Periphery Of Hole Research Articles

Investigation of the Influence of Non-uniform Strain zone on the Crack Propagation of PMMA Material Based on 2D-DIC

Hole defects can lead to non-uniform strain distribution under the impact load, thereby influencing crack propagation behavior. In this paper, 2D-DIC technology was employed to examine the effects of holes of varying sizes and loading rates on crack dynamics in PMMA materials, aiming to elucidate detailed knowledge into the characteristics of crack propagation under complex strain fields. Through DIC analyses, the dynamic evolution of strain fields around the crack tip and hole periphery could be precisely captured, enabling tracking of crack propagation behavior including crack propagation velocity, crack propagation path, and crack deflection angle. It is concluded that the non-uniform strain zones generated by holes exert both inhibitory and attracting effects on crack growth. The influence of non-uniform strain zones on crack propagation increases with the elevation of loading rate and hole size. However, as the loading rate increases, the kinetic energy of the crack itself also increases, necessitating sufficiently large hole sizes to effectively influence crack propagation. Overall, this study provides a detailed experimental explanation of the effects of holes on cracks, which will aid engineers in maximizing the positive impact of holes on material performance and their application in the design of microstructure materials.

Assessment of surface integrity and hole quality in graphene-based NMQL Micro-drilling of ceramic-coated Nimonic 90 for gas turbine applications

Nickel-based superalloys have superior strength properties at higher temperature ranges and thus have become increasingly important in manufacturing gas turbine components for aerospace industry. However, the desire for a larger thrust-weight ratio has raised the typical operating temperature in a gas turbine; thus, thermal barrier coatings are essential. The present work compares the micro-drilling performance of ceramic-coated Nimonic 90 nickel superalloy under dry, flood and 0.5% graphene-based NMQL conditions. The biodegradable acid oil was used as a base oil, and the assessment comprised surface integrity in terms of surface roughness inside the hole and micro-crack formation and hole quality based on the diametrical overcut and taper ratio. Spindle speed (1000, 2000 and 3000 rpm) and feed rate (3, 6, and 9 μm/rev) were changed in three levels, and Taguchi L9 array was applied for the design and analysis of the experiments. Ti-Al-N coated tungsten carbide drill of diameter 700 μm was used, and Analysis of variance (ANOVA) revealed that spindle speed was the utmost important parameter impacting surface roughness, while speed and feed rate both influenced overcut and taper ratio. 0.5% Graphene-based NMQL lubrication condition significantly diminished the surface roughness by 52.67%, overcut by 46.86% and the taper ratio by 48.87% as compared to dry condition. Furthermore, in the NMQL condition, micro-crack development and ceramic layer damage were minimized, resulting in better surface integrity. In addition, burr development was minimized at the hole periphery, and tool wandering was not seen in the NMQL condition. Hence the hole quality was superior in NMQL conditions as compared to the dry and flood lubrication.

CFRP composite drilling through electrical discharge machining using aluminum as fixture plate

Recent developments in manufacturing require holes on composite materials, especially on the carbon fiber reinforced polymer (CFRP) with smooth hole periphery, low delamination, burr formation, taper, better circularity, and a high processing speed. Its non-conductive surface (epoxy layering) limits its machining through electrical discharge machining (EDM). To overcome this limitation, an aluminum fixture has been designed to guide the copper electrode of EDM for producing holes on a CFRP sheet of 1 mm thickness at low machining complexity, cost, time, delamination, burr in hole periphery and without affecting the material’s surface quality and performance. Even components with high geometrical complexity can also be drilled through this approach. Here, a multi-quality analysis called grey relational analysis is developed for examining the hole quality attributes, considering peak current, pulse on and off time, and flushing pressure as input parameters. This approach points out the optimum factor level setting and critical parameters (pulse-on time and peak current) that regulate the hole attributes (entrance and exit diameter, circularity, taper, material removal, and tool wear rate). An artificial neural network model has been designed and trained through experimental data sets. This model can also be adopted during the determination of hole quality attributes when the parameter settings are beyond a defined boundary, as the regression analysis value is very close to 1, and model performance is 4.99e-10. Peak current = 4 A, pulse-on time = 25 µs, pulse-off time=25 µs, and flushing pressure = 0.6 MPa were the optimum drilling parameters. In the initial hole, average burr length is 391.75 μm, and delamination of 539.3 μm is noticed. But burr formation is very negligible with delamination of 350.7 μm being observed with uniform circularity (0.979), low taper angle (−0.81354°), and TWR (0.000069 g/min) under optimum drilling conditions through this drilling approach.

