Glossary of Testing Terms

Materials Testing Glossary

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Absorption – The process in which one substance permeates another; a fluid permeates or is dissolved by a liquid or solid

Accuracy – The degree of conformity of a measured or calculated quantity to its actual (true) value. Accuracy is closely related to precision, also called reproducibility or repeatability, the degree to which further measurements or calculations show the same or similar results

Adherence – The extent to which a coating bonds to a substrate.

Adhesion Test – This test determines the strength of adhesion between two layers, or the strength of adhesion between a top layer and a substrate material. Applicable ASTM standards. (ASTM D3359)

Alfa Rockwell Hardness – Index of the resistance of a plastic to surface penetration by a specified indenter under specified load applied with a Rockwell hardness tester. Higher values indicate higher indentation hardness (ASTM D785)

Auto Return – A feature in Thwing-Albert machines that automatically returns the crosshead to the original start position at the end of each test.


Basis Weight – The weight in pounds of a ream (500 sheets) of paper cut to a specified, standard size. Within a specific grade or line of paper, a lower basis weight indicates that less fiber was used to produce the paper. TAPPI T460

Bend – Measures the maximum force to bend a carton sample up to 90°. Measure bending stiffness, score ratio of scored vs. unscored paperboard and carton fold springback force. 1270 PCA Score Bend.

Break Elongation – The elongation of the specimen to the breakpoint.

Breaking Load – Load which causes fracture in a tensile, compression, flexure, or torsion test. Also called Breaking strength when working with textiles and yarns.

Bulk Modulus of Elasticity – Ratio of stress to change in volume of a material subjected to axial loading.


Coefficient of Friction – The coefficient of static friction is defined as the ratio of the maximum static friction force (F) between the surfaces in contact to the normal (N) force. The coefficient of kinetic friction is defined as the ratio of the kinetic friction force (F) between the surfaces in contact to the normal force: Ff/N. In simpler terms, static friction is considered the amount of force required to get the sled moving along the sample. Kinetic friction is the amount of force required to maintain the sled moving along the sample.

Complex Modulus – Measure of dynamic mechanical properties of a material, taking into account energy dissipated as heat during deformation and recovery. It is equal to the sum of the static modulus of a material and its loss modulus.

Compression-Deflection Test – Nondestructive method for determining the relationship between compressive load and deflection under load for vulcanized rubber. (ASTM D575)

Compression Fatigue – Ability of rubber to sustain repeated fluctuating compressive loads. (ASTM D623)

Creep – The tendency of a material to move or to deform permanently to relieve stresses. Material deformation that occurs as a result of long term exposure to levels of stress that are below the yield or ultimate strength of the material.

Cross-direction – Direction running against the grain of the paper. Paper is weaker and more susceptible to moisture damage in the cross direction than with the grain


Deflection – The degree to which a structural element is displaced under a load.

Delamination – Measure of the node-to-node strength of honeycomb core materials. It is equal to the tensile load applied to a honeycomb panel at fracture divided by its width times its thickness (ASTM C363)

Dimensional Stability – Ability of a substance or part to retain its shape when subjected to varying degrees of temperature, moisture, pressure, or other stress.


EASL – Elongation at a specified load

EDANA – The European Trade Association for the nonwovens and hygiene products converters industries. The letters “E.D.A.N.A.” stand for “European Disposables and Nonwovens Association”. Thwing Albert offers the ProGage Thickness Tester which adheres to the EDANA standard 30.4 89

Edge Tearing Strength – Measure of the resistance of paper to tearing when folded over a V-notch beam and loaded in a tensile testing machine. Results are reported in lb or kg.

Elasticity – A material is said to be elastic if it deforms under stress (e.g., external forces), but then returns to its original shape when the stress is removed. The amount of deformation is called the strain.

Elastic Hysteresis – Elastic Hysteresis is the difference between the strain energy required to generate a given stress in a material, and the material’s elastic energy at that stress. This energy is dissipated as internal friction (heat) in a material during one cycle of testing (loading and unloading).

Elmendorf – A technique used to measure the tearing resistance of a material. The radius sample is recommended for film samples. Click here for the three different samples.

