Browse Topic: Fasteners

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Mitigating Cracking in COP Optics through Annealing and Step-Torquing2026-26-0764To be published on 06/01/2026
Polymeric optical materials such as Cyclo Olefin Polymer (COP) are adopted in aerospace lighting systems due to their excellent optical clarity, dimensional stability, moldability and weight saving advantages over glass. However, their relatively low toughness and the presence of residual molding stress make them prone to crack initiation during mechanical fastening. During its installation, crack formation was consistently observed around self-tapping screw interfaces, raising concerns over reliability, maintainability, and compliance with durability requirements. A structured Design of Experiments (DOE) was performed to identify root causes and evaluate potential mitigation methods. The investigation revealed that residual stresses in the COP material, combined with localized stress concentrations during screw tightening, were the primary drivers of crack initiation. Two complementary process improvements were identified and validated as part of mitigation plan: (i) annealing of the
S, Nikhil, Singh, Abhimanyu Kumar, Katageri, Praveen, SP, Pradeep, Chandra, Praveen
Finite Element Approach for Fatigue Life Prediction of Threaded Bolts with Experimental Validation2026-26-0745To be published on 06/01/2026
Predicting the fatigue life of threaded bolts is crucial in aerospace and mechanical assemblies where cyclic loading can cause early joint failure. Existing studies, like [1], have created S-N curves for high-strength bolts under different pretension and temperature conditions through experimentation. However, there are few numerical methods that can replicate these results, especially for bolts without pretension. This study develops and validates a finite element analysis (FEA) methodology to predict the fatigue performance of pretensioned threaded bolts under axial loading, using the experimentally derived Series-2 S-N data for M20 high-strength bolts with pretension. The approach employs a detailed 3D solid model with explicit thread geometry and a two-step transient structural analysis. This first simulates the bolt tightening process to establish a realistic preload, followed by the application of a service tensile load. Local stress distributions are analyzed to extract peak
K R, Lesanth, S, Suhail Ahmed, C, Arunvetrivel, P, Krishnakumar, P S, Premkumar, Vasantharaj, C
Design Optimization of Aircraft Light Optics: Eliminating Fasteners by Flexure-Based Clamp to Mitigate the Crack Formation and Validation through HALT2026-26-0750To be published on 06/01/2026
Aircraft lighting systems play a vital role in ensuring operational safety, visibility, and regulatory compliance. Exterior lighting systems are essential for aircraft identification, navigation, collision avoidance, and ground operations under varying environmental conditions. These systems typically include navigation lights, anti-collision lights, landing and taxi lights. An aircraft lighting system comprises light sources, optical elements, electronic control units, power interfaces, wiring harnesses, and mechanical mounting structures. Among these components, optics are critical as they control light distribution, intensity, color accuracy, and efficiency while withstanding harsh aerospace environments such as vibration, thermal cycling, and aerodynamic loads. Aircraft exterior lights are subjected to severe thermo-mechanical stresses due to aerodynamic loading, vibration, and thermal cycling. The use of high-performance optical polymers such as Cyclo Olefin Polymers (COP