Observation of Portevin-le Chatelier effect in aluminum alloy 7075-w under a heterogeneous stress field

The kinetics of Portevin-Le Chatelier (PLC) bands in the hole-expansion of a circular hole using a flat-headed punch are investigated for a solid-solution heat-treated AA7075 aluminum sheet. This experiment is performed under quasi-static strain-rate and at room temperature. The full strain field in the hole periphery during the entire deformation is measured by a stereo-type digital image correlation system. The observations of PLC band activity are based on the thickness strain-rate field. Each individual PLC band appears aligning along the radial direction, spanning diverse stress states, and propagates along the circumferential direction during the life time from nucleation to dissipation. Furthermore, the nucleation sites of all the PLC bands are recorded during the experiment, which shows that the nucleation frequency of a PLC band is influenced by the plastic anisotropy, and that it increases proportionally to the level of thickness strain.

Role of PVD coating on wear and surface integrity during environment-friendly micro-drilling of Ni-based superalloy

Owing to its capability to significantly mitigate the detrimental effects of flood cooling, minimum quantity lubrication (MQL) has emerged as a potential cooling technique for environment-friendly machining. Although coated cutting tools are widely used in the industry, the role of surface coating on micro tools during mechanical micro-machining is relatively unknown. The current research work seeks to explore the mechanism of physical vapour deposition (PVD)-based TiAlN coating during micro-drilling of a Ni-based superalloy (Incoloy 825). MQL was employed considering potential of tool coating to minimize the usage of cutting fluid. Results indicated increase in edge radius due to coating hindered the performance of coated micro-drill while machining with very low feed (1 μm/rev). This was attributed to ‘size effect’. However, elevation of feed, cutting speed and also machining duration (number of holes drilled) was found to be effective for TiAlN coated micro-drill. Thrust force, oversize error and deformed layer thickness along with hole periphery could be satisfactorily reduced under elevated machining condition. Similarly, improvement in resistance to wear of TiAlN coated micro-drill was evident after drilling 58 number of holes. Overall, a reduction in average flank wear up to 43% was observed for coated micro-drill after 168 number of holes when compared to uncoated micro-drill. Therefore, it is recommended to carefully work out a machining condition conducive for successfully utilizing coated micro-drill in machining of Ni-based superalloy.

On the expansion of a circular hole in an orthotropic elastoplastic thin sheet

The expansion of a circular hole in an orthotropic sheet of AA6022-T4 is examined using a combination of experiments and analysis. This deformation mode is accomplished by stretching a hole at the bottom of a cup during drawing in a hydraulic press with a flat-headed punch. The strain fields are acquired continuously throughout the hole-expansion experiment, using stereo-type Digital Image Correlation. This reveals that despite the axisymmetry of the set-up, non-uniform thinning is observed around the hole throughout the expansion, due to the anisotropy of the material. The greatest thinning occurs at ±45° from the rolling direction. The strains that develop at the hole periphery are significantly higher than the uniform elongation in uniaxial tension (true strain of 0.37 vs. 0.18, respectively). Furthermore, the strain paths change from uniaxial tension around the hole to plane-strain tension and biaxial stretching farther away. The experiments are simulated using finite element analysis. The orthotropy of the material is modeled with the non-quadratic anisotropic yield criterion Yld2000-2D, calibrated by uniaxial tension, plane-strain tension and disk compression experiments. Special attention is placed on the identification of the large-strain hardening curve, which is accomplished by acquiring the strain fields inside the growing neck in uniaxial tension, and using them to minimize the difference between internal and external work. For the material at hand, the Voce hardening law is found to provide the best fit, while the impact of plastic anisotropy on the identification is negligible. It is shown that this modeling framework not only reproduces the structural behavior (e.g., the punch force-displacement) very well, but it also provides accurate predictions of the thinning variation around the hole.

