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The links herein are ones crew members find particularly useful in both professional and personal capacities. NOTE: these links will navigate away from Polycrew.com.


Olson, Tyler. "Preload Influences on Fastener Fatigue Life." Fastener Technology International Aug/Sept 2015: 36-37
Comments: An article showing how achieving and maintaining a high joint clamp load will reduce the cyclical load amplitude on a fastener and thereby increase fatigue life.


Fastenal leads the fastener distribution industry for knowledge of fasteners and providing customer resources, trainings, and services. Consult with Fastenal for any technical questions you have on fasteners. Link


From Roymechx website: "This site provides useful information, tables, schedules and formula related to mechanical engineering and engineering materials. It provides convenient access to data for design engineers and engineering draughtsmen. The site also lists useful engineering standards and includes equipment suppliers." Link


This website is well named as Bolt Science provides literature, training, softwear and services including consultation as related to joints and fastening. Link


From IFI website on their mission: "To represent the North American fastener manufacturers to its suppliers, customers, the government, and the public at large to advance the competitiveness, products, and innovative technology of the IFI Member Companies in a global marketplace."
The IFI is the primary fastener database and resource outside of the standards organizations (e.g. ASTM, ISO, SAE, ASME). Main website
Hydrogen Embrittlement in Fasteners, Research Paper


Bootstrap is the foundation on which this website was built. Bootstrap makes it easy to develop a responsive webpage for all screen sizes. Link


From the Inkscape website: "Inkscape is professional quality vector graphics software which runs on Linux, Mac OS X and Windows desktop computers." This program permits users to create their own SVG files (SVG stands for Scalable Vector Graphics) such as the icon to the right. This program is very powerful and packed with features. Link


IcoMoon has an app that is a free online service that allows users to create the code files necessary to incorporate SVG files into websites. Link

Fastener Related Equations


This document is only available in PDF format due to its equation heavy nature.

PDF

Socket Set Screws are Designed for Compression Only


  1. Abstract

    Specifications which define requirements for socket set screws (SSS), such as ASTM F912 or ISO 898-5, state this style of product shall be used for compression applications only. Socket set screws that meet industry standard specifications have been known to fracture due to tensile loads. If the SSS ever engages two internally tapped components at the same time there is a risk of tensile loads being applied to the SSS.


  2. Specifications

    ASTM F912, Clause 1.3: “These set screws are intended for compression applications only and are not customarily subjected to embrittlement tests. For tensile applications, consult with the manufacturer for proper alloy and hardness.”

    ISO 898-5, Clause 1: “Fasteners in conformance with this part of ISO 898 are classified to specified hardness classes and are intended for use under compressive stress only.”


  3. Discussion

    Each fastener made to an industry specification has been designed to serve a specific purpose. For example, structural bolts such as ASTM F3125 Grade A325 are designed for high strength steel-to-steel connections; i.e. structures for bridges, buildings, and stadiums. A designer would not use a structural bolt for a wood-to-concrete application. The same holds true for SSS; they are designed for the purpose of preventing relative motion of two components, e.g. a collar with a tapped hole and a shaft.

    Through hardened SSS are typically made from medium carbon low alloy steel that have been quench and tempered to 45-53 HRC. Though no specific minimum tempering temperature is required for SSS specifications, a common temper is 650 °F. With all companies looking to lower costs, the economy alloys that are used today require a low tempering temperature to assure hardness requirements are still met. This leaves the SSS material with little toughness/ductility yet excellent compressive capabilities.

    When SSS are used in tension a common delayed failure mode is hydrogen induced cracking (HIC). In this case, though the failure mode of the SSS is HIC, the fundamental root cause is this fastener is not designed for the intended application, i.e. tension loads.

    If a SSS geometry is necessary for a particular application involving tensile loads applied to the fastener, then, a unique fastener must be designed and fabricated. The alloy and material conditions need to reflect the design criteria and both purchaser and supplier need to agree to the requirements and test procedures of the part.


Respectfully,
Tyler Olson
Fastener Enthusiast
Polycrew Contributor

PDF


Caution: All information in Polycrew Articles is advisory only and the use of this information is voluntary. Polycrew has made a determined effort to present the contents accurately.

“Williams” Washers Cannot Support Bending Stresses


  1. Abstract

    “Williams” washers (WW) are excellent when used as spacers or when subjected to purely compressive stresses. When they are used under the head of a bolt or nut, the stresses are never purely compression. When WW experience a tensile stress (imagine a washer bending while used in a slotted hole) they tend to fracture perpendicular to the tensile load: this type of part is expected to fail when loaded in bending.


