The Mechanics of Threaded Fasteners and Bolted Joints for Engineering and Design

Description

The Mechanics of Threaded Fasteners and Bolted Joints outlines how threaded fasteners and bolted joints fail, how these failures can be remedied, and ultimately how to avoid them altogether through tightening methods, material strength, and avoiding loosening. The book demonstrates how to select the appropriate tightening method and determine the optimal tightening procedure for varying nominal diameters. Using the finite element method, it discusses characteristics of stress concentration and fatigue strength and covers bolt force variation due to elastic interaction. The separation of the plate interface via increased external force as the primary cause of fatigue failure in threaded fasteners is discussed, with effective countermeasures provided. Empirical equations of thermal contact coefficient and apparent thermal contact coefficient in simple form are included as well.   Front Cover The Mechanics of Threaded Fasteners and Bolted Joints for Engineering and Design Copyright Contents Preface List of symbols Chapter 1: Thread standards and forms 1.1. Brief history of screw threads and relevant research activities 1.2. Geometry and application purposes of screw threads 1.3. Standards of screw threads 1.3.1. Standard specifications of screw threads 1.3.2. Basic profile of screw threads 1.4. Thread pitch and number of threads 1.4.1. Mathematical expression of Helix 1.4.2. Coarse screw threads and fine screw threads 1.4.3. Number of threads and lead angle 1.4.4. Contact area between male and female threads 1.4.5. Nonsimilarity of threaded fasteners 1.5. Clamping configuration and various threaded fasteners 1.5.1. Bolt-nut connection and stud 1.5.2. Geometric factors affecting mechanical behavior of threaded fasteners 1.5.3. Contact pressure distribution at plate interface and shape of pressure cone 1.6. Strength, thermal and mechanical properties of threaded fastener materials 1.6.1. Materials used for threaded fasteners 1.6.2. Factors to consider in selecting materials Chapter 2: Fundamentals of threaded fasteners 2.1. Strength of threaded fasteners 2.1.1. Occurrence locations of rupture and failure of threaded fasteners 2.1.2. Strength in tightening process 2.1.3. Strength in service condition 2.1.4. Friction coefficients affecting mechanical behavior of bolted joints 2.2. Stiffness of threaded fasteners 2.2.1. Relationship between stiffness and mechanical behavior in bolted joints 2.2.2. Stiffness evaluation using one-dimensional spring elements 2.2.3. Equivalent lengths of engaged threads and bolt head 2.2.4. Compression stiffness of fastened plates 2.2.5. Evaluation of spring constants composing a bolted joint by FEM 2.2.6. Relationship between mechanical behavior and spring constant of each part of a bolted joint 2.3. True profile of cross-section of screw threads 2.3.1. Cross-section of triangular screw threads [41] 2.3.2. Cross-section of screw threads of various shapes [42] 2.4. True cross-sectional area of screw threads 2.5. Finite element models with helical shape of screw threads 2.5.1. Previous modeling schemes of helical thread model Method-1 Method-2 Method-3 Method-4 2.5.2. Helical thread modeling using mathematical expressions of cross-section [49] 2.6. Interface stiffness in bolted joints 2.6.1. Interface stiffness at mating surfaces 2.6.2. Interface stiffness in normal and tangential directions [56] 2.6.3. Simple formula for evaluating interface stiffness in normal direction 2.7. Thermal contact resistance in bolted joints Chapter 3: Mechanics of the tightening process of threaded fasteners 3.1. Summary of various tightening methods and comparison of tightening characteristics 3.2. Torque control method 3.2.1. Relationship between tightening torque and axial bolt force 3.2.2. Simple equation relating tightening torque to axial bolt force through the friction coefficient 3.2.3. Advantages of the torque control method and influencing factors on tightening accuracy Inclination of nut- or bolt head-bearing surface [69] Warping and flatness on plate surface 3.2.4. Self-locking criteria and efficiency of screw threads 3.2.5. Measuring method of axial bolt force, tightening torque, and friction coefficient 3.2.6. Behavior of torque and axial bolt force after releasing tightening torque 3.2.7. Simple strategy for reducing bolt force scatter [75] 3.2.8. Tightening