The Society of Automotive Engineers has selected a paper written by this associate for inclusion in SAE's 2006 Transactions. Described as among the best SAE Technical Papers published 2006, it will be published in one of seven subject-specific volumes.

Abstract

Many methods for damping - attenuating - unwanted noises and vibrations found in vehicles, engineering components, and electronic systems are available. A special type of damping material involves polymer-based coatings whose compositions may be "tuned" to attenuate vibration that may occur over specific temperature ranges. These coatings exhibit both elastic flow and viscous flow, depending on their temperature, and are commonly referred to as viscoelastic materials. Today, viscoelastic materials are used to fabricate many types of engineering components for automotive applications, including engine oil pans, valve covers, dash panels, and shims or insulators for brake noise damping.

No matter their application, expected performance for viscoelastic damping materials is based on two factors : (1) the quality and durability of coating-to-substrate interfaces; (2) the quality and durability of the viscoelastic coating itself. Thus, performance is a complex function of the individual materials and processes used in fabricating the damping material, including but not limited to substrate cleaning and pre-treatment, choices of primers, solvent removal, coating composition, and proper curing.

The paper provides an analysis of potential failure modes of interfaces and coatings in viscoelastic damping materials and reviews their effects on performance. Background information includes comments and data on proper selection of materials, processing parameters, and how damping characteristics may be compared. The oral presentation emphasized materials and their application to damping vehicle brake noise. This approach provides a tutorial on the many factors that should be considered in managing and reducing variability in quality and performance.


 

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Resume of ZQY Chemist, Materials Engineer, Process Engineer Consultant Resumes

Coatings science and technology involve an interdisciplinary approach. For example, polymer science, physics, colloidal chemistry, surface chemistry, organic chemistry, engineering, and other disciplines are all required to some degree to develop new coatings and to make incremental improvements to existing technologies. This associate is experienced in coatings rheology, a branch of physics, and its relationship to coatings science.

Rheology is defined as the science of the flow and deformation of matter. Several important material functions are defined by rheologists. The coatings formulator typically deals with the viscosity as measured by a viscometer. However, most coatings formulations have viscoelastic properties. These viscoelastic properties are generally inaccessible to the formulator but can lead to unexpected results for a given formulation viscosity including rod-climbing behavior, stringing from spray nozzles, shear thinning of viscosity, spatter from roller brush applications, poor atomization from spray applications, variability in roll-coating applications, differences in applied film thickness, and undesirable dried film properties such as brush marks.

The most commonly known and misinterpreted of these viscoelastic features is the one called shear thinning of viscosity. Most coatings formulations are colloidal systems and most colloidal systems have a steady state shear viscosity that varies with shear rate. Shear rate can be defined as the velocity of the moving fluid being applied to a substrate divided by the gap or distance between the substrate and the applicator. Or, for a spray application, the shear rate to a first approximation varies as the flow rate divided by the cube of the hole radius. The shear rate has units of reciprocal seconds, sec-1.

The structure of a colloidal system, e.g., a paint formula, leads to a transient network of elastic junctions that can be characterized by an elastic modulus proportional to the number density of segments between network junctions and a characteristic time given by the ratio of the limiting zero shear rate viscosity divided by the modulus. As the system is sheared at a given shear rate, the non-linear viscoelastic response results in a change in the number of network junctions--usually a decrease in junctions. A decrease in network junctions results in a decrease in the steady state shear viscosity and the fluid satisfies the definition of shear thinning.

In designing new formulas or improving existing formulas, the objective is to match the shear viscosity of the formula to the expected shear rate of the application environment. Types of applications problems include pigment settling and shelf stability, sag and leveling, brushing, roller application, spray application, and transport via piping systems. This act of matching of viscosities of a formulation to a specific application shear rate can easily be done with current rheometer technology; however, low budget low cost users may only have access to viscometers. Viscometers can be used for the same purpose with more difficulty if the test shear rate(s) are thoroughly understood.

