Torsional instabilities in a two-degree-of-freedom system driven by a Hooke’s joint due to random input angular speed fluctuation are investigated. Linearised analytical models are used for calculating the largest Lyapunov exponent. Instability behaviour is then characterised by examining the sign of this exponent. Conditions for the onset of instability via sub-harmonic parametric resonances has been shown to coincide with those for the deterministic case. However, the onset of instability via sum as well as the difference type combination resonance is found to be different from that of the deterministic case. The instability conditions for the system under input angular speed fluctuation have been presented graphically in the excitation frequency-excitation amplitude-top Lyapunov exponent space. Predictions for the deterministic and the stochastic cases are compared. The effect of fluctuation probability density as well as that of inertia loads on the stability behaviour of the system has been examined.

Titanium is widely used in many industry areas (such as automotive industry, aerospace industry, and medical industry) due to its superior properties of low density, high strength to weight ratio, strong corrosion-resistance, etc. However, commercial pure titanium (CP-Ti) parts still have some disadvantages (such as relatively low hardness, and wear resistance) which limit their further applications. In order to reduce these disadvantages, some reinforcement materials (such as ceramics and nanomaterials) are involved to fabricate titanium-based parts Compared with ceramics, low content of nanomaterials could significantly improve the mechanical properties and reduce disadvantages of ceramics (such as poor wettability and low interfacial bonding between reinforcement materials and Ti). Graphene oxide (GO) is a preferable candidate of nanomaterial due to its excellent mechanical properties and low density. The GO reinforced Ti parts have been fabricated by the selective laser sintering (SLS) process. Laser additive manufacturing (LAM) process includes directed energy deposition method and powder bed fusion method. Compared with powder bed fusion method (such as the SLS and selective laser melting (SLM)), directed energy deposition method (e.g. laser engineered net shaping (LENS)) has advantages of parts repairing and gradient parts fabrication capabilities. There are no studies on the fabrication of GO-Ti parts by LENS process. In this study, GO-Ti parts are fabricated by the LENS process. The effects of GO and laser power on fabricating defects of porosity, microstructure, and mechanical properties (including microhardness, elastic modulus, wear rate) were studied, for the first time.

Nickel-Titanium (NiTi) alloy is difficult to be machined and fabricated due to its properties of rapid work-hardening and superelasticity. Traditional manufacturing methods, such as casting, vacuum arc melting, and hot-isostatic pressing, have disadvantages of high cost, time-consuming, and limitation in the complexity of parts’ fabrication. In order to reduce or solve these problems, laser additive manufacturing methods have been studied in the fabrication of NiTi alloy. Among the investigations, laser engineered net-shaping (LENS) in-situ synthesis of NiTi from blended Ni and Ti powders shows its unique advantage of cost-effectiveness and flexibility in tailoring NiTi’s phase transformation properties. In addition, it is reported that LENS in-situ synthesized NiTi parts have comparable properties with NiTi alloys fabricated from pre-alloyed powders. However, there are no existing investigations on the effects of processing parameters on the mechanical properties of the LENS in-situ fabricated NiTi parts. The processing parameters would have great influences on the properties of the LENS in-situ synthesized NiTi parts. This paper, for the first time, reports the effects of laser power, powder feeding rate, and Z increment of the deposition head on microstructure, microhardness, and Young’s modulus of the LENS in-situ synthesized NiTi parts.