Elongation – The permanent extension of a specimen that has been stretched to rupture in a tension test. Test Results can be displayed as a percentage elongation

Extensometer – An instrument used to measure minute deformations in a test specimen of a material. Adheres to ASTM D412.


Fatigue – Fatigue tests are made with the object of determining the relationship between the stress range and the number of times it can be applied before causing failure. Testing usually consists of applying cyclic loading to your test specimen to understand how it will perform under similar conditions in actual use

Finch Wet Strength – The wet tensile breaking strength of a specimen tested using a Finch cup that requires the specimen to be saturated with water and then tested following TAPPI T456.

Force – The capacity to do work or cause physical change; energy, strength.


Gauge Length – Used to calculate elongation. Often stated in industry standards as the distance between the grips.

Grips – A mechanical device that grasps and holds the test specimen. Available grips include mechanical, pneumatic, vice grips, roller grips, yarn, and cord grips, and special fixtures. (Browse the Grip Catalog)


Hand (Handle-O-Meter) – The combined effects of flexibility and surface friction of sheeted materials such as nonwovens, tissue, toweling, and film.

Hot Tack – The strength of a heat seal immediately after sealing while still in a hot condition, i.e. before it has cooled down to ambient temperature and achieved its final strength. Used especially in form fìlling machines


LASE – Load at Specified Elongation

Limits (Upper and Lower) – A safety feature on Thwing-Albert test instruments that suspend motion or shuts off the instrument when the upper or lower limit is reached. The correct setting of the operational limits will reduce the risk of damage to the instrument, the load cell, and the operator.

Load Cell – A force transducer which converts the actual force result into an electrical signal. Make sure to use a load cell that is about 50% of your testing force. Load cells lose accuracy when used under 10% of the accuracy


Maximum Force – The point of highest force (Fm)

Mean Force – The sum of all force data divided by the number of data points


Nominal Stress – Stress calculated on the basis of the net cross-section of a specimen without taking into account the effect of geometric discontinuities such as holes, grooves


Overstressing – Seeing high fluctuating loads at the beginning of a fatigue test and lower loads toward the end. An indication that the fatigue test needs to be sped up.


Peak Force – The point of maximum force

Peel Resistance – Torque required to separate an adhesive and adhered.

Plasticity – Tendency of a material to remain deformed, after reduction of the deforming stress, to a value equal to or less than its yield strength

Preload – Preload is a user-defined force that is applied to the specimen before any measurements begin.

Pretension – A user-defined force in tensile testing that is applied to the specimen before any measurements begin.


Recovery – The index of a material’s ability to recover from deformation in the compressibility and recovery test (ASTM F36), the deformation under load test (ASTM D621) and the plastometer test (ASTM D926).

Residual Elongation – Measure of ductility of plastics. It is the elongation of a plastic specimen measured 1 minute after rupture in a tensile test.


Secant Modulus of Elasticity – Ratio of stress to strain at any point on the curve in a stress-strain diagram. It is the slope of a line from the origin to any point on a stress-strain curve.

Stiffness – Measure of resistance of plastics to bending. It includes both plastic and elastic behavior. (ASTM D747)

Stress – An applied force divided by the original cross-sectional area of the specimen


Tangent Modulus of Elasticity – The instantaneous rate of change of stress as a function of strain. It is the slope at any point on a stress-strain diagram

Tenacity – The tensile stress expressed as force per unit linear density of an unstrained specimen.

Tensile Strength – The ultimate strength of a material subjected to tensile loading. It is the maximum stress developed in a material during a tensile test

Test Definition – Outlines the test methods including calculations and variables

Tolerance – The capacity to endure continued subjection to something.


Variables – User-defined variables that can be used to collect extra information from the user that is not directly generated by the tester.


Yield Point – Stress at which strain increases without accompanying increase in stress. Only a few materials have a yield point (steel).


ZDT (Z direction tester) – Measures the internal fiber bond strength (z-direction tensile strength) of paperboard using an instrument that subjects a normal separation force to a 6.45-cm2 (1-in.2) specimen. TAPPI T541