The present invention in general relates to composite vehicle components and in particular, to fiber preforms with an integral optical fiber strain sensor for unitary reinforced composite based vehicle components.
Weight savings in the automotive, transportation, and logistics based industries has been a major focus in order to make more fuel-efficient vehicles both for ground and air transport. In order to achieve these weight savings, light weight composite materials have been introduced to take the place of metal structural and surface body components and panels. Composite materials are materials made from two or more constituent materials with significantly different physical or chemical properties, that when combined, produce a material with characteristics different from the individual components. The individual components remain separate and distinct within the finished structure. A composite material may be preferred for many reasons: common examples include materials which are stronger, lighter, or less expensive when compared to traditional materials.
As part of an effort to reduce vehicle weight and ease of manufacture vehicle manufacturers have moved towards composite material vehicle components. These composite materials include a matrix material that surrounds and supports the reinforcement materials by maintaining their relative positions. The reinforcements impart their special mechanical and physical properties to enhance the matrix properties. A synergism produces material properties unavailable from the individual constituent materials, while the wide variety of matrix and strengthening materials allows the designer of the product or structure to choose an optimum combination.
The use of fiber and particulate inclusions to strengthen a matrix is well known to the art. Well established mechanisms for the strengthening include slowing and elongating the path of crack propagation through the matrix, as well as energy distribution associated with pulling a fiber free from the surrounding matrix material. In the context of sheet molding composition (SMC) formulations, bulk molding composition (BMC) formulations, and resin transfer molding (RTM); hereafter referred to collectively as “molding compositions,” fiber strengthening has traditionally involved usage of chopped glass fibers. There is a growing appreciation in the field of molding compositions that replacing in part, or all of the glass fiber in molding compositions with carbon fiber can provide improved component properties.
Tailored Fiber Placement (TFP) is a textile manufacturing technique in which fibrous material is arranged on another piece of base material and is fixed with an upper and lower stitching thread on the base material. The fiber material can be placed in curvilinear patterns of a multitude of shapes upon the base material. Layers of the fiber material may be built up to produce a two-dimensional fiber preform insert, which may be used as an insert overmolding or resin transfer process to create composite materials.
Resin transfer molding or overmolding (hereafter referred to synonymously as “RTM”) is a process in which the fiber preform in placed in a mold where a melt processible material is molded directly into the insert. Melt processible materials typically used in overmolding include elastomers and thermoplastics. The major overmolding processes includes insert molding and two-shot molding. Materials are usually chosen specifically to bond together, using the heat from the injection of the second material to form that bond that avoids the use of adhesives or assembly of the completed part, and results in a robust composite material part with a high-quality finish.
Commercially produced composites often use a polymer matrix material that is either a thermoplastic or thermoset resin. There are many different polymers available depending upon the starting raw ingredients which may be placed into several broad categories, each with numerous variations. Examples of the most common categories for categorizing polymers include polyester, vinyl ester, epoxy, phenolic, polyimide, polyamide, polypropylene, PEEK, and others.
As vehicles are increasingly platforms for ever more complex computerized systems, there is a need for sensors throughout the vehicle and its associated components. However, the complexity of such sensor systems throughout a vehicle increases the weight of the vehicle, increases the complexity of a vehicle electrical harness, and increases the time needed for installation. Traditionally, sensors are strategically placed in preselected positions around a vehicle and joined to structural components during vehicle assembly. Sets of wires are cut to predetermined lengths and tied into bundles with connectors to join the sensors to other electrical components of the vehicle. Such sensors and wiring harnesses have become increasingly impractical and time consuming to couple to not only to the vehicle, but also electrical wiring and central processing units (CPUs). Traditional sensor systems are subjected to extreme environments also suffer from vibrationally induced wear caused by vehicle operation. The failure of such sensors or shorting of a wire within an electrical harness is difficult to locate and repair.
Thus, there exists a need to form a vehicle component having an sensor system integral therein.
