COMPRESSION TESTING / COMPRESSIVE FORCE TESTING

COMPRESSION FORCE TESTING

Compression testing is used to determine how a product or material will behave when it is compressed, squashed, crushed or flattened. This is done by measuring fundamental parameters that help to determine the specimen behavior under compressive load.

Compression testing machine is used to:

  • Assess the strength of components and assemblies such as automotive and aeronautical control switches, compression springs, bellows, keypads, package seals, helical springs, PET containers, PVC / ABS pipes, solenoids, etc.
  • Characterize the compressive properties of materials such as foam, metal, PET, plastics, rubber, etc.
  • Assess the performance of products, as in the actuation force to operate a syringe or the load-displacement characteristics of a tennis ball.

Other specific types of test would include: 

  • Compression
  • Compressive Burst
  • Compressive shear
  • Flexural /Bending Test
  • Penetration/Puncture resistance
  • Top load /Axial force/ column crush
FLEXURAL /BENDING TEST:

Flexural or bending test measures the bending behaviour of beams or beam like samples. Bend testing, sometimes called flexure testing or transverse beam testing, measures the behaviour of materials subjected to simple beam loading. Generally a flexure test is carried out until the sample experiences failure. This test is ideal for testing brittle materials.  

This test is commonly performed on materials such as plastic materials, composites, concrete, and ceramics because these materials have low ductility and hence the propensity to break before any permanent deformation occurs.

This helps in the accurate measurement of the flexural modulus and strength. Bend or flex tests apply force via a single upper anvil at the midpoint, which is a 3-point bend test, or two upper anvils equidistant from the centre which would be a 4-point bend test. 

In a 3-point test, the area of uniform stress is small and concentrated under the centre loading point. In a 4-point test, the area of uniform stress exists between the inner span loading points (typically half the length of the outer span).

The test is commonly observed in a:

  • 2-point cantilever bend, where one end of the material is fixed and load is applied at a defined point along its length
  • 3-point bend, where the material is placed horizontally across 2 supports and load is applied centrally by a single anvil
  • 4-point bend where the material is placed horizontally across 2 supports and load is applied by two anvils having a defined span
SIMPLE COMPRESSION:

Compression tester helps to determine a material's behaviour under the application of crushing loads. These tests are typically conducted by applying compressive force to a test specimen (that could be cuboid or cylindrical in shape) using platens or specialized fixtures via a universal testing machine.

During the test, various properties of the material can be calculated and plotted, such as Stress – Strain Diagram. This would help to determine qualities such as Elastic limit, Proportional limit, Yield point, Yield strength and compressive strength.

Compression tests help to assure the quality and performance of finished products such as actuation force of a syringe plunger, firmness of a tennis ball, push-out strength of a tablet from a blister pack and many more.

COMPRESSIVE BURST:

A compressive burst test is a destructive test and performed to determine the pressure overload characteristics of pressure bearing parts. These compressive load tests are usually performed with a fluid.

This test is often performed as a pre-production test to meet safety and quality standards. To verify the reliability of products it is advisable to determine the difference between the maximum working pressure and the pressure when the product fails absolutely (burst pressure).

The integrity of a fluid or gas-filled container can be tested in terms of its propensity to burst at a given value of pressure.

This could involve a failure in the material by splitting, or the seal/seam could give way or even the closure can break loose.

Compression burst test is conducted

  • To determine the maximum burst pressure
  • To determine the safety factor specified in applicable standards
  • To determine the mode of failure
  • To confirm the designing margin of the product 

There are various ways to conduct a compressive strength test such as an inflationary burst created by internal pressure; this could include sensitive gaseous leak detection. However, a simple and pragmatic approach involves compressing a filled container and using a probe with a standard radius or flat tip to measure the force to burst it.

PENETRATION/PUNCTURE RESISTANCE:

Penetration resistance testing involves the insertion of a probe into a material to a known depth.

This can determine the change of state of a material as it cures or sets. It can also characterise the texture of a material (e.g. food, pharmaceutical preparation or cosmetics) where firmness is a measure of its quality.

Ball and cone probes are typically used for gels or viscous materials, needle probes for elastomeric pharmaceutical stoppers, whilst broader radiused probes are used for cement and wet concrete.

Puncture resistance testing involves using a pointed probe to stretch a material until it gets pierced and tears.

Puncture resistance measures the:

  • Tensile strength of a known material. 
  • Resistance of fibers to breaking or being forced apart by a foreign object.

Puncture testing is therefore important for medical devices such as hypodermic and suturing needles, as well as for silicone-stopped vials, gloves and sharps containers.

