Pin Diameter Research Articles

Integration of multi-objective reliability-based design optimization into thermal energy management: Application on phase change material-based heat sinks

Phase change material-based heat sinks are widely used in several industrial applications such as in the field of industrial automation and mechatronics. Nowadays, several researchers aim to obtain an optimal design of these systems in order to ameliorate its performances. Nevertheless, uncertainties are not considered for the majority of these studies. Furthermore, it has been confirmed that deterministic multi-objective optimization (DMOO) may lead to an unreliable design. In this study, a new methodology that leads to perform the Multi-Objective Reliability-Based Design Optimization (MORBDO) for thermal management of a passive cooling system is proposed. It consists in coupling the Finite Element Model (FEM), MORBDO procedures and surrogate approaches. Kriging predictor is used to construct metamodels and then validated using Cross-Validation (CV) and error predictions. A numerical investigation is carried out to study the different DMOO and MORBDO approaches. In this study, a 3D PCM-based round pin-fin heat sink is detailed. The aim of this problem is to minimize two objective functions: the cost (total volume V) and the final cooling time tf by considering both thermal and physical constraints. For this purpose, geometrical uncertain parameters are considered such as length L, height H and ϕ pin diameter of the heat sink. This study leads to develop a well-distributed reliable Pareto solutions by combining the Robust Hybrid Method (RHM) and the Constrained Non-dominated Sorting Genetic Algorithm (C-NSGA-II). Then, the efficiency of the proposed MORBDO-RHM approach for PCM-based heat sink is verified.

The effect of tool pin size and taper angle on the thermal process and plastic material flow in friction stir welding

Friction stir welding (FSW) tool pin, as a critical component of FSW tool, plays an important role in determining the final joint properties by affecting the heat generation, plastic material flow, welding loads, and so on. However, the effects of tool pin on heat and mass transfer in FSW are not elucidated and quantitative studied. In the present study, a validated model was adopted to quantitatively analyze the effects of pin size and taper angle on the thermal process and plastic material flow in FSW. The effects of pin root diameter, pin tip diameter, and pin taper angle on heat and mass transfer in FSW were quantitatively investigated, respectively. It reveals that the torque and transverse force imposed on the pin are increased with the increase of the pin diameters (including its root diameter, its tip diameter, and its size in condition of constant taper angle), while the total tool torque varies a little for the tool pin diameter considered in this study. When the pin diameters increase, the viscosity of the materials near the pin is decreased, while the temperature as well as the flow velocity is increased. More plastic material near the tool could rotate around the tool with an increase of the pin diameter. The TMAZ boundary is enlarged with larger pin diameters in FSW. Particularly, the shear layer thickness of the same horizontal plane in the range of 1 mm < z < 5 mm is significantly enlarged with an increase of pin root diameters. However, the shear layer thickness of the same horizontal plane in the region of z < 5 mm is increased when using a larger pin tip diameter. In addition, maximum width of TMAZ boundary at the top surface of workpiece was not affected by pin diameters. The model is validated by experimental results. It could lay a solid foundation for optimizing the tool pin size and taper angle in FSW.

“ICMPC” Effects due to tool design during FSW process of aluminium alloy AA7075 T-6

ABSTRACT The present study explores the implications of friction stir welding (FSW) geometries of instruments on AA7075 T-6 welds. For tougher materials, it is assumed that threaded FSW instruments are beneficial, like AA7075 T-6. However, the structure of the tool shoulder and the concavity of the shoulder surface also play an important role in determining the quality characteristics of friction stir welds. The effect of threaded FSW instruments on using various shoulder diameters, pin diameters, AA7075 aluminium alloys were investigated. Diameters, concavity of the shoulder surface and speeds. Experiments were to research the effects of these instruments on welds of AA7075 with respect to welding cross-sectional area, tensile strength, and percent elongation. A mathematical trend using response, the effects of the tool geometries on the welds were predicted to the regression analysis of surfaces, diameter of the shoulder and concavity of the shoulder surface. The relationship effects of the control variables (geometrical parameters of the instrument) on the responses such as weld power, weld cross segment and percent elongation have been investigated. The modelling approach developed in this study was found to be sufficient to predict the effects of the FSW instrument welding geometrical variables.