A form for a vehicle component includes a commingled fiber bundle composed of thermoplastic fibers and a reinforcement fiber. The reinforcement fiber being glass fibers, aramid fibers, carbon fibers, or a combination thereof. The commingled fiber bundle is laid out in a two-dimensional base layer that defines a shape of the form. An optical fiber is stitched to the commingled fiber bundle.
A method of forming a unitary reinforced composite component having a sensor system includes the form being placed onto a mold platen. The preform is heated to promote fusion of the thermoplastic fibers therein. The preform is cooled until solidified with contours of the component. The vehicle component is then removed from the mold platen.
The subject matter that is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The present invention has utility as a unitary reinforced composite based panel component, and methods of construction thereof inclusive of optical fiber. A vehicle component is prepared with resort to selective commingled fiber bundle positioning (SCFBP) to selectively place co-mingled fibers that are in some inventive embodiments enriched in carbon fiber as a reinforcement relative to other region that rely on a relatively higher percentage of glass fiber reinforcement while internalizing optical fiber within the vehicle part. By internalizing an optical fiber within a vehicle part, vehicle assembly is simplified, capabilities of sensor systems are increased, and vibrationally induced wear and environmentally induced wear observed on traditional sensors is eliminated.
In specific inventive embodiments, commingled fibers of thermoplastics, and reinforcing fibers of glass, carbon, polyaramid, or a combination thereof are used to form a yarn that has predictable strength, and where the ratio of different fiber types is varied to create different properties along a given length. The commingled fiber-based yarn may be used in the formation of the SCFBP forms, and are able to be embroidered directly into complex shapes thereby eliminating trimming waste and inefficient usage of comparatively expensive carbon fiber. In specific inventive embodiments, SCFBP forms include from 3 to 20 layers that vary in fiber types in three dimensions (3D). Optical fiber is also stitched by the SCFBP process into the form to create pre-selected pathways. The final panel is them formed by melting thermoplastic fibers within the SCFBP form in contact with at least one mold platen complementary to the finished vehicle component to form a vehicle panel such as a dashboard, body panel, door component, roof components, or decklids.
It is to be understood that in instances where a range of values are provided that the range is intended to encompass not only the end point values of the range but also intermediate values of the range as explicitly being included within the range and varying by the last significant figure of the range. By way of example, a recited range of from 1 to 4 is intended to include 1-2, 1-3, 2-4, 3-4, and 1-4.
SCFBP-technology offers several advantages including varying the angle of fiber positioning during the lay-up process freely between 0 and 360°; repeated fiber positioning on the same area allows for local thickness variations in the fiber form suited for a fiber composite component; the conversion of the desired fiber orientation in a fiber positioning pattern for an embroidery machine requires minor development times and costs; the process allows a near-net-shape production, which results in low waste and optimal fiber exploitation; and the ability to process a variety of fibers such as natural, glass, aramid, carbon (high strength and high modulus) and ceramic fibers.
As used herein, a veil includes woven sheets, non-woven sheets, and films of thermoplastics, glass, or aramids; or woven sheets, non-woven sheets of carbon fibers.
As used herein, any reference to weight percent or by extension molecular weight of a polymer is based on weight average molecular weight.
As used herein, the term melting as used with respect to thermoplastic fibers or thread is intended to encompass both thermofusion of fibers such that a vestigial core structure of separate fibers is retained, as well as a complete melting of the fibers to obtain a homogenous thermoplastic matrix.
Commingled fibers as a roving are made up of commingled reinforcing fibers, illustratively including those made of carbon, glass, or aramid fibers, and thermofusible fibers which serve to provide a matrix in a composite material made of both reinforcing and matrix fibers. The matrix fibers, being of a thermofusible nature may be formed from material such as, for example, polyamide, polypropylene, polyester, polyether ether ketone, polybenzobisoxazole, or liquid crystal polymer. The reinforcing fibers may also be of a material that is meltable with the proviso that melting occurs at a temperature which is higher than the matrix fibers so that, when both fibers are used to create a composite, at the temperature point at which melting of the matrix fibers occurs, the state of the reinforcing fibers is unaffected.
