Five-axis machining center, combined three linear and two rotary axes, has been increasingly used in complex surface machining. However, as the two additional axes, the machined surface under table coordinate system is usually different from the tool motion under machine coordinate system, and as a result, it is very tough to predict the machined shape errors caused by each axes error motions. This research presents a new kind of sensitivity analysis method, to find the relationship between error motions of each axis and geometric errors of machined shape directly. In this research, the S-shaped machining test is taken as a sample to explain how the sensitivity analysis makes sense. The results show that the presented sensitivity analysis can investigate how the error motions affect the S-shaped machining accuracy and predicted the influence of error motions on certain positions, such as the reversal errors of the axes around motion reversal points. It can be proved that the presented method can help the five-axis machining center users to predict the machining errors on the designed surface of each axes error motions.

The effect of graphene nanoplatelets (GNPs) on enhancing the interlaminar fracture toughness of glass fiber/epoxy composites was investigated. The GnPs were physically deposited on the fiber surface by the dip coating technique. The composites were fabricated by hand layup technique followed by the compression molding process. Mode-I fracture test was conducted on the composite specimens. Crack propagation was studied by the digital image correlation (DIC) technique. Mode-I fracture toughness for composites loaded with 0.5 wt.% GnPs showed improvement by an average of 60% when compared to the pristine composites. It is concluded that the addition of GnPs produces a strong fiber/matrix interface bonding which effectively limits the crack propagation.

It is well known that the chip morphology predictions in machining simulations depend on the separation criteria used for modeling chip formation. In this paper, we propose to use two different criteria for chip separation and serration along with the Johnson-Cook damage model. The threshold value for chip separation is determined from machining experiments using the methodologies discussed in Patel et al. [1]. In addition, two separate damage evolution laws for chip separation and serration are used. Our results indicate that the choice of the evolution law and the threshold values of G c used for chip separation and serration have a significant effect on chip shape and other field variables such as the equivalent plastic strain, cutting force, temperature, etc.

Next generation defense applications for structural steels require new alloys that eliminate or reduce critical materials from their composition, while maintaining or exceeding the high strength and toughness requirements for extreme shock or dynamic loading environments. A new alloy system has been developed for this purpose and characteristics of its manufacture and material response in component manufacturing must be understood. In the present study, the relative machinability of a new structural steel, denoted as AF9628, was evaluated relative to a surrogate steel benchmark (AISI4340). The effects of machining parameters employed in milling across a range of machining speeds, feed rates and cooling conditions was investigated by measurements of force signatures and surface roughness. Machined chips were collected and measured to determine the relative effects of these parameters on evolved microstructure. Changes in chip hardness and microstructure were observed due to the effect of cooling conditions in the milling process. Subsurface microstructure was measured using electron backscatter diffraction. The utility of these methods for understanding machinability for defense alloys and components is briefly discussed.

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 amino functional group to form a micron-size rough surface. Consequently, the long chain of PSU entangles into crosslinked thermoset epoxy network, additionally, epoxide group on PSU further improves the bonding through chemical connection to the epoxy network and amino group on 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 crosslinking 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 crosslinking density and interact with the modified fiber.

Fused silica is difficult to machine through conventional machining, mainly due to its high brittleness and strength, low fracture toughness and poor plastic deformation. This study was attempted to explore the machinability of fused silica with laser-assisted machining by heating workpiece through a pulse CO 2 laser beam. During the LAM of fused silica, the bonding and wavelike texture on the machined surface indicated the behavior change of material deformation by the local heating in front of the cutting tool. The semi-continuous chips were obtained as an evidence of material removal mechanism which was a hybrid of quasi plastic deformation and brittle fracture. Moreover, the machinability of fused silica was evaluated. The experimental results demonstrated that considerable improvement in the machinability of fused silica was achieved such as better surface roughness, smaller cutting force as well as lower tool wear.

