ASTM D903 Test for Peel or Stripping Strength of Adhesive Bonds

Scope of ASTM D903 Test

The standard test method ASTM D903 describes how comparative peel or stripping strength properties of adhesive bonds can be obtained using standard-sized specimens at specified pretreatment and test conditions. Peel or stripping strength is the average load per unit width of bendline required to peel one adherend from the other, till a 180° separation angle is reached. It is expressed in kilograms per millimeter of width. The adhesive needs to be flexible. The ASTM D903 test involves adhesively bonding the flexible adherend to a substrate, peeling it back at the specified rate by a 180° angle, and measuring the average peel strength. The substrate is a rigid material that can be clamped in a fixed vertical position in the testing machine. The testing machine may be power-driven, with a control system, capable of peeling the specimen at a constant, specified rate. It can also be an inclination balance type or a pendulum type. In any case, it is necessary to be able to measure and display the load versus position continuously and calculate the average load since there will be peaks and troughs during the peeling process. The testing machine has a vise grip attached to the moving crosshead, to hold and peel the free end of the flexible specimen.

Procedure:

The ASTM D903 specimens are in the form of long narrow flexible adherend strips bonded to a rigid strip of any suitable material that forms the substrate. The required test length of the flexible strip is bonded to the rigid substrate and a sufficient free length is allowed that will be folded back and used to grip and peel back the flexible strip. Before bonding, surface preparation, adhesive application, and curing must be done as per the manufacturer’s recommendations. Specimens must be conditioned at the specified temperature of about 23°C and relative humidity of 50% in an environmental chamber or desiccator, for a sufficient time and tested soon after conditioning. The substrate is fixed vertically and the free end of the flexible strip is folded back, to be held firmly in a grip attached to the moving crosshead of the testing machine. Half of the flexible adherend is peeled back to a 180° angle at a separation rate of 152.4 mm/min (or 6 inches /min) and the peel force is continuously recorded. 

Video 01: ASTM D903 Peel strength testing of adhesive bonds

Specimen size:

A typical substrate used in ASTM D903 testing would be a strip 25.4 mm (1 inch) wide, and 304.8 mm (12 inches) long, with thicknesses between 1.6 mm to 3.1 mm (1/16 inches to 1/8 inches). The flexible strip would be sufficiently long, to be folded back for holding it in the movable crosshead grip.

Result:

The ASTM D903 peel strength is expressed in kilograms per millimeter of width.

Conclusion:

The standard test method ASTM D903 describes how comparative peel or stripping strength properties of adhesive bonds can be obtained using standard-sized specimens at specified pretreatment and test conditions.