Hook Bolt Cross Section for Shear Resistance
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Solution Overview
Problem
Conventional hook-bolt locks are prone to failure under high forces, particularly shear forces, which can lead to deformation or failure of the bolt, striker plate, and forend, making them vulnerable to forced entry and destruction.
Innovation Solution
A hook bolt with a specially designed cross section featuring an inner rectangular portion and an outwardly tapering outer portion, along with a guiding cam that matches the shape of the outer portion, reduces shear forces and friction, enhancing security and stability while optimizing material use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional hook bolt with a flat cross section is used, then the lock structure is simple and easy to manufacture, but the bolt is prone to failure under high shear forces, especially at the corners of the bolt opening
Solution Approach 1:
The hook bolt employs a non-uniform cross-section design where the thickness varies along its length. Specifically, the bolt has a greater thickness at the engagement point with the striker plate and a reduced thickness towards the pivot axis, creating local quality variations that optimize strength where needed while reducing material elsewhere. This resolves the contradiction by providing high strength at critical locations without requiring a uniformly complex structure throughout.
Solution Approach 2:
The hook bolt features rounded corners and curved transitions instead of sharp angles. The cross-section includes rounded corners at the engagement point and a curved transition between the thicker and thinner sections. This curvature eliminates stress concentration points that would occur at sharp corners, significantly improving resistance to shear forces while maintaining a relatively simple overall shape that is easy to manufacture.
2Strength
If the forend has a rectangular bolt opening with sharp corners, then the manufacturing is simple, but stress peaks occur at the corners leading to forend failure under forced entry
Solution Approach 1:
The bolt opening in the forend features rounded corners instead of sharp rectangular corners. The opening has a curved profile that matches the rounded corners of the hook bolt. This curvature eliminates stress concentration at the corners of the opening, preventing forend failure under high shear forces during forced entry attempts, while still being relatively simple to manufacture using standard machining or molding processes.
3Strength
If countersunk bolts are used to assemble the lock casing, then the assembly is simple and secure, but material is removed around the screw apertures creating local weak points
Solution Approach 1:
The invention extracts or removes the countersunk bolt assembly method from the lock casing construction. Instead of using traditional countersunk bolts that require material removal and create weak points, the lock casing is designed as an integrated or alternatively assembled structure that eliminates the need for countersunk fasteners. This removes the source of local weak points while maintaining assembly simplicity through alternative joining methods.
4Strength
If a hook bolt with greater thickness is used to increase strength, then resistance to shear forces improves, but the friction between the bolt and forend/striker plate increases requiring higher operating forces
Solution Approach 1:
The hook bolt uses a non-uniform thickness design with greater thickness at the engagement point with the striker plate to maximize shear resistance where needed, and reduced thickness in other areas. This localized thickness variation provides high strength at the critical engagement point while minimizing the overall mass and friction surfaces, allowing the bolt to operate smoothly with moderate forces despite its enhanced strength characteristics.
Solution Approach 2:
The rounded corners and curved surfaces of the hook bolt reduce contact friction during operation. The curved profile allows for smoother engagement and disengagement with the forend and striker plate, reducing the operating forces required. This curvature maintains strength through optimized stress distribution while minimizing frictional resistance during normal lock operation.
Data Source
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AI summary
A lock (1) comprising: a hook bolt (8) which is mounted in the lock, pivotally movable about a pivotal axis, between a retracted position and an extended position and a forend (18) exhibiting a bolt opening (34), through which the hook bolt (8) extends in the extended position. A lock mechanism (6) is connected to the hook bolt (8) for driving the hook bolt (8) between the retracted and the extended position. The hook bolt (8) exhibits a first cross section (A) which, in the extended position, is arranged in a plane of the bolt opening (34) and which exhibits an inner portion (52) and an outer portion (54), said inner portion (52) being arranged closer to the pivotal axis than said outer portion (54). The inner portion (52) of the first cross section (A) is generally rectangular and that the outer portion (54) of the first cross section (A) is outwardly tapering.