Reducing stress concentration factor by strengthening circular hole with functionally graded incompressible material layer

Abstract The reduction in the stress concentration factor (SCF) around a circular hole in an infinite panel by adding an isotropic functionally graded incompressible material (FGIM) lining is analytically investigated. We assume that the shear modulus varies only in the radial direction either as a power-law function or an exponential function. For a panel subjected to far field uniaxial tension, the problem is solved by superposing the solution of two independent problems – one of biaxial tension and the other of pure shear loading. The former has a closed-form solution and latter's solution is either closed-form or in the form of the Frobenius series which depends on the functional form of the shear modulus. We also study tailoring the FGIM shear modulus in the radial direction to achieve a desired value of the SCF. For the biaxial tension loading, the required shear modulus variation is explicitly obtained, but for the uniaxial tension loading the approximate variation is numerically found. Numerical results for a few example problems reveal that the SCF strongly depends upon the sign of the shear modulus slope at the hole periphery. The FGIM lining alleviates the SCF at the hole periphery and in some cases migrates the point of the maximum hoop stress to the panel interior. Thus not only the SCF but also the maximum hoop stress in the panel interior must be considered in the panel design. The analytical results presented here should serve as benchmarks for verifying the accuracy of approximate/numerical solutions for a panel with a circular hole.

Comparative analysis of chipping mechanics of float glass during rotary ultrasonic drilling and conventional drilling: For multi-shaped tools

Float glass has immense applications such as sensor glass, micro-processor glass and decorative glass; because of its exceptional wear resistance, chemical and thermal characteristics. Nevertheless, researchers are still bearing decisive issues, which affect its application. These issues are profile inaccuracy and chipping because of its poor machining characteristics and hence high precision machining. The objective of the present study is to condemn the chipping related hindrances while using multi-shaped diamond abrasive tools to create blind holes. The tools, which applied, are named as hollow abrasive tool, pinpointed conical tool, flat cylindrical tools and concave circular tool. The experimental trials were performed by rotary ultrasonic drilling (RUD) and CNC conventional drilling (CD). The actual industrial conditions and parameters were considered throughout the experimentation. Physics behind the formation of chipping on hole periphery by RUD and CD are revealed. In addition, individual mechanisms of multi-shape tools with respect to chipping are analyzed. The results show that RUD process has attained the smallest measurement of chip radial distance as compared to CD for all types of tool. Finally, the concave circular tool is found as the best tool particularly to get least chip radial distance during drilling i.e. 0.1145 mm.

Fatigue Life Benefits of Cold Worked Holes in Fastener Joints

Lug joints with fasteners play a vital role in connecting major components of flight vehicles by acting as primary load carrying members. The structural integrity of these fastener joints and in particular fatigue life is of prime concern from the design point of view. Cold working of holes is one of the methods of achieving enhancement of fatigue life of these joints and this aspect is computationally addressed in this paper. The process of cold working is modeled, consists of introduction of a large diameter mandrill into the hole and withdrawing it leaving behind plastically stretched material around the hole periphery. Later one can use this hole with interference or clearance fit pins for better fatigue life. Material non-linear analysis is employed during the cold working process. These issues are addressed in this paper through computational approach using FEM software MSC NASTRAN/PATRAN. The fatigue life is computed at the identified critical locations through stress analysis using modified Basquin’s equation with Morrow’s mean stress effect. Life of the lug joints before and after cold working of the hole are estimated and compared.

