A general physical property test requires that the material sampled be uniform. Most of the performance test standards stipulate the sampling method, which requires 3 to 10 samples to be different, and the average performance index after the test.Tensile strength and elongationTensile strength is an important technical index of TPU materials. The tensile strength and elongation of polyurethane foam plastics, elastomers, adhesives, waterborne polyurethane film, waterproof coating film and synthetic leather resin film are all required to be measured. According to GB/T 1040 and other standards, tensile strength is defined as: in the tensile test, the maximum tensile stress per unit area of the sample until fracture. Elongation at break (elongation for short) is defined as the ratio between the increment of the distance between the standard lines and the initial standard distance when the sample is broken, expressed as a percentage. In addition, elastomers sometimes have a constant elongation strength or modulus) index, which refers to the tensile stress at a specific elongation rate.Different materials have different tensile properties test standards, such as :GB/ t1040-2006 for plastic tensile properties test standard, GB/T 528-2009 for vulcanized rubber tensile properties test standard, GB/T 6344-2008 for soft foam polymer tensile properties test standard, GB/ t2568-1995 for resin castable tensile properties test method. The tensile properties are usually measured in dumbbell shape.
Different test standard for the size of the sample has a variety of rules, rubber dumbbell shaped specimen size refer to GB/T 528-200, a hard material specimens dumbbell shape size refer to GB/T 1040-2006, the most commonly used rubber and plastic (minimum) the total length of the size of the specimen to L - 115 - mm, fixture In 80 mm, the distance between parallel middle night at a part of Li 33 mm In length, range (In parallel to the central part of the picture of the parallel tag In the middle of the distance, is used to measure tensile elongation) Lo 25mm, w-25mm end width, wo-6mm for a small part, sample thickness D Imm, 2mm or 4mm, 1.152mm, La 55mm, Lo 25~ 50mm, W = 25mm, wo-13mm for a small part, sample thickness D= 10-15mm· for polyurethane elastomer sheets (thin films) and polyurethane soft foam materials, dumbbell shaped samples can be made by cutting prototype or knife die punching. Due to the brittleness of rigid polyurethane foam, care should be taken during preparation and blanking method should not be used.When the specimen is clamped in the tensile testing machine and drawn at a fixed tensile speed, the maximum tensile stress is the tensile strength. The tensile stress and elongation can be simultaneously measured to obtain the stress-strain curve, as shown in figure 13-6. The tensile stress is the ratio of the tension F applied to the specimen to the original sectional area (width Wox thickness D) of the specimen (narrow strip section), which is generally converted into MPa (impa-1n /mm? ) the curves in figure 13-6 are brittle plastics, ductile materials with yield point, and ductile materials without yield point. The tensile stress at point a. c. E is the tensile strength of the three specimens respectively, and the elongation at point a. D.E is the elongation at break. Point B is the yield point, and point D produces tensile fracture stress.
The sample after teared was placed for 3 minutes and the two parts of teared were matched. Then the geodesic value was measured. The difference between the original teared distance and the original teared distance was divided by the original teared distance, and the permanent deformation of the tear was obtained (expressed as a percentage).