Countersunk Holes Research Articles

Ultimate Strength Study of Structural Bionic CFRP-Sinker Bolt Assemblies Subjected to Preload under Three-Point Bending.

Countersunk head bolted joints are one of the main approaches to joining carbon fiber-reinforced plastics, or CFRP. In this paper, the failure mode and damage evolution of CFRP countersunk bolt components under bending load are studied by imitating water bears, which are born as adult animals and have strong adaptability to life. Based on the Hashin failure criterion, we establish a 3D finite element failure prediction model of a CFRP-countersunk bolted assembly, benchmarked with the experiment. The analysis shows that the simulation results under specified parameters have a good correlation with the experimental results, and can better reflect the three-point bending failure and fracture of the CFRP-countersunk bolted assembly. Based on the specified parameter of the carbon lamina material change, we used the countersunk bolt preload to investigate the stress distribution near the counterbore zone, and to investigate the effect of bolt load on the three-point bending limit load. The results obtained using FEA calculations indicate that the stress distribution around the countersunk hole is related to the laminate direction. The bolt preloading force increasing reduces the load value at the initial damage, and the appropriate preload force will increase the ultimate load of the joint.

Design of the gripper interlock that engages with the DEMO breeding blanket during remote maintenance

The DEMO breeding blanket (BB) must be replaced during the machine lifetime due to the material degradation caused by the neutron irradiation. The large BB segments can therefore be removed through the upper ports of the vacuum vessel by a remotely operated transporter. The size of these ports is however restricted by the magnetic coils causing some of the BB segments to be accessible only on their extremities. The lifting point of these BB segments therefore is away from their centers of gravity also requiring the transfer of bending moments. A concept of the BB transporter was developed recently [1]. It has the required payload capacity and is capable of carrying out also the tilting maneuvers required to extract the BB segments from the VV. The gripper interlock is the interface to the BB segments and is described in this article including the function of its locking mechanism. It has the tightest space constraints of all BB transporter components, and its design is particularly challenging given the large loads to be transferred. The basic concept of the gripper interlock resembles a massive pin with a diameter of approximately 500 mm that is inserted into a countersunk hole in the backside of the BB segment and then locked by an actuated mechanism. The concept allows on the one hand the transfer of large bending moments. The engagement is on the other hand more challenging as compared to the hook of a conventional crane that is required to transfer vertical loads only. In addition the gripper interlock must be designed according to the rules defined for lifting equipment in nuclear power plants and considering increased requirements regarding qualification and in-service inspection since its failure can cause a load drop with the potential to damage the primary confinement.

A Mobile Agent-Based Method to Counter Sinkhole Attacks in Wireless Sensor Networks

A Mobile Agent-Based Method to Counter Sinkhole Attacks in Wireless Sensor Networks

Effect of the countersunk hole depth on tensile-tensile fatigue behavior of riveted specimens of AA2024-T3 alloy

This study investigated the effect of countersunk hole depths (0.65, 0.90, and 1.20 mm) on the fatigue performance of the riveted AA2024-T3 alloy. The fatigue fracture of the samples was observed by scanning electron microscopy. The strain at the countersink hole was analyzed by finite element (FE) method. The stress intensity and stress concentration factor of the countersunk holes were calculated. The rationality of the FE analysis and theoretical calculation was verified by measuring the strain near the countersunk holes. The high cycle fatigue life of the samples with a countersunk depth of 1.20 mm was far less than the other samples. In contrast, the low cycle fatigue life changed insignificantly.