One of the versatile additive manufacturing processes is laser based Selective Laser Melting (SLM) which allows to build complex intricate shapes directly from its three dimensional digital images. Layer by layer deposition and depending upon build orientations, SLM parts tends to be anisotropic in nature. Also non-uniformity in thermal loading across the part leads to inhomogeneous microstructure which may have detrimental effect on various mechanical properties. Heat treatment of as-built SLM parts could be used as a post processing technique to reduce the anisotropy and produce homogenous microstructure to ensure reproducible mechanical properties. Application oriented mechanical properties can be obtained for precipitation hardened stainless steel by suitable heat treatment process. Present study is based on effect of heat treatments namely solution annealing, ageing and overaging on impact toughness of SLM 15-5 PH stainless steel. In order to support experimental observations, various metallurgical techniques have been applied. Effect of notch orientations causes anisotropy in impact toughness but this anisotropy is reduced with application of suitable heat treatment. In case of ageing, Transmission Electron Microscopy (TEM) analysis shows formation of fine spherical Cu precipitates which solution strengthens but makes the specimen brittle. As a result relatively lower impact toughness is obtained as compared to overaged condition where combined effect of coarsening of Cu precipitates and increased retained austenite makes the specimen ductile. Increased ageing temperature and soaking time does not have significant effect on impact toughness. However, solution annealing before ageing is recommended for homogenous precipitation throughout the specimen and statistically less scattered data. In all the cases SLM specimens have lower impact toughness to that of cold rolled 15-5 PH stainless steel. Present study could be used as a guideline to get application oriented mechanical properties mainly impact toughness.

A low concentrated polystyrene (PS) additive to epoxy is used since it is able to reduce the curing reaction rate but not at the cost of increasing viscosity and decreasing glass transition temperature of the curing epoxy. The modified epoxy is co-cured with a compatible thermoplastic interleaf during the vacuum assisted resin transfer molding (VARTM) to toughen the interlaminar of the composites. Using viscometry, the solubilities of thermoplastics polycarbonate (PC), polyetherimide (PEI), and polysulfone (PSU) are determined to predict their compatibility with epoxy. The diffusion and precipitation process between the most compatible polymer PSU and epoxy formed semiinterpenetration networks (semi-IPN). To optimize bonding adhesion, these diffusion and precipitation regions were studied via optical microscopy under curing temperatures from 25 C to 120 C and PS additive concentrations to epoxy of 0% to 5%. Uniaxial tensile tests were performed to quantify the effects of diffusion and precipitation regions on composite delamination resistance and toughness. Crack paths were observed to characterize crack propagation and arrest mechanism. Fracture surfaces were examined by scanning electron microscopy (SEM) to characterize the toughening mechanism of the thermoplastic interleaf reinforcements. The chemically etched interface between diffusion and precipitation region showed semi-IPN morphology at different curing temperatures. Results revealed deeper diffusion and precipitation regions increases energy required to break semi-IPN for crack propagation resulting in crack arrests and improved toughness.

Alumina powder was sprayed on low carbon steel substrate using atmospheric plasma spray process. Two different powders namely crushed and agglomerated powders were used and current was varied to study their effect on fracture toughness. Theoretically, with increase in arc current, melting of ceramic oxide shall increases and in turn dense coating should form. However, it was observed that if the arc power is too high and particle size of the powder being small (∼ 30 μm), the particles tend to fly away from the plasma core. Similarly, particle size distribution and powder morphology also affects the coating properties. Smaller particle should allow more melting resulting in dense coating and agglomerated powder allows flowability as well as better coating efficiency. Conversely, smaller particles tend to fly away from the plasma making the process difficult while the agglomerated particles showed a bimodal structure marked by presence of unmelted region in the splat core. All these factors lead to substantial variation in the fracture toughness of the coating. The present paper attempts to correlate plasma spraying parameters and microstructure of the coating with fracture toughness of the same.