Vialta, Frederico, S, Nikhil, Katageri, Praveen, SP, Pradeep, Singh, Abhimanyu Kumar
BOLT, MACHINE - DOUBLE HEXAGON, EXTENDED WASHER HEAD, CLOSE TOLERANCE SHANK, UNS N07001, 165 KSI, .3750-24 UNJF-3AAS9726A (Current)5/7/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - DOUBLE HEX EXTENDED WASHER HEAD, PD SHANK, UNS N07718 - 185 KSIAS3580B (Current)5/7/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - DOUBLE HEXAGON, EXTENDED WASHER HEAD, CLOSE TOLERANCE SHANK, UNS N07001, 165 KSI, .1900-32 UNJF-3AAS9723A (Historical)5/7/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - DOUBLE HEXAGON, EXTENDED WASHER HEAD, CLOSE TOLERANCE SHANK, UNS N07001, 165 KSI, .3125-24 UNJF-3AAS9725A (Current)5/7/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - DOUBLE HEXAGON EXTENDED WASHER HEAD, CLOSE TOLERANCE SHANK, AMS4967 (UNS R56400), 160 KSI, .1900-32 UNJF-3AAS3147C (Current)5/6/2026
E-25 General Standards for Aerospace and Propulsion Systems
NUT, SELF-LOCKING, DOUBLE HEXAGON, SILVER PLATED, EXTENDED WRENCH PAD 180 KSI, 1400 °F, UNS N07001AS3552B (Current)5/5/2026
E-25 General Standards for Aerospace and Propulsion Systems
NUT, SELF-LOCKING, DOUBLE HEXAGON, SILVER PLATED, COUNTERBORED 180 KSI, 1400 °F, UNS N07001AS3553B (Current)5/5/2026
E-25 General Standards for Aerospace and Propulsion Systems
ASSEMBLY NUT AND CLIP, REMOVABLE SELF-LOCKING NUT, UNS S66286, CLASS 160 KSI/1200 °FAS3547B (Current)5/5/2026
E-25 General Standards for Aerospace and Propulsion Systems
STUD, LOCKED IN, KEY LOCKED, UNS S66286, 140 KSI/1200 °F HEAVY-DUTY, SELF-BROACHING KEYSAS3544A (Current)5/5/2026
E-25 General Standards for Aerospace and Propulsion Systems
NUT, SELF-LOCKING, DOUBLE HEXAGON, SOLID FILM LUBRICATED, EXTENDED WRENCH PAD, 160 KSI, 800 °F, UNS S66286AS3563E (Current)5/5/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, SHEAR - DOUBLE HEX HEAD, UNS N07718 - 185 KSIAS3574C (Current)5/4/2026
E-25 General Standards for Aerospace and Propulsion Systems
RECESS, INTERNAL, TORX® PARALOBE® DRIVE, DIMENSIONS OF RECESS AND GAGEAS8538 (Current)5/4/2026
THIS STANDARD SPECIFIES BASIC DIMENSIONS, CHARACTERISTICS, AND ENGINEERING REQUIREMENTS FOR TORX® PARALOBE® RECESSES.
E-25 General Standards for Aerospace and Propulsion Systems
INSERT, SCREW THREAD, SELF-LOCKING LOCKED IN, KEY LOCKED, EXTRA HEAVY DUTY, SELF-BROACHING KEYS, UNS S66286AS3546B (Current)5/4/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - DOUBLE HEXAGON EXTENDED WASHER HEAD, CLOSE TOLERANCE SHANK, COBALT-NICKEL ALLOY, UNS R30159, 260 KSI MINAS3658B (Current)5/4/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - DOUBLE HEXAGON EXTENDED WASHER HEAD, DRILLED, CLOSE TOLERANCE SHANK, COBALT-NICKEL ALLOY, UNS R30159, 260 KSI MINAS3659A (Current)5/4/2026
E-25 General Standards for Aerospace and Propulsion Systems
NUT, SELF-LOCKING, DOUBLE HEXAGON, SOLID FILM LUBRICATED, COUNTERBORED, 160 KSI, 800 °F, UNS S66286AS3564F (Current)5/4/2026
E-25 General Standards for Aerospace and Propulsion Systems
INSERT, SCREW THREAD, NON-LOCKING, LOCKED IN, KEY LOCKED, EXTRA HEAVY-DUTY, SELF-BROACHING KEYS, UNS S66286AS3573B (Current)5/4/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - HEXAGON HEAD, DRILLED 1 HOLE, PD SHANK, CRES (UNS S66286), .5000-20 UNJF-3AAS3112B (Current)5/1/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - HEXAGON HEAD, DRILLED 1 HOLE, PD SHANK, CRES AMS5731 (UNS S66286), .3125-24 UNJF-3AAS3109B (Current)5/1/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - HEXAGON HEAD, DRILLED 1 HOLE, PD SHANK, CRES AMS5731 (UNS S66286), .2500-28 UNJF-3AAS3108B (Current)5/1/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - HEXAGON HEAD, DRILLED 1 HOLE, PD SHANK, CRES AMS5731(UNS S66826), .4375-20 UNJF-3AAS3111B (Current)5/1/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - HEXAGON HEAD, DRILLED 1 HOLE, PD SHANK, CRES AMS5731 (UNS S66286), .3750-24 UNJF-3AAS3110B (Current)5/1/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - HEXAGON HEAD, DRILLED 1 HOLE, PD SHANK, CRES AMS5731 (UNS S66286), .1900-32 UNJF-3AAS3107B (Current)5/1/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - HEXAGON HEAD, DRILLED 1 HOLE, PD SHANK, CRES AMS5731 (UNS S66286), .5625-18 UNJF-3AAS3113B (Current)5/1/2026