Effects of the pre-hole geometry on the final shape of the countersunk hole

The main objective of this study is to characterize the effects of the pre-hole geometry on the countersinking process. The final shape of the countersunk hole and the punch load were investigated. A finite element model was developed using ABAQUS/Standard. A configuration with maintained blank-holder was used for this study. The adopted model was performed with an elastoplastic behavior and isotropic hardening rule for the workpiece. In this study, an approach based on the definitive screening design (DSD) was performed to perform a parametric study and a statistical analysis to investigate the effects of the geometrical parameters of the pre-hole and their interactions on the countersinking process. The evolution plot of the parameters of the final countersunk hole shape, during the process, was an additional tool to better understand the obtained results. It was concluded that the inner radius of the pre-hole had the most important impact on this final shape. In addition, it was found that the punch load was more affected by the fillet radius of the pre-hole than the other parameters. Concerning the thickness of the workpiece, it had the lowest influence on the process. The experiments were carried out and the obtained results were in good agreement with the numerical ones.

Effects of Countersink Hole on Driving Torques of Screw in Joints Constructed of Medium Density Fiberboard

Aim of study: The aim of this study was to investigate the effect of
 countersink along with some other factors affecting screw driving torques in
 joints made of medium density fiberboard (MDF). There is limited research has
 been done in the field of screw driving torques in wood based composites. In
 all of these studies, the specimen consisted of a single wood-based composite
 material and metal plate which was used for the consistency of the screw
 driving data. However, in this study, the screw driving torques were obtained
 by the specimens consisted of two MDF testing blocks jointed by a screw.
 
 Material and Method: In general, there were two main screw driving
 torques; seating torque (SET) and stripping torque (STT). The MDF testing
 blocks had dimension of 150 mm long × 75 mm wide and two different thicknesses
 were used. For upper testing block, 8-mm-thick MDF and for lower testing block,
 18-mm-thick MDF were used. Torques measurements were obtained by an adjustable
 torque screwdriver. Factors were embedded screw orientation (face-to-face and face-to-side),
 pilot-hole diameter (2.5 and 3.0 mm), pilot-hole depth (12 and 16 mm) and
 countersink type (with and without countersink).
 
 Main results: The results of statistical analysis indicated that the
 four-way interaction among the embedded screw orientation, screw length,
 countersink type and pilot-hole diameter was significant on the mean SET and
 STT in the MDF joints.
 
 Highlights: This study will help MDF manufacturers to understand
 the screw performance of their products in terms of screw driving torques.

Stress concentration factor analysis of countersunk holes using finite element analysis and response surface methodology

ABSTRACT In this paper, finite element analysis and response surface methodology (RSM) were used to analyse and study the stress concentration factor (SCF) of a uniaxially loaded isotropic plate with a centrally placed countersunk hole. In this study, the finite element (FE) model was built in ANSYS and employed to generate SCF values. This FE model was first optimised in terms of mesh properties and then validated with literature data. Using RSM, the effect of the plate and countersunk hole geometries, which was implemented by four dimensionless parameters, on the SCF was presented. Additionally, as suggested by RSM and using ordinary least squared method, a high-accuracy second order equation to predict the SCF value based on the non-dimensional geometric factors was formulated. Finally, this paper suggests an optimum plate and countersunk design geometries to minimise the SCF in countersunk holes in isotropic plates.

Open hole and filled hole progressive damage and failure analysis of composite laminates with a countersunk hole

Countersunk holes are used in bolted joints for creating non-protruding smooth surfaces. As a first step towards a detailed progressive damage and failure analysis of bolted joint configurations, a new model referred to as the Intra-inter crack band model (I2CBM) is used to study open hole tensile/compressive and filled hole tensile/compressive progressive damage and failure. The I2CBM is a unified approach for modeling intralaminar and interlaminar progressive damage and failure in polymer matrix composites. 3D finite elements in the I2CBM formulation can be adapted for modeling individual lamina elements or to model interface delamination elements. A path for communication between the intralaminar and interlaminar failure mechanisms is enabled in the model to overcome limitations associated with homogenized element modeling and to capture complex interactions in a physically correct manner. A non-local crack spacing method is implemented for tracking matrix cracks. Comparisons between test results and I2CBM predictions for the open hole tensile/compressive and filled hole tensile/compressive cases with a countersunk hole configuration are discussed. The effect of bolt pretension on the filled hole failure analysis case is also presented and the failure mechanisms are discussed.

