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Flexure - Capability Statements

Lipstick bullet bend flexure testing

Lipstick bullet breakage by cantilever bend flexure

The important attributes for cosmetic products are related primarily to aesthetics and texture. Colour depth, choice of lustrous shine or matte finish and the feel of the product upon application to the skin, for example, are key selling points for lipsticks. Of equal importance (but less obvious to the consumer) is the durability of the cosmetic through repeated application – influenced by composition. The bullet-style dispenser for lipstick must perform reliably under cantilever-type flexure loading through forces applied by the lip at the tip of the bullet, and resisted at the end of the barrel container. The test system must replicate the conditions under which the lipstick will be stressed – holding the dispenser firmly and applying the force with a special fixture to ensure the sample will break due to bending force rather than being cut. The lipstick may fail either in shear or by the classic pure bending compression/tension force distribution: this test will determine either characteristic in the sample. By repeatability and accurately measuring the peak force at break, the manufacturer is able to evaluate the effect of formulation changes upon the performance of the product, either for aesthetic reasons: improving colour, finish and texture, or for manufacturing changes such as using different raw materials. This bend test is also applicable to differing designs of the lipstick tip – bullet, bullnose or chisel – due to the design of the fixture.

Mecmesin Systems: MultiTest motorised test system

Case Study: Lipstick bullet breakage test

Plant cantilever flexure measurement

Agricultural crop shoot cantilever bend flexure

Improving the reliability of the yield of foodstuffs is of global concern to the agricultural industry. An increase in the variety of specific dietary requirements for an individual’s health choice and the need to cater for population growth mean that achieving high quality yield from crops is essential. One reason for crop failure is lodging or permanent displacement, where the individual plant bends to lie flat on the ground – or displaced enough through flexure from upright to be unable to be harvested in an efficient manner – causing any number of remedial actions at cost to the crop-producer. Whether the lodging is caused by wind, soil composition or other factors, the application of a scientific approach to the forces and torques which the actual plant can resist will improve the understanding and ultimately success rate of the yield. The shots are considered cantilevers, anchored at their roots into the soil. The ability to test the crop bend flexure in the field necessitates not only a scientifically designed test, but also custom-engineered equipment which is simple, reliable, robust and portable. A tool to apply a controlled torque and an accurate digital gauge to measure of fundamental mechanical attributes of the shoots: centre of gravity, balance point and gravitational moment will allow food producers to evaluate the effects of changes to the processes which can influence the plants themselves, from nutrition to genetics. 

Mecmesin Systems: Static torque screwdriver, digital force and torque indicator

Case Study: Testing roots and shoots

 

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Surfboard foam sample 3-point bend tesing

Surfboard polyurethane foam 3-point bend flexure

A manufacturer of performance sports equipment, which is then sold on to customers in its own supply chain for final production design, must ensure that the fundamental product meets the highest quality standards. The polyurethane (PU, PUR) foam used for the manufacture of surfboard blanks is subsequently coated for various design reasons, but the fundamental strength characteristics should assure safe, reliable performance for this lightweight material.  For the manufacturer to provide a guarantee of product performance to its customers and to also obtain objective judgements regarding the raw materials received from its own suppliers, a repeatable, representative strength test is needed. The localised forces exerted by the surfer on the upper side of the board and the more generalised forces from the wave on the lower surface result in 3-point flexure being the relevant test type to measure the rigidity and strength of the product. A 3-point bend jig, with adjustable lower support arms and the capability of friction-free force application can be used to accurately apply the flexure symmetrically across the sample. A constant axial compressive load is produced by means of a constant speed application of the blade by the motorised test stand. Connection of a digital gauge and graphical output from software enables the manufacturer to compare the peak load data for different board constructions.

Mecmesin Systems: Motorised test stand, gauge and software combination, 3-point bend fixture

Case Study: Surfboard 3-point bend test

 

Polyester-mica film tape stiffness flexure test

Electrical insulating polyester film rigidity by 3-point bend flexural test

To maximise the service life and optimise the functionality of electrical systems – generators, motors, etc. – the electrical insulation component is vital. Often in the form of tapes, comprised of combinations or layering of polyester, mica (or mica paper) and glass fibre, these elements must have a certain degree of flexibility in their mechanical properties and prevent electric flashover and conduct away any dissipated heat. International electrical standards define specific tests to measure the stiffness of insulating materials based on mica. To meet these standards a purpose-built tape bend fixture will be required which performs a 3-point bend along the axis of the tape test specimen. The insulation film, mica uppermost (if layered, with the faced material uppermost) is placed symmetrically over a 5mm wide slot in the support platform and a tapered penetration bar is lowered until a peak resistance force is achieved. The stiffness is defined as a rigidity calculation – the ratio of maximum flexural load to sample length. The test for an individual product type is performed on 5 representative samples and the mean, maximum and maximum calculated rigidity values are reported for compliance, in addition to the temperature conditions (required to be 23 °C ± 2 K) and humidity.

Mecmesin Systems: MultiTest console-controlled force test system

Standard: IEC 60371-2

Toothbrush bristle pull-out testing

Toothbrush bristle cantilever bend and pull-out testing

The action of brush bristles in any in-service situation is quite a complex system. Many forces are applied, often in multiple directions and the action of frictional forces also has an impact on the durability of the product. In addition the retention of the bristles (filament shedding performance) is an important consideration. A simple manual toothbrush is subjected to these conditions, as well as industry test methods applicable to cosmetics and personal health – specifically dental equipment standards. A versatile and complete testing solution should be able to perform the bristle stiffness test, in which the complete brush tufted area is rubbed against a metal grid at constant speed – subjecting the bristles to a cantilever bend force. The forces recorded then categorise the toothbrush into consumer categories from soft, through medium, to hard. Shedding performance can be measured by pull-of/pull-out for individual filaments or a ‘tuft’ of bristles with a surgical clamp and a pin chuck fixture, respectively. Location of the toothbrush head should be secure in order to eliminate flexure in the plastic (polypropylene) housing itself. A robust console-operated system would allow testing in a mass manufacturing environment, with simple operation for production staff, giving the confidence to meet stringent quality standards.

Mecmesin Systems: MultiTest console-controlled force test system

Case Study: Toothbrush Stiffness Tester

Card crease force testing

Card and paper crease line testing

A packaging production company needed to test the maximum crease force in 90 degree folds in various materials. This required continuous accurate measurement by cantilever bend, through the folding movement.

Mecmesin designed a customised fixture to manually rotate the gripped card against a compression bar attached to one of our 100 N advanced digital force gauges. Clickstops at 45 and 90 degrees allowed the folding force to be recorded consistently at each angle for any material. Mounted on a manual test stand, this was a very cost-effective solution to their requirements.

Insulation film bend stiffness testing

Insulation film stiffness testing

Familiar with three-point bending? Our client needed to fold insulating film strip along its length rather than end to end, so the usual flexure fixtures were not appropriate. Instead they needed a blade and slot fixture with sufficient width.

Mecmesin designed and manufactured a slotted anvil with graduations for accurate sample placement, and a polished chrome plated blade, for consistent insertion and fully repeatable testing.