characteristics and strength of bottoming studs 3.2.9. Bolt strength in tightening process 3.3. Elastic angle control method 3.3.1. Tightening principle 3.3.2. Equation relating axial bolt force to nut rotation angle by taking account of surface roughness 3.3.3. Application range and tightening guidelines Suitable application range Guidelines for tightening operation 3.4. Direct tension method using hydraulic tensioner 3.4.1. Tightening principle 3.4.2. Effective tensile coefficient 3.4.3. Effects of surface roughness and nut rundown torque 3.4.4. Application range and tightening guidelines Suitable application range Guidelines for tightening operation 3.5. Thermal expansion method using bolt heater 3.5.1. Tightening principle [81] 3.5.2. Simplified model for evaluating tightening process 3.5.3. Equation relating axial bolt force to heating temperature [82] 3.5.4. Application range and tightening guidelines Suitable application range Guidelines for tightening operation 3.6. New tightening method utilizing real-time measurement of nut factor [85] 3.6.1. Development intention 3.6.2. Tightening principle 3.6.3. Verification of proposed method using prototype tightening device 3.7. Sequential tightening of multibolted joints and induced elastic interaction 3.7.1. Tightening operation of bolt-nut connections and elastic interaction 3.7.2. Effect of joint geometry on elastic interaction 3.7.3. Estimation of bolt force scatter and optimal tightening procedure 3.8. Energy required for tightening threaded fasteners 3.8.1. Tightening energy consumed in the torque control method [94] 3.8.2. Calculation of tightening energy for various influencing factors Chapter 4: Static and fatigue strengths of threaded fastener 4.1. Load distribution and ratio of flank loads of engaged threads 4.1.1. Load distribution in bolt-nut connections 4.1.2. Load distribution in eyebolts and eyenuts 4.1.3. Analysis of ratio of flank loads by FEM 4.2. Static strength and stress concentration in threaded fasteners 4.2.1. Stress concentration and stress concentration factor 4.2.2. Stress concentration in threaded fasteners 4.2.3. Mechanism of stress concentration at thread root 4.2.4. Evaluation of stress concentration at thread root 4.2.5. Stress concentration and plastic deformation of threaded fasteners 4.2.6. Reduction strategy of stress concentration at thread root 4.3. Stress distribution along thread root 4.3.1. Stress concentration in bolt-nut connections 4.3.2. Effect of thread pitch and number of threads 4.3.3. Stress concentration of engaged threads in main body side 4.4. Fatigue failure of screw threads 4.4.1. Relationship between metal fatigue and stress amplitude 4.4.2. Fatigue failure of threaded fasteners 4.4.3. Influencing factors on fatigue strength of screw threads 4.5. Evaluation method of fatigue strength of threaded fasteners 4.5.1. Summary of the bolted joint diagram 4.5.2. Essential problems involved in the bolted joint diagram 4.5.3. Verification of bolted joint diagram by FEM 4.5.4. Axial bolt force vs external force diagram 4.5.5. Estimation method of fatigue strength and stress amplitude of threaded fasteners 4.6. Separation phenomena of plate Interface and stress amplitude 4.6.1. Stress amplitude in bolted joints under eccentric external load 4.6.2. Verification of interface separation phenomena by FEM 4.7. Stress amplitude along thread root 4.7.1. Finite element analysis using helical thread models 4.7.2. Stress amplitude and fatigue failure of bolt-nut connections 4.7.3. Stress amplitude and fatigue failure of engaged threads in main body side [20] 4.7.4. Stress amplitude and plastic deformation [20] 4.8. Improvement measures of fatigue strength of threaded fasteners Chapter 5: Bolted joints under thermal load 5.1. Fundamentals of thermal and mechanical behaviors of bolted joints 5.1.1. Thermal deformation and thermal stress [120] 5.1.2. Mechanism of bolt force variation due to thermal load 5.1.3. Simple formula for calculating bolt force variation 5.2. Evaluation method of amount of heat transferred through contact surface 5.2.1. Measuring method of thermal contact coefficient 5.2.2. Thermal contact coefficient at interface composed of identical materials [122] 5.2.3. Thermal contact coefficient at interface composed of dissimilar materials [121] 5.3. Evaluation method of amount of heat transferred through a small gap [124] 5.4. Thermal contact coefficient and apparent thermal contact