Tension–shear interaction domain for EVA-laminated countersunk point-fixing devices

The present paper aims is to characterize the mechanical behavior of a new embedded point-fixing device for laminated glass for combined tension–shear load cases. This kind of support is based on the principle known as “interlayer junction” in which the anchor is bonded to the interlayer and embedded in the glass panes during the lamination process. The purposes of this innovative point-fixing device are nowadays mainly focused on interior architecture applications: e.g. balustrades, stairs, doors, elevator cars and wells, design furniture, etc., taking advantage of the beautiful aesthetic of an “all-glass” element. This is due to the fact that, contrary to traditional point-fixing bolted connections, the countersunk hole is not passing through the outer glass layer, so that the stainless steel anchor looks like embedded in the glass mass. A comprehensive experimental investigation on the load-bearing capacity under the combined action of tension and shear forces is performed by means of specifically designed test apparatus and procedure. The failure modes in the different direction of load applications are identified and discussed. Finally, in addition to the interaction domain given for combined load cases between tension and shear forces, a simplified analytical interaction expression is also proposed, intended to be used in the practical design applications.

Numerical Analysis of the Influences of Geometrical Deviation on Delamination in Composite Laminates around the Countersunk Hole

During countersunk hole machining, defects like geometrical deviation of the chamfer angle and delamination are easily introduced into the structure. To investigate the influences of geometrical deviation on delamination propagation around the countersunk hole during assembly, a progressive damage model (PDM) combining cohesive element was proposed and validated. Numerical analyses were then carried out to study delamination propagation behavior under the influences of geometrical parameters including delamination factor, chamfer angle, and location of delamination. The results show that when delamination appears at the transition area of the countersunk hole, the load causing the delamination evolution is much smaller than other cases.

Removable shear connector for steel-concrete composite bridges

The conception and experimental assessment of a removable friction-based shear connector (FBSC) for precast steel-concrete composite bridges is presented. The FBSC uses pre-tensioned high-strength steel bolts that pass through countersunk holes drilled on the top flange of the steel beam. Pre-tensioning of the bolts provides the FBSC with significant frictional resistance that essentially prevents relative slip displacement of the concrete slab with respect to the steel beam under service loading. The countersunk holes are grouted to prevent sudden slip of the FBSC when friction resistance is exceeded. Moreover, the FBSC promotes accelerated bridge construction by fully exploiting prefabrication, does not raise issues relevant to precast construction tolerances, and allows rapid bridge disassembly to drastically reduce the time needed to replace any deteriorating structural component (e.g., the bridge deck). A series of 11 push-out tests highlight why the novel structural details of the FBSC result in superior shear load-slip displacement behavior compared to welded shear studs. The paper also quantifies the effects of bolt diameter and bolt preload and presents a design equation to predict the shear resistance of the FBSC.

Fatigue Reliability Analysis of 6156-T6 Riveted Joints based on Detail Fatigue Rating

The fatigue behavior of two kinds of riveted joints 6156-T6 aluminum alloy structures was experimentally investigated. The detail fatigue rating (DFR) values of 6156-T6 is calculated based on statistical analysis of fatigue tests. The fatigue crack initiation and propagation behavior are examined using scanning electron microscopy. The results show that DFR value of 6156-T6 aluminum alloy with riveted lap joints is 97.81MPa, and the DFR value of rivet-filled countersink hole structure is 168.39MPa. The crack initiation sites occurred at the vicinity of the fastener hole in all specimens. The fatigue striations were uniformly spaced in the region of stable crack growth.