Surface machining of carbon fiber reinforced plastic (CFRP) using rotary ultrasonic machining (RUM) with vertical ultrasonic vibration was effective in reducing many issues, including high cutting force, high torque, and high tool wear rate. The vertical ultrasonic vibration also induced damages to machined CFRP surfaces and then resulted in increased surface roughness. To simultaneously decrease surface roughness and cutting force, the direction of ultrasonic vibration needed to be parallel with the surface generation direction (horizontal feeding direction). The horizontal ultrasonic vibration was then developed and applied for RUM surface machining of CFRP. The application of horizontal ultrasonic vibration in RUM surface machining produced simultaneously decreased surface roughness and cutting force. However, there were no investigations on delamination in such a process, and delamination was considered as one of the major factors to reject the machined CFRP products. This investigation would study the delamination under different machining-variable groups, the delamination generation mechanisms, and the relationships between delamination and cutting forces through the experimental method in surface machining of CFRP using RUM with horizontal ultrasonic vibration. Smaller cutting force and delamination thickness would be produced by the smaller depth of cut, smaller feedrate, or larger tool rotation speed. Smaller indentation depth was generated by larger tool rotation speed or smaller feedrate. Smaller material removal rate and abrasive-grain number taking part in the cutting process were produced by the smaller depth of cut. The delamination initiation at larger uncut CFRP thickness would be induced by higher cutting force.

Performance degradation of gas turbine is a common phenomenon during operation. Maintenance of the degraded gas turbines and improving their performance at a low cost are important in engineering. In this paper, the maintenance method based on reassembling degraded components of existing gas turbines was studied. This research was based on a type of 2MW gas turbine engine. Blue ray scanning was carried out to rebuild the 3D flow-path geometries of the compressor and turbine of a degraded engine. Then CFD simulations were carried out to compare the characteristic maps of new and degraded components. Secondly, performance tests of six engines were carried out. A correction method was developed to get the specific component characteristics using test data, which can also analyze and quantify the degradations. Also, a gas turbine performance prediction program was used to find the promising component-exchange plan within 5 given gas turbines to improve total thermal efficiency. Finally, additional test was carried out to verify the performance of the reassembled gas turbine. Through the developed method including 3D scanning, CFD simulation, and correction of component characteristics with engine test data, the component performance degradation of a specific gas turbine can be obtained in quantity. The gas turbine performance predictions based on the acquired characteristic maps showed good agreement with test data. With the help of the method developed in this work, a new gas turbine engine was obtained through exchanging the components of degraded engines, which is at a very low cost and in a short time. The improvement in total thermal efficiency was about 0.3 percentage, which was verified by engine tests.

We are investigating the impact on 3D printed part strength when the extruder is positioned using articulated robotic arms in place of a traditional x-y gantry-style system. One of our printer designs is called the DeXter printer [1] which uses two selective compliance assembly robotic arms (SCARA) to position dual extruders. An advantage of using dual robotic arms is that two extruders can move independently drastically reducing build times, or the second arm can perform additional operations like segment stimulation during the build process [2]. In either case the arms require a collision avoidance process to prevent them from colliding in the part space. A possible drawback of the collision avoidance requirement is that it can result in a time delay along some sections of the layer which, due to cooling, could have adverse effects on the part strength. This research aims to determine how this cooling time will affect the strength of ABS extruded parts. We performed tensile tests on 3D printed part samples for which we altered the g-code to produce a variable time delay during the printing process. Our control sample had a zero-dwell time, and as we increased dwell time we found that the ultimate tensile strength (UTS) did decrease.

Additive manufacturing processes, especially those based on fused filament fabrication (FFF) mechanism, have relatively low productivity and suffer from production scalability issue. One solution is to adopt a collaborative additive manufacturing system that is equipped with multiple extruders working simultaneously to improve productivity. The collaborative additive manufacturing encounters a grand challenge in the scheduling of printing path scanning by different extruders. If not properly scheduled, the extruders may collide into each other or the structures built by earlier scheduled scanning tasks. However, there existed limited research addressing this problem, in particular, lacking the determination of the scanning direction and the scheduling for sub-path scanning. This paper deals with the challenges by developing an improved method to optimally break the existing printing paths into sub-paths and assign these generated sub-paths to different extruders to obtain the lowest possible makespan. A mathematical model is formulated to characterize the problem, and a hybrid algorithm based on an evolutionary algorithm and a heuristic approach is proposed to determine the optimal solutions. The case study has demonstrated the application of the algorithms and compared the results with the existing research. It has been found that the printing time can be reduced by as much as 41.3% based on the available hardware settings.