Evaluation of the Structural Behaviour of a Unilateral External Fixator for Osteosynthesis

Background: External fixation is an osteosynthesis technique particularly useful in trauma surgery and Damage Control Orthopedics (DCO). However, complications, such as pin loosening and pin tract infections, are fairly common. For reducing thermal damage and infection rates, monocortical pins have been proposed as an alternative to the most used bicortical pins. However, there is a lack of studies regarding their mechanical properties. Objective: The aim of the study is to assess the static and dynamic stability of a unilateral external fixator experimentally when applied through monocortical pins for the reduction of femur and tibia fractures. Methods: A modular unilateral external fixator was used and a total number of 6 pins were used per test. The static tests were performed in displacement control by applying a vertical displacement to the upper fixture at 1 mm/min until a tension load of 380 N was reached. The dynamic tests were performed by applying a sinusoidal displacement. During each test, forces and crosshead displacements were acquired. Two different stiffness indexes were assessed. Results: By comparing the two anatomic regions, it was found that the fixator behaves stiffer when mounted on the femur, regardless of the pins used, while stiffnesses comparable to the femur ones are reached by the tibia when 4 mm diameter pins are used. Static analysis revealed excellent fixator stability when implanted with 4 mm diameter monocortical pins on both anatomic regions. On the contrary, two tibia and one femur samples showed failures at the bone-pin interface when 3 mm diameter pins were used. Conclusion: Dynamic analysis showed no substantial difference between the tested configurations and confirmed the fixator's ability to sustain cyclic loading without further damage to the sample.

Effect of tool size on AA6061‐T6 double‐sided friction stir welds

The present work investigates the effects of tool size on microstructural evolution, tensile strength, and microhardness on double-sided friction stir welding of 12.7-mm-thick AA6061-T6 plates. Three different tools were designed having pin diameters equal to pin lengths of 6.25, 7.5, and 8.5 mm and corresponding shoulder diameters of 18.75, 22.5, and 24.5 mm, respectively. The welds obtained with these three tools were designated as Welds A, B, and C, respectively. Results showed the highest tensile and yield strength for Weld B. The tensile fracture appearance of Welds A and B indicated reasonable necking with crack initiation and propagation through heat affected zone on the advancing side of the weld. However, in the Weld C, fracture appeared in the stir zone near the confluence of thermo-mechanically affected zone. Electron back scatter diffraction indicates dominance of high angle grain boundaries and major shear textures C and components which corresponds to {001}<110>, <110>, and < > textures in the weld nugget.

Friction stir welding of AA2024 and AA6061 using various pin profile

The research work deals with to join two dissimilar aluminum alloys by solid state welding process compared to fusion welding processes and compared with fusion welding process, fusion welds tend to produce more defects while joining dissimilar materials. The major problem of the two dissimilar metals involve in welding process have different mechanical properties and microstructures which in turn may affect welding parameters like weld current, hold time, weld force etc. In order to overcome these issues, Friction Stir Welding (FSW) can be used to get rid of defects since it uses a non-consumable tool and also produces defect free welds compared to other welding processes. This thesis work aims to joining an aluminum alloy of 2024 and aluminum alloy of 6061. The plates are joined by means of octagon probe tool made of high carbon high chromium steel (D2 tool steel). Other issues while welding dissimilar aluminum alloys are phase transformation change and selection of welding parameters (rotational speed, transvers speed, pin diameter, shoulder diameter, D/d ratio and etc.) From conducted trail experiment aluminum alloy of 2024 and aluminum alloy of 6061 by using octagon probe tool made by HC-HCR tool it was observed that a lower welding speed 500 rpm at starting stage lack of filling took place and after thermo-mechanical heating took place that produce better weld while compared to weld at higher speeds (710 rpm, and 1000 rpm) with same transvers speed of 20 mm/min.