Stiffness analysis and optimization in robotic drilling application

Low stiffness characteristics limit the application of industrial robots in the field of precision manufacturing. This paper focuses primarily on the stiffness properties of drilling robots by further studying the stiffness ellipsoid model. A Cartesian compliance model is proposed to describe the robot stiffness in Cartesian space. Based on the compliance model, a quantitative evaluation index of the robot’s processing performance is defined. By choosing a proper drilling posture, the performance index in the cutting tool direction is optimized. Higher accuracy of the countersink depth and hole axial direction can be guaranteed. From the perspective of the robot processing mechanism, the key role of the per-load pressing force is first indicated. By applying a per-load pressing force, the performance index on the machining plane is enhanced. Hole diameter accuracy is improved significantly. A stiffness improving factor used to evaluate the stiffness promotion degree is also proposed. Finally, experiments were conducted to verify the correctness of the proposed model. Drilling experiments were performed to investigate the effectiveness of the robot processing performance index improving methods The principle of pressing force used in engineering applications is given based on processing parameters.

Recognition of Machining Features Based on Identification of Inner/Outer Loops on Basic Face

There exists different feature definitions, but they all agree upon the point of view that considers features as high level entities. Solid models are built from features instances, which are designated as feature attributes, consisting of feature shape attributes, position and orientation of feature with respect to established coordinate system, material characteristics, geometric tolerances. The definition of manufacturing features links the ensemble of interrelated geometric elements to appropriate manufacturing method. This paper proposes a feature recognition algorithm that identifies features, such as simple hole, tapered hole, counterbored hole, counterdrilled hole, countersunk hole, step through/blind, slot through/blind, pocket through/blind, chamfer, fillet, filleted/chamfered slot, filleted/chamfered pocket, pocket/slot island or boss, based on a set of established definitions, with exemplification on slot features.

On geometrical accuracy and integrity of surfaces in multi-mode abrasive waterjet machining of NiTi shape memory alloys

NiTi shape memory alloys are largely employed in the manufacture of high-tech products (e.g. medical, aerospace, sensing). This research reports on the use of multi-mode (i.e. through cutting, countersinking and milling) abrasive waterjet machining of NiTi by investigating the influence of process parameters on the integrity and geometrical accuracy while taking into consideration the secondary temperature and mechanical induced transformations in the workpiece material. The research proved that AWJ machining, if optimally conducted, can generate surfaces that can fulfill the quality requirements (e.g. cut surface: roughness <4μm; countersunk hole: circularity <0.04mm, concentricity <0.15mm; milled surface: roughness <5μm) to make them used for manufacturing parts for the aerospace industry.

Stress concentration analysis for countersunk rivet holes in orthotropic plates

Abstract This research investigates the in-plane stress concentration factor (SCF) in countersunk rivet holes in orthotropic laminated plates under uniaxial tension load. Finite element analysis (FEA) using ANSYS software is used to build and mesh the geometry of a plate containing a countersunk hole, define the boundary and loading conditions, run the analysis and obtain the SCF results. The effect of several geometric and material parameters such as plate thickness, straight-shank radius, countersunk angle, countersunk depth, plate width, and the laminate ply angles on the SCF is also investigated. Finally, multi parameter fit and factorial analyses are applied to establish the relationships between the SCF and the various geometric and material parameters, and to formulate a general equation for the SCF. Based on the results, it is found that the values of the SCF obtained by means of the formulated equation are within 7% of the finite element (FE) results for 96% of the runs and that the maximum overall error is less than 14%.

