Splitting Hairs with Precision: LINK Develops Improbable Measuring Capabilities

Mar 17, 2015

Link Engineering Develops Improbable Measuring Capabilities for Compressibility Testing

Microscopic variations in friction materials can have non-desirable effects on vehicle braking systems and consumer perception of the brake behavior and response. High levels of wear-and-tear on brake rotors, adverse deceleration performance, and dangerous temperature levels can result from such variations. Other flaws might include excessive noise, vibration, or odors during brake application. Pedal feel, brake ABS, traction control, and the system’s compliance during electronic stability control maneuvers may be influenced by the compressive behavior of the friction materials.

If impacts such as these occur as a result of microscopic variations in friction material, then testing those variations must be done with microscopic precision. Up until early 2014, resolutions of 0.5 µm and accuracies of 10 μm or more were the standard. That was before Link Engineering released the Model 1620H Hydraulic Compressibility Machine, which was granted full GM approval earlier this year for the GMW15334 procedure.

The history of the Model 1620H has its origins at the SAE Brake Colloquium of 2009 where an industry leader in brake pad engineering explained the need for compressibility machines with 0.1 µm measuring capabilities (…1/250th the width of the average human hair). His thought process was to better support brake caliper design, brake corner performance, and to feed simulation models for ABS, traction control, and disc thickness variation.

Initially, the industry consensus not only determined the notion irrelevant, but downright improbable. Link Engineering Chairman and CEO, Roy Link, initially had his doubts as well. Yet the engineer wasn’t just splitting hairs with the idea. He was on to something. With a bit of nudging, Link put together a team of the company’s brightest engineers to meet GM’s challenge and to support a SAE Task Force. For months, the team met to brainstorm ideas.

“We would come up with ideas and tell each other why it wouldn’t work,” said Carlos Agudelo, Link Engineering’s Director of Technology Development for Testing Services. “Then, we decided to stop talking about it, roll up our sleeves, and do it.”

Several design changes were made to the, then, standard compressibility machine in order to achieve the level of precision being requested. The team removed the machine’s pneumatic system, allowing stiffer hydraulic oil force to provide increased control accuracy. The heavy loading block is now lighter to allow for a 30 Newton pre-load. They also gave the model a longer stroke cylinder to allow for a wider range of sample thicknesses; including some brake lining for drum brakes and drum-in-hat parking brakes. The result of such changes took testing accuracy from 0.5 µm to 0.1 µm while maintaining machine-to-machine variations under 3 μm using actual friction materials. Engineers enhanced platen temperature control from the standard 400° C. and can now maintain temperatures from ambient to 600° C.

Lastly, John Davis, Link Engineering Software Engineer, incorporated customized ProLinkTM software to make the equipment more user-friendly. It has an interface specifically designed to enter test parameters and define testing sequences with the Model 1620-H. This allows the user to easily conduct testing according to SAE J2468 and ISO 6310 procedures. And, in addition, the new Link’s 1620H system can perform dynamic loading using sinusoidal control up-to-45 Hz or 50 kN of amplitude at different preloads.

According to Davis, “This new compressibility machine is a huge step forward in microscopic testing. It offers our customers unparalleled repeatability and accuracy while simultaneously increasing testing throughput.”

A new 1620H system was provided to a third party for further assessments and full development of the upcoming SAE J3079 recommended practice. Today the stats are in and engineers are pleased with the 1620H’s precision and looking forward to future developments of the 1620H system.

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Type of TestTest HighlightsEquipment UsedExample Procedures
Chemical TestingMeasurement of copper, asbestos and other elements in brake friction materialsICP-OES / PLMJ2975
Materials TestingPhysical properties including quality control for friction, wear, compressive strain, shear strength, corrosion resistance, swell and growthChase Machine / Compressibility Machine/ Shear Machine / Corrosion Chamber / Environmental Chamber / OvenJ661, ISO 6310, ISO 6311, ISO 6312, ABNT NBR 9301, ABNT NBR 5505, ABNT NBR 5537, ASTM B117
Frequency ResponseComponent Frequency ResponseLaser Vibrometer Test StandSAE J2933, J3001, J2598, L-4375
Structural Fatigue and
Breaking strength, cyclic fatigueServo Hydraulics, Torque FlexJ2995, C419, C441, GMW18022
Caliper FingerprintingCaliper characteristics such as knockback, rollback, fluid displacement, deflection...Caliper Test Bench / Brake DynamometerL-4177, PF.90257
Brake Drag and DTVResidual drag, disc thickness variation, brake feel and vehicle fuel mileageOff Brake Drag Stand / Brake DynamometerJ2923, GMW14926, GMW14351, PF.90257, L-13080
PerformanceHydraulic, air and electric brakes, friction levels, stopping distance, corrosion, cleanability, brake torque variation, rotor cracking, regulation, stability control, coastdownBrake Dynamometer, Model 4000 DASJ2784, J2928 IS026867, GMW14985, PF.90210, PF.90244, L-405, FMVSS 121, FMVSS 122, FMVSS 105, FMVSS 135, FMVSS 126, FMVSS 136, ECE R13H, AMS
WearRotor wear, drum wear, lining wear, DTV, durability, city traffic, suburban trafficBrake Dynamometer, Model 4000 DASJ2707, USCT, L-423, PF.90244, Los Angeles, Detroit, Phoenix, Birmingham, Marquette
NVHBrake squeal during drag and decel events at different temperatures, pressure and torque levelsNVH Brake DynamometerJ2521, L420, 1430, GMW17427, PF. 90244
Brake EmissionsBrake dust particle size, count, concentration and massBrake DynamometerWLTP, CARB, Duty cycle