Surface integrity of high performance components has a profound influence on the final performance. Therefore, surface integrity is a key point for realizing high performance manufacturing by which manufacture processes and parameters can be pre-selected according to a required functional performance of components, i.e., solving inverse problem of manufacturing, as long as correlations could be established respectively for between processes and surface integrity, and between surface integrity and performance. However, in practice it is still difficult in correlating processes to performance through surface integrity, due to the material and geometry constraints hindering achievability of a desired surface integrity during conventional manufacturing as well as the complex influence of multiple surface integrity parameters on a final performance. In this study, thermally sprayed WC-10Ni coatings onto stainless steel using high velocity oxy-fuel (HVOF) spraying process are investigated to identify the surface integrity predominantly determining the water-lubricated wear performance of coated steel, and then to correlate it to process parameters. The controllable surface integrity facilitates identifying responsible surface integrity parameters for a required high performance, and subsequently deriving necessary process parameters for achieving the desired responsible surface integrity. Specifically, HVOF process parameters are adjusted by changing the oxygen-to-fuel (O/F) ratio to control thermal and mechanical processing loads, i.e. temperature of heated in-flight spraying powders and impact velocity of the molten splats onto stainless steel to form the coatings. Surface features including porosity and phase structure, and surface characteristics including hardness, elastic modulus, and fracture toughness were studied with respect to the wear performance. The porosity and WC phase composition of coatings are identified responsible for the wear performance, as two essential surface integrity parameters that in turn greatly affect the surface characteristics including coating hardness, elastic modulus and fracture toughness. Consequently, the process parameter O/F is feasibly correlated to wear resistance through the responsible surface integrity parameters, as elucidating the coating formation mechanism of influence of particle velocity and temperature on the coating porosity and WC decomposition.

A novel surface technique, ultrasonic nano-crystal surface modification (UNSM), was used to process BMGs (Bulk Metallic Glasses) to improve the fracture strength and strain. It has been found that the fracture strength and strain are increased by 14.6% and 15.3% respectively after UNSM. In addition, micro-defects (voids and cracks) are found at the surface layer of UNSM-treated specimen after fracture, while there are fewer micro-defects observed in the untreated sample. We attribute the improvement of fracture stress and strain to two mechanisms. First, the excess free volume generated in BMGs by UNSM helps the nucleation of shear bands and the redistribution of the localized deformation. Second, the compressive residual stress generate by UNSM can slow down crack propagation. Both mechanisms lead to the improvement of BMGs fracture strength and strain.

Temperature responsive hydrogel has attracted considerable attention as an outstanding material for creating a variety of reconfigurable structures. As a well-known temperature responsive hydrogel, poly(N-isopropylacrylamide) (PNIPAAm) has been widely used in various applications. Here, we report high resolution 3D micro fabrication of PNIPAAm structures using projection micro-stereolithography (PμSL). We also show the controllability of degree of swelling and transition temperature of 3D printed PNIPAAm structures by controlling process parameters of PμSL. In addition, we demonstrate improvement of mechanical properties of PNIPAAm by introducing ionic crosslinks into 3D printed PNIPAAm structures to form ionically and covalently crosslinked hybrid networks.

Machining of hard and brittle materials such as ceramics and semiconductors has been a challenge for many years. They have many applications in optics, MEMS and electronic industries due to their many desirable properties, such as being light weight, strong, and hard. Achieving good surface finish, avoiding surface and subsurface damage and at the same time achieving a high material removal rate are extremely challenging for these materials. Materials such as single crystal silicon and sapphire have a crystal orientation or anisotropy effect which makes their machining even more difficult. Because of this characteristic, their behavior is directional and they have different fracture toughness for each direction. In past works in our research group, it has been demonstrated that machining of brittle materials in ductile regime is possible due to the high pressure phase transformation (HPPT) occurring in the material caused by the high compressive and shear stresses induced by a single point diamond tool tip. In the current study scratch tests were performed on the monocrystal sapphire in four different perpendicular directions and to further augment the process, traditional cutting is coupled with a laser to heat and soften the material to either enhance the ductility, resulting in a deeper cut, or reducing brittleness leading to decreased fracture damage. Results of scratch tests, with and without laser heating, for different cutting loads have been compared. The effect of laser heating was studied by analyzing the image of cuts and verifying the depth of cuts which were made using varying laser power during the process. Microscopic images and three-dimensional profiles of the cuts taken by using a white light interferometer were investigated.