A modified equation for the stress concentration factor in countersunk holes

The present study introduces an accurate and modified equation for the stress concentration factor of a uniaxially loaded isotropic plate with a centered countersunk hole. ANSYS Parametric Design Language (APDL) was used to build a finite element (FE) model for the plate and to run the analysis. The FE modeling strategy was initially verified and then used to solve for the maximum stress concentration factor at the countersunk hole. The effect of the dimensions of the plate and the countersunk hole, which were represented by four governing dimensionless parameters, on the value of the stress concentration factor was examined by performing several runs of the FE code. Factorial and multi parameter fit analyses were conducted on the FE results to formulate a general parametric equation for the maximum stress concentration factor in terms of the four dimensionless geometric parameters. A comparison between the results of the present equation and an older equation has shown a higher accuracy in the maximum stress concentration factor of the present equation especially at high ratios of countersink depth to plate's thickness for very thick plates (thickness equal to or greater than twice the radius of hole). ► 3-D FE model was built to study the stress concentration around countersunk holes. ► Factorial analysis has determined the main geometric parameters of the SCF equation. ► A general equation of the SCF around countersunk holes was formulated and tested. ► The new equation reduced the error in the SCF of deep sinking holes of an older equation.

Stress intensity factors for surface cracks at countersunk holes

Fatigue crack growth from countersunk fastener holes loaded in remote tensile loading was studied using the transparent polymer PMMA. A single edge corner crack at the bottom of the plate and a single internal surface crack at the sharp intersection between the bore and the countersink were induced in the PMMA specimens by pre-cracking. The specimens were then fatigue tested under constant amplitude remote tensile loading and the ‘back-calculation’ method was used to determine stress intensity factors at several crack front locations. When variations in fatigue crack closure were taken into account, the experimental stress intensity factors agreed well with the computational results at selected crack fronts.

Spectrum Coupon Testing of Fatigue-Resistant Fasteners for an Aging Military Aircraft

Abstract An experimental program of work was undertaken to assess the life improvement gained through utilizing cold expansion technology to enhance the resistance of cracking at fatigue critical locations (FCLs) in an aging military trainer aircraft. The FCLs considered included a countersunk hole and nutplate on two different wing spars. The overall goal of the experimental work was to provide a comparative assessment of the influence of the major variables examined, which included cold expansion method and process, hole size, countersink size, nutplate geometry, flight spectrum, and joint configurations. The results of this work clearly illustrated the inherent sensitivity of life improvement factors to the myriad of variables involved. Nevertheless, the foregoing experimental work clearly demonstrated the valuable life improvement that is provided by cold expansion for nearly all cases examined.

Die Zugschraubenarthrodese von Fingergelenken

Arthrodesis of proximal and distal interphalangeal joints. Joint destruction after primary or secondary arthritis accompanied by activity related pain. Joint instability interfering with pinch and not amenable to soft tissue procedures. Irreversible contracture in flexion or extension. Acute infection. Lack of bone stock. Unusually large medullary canal precluding safe anchorage of the screw. Supine, hand table. Roll of towel under fingers. Tourniquet at upper arm. Elastic band around base of finger in instances of DIP arthrodesis. Regional: plexus- or ring anaesthesia. Arthrodesis using the lagscrew principle. After resection of the destroyed joint surfaces compression of the fragments using screws of the Martin miniset and applying the lagscrew principle. The screw head will be countersunk. Immobilization on a plaster slab supporting forearm, operated and 1 neigh-bouring finger. Physiotherapy. Scew removal is usually not necessary. The screw head sinks into the medullary canal. Lack of sufficient stability. Lack of bony union. Infection. Gaping at site of arthrodesis. Detachment of the extensor tendon. Countersink hole of insufficient size. Between 1982 and 1992 51 patients had 54 lagscrew arthrodeses. 51 arthrodeses in 48 patients could be reexamined at the end of 1992. Average time of follow-up: 3 1/2 years (6 months to 10 years). No postoperative complication was observed and primary fusion was seen in every patient 4 to 13 weeks postoperatively. In 5 instances the screw had to be removed. The angle of arthrodesis varied between 10° and 54°, a vallue determined preoperatively to accommodate the individual needs. The pinch strength reached 75% of that of the finger of the opposite hand in 2/3 of the patients. Symptom-free were 44 patients, 4 had occasional pain (2 had activity related pain of the entire finger and 2 felt pain with changing weather). 86.8% of the patients assessed their result as good or excellent.