Type of TestTest HighlightsEquipment UsedExample Procedures
Wheel BearingWater intrusion and durability when exposed to mud and saltBearing Test StandLINK Hub and Bearing, GMW16306, GMW16310
Passenger car, sport/performance and open bed vehicle wheel bearing spallingBearing Test StandGMW16311, GMW16308, GMW16309
Brinelling resistance validates long-term reliability/durabilityBearing Test StandGMW16305
Rotary fatigue lifeRotary Fatigue MachineGMW16325
Wheel HubRotary bending fatigue life characteristicsRotary Fatigue MachineGMW14249
Hub/BearingEvaluate hub and bearing performance, durability, seals and NVH when exposed to extreme environmental effects such as temperature and mud/salt solutionBearing Test Stand/Rotary FatigueTIP-000037A, LINK Hub and Bearing, SAE J1095, LINK Impact
Hub FatigueHub fatigue using biaxial loadingBiaxial Test StandSAE J2562


Type of TestTest HighlightsEquipment UsedExample Procedures
ChemicalEvaluates filiform corrosion on painted aluminum wheels and painted aluminum trimICP-OESASTM E3061
Wheel Corrosion and CoatingsEvaluates filiform corrosion, tape adhesion, degree of rusting on painted aluminum wheels and painted aluminum trimCorrosion ChamberSAE J2635, ASTM B368, ISO 9227,
ISO 2409, ASTM D3599,
ABNT NBR 11003, ASTM D610,
ASTM D1654
Wheel FatigueLoad simulation test of aluminum alloy wheelsBiaxialBMW QV36026, SAE J2562, FORD
L-307, GMW14340
Dynamic Cornering Fatigue and Dynamic Radial Fatigue - Steel wheelsEccentric Mass and RadialABNT NBR 6750
Rotational fatigue, Radial load fatigue and biaxial load fatigue of steel and aluminum wheelsEccentric Mass, Radial and BiaxialABNT NBR 6751
Dynamic Cornering Fatigue and Dynamic Radial Fatigue and Impact resistance of temporary use and normal highway use aluminum wheelsEccentric Mass, Radial and Drop TestABNT NBR 6752
Wheel Radial FatigueRadialGMW14909
Wheel ImpactWheel Inboard Rim Flange Vertical ImpactDrop TestGMW15321
Wheel radial impactDrop TestCETP 04.04-L300
Wheel Lateral ImpactDrop TestGMW14910, SAE J175
Wheel StiffnessFrequency Response Function (FRF)Frequency ResponseGMW14876
Deformation of the wheelServo HydraulicsJ2315
Center cap heat
Center Cap deformation under elevated temperature conditionsBench TestBrake Heat Center Cap


Type of TestTest HighlightsEquipment UsedExample Procedures
Parking ForcesAllows proper sizing of power steering componentsForce and MotionLINK Parking Forces
Tire FootprintDetermines the contact patch geometryForce and MotionTire Footprint
Tire Modeling
Determine tire inertia which is then used Ftire and other models and simulationsInertia MachineLINK Tire Inertial Properties
On-center parking effort test for Ftire inputForce and MotionSWP
Determine static stiffness (X, Y, Z, Alpha) for Ftire inputStatic Stiffness MachineSAE Static Stiffness
Determine how the tire envelopes an obstacleCleat MachineJ2731
Measure the forces and moments generated at a high frequency response spindle when the tire impacts a cleatCleat MachineJ2730
Braking and Cornering PerformanceDetermine the straight line braking performance of a tireForce and MotionJ2673
Determine the free rolling cornering properties of a tireForce and MotionSAE TIME, J1987, SWP
Measure the combined cornering and braking performance of a tireForce and MotionJ2675
Tire StiffnessMeasure rolling vertical stiffness of a tire at speedRolling Vertical Stiffness
Rolling ResistanceMeasure tire rolling resistance using a drumForce and Motion, Rolling ResistanceJ1269, J2452
Tire WearAssess tire wear in the labForce and MotionLINK Wear Test
Tire NVHTest tire sizzle, cornering noise, pass-by noise, steering wheel dither, freeze crack impacts, high speed uniformity and imbalance sensitivityForce and Motion, Dynamometer, Model 4000 DASNoise, Vibration, Harshness