Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2003-03-03
2004-08-10
Crispino, Richard (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S345420, C156S583200, C428S617000
Reexamination Certificate
active
06773535
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to separable adhesively bonded elements, to articles and assemblies including such separable adhesively bonded elements and to a method for separating such adhesively bonded elements from articles and assemblies. More particularly, the present invention relates to articles and assemblies having adhesively bonded shape memory alloy elements, to articles and assemblies including separable adhesively bonded elements and adhesively bonded shape memory alloy elements, and to a method of bonding and easily separating adhesively bonded elements, such as external components, employing shape memory alloy elements.
2. Brief Description of Related Art
In many industries, notably those related to the construction and/or manufacture of structures and devices in which later partial disassembly is required or anticipated, elements must be securely joined or affixed to one another for extended periods of time and still be capable of being easily separated without damaging or destroying one or more of the elements at the time of disassembly. This is of particular interest in certain aspects of the aircraft and automotive industries and in military vehicular applications, such as both wheeled and tracked ground vehicles and munitions carriers. In the construction of both fixed wing and rotary wing aircraft, such as helicopters, a particular concern is the attachment and removal of access panels and skin panels. Traditionally, such panels have been attached using mechanical fasteners. However, in modem aircraft such panels are generally constructed from advanced composite materials to reduce weight and radar cross-section. These composite materials are typically formed from fiber-reinforced polymers, such as glass or graphite fibers in an epoxy matrix. Tests have demonstrated that placing holes in composites, as is necessary when using mechanical fasteners, causes a significant loss in fatigue and static mechanical properties of the composites. Mechanical fasteners also increase the radar cross-section of the aircraft.
In order to avoid these problems, adhesives have frequently been employed to join such elements. These adhesives are designed to achieve high strengths and thereby provide necessary load transfer between the adhered elements. However, in some cases, the bonded panels need to be removed in order to repair or replace the panels, or to gain access to underlying components. For this reason, procedures are needed for the subsequent separation and disassembly of the adhered elements.
Currently, most structures having adhesively joined elements or components are debonded mechanically. This process typically includes physical prying, chiseling, grinding, sanding, and scraping of the adhesive and/or adhered element. This approach is slow and inconsistent, requires skilled technicians, may be environmentally hazardous both to the technicians and to the aircraft itself in releasing airborne particulates, and in many cases results in significant damage to the separated components or underlying structural members or skin. Damage to the separated components is particularly undesirable during removal of access panels, since it is preferred to reuse or reattach the panel after removal. If the panel is damaged during removal, then repair or replacement of the panel incurs additional time, cost, and logistical problems.
To avoid such problems, other variations of the foregoing adhesive bonding/debonding method have been tried. Most of these have involved a selective choice of adhesive employed and a specialized treatment of the adhesive in the debonding stage of the process. Examples of those adhesives (and the concomitant processes) that have been tried or considered have included hot-melt adhesives, solvent-specific removable adhesives, thermally removable adhesives, electrically debondable adhesives, and pressure-sensitive adhesives.
Hot-melt, or meltable, thermoplastic adhesives are weakened by heating the adhesive above the melt or glass transition temperature of the adhesive. However, only a partial loss in adhesive strength is achieved, so that significant mechanical force must also be applied to separate the adhered elements (adherends). Furthermore, separation must be achieved while the adhesive is hot since bond strength resumes upon cooling.
Solvent-specific-removable adhesives can be dissolved using solvents (including, inter alia, water). These adhesives, however, by nature, offer limited solvent resistance, which restricts their environmental and service durability. Adhesives that are formulated to dissolve in only strong solvents also present environmental concerns during adhesive removal.
Thermally removable adhesives have been developed which undergo a dramatic loss in mechanical properties at a given temperature due to a thermally initiated chemical reaction within the adhesive. Unlike hot-melt adhesives, a complete loss in mechanical strength occurs at the transformation temperature. Only limited performance data is available, so the mechanical strength and environmental durability of these adhesives is not known.
Electrically debondable adhesives have been developed which debond by passing a small electrical current (~1 mA) of low voltage (~10 V) through specially formulated epoxy adhesives to weaken and ultimately debond the adhesive. Typically, electrodes are embedded at the bondline with electrical leads to permit local voltage application. The fabrication, placement, and maintenance of these electrodes often present significant cost, design, and logistical burdens. Additionally, these adhesives currently offer low to moderate structural strengths, with significant loss in mechanical properties at elevated temperatures. The long-term durability of these adhesives is also not well-characterized.
Pressure-sensitive adhesives are low strength, removable adhesives. Their mechanical properties are not sufficient for most structural applications.
An additional limitation of all of these removable adhesives is that the debonding properties are enabled through specially designed adhesive chemistries. For many critical applications, especially in the aircraft industry, any new adhesive must be fully certified before it can be implemented in the final design. This certification process, including full environmental testing, is typically very expensive and requires long test durations. These factors often make implementation of these novel adhesives impractical.
Accordingly, it is an object of the invention to provide a more expeditious, facile and predictable means for affixing and later removing components than is currently available. To this end, it is also an object of the present invention to provide an adhesive bonding system and a method employing the adhesive bonding system to adhesively and securely join or bond at least two elements or components to one another with high bond strength and subsequently, optionally, and under preselected, specified conditions, debond and separate the bonded elements or components by weakening the strength of the adhesive.
It is also an object of the present invention to provide, particularly to vehicular means including, but not limited to, ground vehicles, both wheeled and tracked; aircraft, both fixed wing and rotary; and watercraft, an adhesive bonding system employing currently existing adhesives, and a more expeditious, facile and predictable method than is currently available of adhesively bonding at least two elements to one another with high bond strength and subsequently easily separating the adhesively bonded elements, using the adhesive bonding system under predetermined conditions.
It is another object of the present invention to provide an adhesive bonding system and a method of adhesively bonding at least two elements to one another with high bond strength and subsequently separating the adhesively bonded elements with little or no damage to the separated elements such that the elements may be subsequently rebonded.
It is a further object of the pr
Chan Sing P.
Crispino Richard
Stolarun Edward
The United States of America as represented by the Secretary of
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