Effect of tool material and process parameters on friction stir weld formation of maraging steel

ABSTRACT 18% Ni maraging steel is an ultra-high strength steel widely used in defence and aerospace applications. Fusion welding of maraging steel is encountered with a drop in properties due to the segregation of alloying element and hence, solid-state welding process such as friction stir welding (FSW) is a possible alternative. However, welding of high strength material using FSW is a challenge considering the tool material durability, tool material cost, and selection of tool geometry and process parameters. Therefore, the main focus of this paper is towards the selection of tool geometry, tool material, and process parameters that will result in least tool wear/failure in addition to obtaining defect-free welds of maraging steel using FSW. It was observed that polycrystalline cubic boron nitride (PCBN) and tungsten-molybdenum are durable tool material for welding maraging steel. It is recommended to use a minimum tool pin diameter (top 12 mm and bottom 8 mm) and shoulder diameter (20 mm) below which failure of pin and surface defects are encountered during FSW. It is also observed that there exists a narrow range of tool rotational speed (250–450 rpm) and tool travel speed (25 mm/min) at which defect-free maraging steel welds can be obtained.

Assessment of heat transfer and pressure drop of metal foam-pin-fin heat sink

Numerical investigation on Metal Foam Pin-Fin Heat Sink (MFPFHS) has been conducted and compared to the traditional Solid Pin-Fin Heat Sink (SPFHS). For investigating turbulent convection heat transfer and friction factor characteristics in the MPFHS, the 3D steady continuity, momentum, and energy equations are discretized using the finite volume approach. The key parameters investigated here are; the pin diameter ratio (DR) i.e., reducing the upper diameter and increasing the lower diameter simultaneously, the number of pins and the pins’ height ratio (HR) i.e., reducing the pin height and increasing its diameter simultaneously. The overall pin volume is retained constant throughout the whole study. The results show that (i) the MFPF exhibit a superior enhancement in the heat dissipation and reduction in the frictional losses compared to the solid pin-fin (SPF), (ii) a great heat transfer and PEC enhancement is observed when DR increases associated with a decrease in the friction factor, (iii) heat transfer and performance evaluation criteria (PEC) enhancement (with a maximum value of 3.7) is obtained when the number of MFPF increases with a large decrease in the friction factor, (iv) high augmentation in PEC with a peak value of 3.8 but up to a certain value is seen, however, with an association of high increase in the friction factor.

An Approach to Improving the Mechanical Properties of Friction Stir Spot Welded Joints on the Basis of Hook Formation Mechanism

Background: Partial metallurgical bond (namely 'hook') is formed between the overlapped metal sheets during friction stir spot welding (FSSW). The geometry of hook is found to significantly affect the mechanical performance of FSSWed joints, while that how to adjust hook geometry to a better state remains to be studied. Methods: The conventional FSSW joints under different plunge depths and dwelling time were obtained. The cross-sectional morphology of each spot weld was investigated to clarify the material flow behavior and deduce the formation mechanism of hook. The tensile shear strength and fracture features were examined to reveal the effect of hook geometry on the mechanical properties. Results: The weld geometry affects the tensile shear strength of FSSWed joints by determining their fracture modes. The formation mechanism of hook is deduced by a material flow model. In the toolplunging stage, the faying interface is broken by upward-flowing materials, hook is therefore initiated and driven up gradually. During the tool-dwelling stage, hook continues to migrate to the lowpressure zone, surrounding the stir zone. Conclusion: The uncertainty of crack-propagating endpoint along hook makes it difficult to ensure the mechanical properties of welds. If the hook endpoint has not yet reached the low-pressure zone at the end of welding process, welds with ideal hook geometry can be obtained. Target friction stir spot welds were produced by the use of a tool possessing smaller pin diameter.

Hysteretic and seismic performance of dual self-centering variable friction damper braces

A novel dual self-centering variable friction damper (DSC-VFD) brace was introduced to achieve greater post-yield stiffness and a better energy dissipation capability. To evaluate its hysteretic response with a novel flag shape, a new uniaxial material with different loading and unloading stiffnesses was developed based on the OpenSees platform in this study. The actual initial stiffness of the DSC-VFD brace was significantly lower than the theoretical value because of the tube length and pin diameter tolerances. The initial stiffness modification coefficients of the DSC-VFD brace were defined, and their calculation equations were established. Because of the uneven gap openings along the friction plates, the matrix displacement method was applied to determine the different gap openings under the tension and compression stages. Then, the hysteretic response of the DSC-VFD brace was calculated with the user-defined model; the model results were in good agreement with the experimental result, verifying the reliability of the proposed model. Simulation models were used to study the crucial parameters for the hysteretic response of the DSC-VFD brace. Finally, nonlinear dynamic analyses of a four-story braced frame were conducted to study the seismic performance of the DSC-VFD brace with a novel flag shape. The results showed that the DSC-VFD brace with a larger post-yield stiffness provided stable self-centering behavior and an effective energy dissipation capability. The high loading stiffness and energy dissipation ability effectively decreased the deformations of the braced structures and improved their seismic responses.

