formability during the following forming process. Vickers hardness tests are conducted to analyze the microhardness distribution on the shear surface, which is proved to have significant effect on the local formability of the sheared edge. Furthermore, two kinds of bending tests and simulation are employed to study the edge cracking phenomenon, and the results indicate that the junctional zone of burnished zone and fracture zone, which is defined as peak hardness zone (PHZ), has a significant impact on major strain distribution on shear surface in the side bending test and this region is the main cause of edge cracking in normal bending test.

Machining of titanium alloy is a severe fracture procedure associated with localized adiabatic shearing process. Chip segmentation of titanium alloy is usually characterized with adiabatic shear band (ASB) and localized microfracture evolution process. ASB has been recognized as the precursor of fracture locus due to its sealed high strain intensity. Besides strain intensity, stress triaxiality (pressure-stress states) has also been identified as a significant factor to control fracture process through altering critical loading capacity and critical failure strain. The effect of stress triaxiality on failure strain was traditionally assessed by dynamic split Hopkinson pressure bar (SHPB), quasi-static tests of tension, compression, torsion, and shear for finite element (FE) analysis. However, the stress triaxiality magnitudes introduced by these experiments were much lower than those generated from the high speed machining operation due to the fact that ASBs in chip segmentation are usually involved in much higher strain, high strain rate, high stress, and high temperature associated with phase transformation. However, this aspect of fracture evolution related with stress triaxiality and phase transformation is not well understood in literature. This paper attempts to demonstrate the roles of stress triaxiality and phase transformation in chip segmentation especially in the high speed machining of titanium alloy in FE framework. Johnson–Cook (JC) failure model is calibrated by addressing the characteristics of stress triaxiality and phase transformation associated with high speed machining. This research confirms that the selection of failure criterion parameters incorporated the effects of stress triaxiality and the alpha–beta phase transformation is indispensible to successfully predict fracture behavior during chip segmentation process in the high speed machining of titanium alloys.

The working surface condition of abrasive tool is one of the important issues in grinding process. This article discusses the effects of the ultrasonic vibration on the working surface condition involving chips adhesion and abrasive grains wear during ultrasonic-assisted grinding (UAG) of Inconel 718 with an electroplated cBN grinding quill as the abrasive tool. In this study, scanning electron microscopic (SEM) observations were performed on the quill working surface before and after grinding at different vibration amplitudes, and the SEM images were filtered, extracted, and binarized by using image-pro plus to evaluate the quill working surface condition. The obtained results demonstrated that (1) the wear of grinding quill is dominantly attributed to chips adhesion, grains releasing, and grains fracture; (2) both the percentage of chips adhesion area and the size of chips adhered tend to decrease as the vibration amplitude increases; in contrast, the effect of ultrasonic vibration on the number of chips adhesion is not noticeable; (3) the percentage of the number of grains released/fractured decreases as the vibration amplitude rises, e.g., the percentage in UAG at vibration amplitude of A p – p = 9.4 μ m was decreased by 40% compared to that in conventional grinding (CG); and (4) higher distribution density of effective cutting edges can be achieved under larger vibration amplitude, and the mean area of effective cutting edges in UAG is smaller than that in CG, demonstrating that the ultrasonication enhances the grinding quill sharpness.

Dissimilar joining of aluminum to steel poses a challenge for arc welding. In this study, aluminum AA6061-T6 and hot dipped galvanized DP590 steel were joined using the Fronius cold metal transfer (CMT) welding process applying an edge plug welding mode (EPW). The correlation of the welding parameters, weld characteristics, and weld strength was systematically investigated. It was found that the EPW mode created a zinc-rich zone at the weld root along the Al–steel faying interface which transitioned to a continuous and compact intermetallic compounds (IMC) layer in the middle portion of the joint. The fracture propagation in lap-shear specimens was affected by this increase of IMC layer thickness. At a wire feed speed (wfs) of 5.6 m/min, the fracture initiated along the zinc-rich layer at the faying interface and then, upon meeting the compact IMC layer, propagated into the aluminum weld nugget. Propagation followed a path within the weld nugget along the boundary between columnar and equiaxed grains leading to weld nugget pullout upon fracture. For IMC layer peak thicknesses below 10 μ m, the strength increased as a function of weld nugget diameter. However, larger heat inputs resulted in IMC layer thicknesses greater than 10 μ m and interfacial fracture.