Incremental forming is an emerging technique for reducing the cost of tooling, increasing the flexibility and reducing the thermal energy usage in forming of thermoplastic polymer surfaces. This paper examines the effect of Single Point Incremental Forming (SPIF) on the mechanical properties of a semi-crystalline Polyamide (Nylon 66) material. The effects of incremental depth and tool rotation speed on these properties, and on the sheet temperature during forming are quantified. Differential Scanning Calorimetry and X-ray Diffraction are performed to understand changes in crystallinity and chain orientation of the polymer due to SPIF. It is found that the formed material has a substantial higher toughness and ductility, but reduced yield stress and Young’s modulus, as compared to the formed material. Stress relaxation tests show similar relaxation behavior for the formed and unformed polymer. The effect of SPIF on the chain orientation and its link to the mechanical properties are discussed.

Tissue simulants are commonly used in medical procedure training and research to test the insertion and cutting mechanics of medical devices. Accurate representation of the forces and tissue properties is important for the efficacy of the training and research studies. This paper provides a quantitative method of determining the performance of tissue simulants. A force model was used to determine the three component forces: tearing, spreading, and friction forces, of a needle passing through six different skin simulants. Experiments were performed to determine the fracture toughness, shear modulus, friction between the simulant and needle, and the crack length in the simulant made by the needle. Polyurethane with Shore hardness 40 A was shown to be the best simulant by having the composition of forces most similar to porcine skin tissue: 39% and 61% for the tearing force, 18% and 32% for the spreading force, and 29% and 21% for the friction force for the polyurethane and porcine skin respectively.

In this study, micro-laser assisted machining (μ-LAM) technique is used to perform scratch test on a granite sample. Rocks are generally considered as brittle materials with poor machinability and severe fracture can be resulted when trying to cut them due to their low fracture toughness. Due to increasing demand for these materials in industry with many applications, finding a fast and cost effective process with higher product quality seems essential. In past research in our research group, it has been demonstrated that machining of brittle materials such as semiconductors and ceramics in ductile regime is possible due to the high pressure phase transformation (HPPT) occurring in the material caused by the high compressive and shear stresses induced by a single point diamond tool tip. Scratch tests were performed on the granite sample and to further augment the process, traditional cutting is coupled with the laser to soften the material and get the higher depth of cut. In this research, results of scratch tests done on granite, with and without laser heating have been compared. The effect of laser heating was studied by verifying the depths of cuts for scratch tests with varying the laser power during the process. Microscopic images and three-dimensional profiles of cuts taken by using a white light interferometer were investigated. Results show that using laser can increase depth of cut and with 15 W laser power it is increased — for different regions of granite sample — from 25% to 95%.

Strength and fracture toughness of ceramic tool materials can be enhanced by adding ductile phases. However, the hardness will be decreased, which is undesirable especially for cutting tool materials. Combining with functionally gradient materials (FGMs), the mechanical properties can be tailored so as to achieve high hardness at the outside of the ceramic materials leaving a relatively tough core inside. In this paper, a Si 3 N 4 /(W, Ti)C/Co graded composite ceramic tool material was fabricated by hot pressing technique. The composites without Co were used as the surface layers and the composites containing Co were used as the inner layers. Subsequently, the cutting performance of the graded ceramic cutting tool in turning iron-based high temperature alloy GH2132 was studied in comparison with common reference tool. The cutting forces, cutting temperature, tool wear modes and failure mechanisms were discussed. Results revealed that the resultant cutting forces firstly decrease and then increase with the increase of cutting speed, while the maximum cutting temperature increases gradually. Tool live of the FGM tool exceeds that of the corresponding common ceramic tool with the same composition systems. Formation of the residual compressive stress in the surface layer induced by the graded structure contributed to the longer tool life. The main failure modes of the FGM tool were adhesion, groove wear on the rake face and notch wear on the flank face. The graded tool shows better notch wear resistance than the common reference tool.

