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A Beginner’s Guide To Tyre Testing – Part 3

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This is the concluding part of A Beginner’s Guide To Tyre Testing by Dr.S.N.Chakravarty.

Dynamic Tests

The dynamic tests are performed on the large test drum. Most of the dynamic tests are restricted to pure slip conditions. On the large drum different test stands can be mounted.

Shearography is a contact less, image producing measurement procedure which is very suitable for non destructive testing of lightweight structures. Compared to testing methods like Ultrasonic testing, X-Ray measurement or the Eddy Current method, Shearography has the advantages of full field measurement and requires accessibility from only one side of the specimen.

Shearography is an interferometric measurement technique. The shearing optics is completely integrated into a compact measurement head. Shearography is in principle insensitive against whole body deformations which results in a high resistance against disturbing factors. With the CCD-camera technique no photo laboratory is required.

This makes it possible to practically use shearography as a means of non-destructive testing in InService-Inspection.

The progress and development in computer technique and digital image processing have further improved the practical suitability of shearography. The development of the spatial phase shift with which for each object state only one video image has to be recorded leads to a simpler measurement set-up and a faster image acquisition.

This results in improved robustness and longer lifetime of the measuring system since a mechanical phase shift module is no longer required. The actual measurement process is faster and, thus, less sensitive for disturbances.

  1. Shearography in the production line for quality control
  2. Shearography in Service as a mobile test system in field measurements

Here’s a 2.11 min video of Tire Testing with the STEINBICHLER INTACT 30 System.

Tire Testing - Shearography

Video of Tire Testing – Shearography

Measurement Principle

The shearography is an interferometric method with which it is possible to detect component deformation respectively the gradient of the deformation created by mechanical strain. The process is very sensitive due to the interferometric measurement principle: deformations in the range of few micrometers can be detected.

The measurement sample is illuminated by laser light. With a CCD-camera, the object is supervised. For the reproduction of the object on the CCD target of the camera (image plane), the so-called shear optics is applied. It reproduces the object on the CCD target twice: this is called image shearing. A point of the object is shown on two positions in the image plane. In other words: two neighboring object points are displayed one over the other in the image plane.

When the specimen deforms under strain, the intensity of the laser light reflected by the object changes. Superposition of the picture of two neighboring object points on the CCD target makes it possible to determine the difference of the deformation of all object points. Evaluating the intensity measured by the CCD target in each image point does this. Thus, with shearography the gradient of the deformation of the measured object in shearing direction can be measured.

L- Ray

The science behind Holography, Shearography and L-Ray’s “Differometry” is that we are building a topographical map of the inside of the tire. Essentially, we determine very accurately the distance from the camera lenses to the surface of the tire. We take the first image with no vacuum.  When a vacuum is pulled, any separations or defects inside the plies of the tire will allow the rubber to move creating a bubble.  When the moving rubber moves closer to the camera lens, the computer can detect the difference in the distance from the “at rest” condition and the vacuum condition.

It is not recommended to install a special foundation for the machine for two reasons.

First is that the machine is sitting on floor mounts that have a rubber insert that will provide some level of isolation. Second, the upper machine plate that holds the lower dome and the camera assembly is mounted on four airbags with an automatic leveling  system.

This airbag system provides the best possible isolation from factory vibrations.  However, if the machine were to be put in an environment where it is next to very significant pounding (like a forge press or something like that), the machine would most likely be affected by this severe vibration.

Most tire or retread factories do not have this type of situation so we generally don’t worry about it. The most common defect detected by the machine is a separation between plies of the tire rubber.  This is when two of the plies come apart due to excess heat, contamination during manufacturing, improper materials, etc.

L-Ray Tire Testing

Video L-Ray Tire Testing

Rolling Resistance

The question often arises whether a small cross-section tyre has lower rolling resistance than a larger one. The answer, as often, is yes and no, because unseen factors come into play.

Rolling resistance of a tyre arises almost entirely from flexural rubber losses in the tyre and tube. Rubber, especially with carbon black, as is commonly used in tyres, is a high loss material. On the other hand rubber without carbon black although having lower losses, wears rapidly and has miserable traction when wet.

Besides the tread, the tube of an inflated tyre is so firmly pressed against the casing that it, in effect, becomes an internal tread. The tread and the tube together absorb the majority of the energy lost in the rolling tyre while the inter-cord binder (usually rubber) comes in far behind. Tread scuffing on the road is even less significant.

Patterned treads measurably increase rolling resistance over slicks, because the rubber bulges and deforms into tread voids when pressed against the road. This effect, tread squirm, is mostly absent with smooth tyres because it cannot be bulge laterally by road contact because rubber, although elastic, is incompressible.

Small cross-section tyres experience more deformation than a large cross-section tyre and therefore, should have greater rolling resistance, but they generally do not, because large and small cross-section tyres are not identical in other respects. Large tyres nearly always have thicker tread and often use heavier tubes, besides having thicker casings. For these reasons, smaller tyre usually have lower rolling resistance rather than from the smaller contact patch to which it is often attributed.

Tyre Performance Testing

  • Single-Wheel Braking, Driving, and Lateral
  • Traction
  • Stopping Distance
  • Subjective and Objective Ride and Handling
  • Subjective and Objective Noise and Vibration
  • Mountability
  • Rim Slip
  • Bead Roll-Off/Unseating
  • Treadwear
  • Cornering Response – J-Turn and Tethered
  • Circle
  • Tri-Axial Force Measurement with
  • Non-Rotating Moment Compensating Wheel
  • End Transducers
Tyre Durability/Reliability Testing

  • Thermal Profile/Reliability
  • Mechanical Reliability
  • Multi-mode Durability
  • Puncture Resistance
  • Cut Resistance
  • Cut/Crack Resistance
  • Rib/Lug Tear Resistance
  • Curbing
  • High Speed Operation (150 mph)
  • Ton Mile Per Hour
  • Sequentially Advanced Accelerated
  • Wear and Durability (SAAWAD)

Tyre Mobility Testing

  • Dynamic Traction – Soft Soils/Winter
  • Drawbar Pull System Evaluation
  • Closed Circuit Operations
  • Marginal Terrain Go/No-Go

Resilometer or drum tests have been developed to evaluate separation resistance, bead durability, fatigue resistance, flat spotting, heat generation, bruise resistance, standing wave characteristics, growth rolling resistance and weathering resistance.

The best method to determine the integrity of a new tyre construction is to examine its performance when the tyre is subjected to actual road tests. Vehicle testing of tyres is conducted on industry proving ground of highway, extensive graveled roads and zigzag stretch. Proving track testing is utilised to evaluate general durability, high-speed performance, tread wear under varying service conditions, traction, skid resistance, gravel durability, fuel economy, cracking resistance, cut resistance and retreadibility.  Often tyre testing involves instrument fitted  vehicles  to evaluate ride, response, harshness, cornering forces, handling, stability and general vibration analysis.

Several new testing techniques are of interest. A glass plate facility permits a road view of the tyre. As a tyre rolls over the glass, a high-speed camera photographs the action of the tyre tread.This permits traction and tread wear behaviour analysis.

Another new development utilises telemetry to continuously monitor the internal forces of a tyre being tested on a vehicle. This is a powerful tool which can permit analysis of dynamic tyre behaviour.

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Author: Prasanth Warrier

Co-Founder | #B2B Strategy, Marketing & BD Consultant | Speaker | Trainer | Enjoys Traveling, Reading & Meeting People | #SocialSelling | #Blogger | Knowledge Sharing | Blessed with Loving Family & Friends | Voracious Reader | Business Leader serving Rubber Industry

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