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https://www.compositesworld.com/articles/structural-adhesives-part-i-industrial
https://www.lord.com/products-and-solutions/adhesives/structural/basics-best-practices
Calculating Adhesive Strength Required
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Official weight of each occupant will be 80kg
Adhesive Mechanical Design
The design of a bonded joint shall satisfy the following conditions:
The failure of a joint should occur either in the adhesive or in its adherends but not in the interfaces
Allowable shear stress and peeling stress of adhesive are not exceeded
Allowable through-thickness tensile stress and out-of-place shear stress should not be exceeded
The design of adhesively bonded joints shall be validated by either calculation or testing to verify that the design can fulfill the performance requirements.
The limit states shall be satisfied in designing adhesively bonded joints and are provided in Table 10.4
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Structural Adhesives
Factors to be considered in adhesive selection:
Adherend materials (such as adhesion compatibility)
Applied loading
Environmental conditions during service
Geometry restrictions
Bonding and curing processes
Costs and other special requirements including health and personnel safety
Partial Safety Factors for Structural Adhesives
The overall safety factor (𝛾m)is the product of four partial safety factors considering the source of adhesive properties (𝛾m,1), the method of adhesive application (𝛾m,2), the type of loading (𝛾m,3), and environmental conditions (𝛾m,4)
𝛾m = 𝛾m,1 x 𝛾m,2 x 𝛾m,3 x 𝛾m,4
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Failure Modes and Critical Limit States
A bonded joint, especially the adhesive, may be subjected to the following stresses:
Shear stresses produced by tensile/compressive, torsional, or shear loads imposed on its adherends
Peeling or cleavage stresses at the joint’s edges or corners produced by out-of-plane loads acting on adherends or due to unbalanced banding moment
Out-of-plane tensile/compressive stresses produced by out-of-plane tensile/compressive loads
In-plane tensile/compressive and shear stresses produced by in-plane tensile/compressive and shear loads (depending on joint types)
Out-of-plane tensile, peeling, and cleavage stresses should be evaluated with great care and should be avoided when possible
A main principle in designing bonded assemblies is to ensure that the joint works in shear and to minimize out-of-plane peeling.
For the adhesive layer, a preferred design is one that is primarily stressed in shear or out-of-plane compression
Looking at specifically failure modes for adhesives
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Adhesive failure is the rupture due to separation at the adhesive-adherend interface
Failure is mainly caused by insufficient adhesion, due to either material mismatch or inadequate surface treatment
Adhesives are usually considered isotropic
Criterion for cohesive failure of adhesive may be described by maximum stress criterion, that is, the maximum shear or tensile (including peeling) stresses in the adhesive shall be equal or less than the maximum allowable adhesive shear or tensile stresses
Stress Analysis for the Design of Adhesively Bonded Joints
Analysis of the structural behaviour of adhesively bonded joints is often conducted by studying a 2D representation of the joints
Behaviour and strength of a joint can be described by normal stresses and shear stresses.
The local stress distribution within an adhesive joint can be obtained by considering three loads acting in the FRp substrates at the end of the joint: the axial force, the shear force, and a bending moment.
whe n considering stresses in the adhesive joints, the out-of-plane normal (or peeling) stress and shear stress are two dominant components of stress
A 3D analysis requires numerical methods such as finite element analysis.
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