Pin Loading Research Articles

Failure of Unidirectional-woven Composite Laminated Pin-loaded Joints

A combined test and numerical study has been conducted for the failure analysis of unidirectional and woven composite laminated joints of an aircraft control rod. Joints with nine different geometries were tested under pin loading to evaluate the effects of the joint geometry on the failure load and mode. Nonlinear finite element analyses are performed with consideration of the contact and friction between the pin and the laminate. Failure was estimated on the characteristic curve using the Tsai-Wu and Yamada-Sun criteria. It was found that a finite element analysis based on the Tsai-Wu failure criterion with a friction coefficient of 0.1 most accurately predicts the failure load and mode of the joints.

Wide-band Circular Patch Antenna with 2-pin Loading for Wireless Communications

A wide-band microstrip circular patch antenna with two short circuiting pin loading is proposed for wireless communications. By using rigorous theory the dominant cavity modes of the patch are studied and it is found that the first four modes of the patch can act as good radiators. Numerical results show that by a proper choice of the pins and feed locations, one can achieve wide band operation with bandwidth as high as 45%. Design examples are presented as wideband patch antennas for wireless communications over the broad band 1.8–3.0 GHz.

Finite Element Analysis of Fastener Joints in Metallic and Orthotropic Structures

Joints are essential to connect different components of a structure or sub-assemblies and they are inevitable in any large scale engineering structure. Among various methods of joining, fastener (pin) joints are common in cases where periodic assembly and dis-assembly are required. To understand the mechanism of load transfer in these joints, extensive studies have been made in the past. In the present work, NISA code for finite element analysis is made use to understand the mechanics of load transfer in such joints. The basic configuration considered is actually a pin in a plate for both metallic as well as orthotropic plates. Both the pin loading and plate loading cases have been studied. The effect of load parameter, stresses and type of fit namely push, clearance or interference on contact/separation angle have been studied and presented. The results obtained could be of immediate value to practical problems.

A Study of Pin Joints in Composite Laminated Structures

Fiber reinforced composites have emerged as high performance materials for a variety of engineering applications due to their higher specific strength and stiffness compared to those of metallic bulk materials. They can be designed to provide the desired strength and stiffness in the required direction in any particular region of structure. Owing to these properties, composites will remain as one of the key materials in structural engineering for years to come. A circular hole in a laminated composite plate with a rigid pin is the basic configuration to study and understand the mechanics of load transfer in a pin joint. Three cases:, clearance, push and interference fit, are studied. Radial and tangential stresses along the whole boundary are studied and presented. Symmetrical composites of different lay-ups with pin loading case are considered for the analysis. NISA finite element software code has been used for the analysis. The results of the analysis demonstrate that the interference fit, where the contact is larger than for push and clearance fits, has the least value of maximum radial contact pressure. The maximum tangential stresses occur near the transition point between contact and separation.

Accurate stress intensity factor solutions for corner cracks at a hole

Laboratory test and in-service experience shows fatigue cracks at holes exhibit unsymmetric growth; thus, the need for the new solutions is paramount. Stress intensity factor, K, solutions for symmetric and unsymmetric corner cracks at a hole subject to general loading were determined using a hp-version of the finite element method (FEM) in conjunction with a mathematical splitting scheme to enable efficient, accurate calculations. In traditional applications of the FEM, mesh generation is labor intensive; however, using the splitting scheme, stress intensity functions are obtained without explicitly including the crack in the FE mesh of the global structure. By using the hp-version of FEM, a set of K-solutions converging exponentially fast to the exact solution is obtained. The crack is analyzed in the local domain with easily generated FE meshes. All structurally significant crack shapes were considered; specifically, crack depth to crack length ratios ( a/ c) of 0.1–10.0, crack depth to sheet thickness ratios ( a/ t) of 0.10–0.99, and hole radius to sheet thickness ratios ( r/ t)=1.0. The loading conditions were remote tension, remote bending, and pin loading (bearing). In addition, all combinations of a/ c and a/ t are analyzed at each side of the hole; thus 226,875 solutions were developed with control of the error in the computed K solutions. Calculated relative error is generally much smaller than 1% along the entire crack front including the vertex regions. Comparisons are made to solutions in the open literature. The new K solutions show the literature solutions are, in general, accurate for all three load conditions; however, for the extreme cases of a/ c, a/ t, and r/ t; the literature solutions differ by as much as 26%.