Quality Evaluation of Micro Drilled Hole Using Pulsed Nd:YAG Laser: a Case Study on AISI 316

Laser drilling is increasingly becoming a suitable choice for performing micro-drilling on advanced engineering and bio-compatible materials. In laser drilling operation, two types of major defects like spatter deposition and taper are generally encountered. In order to reduce the drilling defects, understanding the influence of process parameters on quality of hole is highly desirable. The influence of process parameters such as laser energy, pulse repetition rate, pulse width and gas pressure on the quality characteristics viz. circularity at entry and exit, taper and spatter area is studied in this work using Taguchi’s L27 orthogonal array. Analysis of variance (ANOVA) indicates that pulse width is most influencing parameter having percentage contribution of 43.981, 51.93, 88.28 and 39.94 for circularity at entry, circularity at exit, taper and spatter area respectively. It is observed that spatter area and heat affected zone (HAZ) increases with increase in laser energy and pulse width. This is due to the fact that heat input increases causing more material to melt but sufficient time is not allowed to completely flush away the molten material. As a result, heat is not dissipated adequately resulting in spatter formation and heat affected zone. The analysis also reveals that increase in pulse repetition rate and gas pressure leads to decrease in spatter area. Increase in pulse repetition rate causes increase in laser power leading to formation of laser supported absorption (LSA) wave which may cause the blockage of input energy. Hence, material ejection becomes less and scope for formation of spatter turns out to be less. Micrographs of drilled surface are analyzed using scanning electron microscope (SEM). The micrograph study suggests that increase in laser energy leads to increase in HAZ and circularity. The study also reveals that increase in pulse repetition rate leads to increase in burr formation in the hole periphery. Empirical models have been proposed to predict the quality characteristics of drilled hole. Mean relative error within 10% between the predicted value from empirical relations and experimental value for quality characteristics of hole indicates the validity of the proposed models. In order to obtain optimum parametric setting for all the quality characteristics, a well-known evolutionary approach known as genetic algorithm (GA) is used. The suggested best parametric conditions are definitely useful for the practitioners to avoid trial-and-error process of setting the process parameters for obtaining laser drilled holes of desired quality.

Study of drilling-induced defects for CFRP composites using new criteria

Drilling carbon fiber reinforced polymer (CFRP) composites is liable to generate serious defects including burrs, tearing, delamination, fiber pullouts and matrix degradation because of their inherent anisotropy in mechanical properties. A comprehensive analysis of the drilling-induced damage for CFRP composites plays a vital role in accurate evaluation of machined hole quality and in assessment of utilized tool performance. The present paper aims to propose a series of adjusted damage criteria allowing a reliable quantification of extents of the most critical defects in drilling CFRP laminates including burrs, tearing and delamination. To verify the applicability of the proposed evaluation criteria, a number of drilling tests were performed on T800/X850 CFRP laminates using three types of drills including brad spur drills, twist drills and dagger drills. The superficial drilling-induced defects residing around the hole periphery were examined by a digital microscope and the interlaminar delamination was characterized using a high-frequency scanning acoustic microscope (SAM). The comparative effectiveness of specialized drill bits in drilling CFRP laminates was evaluated by means of the newly-developed damage criteria. The obtained results highlight the feasibility of the proposed evaluation method in quantifying the drilling-induced defects of CFRP laminates and in distinguishing the cutting performance between utilized drill bits.

Novel internally LVL-reinforced glued laminated timber beams with large holes

A novel timber composite is presented, consisting of glued laminated timber (GLT) from softwoods and intercalated cross-layered plates of laminated veneer lumber (LVL) made of hardwood species, specifically beech. The structure is especially suited for beams with multiple, large rectangular holes, where the LVL acts as a highly efficient internal reinforcement and contributes to a damage-tolerant ultimate load behavior. The load capacity of the composite beam is not induced by the stress concentrations at the corners of the hole, which, in contrast to generic GLT, lead to a sudden propagation of cracks and brittle failure. It is shown that the structure, including the holes, can be designed analytically in a transparent manner by using beam theory, a parallel system approach, and modifications from FEM analysis for the verification of tensile forces at the hole periphery. The composite, firstly used in a recent multi-story building in Australia, significantly improves the competitiveness of timber in building works, which have been limited to steel and reinforced concrete structures.