Thermal design and management of micro-pin fin heat sinks for energy-efficient three-dimensional stacked integrated circuits

Three-dimensional stacked electronics have substantially improved the electrical performance of integrated circuits. However, given the geometrical complexity and high pressure drop they entail, thermal management difficulties and energy requirements are exacerbated owing to the inapplicability of thermal management schemes. In this study, the thermal and hydrodynamic characteristics of various micro-pin fin arrays were investigated to maximize heat dissipation while minimizing the energy consumption. Specifically, a 10 × 10 mm2 micro-pin fin array was fabricated on an eight-inch silicon wafer via microfabrication. A Pyrex cover was bonded anodically with the top side of the micro-pin fins to prevent leakage, and a titanium/gold thin film serpentine heater was used to supply uniform heat flux on the backside of the micro-pin fin array. Subsequently, the heat transfer and pressure drop in the micro-pin fin heat sinks were obtained experimentally with various micro-pin fin geometries having pin diameter Df = 38–100 µm, transverse pin spacing ST = 74–301 µm, longitudinal pin spacing SL = 74–301 µm and pin height Hf = 90–207 µm. Thereafter, the geometrical and operational effects on heat transfer and pressure drop were investigated based on a consolidated database cumulated from the literature. Altogether, 256 data points from 21 geometrical combinations were explored from existing relevant studies to obtain optimized geometric and operating conditions in the micro-pin fin arrays over a wide range of geometrical and operating conditions: Reynolds number Re = 35–491.3, heat flux q" = 0–114 W/cm2, pin diameter Df = 38–559 µm, pin spacing S = 74–800 µm, and pin height Hf = 90–845 µm. Subsequently, new empirical correlations based on the consolidated database were formulated to describe the Nusselt number and fanning friction factor in the micro-pin fin arrays. These correlations provide suitable predictions in comparison with those based on extant correlations.

Finite Element Analysis of Different Pin Diameter of External Fixator in Treating Tibia Fracture

Biomechanical perspective of external fixator is one of the biggest elements that should be considered in treating fracture bone. This is due to the mechanical behavior of the structure could be analyzed and optimized in order to avoid failure, increase bone fracture healing rate and prevents preterm screw loosening. There are three significant factors that affect the stability of external fixator and those are the placement of pin at the bone, configuration and components of external fixator. All these factors contribute to a question, what is the optimum pin diameter which exerts good stress distribution? To date, the research on the above-mentioned factors are limited in the literature. Therefore, this study was conducted to evaluate the unilateral external fixator with different pin sizes in treating tibia shaft fracture via the finite element method. First and foremost, the development of the tibia shaft fracture was conducted using Mimics software. The computed tomography (CT) data image was utilized to develop three-dimensional tibia bone followed by crafting fracture on the bone. Meanwhile, the unilateral external fixator was developed using SolidWorks software. In this study, five pin diameters (4.5, 5.0, 5.5, 6.0 and 6.5 mm) were developed and analyzed. Both tibia bone and external fixator were meshed in 3-matic software. Simulation of this configuration took place in a finite element software, Marc.Mentat. From the findings, it is shown that the larger diameter of pin demonstrated the lowest stress distribution. The size of the 5.5mm pin shows optimum diameter in terms of stress distribution with the value of 21.50 MPa in bone and 143.33 MPa in fixator. Meanwhile the displacement value of 1.42mm in bone and 1.20mm in fixator. In conclusion, it is suggested that the pin diameter of 5.5 mm is the most favorable option in treating tibia shaft fracture in terms of mechanical perspective.