For example, here is a list of desired room temperature viscosities for water based paints based on our research of the literature and our experience :

  1. Minimize pigment settling and coagulation. Shear rate < 0.01 sec-1. Viscosity > 500 poise.
  2. Maximize leveling and minimize brush marks. Shear rate 0.01 to 0.1 sec-1. Viscosity < 100 poise.
  3. Minimize sagging and appearance problems. Shear rate 0.01 to 0.1 sec-1. Viscosity > 100 poise.
  4. Optimize brush loading (from paint can to paint brush). Shear rate 50 to 100 sec-1. Viscosity of 10 to 12 poise.
  5. Optimize brush drag on paint application. Shear rate 1000 to 10000 sec-1. Viscosity less than 3 poise.
  6. Optimize film build and film thickness. Shear rate 2000 to 10000 sec-1. Viscosity 1 to 3 poise.
  7. Optimize droplet formation for spray applications. 5000 to 10000 sec-1. Viscosity less than 0.6 poise.

Different application techniques and film property objectives will require a different set of guidelines. For example, a large volume spray paint application for automobiles will require a special set of properties to minimize pinholes, craters, and other appearance defects.

Some of the limits shown above are in conflict. Therefore, it is common in coatings formulations to make trade-offs between various objectives. For example, a paint formula with excellent sag control would probably exhibit poor leveling and appearance problems from brush marks. To make matters worse, rheology control is critical at every level in formulations from pigment dispersion quality, to letdown of the pigment dispersion with the binder system, to selection of the rheology modifiers and their order of addition, to the time behavior of the coatings rheology after the final additions have been made. And, selection of a rheology control package must take in to account the effect of the additive on the colloidal stability of the dispersion. Some thickeners may result in a water sensitive coatings or appearance problems due to volume exclusion flocculation of the pigment.

Expert Analysis

In summary, formulation design can require knowledge of many areas of science and engineering. We have given some guidelines for rheology control of formulations in this short article. Our experience in designing formulations that meet the many challenges of formulation design has been very rewarding.


 

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Resume of OQD Rheology, Coatings Scientist, Colloidal Chemistry, Expert Consultant Resume

At issue in the 26-week project summarized here were adhesive bonds used to attach sub-miniature electronic microphones to plastic fixtures that allow the assembly to be incorporated into application-specific packaging. Specifically, the microphone cases are made of stainless steel and the mounting fixtures are glass-filled Nylon. These devices are in actual service for many years and are continuously exposed to high humidity and a temperature of ~95 °F. The specific goal of the project was to identify alternative adhesives that would significantly enhance bond strengths and would be less susceptible to warm, high humidity environments. The result would be longer service life in current applications and development of new applications.

Selections of candidate alternative adhesives were based on three technical issues: (1) the bonded assembly comprises one adhesive layer and two dissimilar interfaces that must be more resistant to temperature and humidity; (2) due to the heat sensitivity of the electronic device itself, thermal curing of an adhesive would be limited to about 150 °F; and (3) application of adhesives during the bonding process would be done manually. The two interfaces noted in item #1 are metal-to-adhesive and the Nylon-to-adhesive.

An initial task in this project was to identify technologies that have solutions to similar adhesive bonding problems. They are :

  • Industrial adhesives for high strength metal-to-metal and metal-to-plastic bonding
  • Dental adhesives for long-term bonding of small ceramic and metal parts to moist, porous, complex surfaces
  • Medical device adhesives for bonding hypodermic needles to various types of plastic hubs
  • Micro-electronics applications requiring bonding dissimilar materials with small bond areas

Physical and / or chemical treatments of substrate surfaces are methods for enhancing bond strengths. Modifications of the stainless steel and Nylon surfaces to enhance bond strengths that were considered for the project include the following :