Owing to its high stiffness and strength, low density, and excellent flexibility, nano-sized graphene oxide (GO) is considered as a competitive material to reinforce metallic materials. Conventional manufacturing methods for GO reinforced metal matrix fabrication include casting and powder metallurgy, both of which demonstrate disadvantages of high reinforcement agglomeration, high cost, and difficulty in fabrication of complex structures. To reduce these problems, it is important to investigate a finely-controlled, cost-saving, and near-net-shaping process for GO reinforced metal matrix manufacturing. Laser additive manufacturing is such a process that mainly includes selective laser sintering / melting (SLS / M) and laser deposition-additive manufacturing (LD-AM). Compared with SLS / M, LD-AM demonstrates parts remanufacturing capability and is capable of fabricating functionally gradient materials. In this investigation, GO reinforced Inconel 718 (IN718) parts, for the first time, are fabricated using LD-AM processes. The effects of GO on flatness, surface roughness, microstructure, microhardness, and wear resistance of LD-AM fabricated GO reinforced IN718 parts are studied. Experimental results show that the introduction of GO is beneficial for enhancing both microhardness and wear resistance but harmful to surface quality of fabricated parts. In addition, the presence of GO has little influence on microstructures.

Carbon fiber reinforced plastic (CFRP) composites were widely used in machinery, automobile, and aerospace industries due to the superior properties of high stiffness, high strength-to-weight ratio, high fatigue resistance, and good wear resistance. In these applications, hole making on CFRP composites was needed for assembly purpose. In different hole making processes, delamination was considered as a crucial issue, leading to premature failure of products. Compared with the conventional CFRP hole making processes (such as twist drilling, milling, grinding, etc.), rotary ultrasonic machine (RUM) had advantages of low cutting force and torque, low surface roughness, and long tool life. Therefore, numbers of researchers worked on RUM processes. The reported investigations mainly focused on the effects of input variables (including machining variables, tool variables, and workpiece properties) on cutting force, torque, surface roughness, and tool life, etc. In addition, effects of cutting tool variables on delamination were also reported. However, there were no reported investigations on effects of machining variables on delamination in RUM of CFRP composites. This investigation, for the first time, reported the effects of ultrasonic power, tool rotation speed, and feedrate on delamination as well as its associated cutting force. Based on the experiments, the results showed that delamination decreased with ultrasonic power increasing, tool rotation speed increasing, or feedrate decreasing. The relationships between cutting force and delamination were also studied.

Carbon fiber reinforced plastic (CFRP) composites have been widely used in many applications due to their superior properties of high strength-weight ratio, high stiffness, and high wear resistance. For assembly purposes, hole making is necessary for different applications of CFRP composites. Rotary ultrasonic machining (RUM) has been proposed and investigated for hole making of CFRP composites. Studies on the effects of machining variables, tool variables, workpiece orientation, and cooling conditions on output variables in RUM of CFRP composites have been investigated. The carbon fiber reinforcement structures of CFRP composites also affect the machining performances and part’s quality. However, there is no reported investigation on studying carbon fiber reinforcement structures’ influences in RUM of CFRP composites. Experiments were conducted for this paper to investigate the effects of carbon fiber reinforcement structure on cutting force, torque, and surface roughness. Three major conclusions can be drawn from the results of this experimental investigation. First, CFRP composites with unidirectional structure led to the smallest cutting force and torque, followed by CFRP composites with plain woven structure and twill woven structure. Second, the surface roughness on CFRP composites with plain woven structure was the smallest, followed by the CFRP composites with unidirectional structure and twill woven structure. In addition, CFRP composites with different reinforcement structures have the same tendencies of output variables with different machining variables.