일방향-평직 복합재 혼합 적층판의 체결부 강도 연구

일방향-평직 복합재 혼합 적층판의 체결부 파손하중 및 파손모우드를 결정하기 위한 실험과 유한요소해석을 수행하였다. 체결부 실험은 끝단거리 대 원공직경의 비 및 시편 폭과 원공직경의 비가 다른 총 9가지의 모델에 대하여 편하중을 가하여 수행하였다. 체결부 파손해석을 위한 방법의 검토를 위해, MSC/NASTRAN을 사용하여 핀과 모재의 접촉 및 마찰을 고려한 비선형 해석을 수행하였다. 파손여부는 특성곡선 상에서 Tsai-Wu 방법과 Yamada-Sun 방법을 사용하여 평가하였다. 적층판의 체결부 파손하중 및 파손모우드는 원공 중심에서 끝단까지의 거리가 작거나, 시편의 폭이 작을 경우 파손하중에 큰 영향을 미치지만, 일정값 이상이 되면 파손하중과 파손모우드의 변화는 거의 없는 것으로 밝혀졌다. 특성길이 방법에 의한 유한요소해석은 대체로 파손하중과 파손모우드를 비교적 잘 예측하는 것을 볼 수 있었다. The failure load and mode of the unidirectional and fabric hybrid composite laminate joints are studied by test and finite element analysis. Test is conducted for the specimens with nine various geometries under pin loading. Finite element analysis is performed considering the contact and friction effects between the pin and laminate by MSC/NASTRAN. Failure is estimated by Tsai-Wu and Yamada-Sun criteria on the characteristic curve. While the failure of the specimens with the small width and edge length are much affected by the joint geometry, the geometry effects are negligible in the specimens with large width and edge length. Finite element analysis based on the characteristic length method reasonably predicts the failure load and mode of the joints.

Stress intensity factors and crack interaction in adjacent holes

In this analytical investigation, stress intensity factors, K, are calculated for oblique part-elliptical through cracks nucleating and growing from an array of collinear holes subjected to remote tension, bending, and pin loading. The finite element method is used with model validation through comparisons to known stress concentration factors solutions. The three-dimensional virtual crack closure technique is used to calculate the new K solutions. This work was motivated by the need to predict fatigue crack growth in transport aircraft fuselage lap-splice skin joints. Fatigue crack growth of adjacent through cracks with oblique crack fronts can now be predicted using the results of this investigation.

Servo-Hydraulic Pin Loading Device (HPLD) for in Situ Ice Testing

A hydraulic test instrument has been designed and fabricated to perform fracture experiments on edge-cracked pin-loaded floating square plates of ice. Because ice has large grains relative to metals, large specimen sizes are necessary. To preserve the natural temperature and salinity distributions in the ice sheet, the fracture tests must be performed in situ. the servohydraulic in situ pin loading device described in this paper uses a two-actuator feedback-control configuration to accurately impart a load while actively controlling the moment about the estimated neutral axis of the ice sheet to be zero. This system can be used to perform tests in both load and displacement control and can perform low load level, high frequency tests not previously possible with a pneumatic flatjack system. Stable crack growth was observed under displacement control.

Bearing Strength of Plain Woven C/C Composites.

This paper describes the mechanical properties of plain woven carbon-carbon composites under pin loading. Bearing strength tests without lateral constraint were performed using specimens with different geometrical parameters : width, edge distance, and thickness. The minimum ratios of both width-to-pin diameter and edge distance-to-pin diameter to induce the bearing failure were estimated. The bearing strength depended on the specimen thickness. Delaminated layers that have no load-carrying capacity proved to affect the bearing strength. The thickness of no load-carrying layers was independent of the specimen thickness and was estimated to be 1.3mm for the materials studied.