  • Grit blasting to increase surface area
  • Chemical etches to increase surface area
  • Physical vapor deposition (PVD) of metallic coatings to act as compliant layers
  • Inorganic and organic primers to act as compliant layers
  • Oxygen plasma processing to chemically modify plastic surfaces and clean metallic surfaces
  • Silane coupling agents to chemically bond substrate to adhesives

Expert Analysis

Twenty-two candidate adhesives were selected. For screening, a standardized test procedure was defined that involved bonding groups of five electronic device cases to a one-inch diameter Nylon mount. The forces required to fail the bonds in shear were determined on as-fabricated and humidity-exposed samples. The photograph shows the shear test in progress.

Using the bond strength measurements coupled with microscopic examinations of fracture surfaces, ten “good” adhesives were identified of which five were identified as “superior.” The superior adhesives exhibited shear values as high as 200 newtons-force (45 pounds-force) for bond areas of only 0.016 square inch. Some of these were put into small-scale manufacturing trials as the first step in adopting them for production.


 

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Resume of ZQY Chemist, Materials Engineer, Process Engineer Consultant Resumes

 

We have applied VIC-3D(r) (see Expertise in Computational Electromagnetics) to the problem of evaluating the remaining life of thermal barrier coatings that are used in high-performance gas turbines. These turbines are increasingly appearing as `topping generators' for electric utilities, as well as stand-along systems for small power stations. The turbines operate at extremely high temperatures that require coatings to maintain structural integrity of the first two stages of turbine blades. When the coatings degrade, the blades become endangered, and the process of replacement of the entire turbine becomes expensive. By using eddy-currents and our special inversion algorithms that are rooted in VIC-3D, we can quickly and reliably estimate the state of the coating, thereby allowing an orderly replacement of the endangered blades.


 

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Resume of IBT Electrical Expert Consultant, Principal Investigator Resume

Commercial, electronics, aerospace, and automotive industries use a wide variety of methods to attenuate - damp - unwanted noises and vibrations. A well-established passive method for controlling structure-borne noise is based on viscoelastic materials that are specially selected for the application. In these cases, the materials are based on organic polymers that exhibit elastic and viscous properties. In the simplest cases, the damping material may be composed of a viscoelastic adhesive applied to one side of a suitable substrate.

Expected performance for these layered assemblies of polymer-based coatings and supporting substrates is based on two factors: (1) the composition, quality, and durability of each coating; and (2) the composition, quality, and durability of each material-to-material interface.

This is the second of two papers about this type of material for noise and vibration control. The objective is to provide readers with an overview of issues affecting design/development of products for controlling vehicle brake noise. Taking the format of a tutorial, it is intended for anyone involved in their design, manufacture, or use. It provides basic information and numerous references that will support evaluating potential failure modes and their effects in relation to choices of materials and provides an appendix with generic root causes.

Summary

Unwanted performance variations in materials for noise and vibration control can be minimized. The viscoelastic damping materials discussed in this paper are multi-layered combinations of various chemical coatings and supporting substrates. In designing and producing these products, there are many opportunities to affect the physical and chemical properties of the interfaces and coatings, for better or worse.

Initially, this requires a detailed understanding of the application-specific requirements for the engineering component made from these materials. Based on these requirements, appropriate selections of raw materials - polymers, additives, metal substrate, paints, adhesives, etc. - can be decided as part of the design/development of new products. The product design phase must consider manufacturing processes capable of converting the raw materials into products with consistency.

The format of the paper is a tutorial intended for anyone involved in the design, manufacture, or use of material for vehicle brake noise control. It provides basic information that will support evaluating potential failure modes and their effects in relation to choices of materials and provides an appendix with generic root causes. It can be used as the basis for preparing a detailed Product Design/Development Potential Failure Mode and Effects Analysis (FMEA).


 

To see the resume of the expert associated with this case study, see the link below.

Resume of ZQY Chemist, Materials Engineer, Process Engineer Consultant Resumes

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