  2. Discussion

    "Williams” washers are typically made from a free machining steel round bar cut into disks and machined to geometry. One common free machining steel used to make these types of washers is AISI 12L14. The MnS stringers in these types of steels aid machinability yet sacrifice mechanical properties. These MnS stringers run along the drawing direction parallel to the axis. Many machine shops will offer customers a reduced price for goods that are fabricated from free machining steels because tool life improves. Additionally, WW are commonly case hardened to improve their wear resistance.

    When free machining steels are stressed in tension parallel to the stringers, or in compression, the steel acts more or less like any other low carbon steel. However, when a free machining steels have a tensile stress applied in the transverse direction to the stringers, the strength of the steel is greatly reduced as compared to other low carbon steels lacking these impurities (aka stringers).

    Nuts and bolts rarely apply a purely compressive stress to a washer; most washers experience bending stresses when used with fasteners. This is because mating holes can be oversized, slotted, and/or rough as well as the bearing surface of the fastener typically being smaller than the washer bearing surface. The surface of the washer in contact with the fastener experiences more compressive stresses and the surface in contact with the mating joint member experiences more tensile stresses. These bending tensile stresses act on the WW in the direction transverse to the stringers.

    Most commonly when WW fracture it was because they were used in bending and not because they were unexpectedly brittle or had “too much” inclusions. “Williams” washers were never designed nor intended for bending stresses; standard low carbon steel flat washers or through hardened flat washers should be used in such applications. “Williams” washers should only be used in applications known to apply purely compressive stresses or as spacers on a shaft to maintain a position of another component.


Respectfully,
Tyler Olson
Fastener Enthusiast
Polycrew Contributor

PDF


Caution: All information in Polycrew Articles is advisory only and the use of this information is voluntary. Polycrew has made a determined effort to present the contents accurately.

Is Welding Heat Treated Fasteners Allowed?


  1. Abstract

    To answer the title’s question: No. Welding on heat treated fasteners would significantly alter their microstructure in the weld and heat affected zone. This microstructural disruption would adversely affect the strength of the fastener. Therefore welding on heat treated fasteners is not advised. Welding on a fastener not specifically designed to be welded likely will void any warrantee on the product.


  2. Discussion

    For the purposes of this document only steel fasteners are considered. Heat treated fasteners should be considered synonymous with high strength fasteners, e.g. Grade 5, Class 8.8 or above. Fastener mechanical property specifications such as ISO 898-1, SAE J429, and numerous ASTM specs, closely control their chemical composition, microstructure, hardness, tensile properties, etc., in order to assure the final fastener is structurally sound and has predictable and repeatable performance. While all aspects of manufacturing and processing have an influence on the final conditions of the fastener, the foundation that establishes its properties is the chemical composition and microstructure. If the chemistry is impure, contains inclusions, tramp elements, etc., these can adversely affect the final properties by weakening the matrix or supplying a catalyst for embrittlement. Likewise if the microstructure is uncontrolled or has incomplete conversion to, e.g. martensite, then the final properties will be affected. To create the microstructure necessary to meet many fastener specifications (i.e. ≥90% tempered martensite) we are typically heat treating the steel by annealing (~1600 °F), quenching (e.g. oil) and tempering (800-1100 °F, depends on the fastener spec).

    When steel joints are formed via welding the harshly simplified process is: joint members locally melt at the interface and re-solidify, fusing the joint members in a permanent high strength connection. Depending on their chemical composition, steels have a range of melting point temperatures which are typically 2500-2700 °F; pure iron melts at 2800 °F. Melting a steel completely resets the microstructure in the weld and alters the microstructure in the heat affected zone (HAZ). If joint members were heat treated their microstructure, and therefore their strength characteristics, would have been erased within the weld and severely disrupted within the HAZ.

    Manufacturers stand behind their product 100%; if they do not, they are not a reputable manufacturer. The warrantee provided by the manufacturer is something every product user does not want to void. When a fastener is welded the part has been altered by the user; no longer does the fastener have the geometry, microstructure, strength, etc., that it did when it was first produced. After welding, effectively the user has become the manufacturer as the user has chosen to alter the part from its original design. The exception to this would be fasteners specifically designed to be welded upon such as weld studs, weld nuts, ASTM A307 Grade A and B with S1, ASTM F1554 Grade 55 with S1.


Respectfully,
Tyler Olson
Fastener Enthusiast
Polycrew Contributor

PDF


Caution: All information in Polycrew Articles is advisory only and the use of this information is voluntary. Polycrew has made a determined effort to present the contents accurately.

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