Effect of Various Parameters on the Temperature Distribution in Conventional and Diamond Coated Hollow Tool Bone Drilling: A Comparative Study

Bone drilling is performed around the world in surgical operations to repair the fractured parts of bones. Significant amount of heat is generated during the bone drilling process which may be one of the causes of thermal necrosis and osteonecrosis. In the present research work drilling experiments were performed on the porcine bone. Efforts were made to reduce the cutting temperature while drilling with the diamond coated hollow tool and the results were compared with the temperature obtained when drilling performed using twist drill bit. Temperature during the bone drilling was measured by embedded thermocouples method which were placed at a location of 1.0, 1.5 and 2.0 mm from the drilled site. Results showed that hollow tool generated lower temperature with respect to the drill bit and temperature continuously decreased with the increase in radial distance from the periphery of drill hole. It was also observed that lower spindle speed, feed rate and drill diameter generated lower temperature for both the drill bits.

Investigating the Potential of Using Off-Axis 3D Woven Composites in Composite Joints\u2019 Applications

The effect of circular notch has been evaluated for three different architectures of three-dimensional (3D) carbon fibre woven composites (orthogonal, ORT; layer-to-layer, LTL; angle interlock, AI) through open-hole quasi-static tension and double-lap bearing strength tests in the off-axis (45°) direction. Damage characterisation is monitored using Digital Image correlation (DIC) for open-hole testing and X-ray Computed Tomography (CT) for double-lap bearing strength test. The off-axis notched 3D woven composites exhibits minor reduction (less than 10 %) of the notched strength compared to the un-notched strength. DIC strain contour clearly show stress/strain localisation regions around the hole periphery and stress/strain redistribution away from the whole due to the z-binder existence, especially for ORT architecture. Up to 50 % bearing strain, no significant difference in the bearing stress/bearing strain response is observed. However when ORT architecture was loaded up to failure, it demonstrates higher strain to failure (~140 %) followed by AI (~105 %) and lastly LTL (~85 %). X-ray CT scans reveal the effect of the z-binder architecture on damage evolution and delamination resistance. The study suggests that off-axis loaded 3D woven composites, especially ORT architecture, has a great potential of overcoming the current challenges facing composite laminates when used in composite joints’ applications.

Fabrication of Si-nanowires controlled by spontaneously formed nanoholes on annealed Au thin films

Si nanowires (Si-NWs) were fabricated by a simple process that consists of deposition of Au thin films, annealing of the Au films to form porous structure and Si wet-etching using the kinetically appearing porous Au films as a template. The deformation behavior of the Au thin films was investigated by scanning electron microscopy and atomic force microscopy. The nanohole diameter and density of the Au films can be controlled by selecting Au film thickness, annealing temperature and annealing time. The formation mechanism of these porous Au films can be explained by a model that consists of nanohole formation at the grain boundaries of the Au films and ridge formation by Au atom diffusion to the hole periphery. The ridge structure suppresses further deformation of the Au films and keeps the nanohole structure kinetically stable. When a thermal energy larger than the activation energy to destroy the ridge structure is supplied, it transforms to the island structure.

Laser Micro-processing of Zr50Cu28Ni7Co15 High-Temperature Shape Memory Alloys

In this paper, an experimental study of laser micro-processing on a Cu-Zr-based shape memory alloy (SMA), which is suitable for high-temperature (HT) applications, is discussed. A first evaluation of the interaction between a laser beam and Zr50Cu28Ni7Co15 HT SMA is highlighted. Single laser pulses at various levels of power and pulse duration were applied to evaluate their effect on the sample surfaces. Blind and through microholes were produced with sizes on the order of a few hundreds of microns; the results were characterized from the morphological viewpoint using a scanning electron microscope. The high beam quality allows the holes to be created with good circularity and little melted material around the hole periphery. An analysis of the chemical composition was performed using energy dispersive spectroscopy, revealing that compositional changes were limited, while important oxidation occurred on the hole surfaces. Additionally, laser micro-cutting tests were also proposed to evaluate the cut edge morphology and dimensions. The main result of this paper concerned the good behavior of the material upon interaction with the laser beam, which suggests that microfeatures can be successfully produced in this alloy.