Surface characteristics modification of lm25 aluminum alloy – 5% sic particulate metal matrix composites by friction stir processing

Stir casting is employed for successful casting of aluminum-based metal matrix composite (MMC) plates of 12 mm thickness. Surface imperfections, porosity and reinforcement agglomeration are the main concerns in stir casting processes. Solid state friction stir processing (FSP) enhances mechanical characteristics by grain refinement and uniform distribution of reinforcement of MMC. Some of the crucial specifications of FSP include the tool traverse speed, tool rotational speed, tool shoulder diameter (D/d) ratio, pin design, pin length and axial force. In this investigation, five varying tool traverse speeds ranging between 20 mm and 60 mm per min were experimented on the stir cast plates. The wear rate, microstructure and microhardness evaluation on FSP plates revealed that wear resistance of 40 mm/min tool traverse speed FSP plate is superior and attribute to significant microhardness values. In addition, fine grains, uniform distribution and SiC particle bonding with aluminum matrix contribute to effective resistance to wear.

Fiber Orientation Mechanism of Continuous\xa0Fiber Reinforced Thermoplastics Hybrid Parts Joined with Metallic Pins

Continuous Fiber Reinforced Thermoplastic (CFRT) hybrid parts offer interesting possibilities for lightweight application, which can exceed the capabilities of mono material metal or CFRT parts. In this case, the joining technology oftentimes is the limiting factor. This study investigates a joining operation with metal pin structures which are additively manufactured via powder bed fusion featuring different diameters and tip geometries, which are inserted into the locally infrared heated CFRT part. The resulting fiber rearrangement is assessed using transmitted light microscopy, confocal laser scanning microscopy as well as micro-computer-tomography. It could be shown that for all assessed pin variants a similar distinct fiber displacement can be seen and that the pin diameter has a significant effect on the resulting fiber orientation with smaller pin diameters being advantageous because of gentle fiber displacement and reduced undulation. The tip geometry has only minor effect on the fiber orientation. Especially in the X/Y plane no systematic influence of the tip geometry on the fiber displacement could be observed. Based on the gained insights a three-stage model of the fiber orientation processes is proposed.

Heat Transfer in Rotating, Trailing Edge, Converging Channels With Partial Length Pin-Fins

AbstractIn the current study, the heat transfer and pressure drop characteristics of a rotating, partial pin-finned, cooling channel that has a trapezoidal cross section and converges from the hub to tip in both the streamwise and spanwise directions are experimentally investigated. To model the geometry of an internal trailing edge cooling passage, the channel is oriented with respect to the direction of rotation (β = 120 deg). Isolated copper plates are used to obtain regionally averaged heat transfer coefficients on the leading and trailing surfaces. Pressure drop is measured using pressure taps placed at the inlet and outlet of the channel. Utilizing Dp = 5 mm diameter pins, a staggered array is created. For this array, the streamwise pin-spacing, Sy/Dp = 2.1, was kept constant; however, the spanwise pin-spacing, Sx/Dp, was varied from the hub to tip between 3 and 2.6 due to the channel convergence. Experiments were conducted for two partial pin-fin sets having pin length-to-diameter ratios of Sz/Dp = 0.4 and 0.2. The rotation number was varied from 0 to 0.21 by ranging the inlet Reynolds number from 10,000 to 40,000 and rotation speed from 0 to 300 rpm. A significant decrease in pressure loss and a slight reduction in heat transfer enhancement are observed with the use of partial pin-fins compared with the previously reported full pin-fin converging channel study. This provides better thermal performances of the partial pin-fin arrays compared with the full pin-fin array, in the converging channels.

Optimization Of Process Parameters For Peak Temperature During Friction Stir Welding Of Aluminum Alloy

Friction stir welding is a solid state joining method used to join materials which cannot be joined by fusion welding. In this joining method, heat produced due to the friction between tool and workpiece is used to weld workpiece material. Heat input depends upon amount of friction caused by process parameters such as rotational speed, weld speed, tool geometry, axial force etc. In the present study, effect of friction stir welding process parameters such as shoulder to pin diameter ratio, rotational speed and weld speed on peak temperature obtained during friction stir welding of aluminum alloy were investigated using taguchi L9 orthogonal array. ANOVA result shows that shoulder to pin diameter ratio (D/d) is the most significant factor affecting on peak temperature obtained during the FSW.

