ASTM D950 Test Method for Impact Strength of Adhesive Bonds

The standard ASTM D950 describes the adhesive impact strength testing of standard wood-to-wood and metal-to-metal adhesively bonded specimens. Impact energy at bond failure is tested using a pendulum type impact machine. The ASTM D950 impact strength is reported in joules per square meter.

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Introduction

ASTM D950 gives a proper framework for testing by ensuring that comparability and quality control are achieved in different adhesive formulations and bonded assemblies. This test technique, which typically uses an impact tester of the pendulum type, is frequently used to ascertain the energy needed to break adhesive connections between two materials. Standardized by the ASTM in ASTM D950, it examines how good the impact strength of the bonds is, which indicates performance at the point of sudden and high-intensity force. The standard’s results make it possible to evaluate adhesives’ dependability and durability in various applications, including construction, automotive, and aerospace, where resistance to dynamic stresses is essential.

Scope

The standard method ASTM D950 describes obtaining the comparative impact strength of adhesive bonds in shear, utilizing standard specimens under specified pretreatment and test conditions. Adhesive impact failure may occur under suddenly applied loads, such as from dropped objects or collisions. Impact strength is the energy the specified test specimen absorbs when it fails from a single blow of a testing machine hammer. The accuracy of adhesive impact strength tests depends on the specimen preparation and bonding process, and each standard specimen must follow the manufacturer’s recommended method.

Procedure

Block shear specimens are subjected to the ASTM D950 test in a pendulum-style impact machine using a hammer with a flat striking face. Adhesively bonded along the face of contact, each test specimen is set up as a tiny adherend block positioned on a larger base block of the same material. A sturdy steel jig securely holds the specimen’s base block. The testing machine’s base has the jig fastened to it with bolts. A screw is included with the jig to secure the specimen. The specimen must be ensured that it cannot move when struck by the testing hammer. After the specimen is fastened, the impact head is raised to the predetermined height and released. The head should move at a velocity of about 3.5 m/s. The smaller adherend block is stuck by the striking face of the test hammer, just at the adhesive bond line, preferably within 0.79 mm (1⁄32 in.). Direct reading of impact energy should be possible in the machine.

Sample size

The following are the technical specifications of ASTM D950:

Sample size

The larger adherend block should be 44.5 mm × 25.4 mm × 19 mm (13/4 inch × 1 inch × 3/4 inch).

Where this size is too large to be fractured by the available testing machine, the top adherend block size may be appropriately reduced.

Sample dimension

In ASTM D950 testing, the smaller adherend is a square block of maximum dimensions 25.4 mm × 25.4 mm × 9.5 mm (1 inch × 1 inch × 3/8 inch)

Result

The ASTM D950 test method determines the impact strength of adhesive bonds, that is, how well the adhesive can resist sudden or shock loading. In the test, a specimen is subjected to an impact load after being bonded with an adhesive, and the energy absorbed by the bond up to breakage is determined.

Conclusion

ASTM D950, Impact Strength Test, describes a method that evaluates the resistance to controlled impact load by an adhesive bond with a pendulum-type tester. This method delivers crucial and dynamic stress information that may be exploited in comparing various adhesives or bonding conditions. It is notably valuable for applications where the materials are subjected to a sudden or repeated impact. Uniform sample preparation and testing ensure that ASTM D950 backs up good examination, facilitating materials selection and quality assurance in any industry relying on adhesive bonding.

FAQ’s

What is adhesive bond strength?

When creating a robust adhesive-bonded structure, adhesive strength—the interfacial strength between the adhesive and substrate—is typically the most crucial factor to consider. However, other important factors contribute to good binding besides adhesive strength.

How to determine adhesive strength?

Several methods use a tensometer to measure the strength of industrial adhesives. The three most common test methods are overlap shear, tensile, and peel testing. The tensometer then gives a unit that indicates how much force it took to break the bond.

What affects bond strength?

As the number of electron pairs in a bond between two atoms increases, so does the bond's strength. In general, bond length reduces as bond strength increases.