Effects of hole machining defects on strength and fatigue life of composite laminates

The effects of hole machining defects on strength and fatigue life of carbon/epoxy laminates subjected to static and fatigue loading are presented. Dry specimens were subjected to pin loading and uniaxial compressive loading at room temperature. The KTH method, a new method which gives defect-free holes, was used to machine holes in the specimens. For comparison, holes were also machined using two traditional drilling techniques causing varying extents of damage. X-ray techniques were used to detect the hole machining defects. The permanent deflection of compressively loaded specimens was monitored during cyclic loading. Hole machining defects significantly reduced the static and fatigue strengths of pin-loaded laminates; the effects on the strengths of compressively loaded laminates were less pronounced.

Optimum Design of a Ceramic Tensile Creep Specimen Using a Finite Element Method.

An optimization procedure for designing a ceramic tensile creep specimen to minimize stress concentration is carried out using a finite element method. The effect of pin loading and the specimen geometry are considered in the stress distribution calculations. A growing contact zone between the pin and the specimen has been incorporated into the problem solution scheme as the load is increased to its full value. The optimization procedures are performed for the specimen, and all design variables including pinhole location and pinhole diameter, head width, neck radius, and gauge length are determined based on a set of constraints imposed on the problem. In addition, for the purpose of assessing the possibility of delayed failure outside the gage section, power-law creep in the tensile specimen is considered in the analysis. Using a particular grade of advanced ceramics as an example, it is found that if the specimen is not designed properly, significant creep deformation and stress redistribution may occur in the head of the specimen resulting in undesirable (delayed) head failure of the specimen during the creep test.

Bearing strength of carbon/epoxy composite laminates

Fracture behavior of carbon/epoxy laminates under pin loading is studied experimentally and analytically. Effects of ratios of specimen width to hole diameter and edge distance to hole diameter on bearing strength are investigated. Characteristic length of the laminates obtained using the HK model is in good agreement with the experimental data. The larger the hole size induced, the lower the bearing strength measured under pin loading. The bearing strength and failure mode could be predicted using the HK model and Zhang's analytical solution of stress distribution around a pin load hole. Chamis' method for prediction of bearing strength is also considered to predict failure mode and bearing strength. A modification of Chamis' method is made using a factor of rupture. The bearing strength predicted by the modified method is reasonably close to the experimental data.

Stress Concentration Equations for Straight-Shank and Countersunk Holes in Plates

Stress concentration equations for straight shank and countersunk holes in a large plate subjected to various loading conditions encountered in service were developed from three-dimensional finite element solutions. For straight shank holes, three types of loading: remote tension, remote bending, and pin loading were considered; and for the countersunk hole only remote tension and bending loads were considered. The equations are within one percent of the finite element results and are valid for isotropic materials with Poisson’s ratio of 0.3.

The Effect of External Fixator Pin Geometry and Dynamic Loading on Bone Remodelling at the Pin-Bone Interface (PBI), in an In Vivo Sheep Tibia Model

SummaryThe purpose of this study was to study the effects of pin design and dynamic loading on the biological response of bone at the pin-bone interface (PBI). An electro-pneumatic pin-loading device was used to mimic the forces that would be experienced by external fixator pins, during patient ambulation following repair of a fracture with external skeletal fixation. The remodelling response was assessed histologically with fluorescence microscopy of plasticembedded undecalcified pin-bone sections, and surface-stained histomorphometry.There were no significant differences between the AO Schanz and Howmedica Apex 5.0 mm diameter self-tapping pin designs when they were inserted in 4.5 mm diameter predrilled pilot holes. When pin type was controlled for, significant differences (p<0.05) existed between loaded and control groups as well as between entry (near) and exit (far) cortices. Less bone resorption was observed in the non-loaded group in comparison to the dynamically loaded group, and bone resorption in the near cortex consistently exceeded the amount of bone resorption in the far cortex for both treatment groups.The purpose of this study was to examine the effects of pin design and dynamic pin loading on the remodelling response of cortical bone at the pin-bone interface (PBI) of intact sheep tibiae. No significant differences were demonstrated between pin designs; however, significant differences (p<0.05) existed between loaded versus control pins, as well as between entry and exit cortices.