Friction Stir Welding of 5052-H18 Aluminum Alloy: Modeling and Process Parameter Optimization

In this paper, rolled sheets of aluminum alloy 5052-H18 were joined by friction stir welding. Several samples were welded by varying the principal parameters including tool rotational speed, linear speed, tool shoulder diameter, and pin diameter. Response surface methodology (RSM) was used as the statistical design of experiment technique for parameter optimization. A predictive model was developed to determine optimum parameters that maximize tensile strength. Results showed that the tool rotational speed was the most important parameters affecting the tensile strength of aluminum alloy 5052 joints. Maximum tensile strength was achieved using the rotational speed of 1233 rpm, the linear speed of 107 mm/min, the shoulder diameter of 12.8 mm, and the pin diameter of 1.8 mm. The difference in tensile strength between the predicted value and the measured value was 2.1%. The effect of tool rotational speed and linear speed on the size of the heat-affected zone was investigated. Consequently, a three-dimensional model was developed to predict the size of heat-affected zone and the temperature history of the material during the FSW process and the results were compared with experimental data.

Multi responses taguchi optimization using overlaid contour plot and desirability function

Optimization is the process of getting an optimal response. The taguchi design is an experimental design that is often used to get robust responses. In the multi-response Taguchi design, the optimization process is carried out by considering all responses simultaneously. Cases study used in this research is aluminum production cases with four treatments, namely tool rotational speed, welding speed, shoulder tool diameter and pin diameter. Each treatment was tried with three levels. Optimized responses are tensile strength, average microhardness and average grain size.The purpose of this research is determining the point of optimization using response surface method and desirability function. The optimization results obtained are tool rotational speed of 1100 RPM, Welding speed of 40 mm/min, Shoulder diameter of 21 mm, and pin diameter of 5.4 mm.

Investigation of Endwall Heat Transfer in Staggered Pin Fin Arrays

Abstract Arrays of staggered pin fins are a typical geometry found in the trailing edge region of modern airfoils. If coolant is supplied by bleeding from the mid-section of the airfoil instead of provided through the root, the channel length is insufficiently long to reach a fully developed flow which is commonly found from the fifth row downstream. This present study focuses on the developing section (four rows) of a staggered array with a height-to-diameter ratio of 2 and a spanwise and streamwise spacing of 2.5, respectively. Measurements are conducted at Reynolds numbers of 10,000 and 30,000 based on the maximum velocity and pin diameter. Stereoscopic particle image velocimetry (PIV) is used to describe the flow field and turbulence characteristics in the wake of the first and third row pin. It is found that the dominating vortical structures depend highly on the Reynolds number. A transient thermochromic liquid crystal (TLC) technique is used to obtain local heat transfer coefficients on the endwall which are then discussed in the context with the vortical structures. The structure of the horseshoe vortex and the transient wake shedding behaves differently in the first and third row. The interaction of both vortex systems affects directly the endwall heat transfer. The results are supplemented by a thorough discussion of TLC and PIV uncertainty.

Influence of D/d ratio on stir zone formation and properties of friction stir welded dissimilar joints of AA5086 and AA6061 aluminum alloys

A well-known method known as Friction stir welding (FSW) is used for combining materials that are distinct from each other. In FSW, a profiled spinning shoulder shifts between sheets of the sections that are to be connected. Heat is produced due to the friction between the base and the tool shoulder when the tool is turning along the weld line. In contrast to fusion welding processes, the heat produced is lower. In these works, the effect of macro/microstructures characterization and the tensile characteristics of the dissimilar AA5086 and AA606I aluminum alloys on the ratio of tool shoulder diameter and tool pin diameter (D/d) used in the FSW were explored. This study shows the superior tensile characteristics on welding components in contrast to the counters made of the sealing units made using a tool profile of threaded cylinders, a 1 ° tool tilting angle, tool rotation speed of 1100 rpm, the welding speed of 22 mm/min and the shoulder diameter is 21 mm. Further, the joints fabricated using threaded cylinder tool profile exhibited superior macro structure compared to its counter parts.