E-25 General Standards for Aerospace and Propulsion Systems
SCREW, MACHINE - HEXAGON HEAD, DRILLED 1 HOLE, PD SHANK, CRES AMS5731(UNS S66286), .1640-36 UNJF-3AAS3106B (Current)4/30/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - DOUBLE HEXAGON EXTENDED WASHER HEAD, PD SHANK, BLACK OXIDE, STEEL, UNS G87400, 125 KSI MIN, .3750-24 UNF-3AAS91601D (Current)4/29/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - DOUBLE HEX EXTENDED WASHER HEAD, CLOSE TOLERANCE SHANK, UNS S66286 - 160 KSIAS3530C (Current)4/28/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - DOUBLE HEXAGON EXTENDED WASHER HEAD, DRILLED, PD SHANK, NICKEL ALLOY, UNS N07718, 185 KSI MIN, .5625-18 UNJF-3AAS3249E (Current)4/27/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - DOUBLE HEXAGON EXTENDED WASHER HEAD, DRILLED, PD SHANK, NICKEL ALLOY, UNS N07718, 185 KSI MIN, .5000-20 UNJF-3AAS3248E (Current)4/26/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - DOUBLE HEX EXTENDED WASHER HEAD, DRILLED, CLOSE TOL SHANK, AMS5643 (UNS S17400), 140 KSI, 2500-28 UNJF-3AAS3175C (Current)4/26/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - DOUBLE HEX EXTENDED WASHER HEAD, DRILLED, CLOSE TOL SHANK, AMS5643 (UNS S17400), 140 KSI, .3125-24 UNJF-3AAS3176C (Current)4/25/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - DOUBLE HEX EXTENDED WASHER HEAD, DRILLED, CLOSE TOL SHANK, AMS5643 (UNS S17400), 140 KSI, .4375-20 UNJF-3AAS3178C (Current)4/23/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - DOUBLE HEXAGON EXTENDED WASHER HEAD, DRILLED, PD SHANK, COBALT-NICKEL ALLOY, UNS R30159, 260 KSI MINAS3623C (Current)4/20/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - HEXAGON HEAD, DRILLED 6 HOLES, PD SHANK, AMS5731, UNS S66286, .3125-24 UNJF-3AAS3116B (Current)4/16/2026
E-25 General Standards for Aerospace and Propulsion Systems
STUD - STRAIGHT, KEY LOCKED, CRES (SIMILAR TO UNS S66286) .3125-24 UNJF X .3125-24 UNJFAS3092A (Current)4/16/2026
E-25 General Standards for Aerospace and Propulsion Systems
STUD - STRAIGHT, KEY LOCKED, CRES (UNS S66286) .3750-24 UNJF X .3750-24 UNJFAS3093A (Current)4/16/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - HEXAGON HEAD, PD SHANK, NICKEL ALLOY (UNS N07001), .3125-24 UNJF-3AAS3308B (Current)4/15/2026
E-25 General Standards for Aerospace and Propulsion Systems
NUT, FITTING, ENGINE, FLAREDAS5205C (Current)4/13/2026
G-3, Aerospace Couplings, Fittings, Hose, Tubing Assemblies
STUD, LOCKED-IN RING, SERRATED, HIGH STRENGTHAS51992D (Current)4/8/2026
E-25 General Standards for Aerospace and Propulsion Systems
A Novel Spot Joint Finite Element for Rapid Stress Analysis of Fasteners in Automotive Structures2026-01-01824/7/2026
Due to the spot weld and mechanical fastener share the similar characteristics to join sheets together with differences in deformation behavior around joint region, a novel spot joint element (user-defined element) consists of regular Mindlin shell elements and equations for different kinematic constraints is proposed to simplify the spot joint representation in lightweight automotive structures. The novel spot joint element can not only provide accurate deformation behavior around joint region but also output mesh-insensitive structural stresses at virtual nodes with the use of traction-based structural stress method for fatigue failure analysis. In this investigation, the structural stress distributions around joint circumference in the lap-shear specimens with spot weld or fastener are first calculated to validate the accuracy of the novel spot joint element. Then, the structural stresses along different cross-sections emanating from joint are also calculated for the specimens with