Additive manufacturing (AM) technologies have been successfully applied in various applications. Fused deposition modeling (FDM), one of popular AM techniques, is most widely used method for manufacturing of plastic materials. Due to the poor strength properties of pure plastic materials, there is a critical need to improve mechanical properties for FDM-fabricated pure plastic parts. One of the possible methods is adding reinforced materials (such as carbon fibers) into plastic materials to form carbon fiber reinforced plastic (CFRP) composites. The investigation in this paper is going to test if the properties of CFRP composites part will be enhanced compared with pure plastic part made by FDM. There are three major steps in this paper including producing thermoplastic matrix CFRP composites filaments extruded after blending plastic pellets and carbon fiber powder, printing parts in FDM process, and conducting tensile test. Effects of carbon fiber content and length on the mechanical properties (tensile strength, Young’s modulus, toughness, ductility, and yield strength) of specimens are investigated. This investigation will also provide guidance for future investigations of fabricating thermoset matrix CFRP composites by AM techniques.

Fusion welding of Aluminum and its alloys is a great challenge for the structural integrity of lightweight material structures. One of the major shortcomings of Aluminum alloy welding is the inherent existence of defects in the welded area. In the current study, tests have been conducted on tungsten inert gas (TIG) welded AA6061-T651 aluminum alloy to determine the effects of defect sizes and its distribution on fracture strength. The information will be used to establish weld acceptance/rejection criteria. After welding, all specimens were non-destructively inspected with phased array ultrasonic and measured the projected area of the defects. Tensile testing was performed on inspected specimens containing different weld defects: such as, porosity, lack of fusion, and incomplete penetration. Tensile tested samples were cut along the cross section and inspected with Optical Microscope (OM) to measure actual defect sizes. Tensile properties were correlated with phased array ultrasonic testing (PAUT) results and through microscopic evaluations. Generally, good agreement was found between PAUT and microscopic defect sizing. The tensile strength and toughness decreased with the increase of defect sizes. Small voids (area ratio <0.04) does not have significant effect on the reduction of tensile strength and toughness values. Once defective “area ratio (cross sectional area of the defect) / (total specimen cross sectional area)” reached a certain critical value (say, 0.05), both strength and toughness values decline sharply. After that critical value both the tensile strength and toughness values decreases linearly with the increase of defect area ratio.

The wear rate of a grinding wheel directly affects the workpiece surface integrity and tolerances. This paper summarizes a combined experimental-modeling framework for life cycle prediction of an electroplated Cubic Boron Nitride (CBN) grinding wheel, typically utilized in nickel-based superalloy grinding. The paper presents an experimental framework to facilitate the formulation of a micro-mechanics based modeling framework. The presented work investigates the topological evolution of the grinding wheel surface and mechanisms of grit failure via depth profiling, digital microscopy and scanning electron microscopy. The results are used to elucidate the statistical evolution of the grinding wheel surface. Different modes of grit failure, including grit attritious wear, fracture and pull out haven been identified. The analysis of the surface topological features indicates a unique grit activation process, leading to a non-uniform spatial distribution of the grit wear. Additionally, single grit pull out experiment has been conducted to assess the residual strength of the grit-wheel interface and the associated state of damage percolation. The experimental results can be utilized in developing a life expectancy model for the CBN grinding wheel to assess the grit mean time to failure as well as grit surface topological evolution as a function of the process parameters.