ASTM D5868 Lap Shear Adhesion Test for Fiber Reinforced Plastic

Introduction:

ASTM D5868 lap shear adhesion test is a widely available standard test method for adhesive bonding strength with FRPs.The lap shear strength is the ability of the adhesive to resist shear forces that apply to the adhesive joint when about two overlapping portions of FRPs. Researchers test the joint by applying force to the bonded joint until it fails, determining the adhesive’s effectiveness on shear stress. The ASTM D5868 Lap Shear Adhesion Test is valuable to industries focused on the safety and performance of adhesives, such as aerospace, automotive, and construction, where the integrity and durability of adhesive joints in composites are critical. The ASTM D5868 Lap Shear Adhesion Test provides essential data to support material selection, quality assurance measures, and design evaluation with reinforcement plastics. 

Scope:

The ASTM D5868 method is versatile and applicable to many single-lap adhesive bonded shear joints in Fibre Reinforced Plastic (FRP) adherents. Specifically, adhesive joints in FRP applications typically need to function in a state of shear, where forces act parallel to the cross-section of the adhesive, thereby causing the adherend surfaces to slide in opposite directions. The single-lap shear test measures the shear strength of a specified adhesively bonded lap joint between FRP plates or between FRP and metal plates. Additionally, researchers can use the ASTM D5868 method for both random and fiber-oriented FRP composites, making it a valuable tool for characterizing and comparing different adhesives, FRP materials, and surface treatments.

Procedure:

The ASTM D5868 single lap shear test is performed on two rectangular adherend pieces of FRP, bonded by an adhesive at the single-lap joint. Researchers test any standard machine capable of applying a controlled tension force. A pair of self-aligning grips hold the composite specimen vertically and firmly, preventing slip or damage. Researchers apply tension forces along the centerline of the specimen by pulling from the opposite ends until the lap joint fails. The ASTM D5868 test for FRP specifies a crosshead speed of 0.5 inch/min, with a tension loading rate of 1200 to 1400 psi of shear area per minute. Researchers record the stress value at joint failure and the type of failure.

Specimen Size:

For ASTM D5868, researchers typically fabricate the specimens from rectangular pieces, each 100 mm long and 25 mm wide, with an adhesive layer thickness of 0.75 mm. Additionally, the overlap length can vary between 12.7 mm and 25.4 mm. Moreover, the adhesive thickness lap shear test depends on the specific FRP type.

Result Analysis: 

The table below summarizes the result analysis of the lap shear adhesion test for fiber reinforced plastics:

Conclusion: 

The ASTM D5868 Lap Shear Adhesion Test represents a vital method for evaluating adhesive bond shear strength in fiber-reinforced plastics (FRPs). The adhesive lap shear test measures the maximum loading capacity each bonded joint can withstand before failure of that joint occurs. The information from lap shear testing is critical for making informed assessments about specific adhesives in a particular industry or manufacturing type. Moreover, it applies to various sectors, including aerospace, automotive, construction, and composite industries. Information about lap shear strength, mode of failure for adhesives (adhesive or cohesive failure), and the effects of specific parameters such as temperature and surface preparation can inform the adhesive practice for a practitioner. 

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