Glossary of Technical Terms

Mechanical Terms

Compression yield

Compression yield strength is the stress required to cause plastic deformation. Plastic deformation is the permanent change in shape or size of a solid body without fracture, resulting from sustained stress beyond the elastic limit. Cylinder-shaped specimens are placed in a test machine that applies an increasing compressive force until plastic deformation weakens the sample. The highest force recorded prior to deformation is the compression yield strength.

Flexural modulus

Flexural modulus is calculated by measuring the deflection of a beam during the flexural strength test. In a manner similar to the calculation of tensile modulus, the deflection and stress are used to determine the flexural modulus.

Flexural strength

Flexural strength is a measurement of the maximum amount of bending stress a sample can withstand before fracturing. The sample is simply supported at each end and an increasing load is applied in the centre. The stress caused by bending is calculated and the amount that results in failure is recorded.

Lap shear strength

Lap shear strength measures the strength of an epoxy-bonded joint when loaded in shear. The test is performed by bonding two metal coupons together with an overlap and then pulling them apart in tension in a test machine. The tensile force creates a shear force in the bond line and the resulting stress is reported as the lap shear strength.

Tensile adhesion strength

Tensile adhesion strength is the stress required to fail a bond line with a force perpendicular to the bonded surface. Two aluminium or mild steel cylinders of 25mm diameter are bonded together using the material to be tested. A device is threaded onto both adherents and applies a pulling force to the bonded joint. The load required to fail the bond is divided by the bonded surface area and the resulting stress is also known as the tensile adhesion strength.

Tensile elongation

Tensile elongation, also referred to as strain, indicates how much the material can “stretch” before it fails. Dog bone-shaped samples are placed in a test machine that applies an increasing tensile force until failure. The change in sample length is measured with an extensometer. The point at which the sample fails is the tensile elongation.

Tensile modulus

Tensile modulus describes the amount of elongation (strain) that results from a specific amount of stress. This property is essentially the stiffness of the material. During the tensile strength test, elongation is measured and recorded at the corresponding stress before the material yields. The stress divided by the strain equals the modulus or the slope of the stress/strain curve.

Tensile strength

Tensile strength is the stress that is required to fracture the epoxy and cause a failure. Dog bone-shaped specimens are placed in a test machine that applies an increasing tensile force until failure. The highest stress recorded prior to failure is the tensile strength.