Fracture analysis of glued laminated timber beams with a hole using a 3D cohesive zone model

Introducing a hole in a glued laminated timber (glulam) beam generally results in a significant decrease in load bearing capacity. Global strength is most often limited by perpendicular to grain fracture with crack initiation at hole periphery and crack propagation in the grain direction. Strength analysis and design is far from trivial, which is reflected by the lack of design criteria in contemporary engineering design codes. This paper presents nonlinear 3D FE-analyses of beams with a hole, carried out using a cohesive zone model based on plasticity theory. Results of numerical analyses are compared to experimental tests showing good agreement. Results of a numerical parameter study relating to beam width and growth ring pattern are presented, showing decreasing nominal beam strength with increasing beam width and that the beam strength is affected by the growth ring pattern. Furthermore, some analyses of the influence of different types of initial cracks are presented.

Fiber laser drilling of Ni46Mn27Ga27 ferromagnetic shape memory alloy

Abstract The interest in ferromagnetic shape memory alloys (SMAs), such as NiMnGa, is increasing, thanks to the functional properties of these smart and functional materials. One of the most evident properties of these systems is their brittleness, which makes attractive the study of unconventional manufacturing processes, such as laser machining. In this work the interaction of laser beam, once focalized on the surface of Ni46Mn27Ga27 [at%] alloy, has been studied. The experiments were performed with a single laser pulse, using a 1 kW continuous wave fiber laser. The morphology of the laser machined surfaces was evaluated using scanning electron microscopy, coupled with energetic dispersion spectroscopy for the measurement of the chemical composition. The results showed that the high quality of the laser beam, coupled with great irradiances available, allow for blind or through holes to be machined on 1.8 mm plates with a single pulse in the order of a few ms. Holes were produced with size in the range of 200–300 μm; despite the long pulse duration, low amount of melted material is produced around the hole periphery. No significant variation of the chemical composition has been detected on the entrance surfaces while the exit ones have been characterized by the loss of Ga content, due to its melting point being significantly lower with respect to the other alloying elements.

Experiment Study on Improving Lubrication of Gundrill under MQL by Shoulder Dub-Off Modification

Coolant for gundrill under MQL is impermissible to be high pressure, large quantity, or direct emission on the interface. These restricts would be seriously unfavorable to lubrication. Experiments reveal that poor lubricating always appear on the hole periphery with dark burns on the hole wall. A prospective solution is to regulate the pressure distribution by modifying the dub-off structure. Its derivation is detailed in this paper. Its validity is demonstrated by practical experiments.

Isolation and characterization of the progenitor cells from the blastema tissue formed at experimentally-created rabbit ear hole.

Objective(s) : Throughout evolution, mammalians have increasingly lost their ability to regenerate structures however rabbits are exceptional since they develop a blastema in their ear wound for regeneration purposes. Blastema consists of a group of undifferentiated cells capable of dividing and differentiating into the ear tissue. The objective of the present study is to isolate, culture expand, and characterize blastema progenitor cells in terms of their in vitro differentiation capacity. Five New Zealand white male rabbits were used in the present study. Using a punching apparatus, a 4-mm hole was created in the animal ears. Following 4 days, the blastema ring which was created in the periphery of primary hole in the ears was removed and cultivated. The cells migrated from the blastema were expanded through 3 successive subcultures and characterized in terms of their potential differentiation, growth characteristics, and culture requirements. The primary cultures tended to be morphologically heterogeneous having spindly-shaped fibroblast-like cells as well as flattened cells. Fibroblast-like cells survived and dominated the cultures. These cells tended to have the osteogenic, chondrogenic, and adipogenic differentiation potentials. They were highly colonogenic and maximum proliferation was achieved when the cells were plated at density of 100 cells/cm2 in a medium which contained 10% fetal bovine serum (FBS). Taken together, blastema tissue-derived stem cells from rabbit ear are of mesenchymal stem cell-like population. Studies similar to this will assist scientist better understanding the nature of blastema tissue formed at rabbit ear to regenerate the wound.