coefficient in bolted joints 5.5. Analysis of thermal and mechanical behaviors of bolted joints by FEM 5.5.1. Evaluation of thermal and mechanical behaviors using an axisymmetric FE model 5.5.2. Evaluation of thermal and mechanical behaviors using a three-dimensional FE model 5.6. Seizure of threaded fasteners 5.6.1. Conditions prone to seizure 5.6.2. Hypothesis proposed on seizure occurrence Chapter 6: Loosening of threaded fasteners 6.1. Rotation loosening and nonrotation loosening 6.2. Why bolted joints are easy to loosen 6.3. Bolt force reduction due to rotation loosening 6.3.1. Mechanism of rotation loosening 6.3.2. Bolt force reduction due to return rotation of nut 6.3.3. Prevention methods of rotation loosening 6.3.4. Finite element simulation of rotation loosening caused by repeated shear load 6.4. Bolt force reduction due to nonrotation loosening 6.4.1. Mechanism of nonrotation loosening 6.4.2. Estimation method of amount of embedment 6.4.3. Bolt force reduction due to embedment 6.4.4. Prevention methods of nonrotation loosening 6.4.5. Loosening due to difference in thermal expansion 6.5. Inspection of bolt tightening state by torque measurement [144] 6.5.1. Inspection methods of bolted joint integrity 6.5.2. Release torque method 6.5.3. Retightening torque method 6.5.4. Marking method 6.5.5. Verification of inspection methods by experiment and inspection guidelines Chapter 7: Thermal and mechanical behaviors of pipe flange connections 7.1. Thermal and mechanical behaviors inherent to pipe flange connections 7.2. Gasket compression characteristics and flange rotation 7.3. Temperature dependency of gasket compression characteristics 7.4. Analysis of thermal and mechanical behaviors in running condition and during shutdown operation 7.5. Thermal and mechanical behaviors of pipe flange connections for low temperature fluids [148,149] Chapter 8: Learning from problems and accidents with threaded fasteners 8.1. Introduction 8.2. Fatigue failure of wheel bolts for large vehicles specified in JIS 8.2.1. Summary of wheel falling-off accidents 8.2.2. Joint configuration, tightening method, and fatigue failure of threaded fasteners 8.2.3. Mechanics of tightening process of wheel bolts and its related problems [151,152] 8.2.4. Scatters in bolt force and friction coefficient and its reduction strategy 8.2.5. Measurement of stress amplitude of wheel bolts [153] 8.2.6. Analysis of stress amplitude of wheel bolts by FEM [154] 8.2.7. Development of tightening apparatus equipped with multiple shafts and torque control mechanism [155] 8.3. Fatigue failure of threaded portion of rollercoaster axle 8.4. Mechanical properties of multibolted joints under shear loads [158] 8.4.1. Multibolted joints clamped by friction type and bearing type 8.4.2. Mechanism of shear force transfer in bearing type joints 8.4.3. Finite element analysis of multibolted joints clamped by bearing type 8.4.4. Analysis of shear load-bearing ratio using spring models 8.5. Strength and load capacity of reamer bolts used for rigid flanged shaft couplings [160,161] 8.5.1. Configuration and rupture phenomena of reamer bolts 8.5.2. Mechanical properties of reamer bolts and its related problems 8.5.3. Shear force transfer ratio and bending stress 8.5.4. Effects of fit, friction coefficient, and bolt stress 8.5.5. Effects of bolt force scatter and alignment error [161] 8.6. Tightening process of reamer bolt by cooled fitting [164] 8.6.1. Tightening procedure and its related problems 8.6.2. Estimation method of amount of bolt force reduction due to temperature increase 8.6.3. Proposition of tightening guidelines 8.7. Sealing performance of oil seal plugs used for hydraulic equipment [166] 8.7.1. Tightening characteristics and geometric errors of oil seal plugs 8.7.2. Relationship between contact pressure distribution and sealing performance 8.7.3. Dynamic analysis of sealing performance using one-dimensional spring models 8.8. Mode analysis of bolted joints [56] 8.8.1. Relationship between axial bolt force and natural frequency 8.8.2. Natural vibration analysis by taking account of Interface stiffness 8.9. Effective finite element analysis for bolted joints 8.9.1. Finite element models of bolted joints 8.9.2. Simple models for engaged thread portion 8.9.3. Two-dimensional bolt model used for bolt force generation 8.9.4. Improvement of computational efficiency utilizing geometric symmetry [175] References Index Back Cover