As the exploitation of oil and gas gradually enters the deep sea, the low-temperature and high-pressure deep-sea environment poses a huge challenge to the flow protection of pipelines (2014a). In this paper, the phase change material sandwich pipeline which uses phase change heat storage and exothermic to maintain the pipeline temperature is taken as the research object, the heat transfer characteristics of the deep-water phase change material sandwich pipe are studied through the combination of theoretical analysis and numerical simulation (2014b). The main contents include: Firstly, through the establishment of two-dimensional and three-dimensional pipe models, analyzed the temperature distribution along the pipeline and the radial temperature distribution of the pipeline under steady oil flow conditions. Secondly, by using transient heat transfer, the effects of phase change material parameters, the proportion of phase change material in the insulation layer, and the difference in the ratio of phase change materials in the insulation layer on the insulation performance are analyzed to obtain the best results. Insulation material and optimal insulation layer layout; finally, the thermal storage and the phase change conditions of the phase-change material sandwich pipe is studied under the re-starting condition. The results show that the effective holding time of the phase change material insulation layer is close to 1.4 times that the non-phase change material insulation layer, and the melting point size has little effect on the insulation material. The closer the phase change material is to the inner tube, the better the insulation effect. This study provide guidance for the design and utilization of phase change material sandwich pipe.

The zirconia toughened alumina (ZTA) parts fabricated by laser engineered net shaping (LENS) process demonstrate problems resulted from poor surface quality. To improve surface quality and to reduce related problems, rotary ultrasonic machining (RUM) process, which combines both grinding process and ultrasonic machining process, has been introduced. In this investigation, the effects of ZrO 2 content and ultrasonic vibration on flatness, surface roughness, microhardness, and cutting force in feeding direction of LENS-fabricated ZTA parts have been studied. Results showed that with the ZrO 2 content increasing, the flatness value increased, the surface roughness value decreased, and the microhardness value firstly increased then decreased. Compared with LENS-fabricated parts, the parts processed by RUM machine exhibited better surface quality with significantly reduced flatness value and surface roughness value. In RUM process, the introduction of ultrasonic vibration was beneficial for reducing cutting force.

As the market demand becomes more diversified and dynamic, the requirements for manufacturing systems feature a high degree of flexibility, low cost, low volume, and short delivery times. One emerging way for such flexible manufacturing is so-called “factory-in-a-box,” by which production modules are installed in a container and transported by a vehicle. The factory-in-a-box manufacturing poses a unique challenge to manufacturing supply chain network since the ease of supply chain reconfiguration when the vehicle moves to a different production site has become a major concern in addition to transportation cost and delivery time. The supply chain design is further complicated by the fact that it is coupled with subassembly planning in manufacturing, which determines appropriate subassembly modules assigned to suppliers. As such, it is critical to understand the interaction between supply chain network reconfigurability and subassembly planning. This paper develops a model using a set of decision variables to jointly characterize the topology of supply chain network and subassembly planning. A binary nonlinear programming model has been developed for the concurrent optimization of subassembly planning and supply chain network with the consideration of reconfiguration of the supply chain structure. One numerical case study was conducted to demonstrate the proposed model by providing a quantitative guideline of reconfiguring supply chain network when the final production site (on a vehicle) changes locations.

Carbon fiber reinforced plastic (CFRP) composites have many excellent properties, which make them be widely used in many applications. After demolding processes, CFRP composites still need additional machining processes to achieve final shape with desired tolerances. Edge trimming is the first machining process performed on composites after their molding processes. Because of carbon fibers’ abrasive properties as well as CFRPs’ properties of inhomogeneity and anisotropy, CFRPs are regarded as the difficult-to-cut materials. Many problems are generated in traditional machining processes. To reduce and solve the problems, edge trimming using rotary ultrasonic machining (RUM) is reported in this manuscript. This paper, for the first time, makes the comparisons on machining performance (cutting forces, torque, and surface roughness) between edge trimming processes with and without ultrasonic vibration assistance. To better understand effects of ultrasonic vibration on such a process, machining mechanisms are also obtained and analyzed. This paper will provide guides for RUM edge trimming of CFRP composites.