Enhancing External Skeletal Fixation Pin Performance: Consideration of the Pin-Bone Interface

SummaryThe integrity of an external skeletal fixator relies heavily on the pin-bone interface (PBI). Investigation of this interface have focused on histological, mechanical, thermal and clinical assessments. In this review the factors which are important for optimizing the strength and longevity of the PBI are presented. Pin design, pin insertion technique, bone quality and tissue response are considered.External skeletal fixation is used increasingly in human and veterinary orthopaedics. Pin loosening and infection are the primary causes of device failure and patient morbidity. Using several different techniques, researchers have identified a number of factors which affect the integrity of the pin-bone interface. These include pin design, pin insertion technique, initial bone quality and the osseous response to pin implantation and loading.

Analytical solutions for load transfer through smooth elastic pin in an infinite orthotropic plate

Analytical solutions are developed for stresses in an infinite orthotropic plate with smooth elastic pin under pin and plate loading. The pin could be of interference, push or clearance fit. A two-dimensional plane stress elastic analysis using a complex variable formulation in conjunction with equidistant boundary collocation scheme for satisfying boundary conditions is carried out. An inverse technique is used to obtain loads, stresses and displacements for a specified contact/separation configuration. Numerical results are presented which bring out the effect of pin modulus of elasticity and the degree of orthotropy of plate on bearing stress, hoop stress and load contact behaviour. The results indicate that decrease in the pin modulus of elasticity relative to that of the plate ( E p E 1 ) decreases the bearing stresses at the pin-plate interface.

Designs of low stress I/O pin attach structures

Three low-stress pin attachment structures were developed for the glass ceramic-copper multilayer ceramic (MLC) packaging technology used in IBM ES 9000 processors. The structures include the multilayer thin-film I/O pads, taper-headed pin and low-stress solder as the joining alloy. All of them were shown to reduce the pin-joint stress significantly and, consequently, are more compatible with the glass-ceramic module. The authors summarize both experimental and finite-element analysis studies to optimize the stress of the pin-attach system such that the pins can be joined to the glass-ceramic MLC with good reliability. The design goal was to have a pin-joint structure in which the ceramic and the pin-joint will survive a pin-pull test up to 10 lbs with a repairable pin-shank failure mode. The combined stresses generated from the braze, pin loading, and I/O pad should not exceed the fracture strength of the ceramic substrate. Finite-element modeling identified high-stress regions and possible failure modes of each pin joint design. The three approaches taken to reduce the stress of the pin-joint are described. >

ピン負荷を受けるＣＦＲＰ積層板の力学挙動および面圧強さの支配因子について

ピン負荷を受けるＣＦＲＰ積層板の力学挙動および面圧強さの支配因子について

Calculation of low-cycle fatigue under nonproportional loading conditions

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Weight function method for three dimensional crack problems—II. Application to surface cracks at a hole in finite thickness plates under stress gradients

The weight function method developed in part I is used to determine stress intensity factors for half-elliptical surface cracks at a hole in finite thickness plates under polynomial crack face loading. Superpositions of these results allow determination of stress intensity factors for this crack configuration under general stress distributions. The approach is demonstrated by obtaining stress intensity factors for a variety of load cases including biaxial tension (compression), wedge loading in the hole and simulated pin loading. Both single and double crack configurations are considered and their difference in stress intensity factors is investigated. These results are compared, where possible, with other solutions available in the literature. Very good agreement is obtained.