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Principles of Tensile Testing

Tensile or tension testing is the application of uniaxial force to measure the performance of a test sample, up to the point of yield or breaking, whether sharp or gradual. In simple terms, it is pulling something apart in a straight line and seeing how it changes. Even where performance to ultimate failure is not required, characteristics of elongation, deformation and relaxation can be accurately recorded, as in elastomers and springs. The sample under test may be a material sample, or a manufactured product.

Tensile testing is an important part of design as well as quality control, for ensuring product safety and integrity, and is an essential part of testing consistency in manufacture and construction.

Practical Applications


Tensile tests are used to measure the strength of textiles and stitching, couplings and connectors, joints and crimp fastenings, industrial fixings and fasteners, or to measure the effort required to open a drawer or door, or in the packaging industry to measure the force required to open a container, flip a cap, pull a stopper, etc. Many have a complementary compressive test (push and pull, open and close) where both are required of a product, and here a universal test stand or gauge fulfils both requirements. Since the shapes and features of manufactured products are so variable, and can be awkward to grip without deformation, Mecmesin frequently designs custom fixtures to suit users' individual products.

For materials testing, what is usually required is to measure the full tensile properties rather than the ultimate strength of a material, such as an elastic modulus. Here the test standards define the sample dimensions, and standard grips and fixtures are used.

Features of Tensile Testing


Key features of tensile testing include accurately controlled speed, extension and force, the ability to hold at extension and load, and the use of appropriate grips and fixtures. Tensile tests need to be representative of the sample as it is used, especially if it is a product rather than a materials test. The Mecmesin range of tensile testers includes models with extended columns suitable for highly elastic tests.

Tensile test results can provide a detailed profile of force, extension and time, including partial failure, slippage, and sharp and percentage break. For materials testing, the data curve of force vs extension is largely used to determine the elastic limit and ultimate tensile strength.

Specific related types of tensile test


Typical Applications


Automotive


  • Quality assessment through tensile testing of interior fittings including: Airbags, carpets, dash, electrical harness (incl. Crimped terminals pulloff force), handles, laminated trim, mirrors, seals and seatbelts and handbrake lever.
  • Quality assessment through tensile testing of exteriors fittings including: Bumpers moulding and trim, door and window seals, emblems and number plates, mirrors, mud flaps, damper springs.

Electrical & Electronics


  • Connector withdrawal force
  • Pull-off forces of crimped, welded or soldered electrical contacts
  • Component-to-PCB pull-off force
  • PCB material tensile strength

Safety, Health, Fitness and Leisure


  • Tensile testing of safety support netting
  • Ergonomic risk evaluations
  • Elastic properties of racquet strings

Medical Applications & Devices


  • Hypodermic needle-to-hub retention force
  • Tensile strength and elongation at break of medical tubing, bandages, dressings and tapes
  • Joint strength of IV connector fittings
  • Suture-to-needle crimp pull out test
  • Tensile strength of suture material and knotting
  • Joint strength and material elongation of respiratory masks
  • Elongation and tensile strength of examination gloves
  • Mechanical strength of orthopaedic implant components

Packages and Packaging Materials


  • Force associated with opening snap-caps, pop-caps and other pushpull closures
  • Elongation of plastic packaging materials

Pharmaceutical Products and Packaging


  • Pull off force of phial and capsule caps

Plastics, Rubbers and Elastomers


  • Joint strength of interlocking plastic components
  • Assessment of material tensile properties

Textile Industry


  • `Pull-off` characteristics of buttons, stitched-on decorations, pressstuds, poppers, zip fasteners, hook-and-loop fasteners
  • Strength testing of vulnerable seams

Paper and Board


  • Openability of card and paper based packaging
  • Folding characteristics of boxes and cartons
  • Force to separate multi-part documents
  • Durability of documents

A Brand You Can Trust

"The MultiTest 0.5-i is a very good and reliable machine and the Emperor™ Software brings great advantages. It’s a very useful tool for these kinds of tests. It’s fully programmable and offers an in-depth analysis of results. It’s a precious tool for everybody involved, especially those who work with plastics and their mechanical performance"

Nikos Michopoulos, Quality Control, Eurofilm Mantzaris S.A.

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