Puncture testing at higher test speeds is typically used for sharps, and for protective clothing such as gloves, stab vests, and fabrics that inflate.

Slow puncture testing employs a radiused probe under load, applied slowly. It is imperative to test materials such as foils, films, construction membranes or geotextiles.

TOP LOAD /AXIAL FORCE/ COLUMN CRUSH:

Top-load/column crush testing is one of the most accurate methods for reliably determining container integrity. Manufacturers of all kinds of containers, especially plastics must ensure that products can withstand certain expected forces that will be experienced during the capping / filling process or warehouse stacking.

This test measures the compressive strength of containers to ensure it does not deform or break when subjected to axial forces during the process of filling, closure, storage or transportation.

There is an ever-increasing need to reduce the weight of plastics that are utilized during packaging, but without compromising on strength and performance.

Top loading test is widely performed in PET bottle manufacturing industries. PET bottles have various applications such as storing liquids, medicines, powder, capsules, etc. Irrespective of the application there should be some amount of strength to resist deformity. In case of a failure the bottle needs to be redesigned.  This test determines weak points in a bottle, especially during a fall when it is filled with fluid. This test also detects flaws in blow-moulding work especially when buckling repeats at the same point.

COMPRESSIVE SHEAR TEST:

Shearing forces are unaligned forces pushing one part of a body in one specific direction, and another part of the body in the opposite direction along the same parallel plane. Compressive shear testing involves pushing a specimen by applying compressive force from opposite sides in a parallel plane. What is noticed is that the material is stressed in a sliding motion.

Typically it is used to test adhesive bonds and layered composites. This is generally the compressive equivalent of a 'tensile lap shear test'.

This test method helps to determine the internal strength of a material that is designed to bear shear forces.

A compressive shear test may be a single-shear, where one part is pushed down across another. Alternatively, it could also be a double-shear where a bonded section is pushed out from between the sections on either side. 

APPLICATIONS OF COMPRESSION TESTING IN VARIOUS INDUSTRIES:

Compression testing guarantees the quality of components, materials and finished products within a wide range of industries. Few applications are listed below

Aerospace and Automotive Industry

Applications of compression testing in the aerospace and automotive industry include:

  • Actuation tests on pedals, switches and solenoids
  • Spring testing
  • Compression tests on passenger safety harnesses
Construction Industry

Applications of compression testing in the construction industry include:

  • Measuring the flexural strength of sheet construction materials, insulation boards and roofing panels
  • Penetration tests on plasterboards, pipes, etc.
Cosmetics Industry

Applications of compression testing in the cosmetics industry include:

  • Actuation force testing of sprays and dispensing pumps
  • Testing of the breaking strength of lipsticks, lip balms, lip and eye liners
  • Compaction strength of powder compacts and eye shadows
  • Testing the force to dispense creams and lotions from tubes, containers and sachets
Electrical and Electronic Industry

Applications of compression testing in the electrical and electronic industry include:

  • Actuation force testing of push buttons and switches
  • Compression testing of LCD screens and keypads
Medical Device Industry

Applications of compression testing in the medical device industry include:

  • 3-point bend testing of needles
  • Actuation force testing of metered dose inhalers and pen injectors
  • Sharpness, insertion and penetration force testing of needles and scalpel blades
  • Syringe plunger actuation and "travel" force assessment
Packaging Industry

Applications of compression testing in the packaging industry include:

  • Compressive strength testing of cardboard packaging
  • Dispensing pump actuation force
  • Stacking test of:
  • Cardboard and plastic containers
  • PET bottles
Paper and Board Industry

Application of compression testing in the paper and board industry include:

  • Compressive strength testing of cardboards
Pharmaceutical Industry

Applications of compression testing in the pharmaceutical industry include:

  • Gel strength and gel rupture testing
  • "Egress" force of blister packs
  • Compression testing of tablets and capsules to measure necessary characteristics.

Plastics, Rubber and Elastomers Industry

Application of compression testing in the plastics, rubber and elastomers industry include:

  • 3-point bend testing to identify flexural properties of plastics
SUSHMA SOLUTION FOR COMPRESSION FORCE TESTING:
  1. Our single/dual column force testing systems are versatile & customizable for any application or budget.
  2. We offer a range of Manual, Motorised & Computer controlled (compressive strength testing machine) force testing systems of 500N to 100kN capacities.
  3. We assist in configuring these systems for ideal compression and Tension force testing
  4. Ideal for product testing, in quality control labs, R&D facilities, production line, or as per the requirements of your testing environment. 

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