Wu, Shengjia, Zhang, Lunyu, Dong, Pingsha
Analyzing Fastened Joints in Hydraulic Dampers Using Simulation and Experimental Methods2026-01-05854/7/2026
The main purpose of this study is to develop and validate an accurate calculation model for a hydraulic damper piston valve joint, enabling reliable torque specification and clamp behavior without full prototype iteration. Joint stiffness is a primary interest point. The joint features a bolted interface with a laminated shim stack of many thin disks with varying outer diameters. Analysis of such joints are uncommon in literature, making it challenging to quantify the effects of load distribution, truncation, and surface contact effects between members. The proposed models discussed in this paper are based on frustum load distribution combined with annular-plate bending and elastic-foundation effects to capture the effects of washer cupping. Concrete outputs of the calculator include member load distribution, bolt and member stiffnesses, torque-to-preload relationships, and an external-load simulation that predicts when individual members lose clamp load. Detailed internal hydraulic
Dresen, Gabriel, Vollmar, Race, Roy Chowdhury, Sourav
Enhanced CAE Methodology to Predict Bolt Shear Failure Using Multi-Layer Approach2026-01-04894/7/2026
Automotive seat system is one of the most complex systems in vehicle for its technical and functional requirements. Seat is designed to meet all regulatory requirements subjecting it to multiple tests with loading patterns which caters to the occupant safety. Varied loading and load path for different test requirements cause seat bolts to experience tensile, compressive, bending moments and shear loading. Shearing along bolt length is one of the common failure modes observed during design validation by physical tests. In the world of CAE, there is an industry approach to find the bolt failures at nut and head for all kind of loads. But shear failures along varied bolt lengths are not accurately predictable as multiple sheet metal parts will transfer loads unevenly onto bolt length and it becomes challenge to find which component is leading to shear failure. Hence by adding multiple rupture layers across the bolt length shear and its location could be predicted. Further, to resolve the
RJ, Jethendra, Chiu, Li-Ban
NUT, PLAIN, HEXAGON, UNS S66286AS9356D (Current)4/1/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - DOUBLE HEXAGON EXTENDED WASHER HEAD, DRILLED, PD SHANK, SILVER PLATED, NICKEL ALLOY, UNS N07718, 185 KSI MIN, .5000-20 UNJF-3AAS3255E (Current)4/1/2026
E-25 General Standards for Aerospace and Propulsion Systems
STUD - STRAIGHT, RING LOCKED, CORROSION AND HEAT RESISTANT STEEL (UNS S66286), .3125-18 UNJC X .3125-24 UNJFAS3321F (Current)3/30/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, TEE HEAD – CHAMFERED, PD SHANK NICKEL ALLOY (UNS N07001),165 KSI MIN UTS .3750-24 UNJF-3AAS3235D (Current)3/30/2026
E-25 General Standards for Aerospace and Propulsion Systems
BOLT, MACHINE - HEXAGON HEAD, PD SHANK, NICKEL ALLOY (UNS N07001), .2500-28 UNJF-3AAS3307B (Current)3/30/2026
E-25 General Standards for Aerospace and Propulsion Systems
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