The commingled fibers used in the present invention are composed of thermoplastic fibers and a reinforcement fiber. Thermoplastic fibers operative herein illustratively include, polypropylenes, polyamides, polyesters, polyether ether ketones, polybenzobisoxazoles, polyphenylene sulfide; block copolymers containing at least of one of the aforementioned constituting at least 40 percent by weight of the copolymer; and blends thereof. The thermoplastic fibers are appreciated to be recycled, virgin, or a blend thereof. The thermoplastic fibers in a commingled fiber bundle constitute from 20 to 80 weight percent of the commingled fibers in the present invention.
The reinforcement fibers in a commingled fiber bundle being glass fibers, polyaramid, carbon fibers, or a combination of any of the aforementioned. It is appreciated that the commingled fibers are either parallel to define a roving or include at some fibers that are helically twisted to define a yarn. It is appreciated that the physical properties of reinforcing fibers retained in a helical configuration within a fixed matrix of a completed vehicle component are different than those of a linear configuration, especially along the reinforcing fiber axis. The relative number of reinforcing fibers relative to the thermoplastic fibers is highly variable in the present invention in view of the disparate diameters of glass fibers, polyaramid fibers, and carbon fibers.
The optical fiber is stitched into the preform. The optical fiber can be included as a fiber in the commingled fiber bundle or may be separately stitched to the commingled fiber bundle via a separate stitching operation. According to embodiments, the optical fiber is a glass or plastic material. The optical fiber has a melting temperature which is higher than melting temperature of the matrix fibers and/or the reinforcing fibers so that at the temperature point at which melting of the matrix fibers and/or the reinforcing fibers occurs, the state of the optical fibers is unaffected. According to embodiments, the optical fiber is a continuous optical fiber having first end and a second end. According to embodiments, the optical fiber includes a plurality of discrete portions of optical fiber that emanate from the same location at one end and each terminate at a second end located in a plurality of locations throughout a vehicle component. According to embodiments, the optical fiber is coated in an ultraviolet-curable resin. According to embodiments, the optical fiber has a diameter of 0.25 mm.
An inventive form is created by laying out one or more commingled fiber bundles on a substrate as a two-dimensional base layer that defines a shape of the form with stitching applied to retain the commingled fibers in a desired placement on the substrate. As is conventional to SCFBP, the substrate can be removed after production of the form, else it is retained and thereby incorporated into the resulting vehicle component. In certain inventive embodiments, the stitching is a thermoplastic thread. The thermoplastic thread in some inventive embodiments is formed of the same thermoplastic present in the commingled fiber bundle. It is appreciated that the thread diameter and melting temperature of the thread used for stitching are variables that are readily selected relative to the properties of commingled fiber bundle. A first end and/or a second end of the optical fiber extends from the inventive preform such that the ends of the optical fiber are exposed and accessible for connection to other sensor system components or to the optical fibers of other vehicle components.
As shown in
As a result of the present invention, the form 210 includes specific features such as the notch region 132 that conventionally would be cut from a base piece. In this way, the present invention eliminates the cutting step, as well as the associated waste generation while including optical fiber within the form, which remains continuous given the omission of any cutting step. In addition to the substantially linear pattern of commingled fiber bundle and optical fiber positioning depicted in
If zero degrees is defined as the long axis of the base layer 124, the subsequent layers are overlaid at angles of 0-90°. For example, an angular displacement between adjacent layers is 45° resulting in a 0-45-90-45-0 pattern of layers. Further specific patterns illustratively include 0-45-90-45-0, 0-45-60-60-45 0, 0-0-45-60-45 0-0, 0-15-30-45-60-45-30-15 0, and 0-90-45-45-60-60-45-45-90-0. While these exemplary patterns are for from 5 to 10 layers of directional SCFBP, it is appreciated that the form 210 may include from 3 to 20 layers. It is appreciated that the form layers may be symmetrical about a central layer, in the case of an odd number of layers, or about a central latitudinal plane parallel to the players.
The stitching 122 or 122′ is applied with a preselected tension, stitching diameter, stitch spacing. The stitching 122 or 122′ is typically present in an amount of from 0.1 to 7 weight percent of the commingled fiber bundle 112′.
While
A cross-sectional view of an exemplary form similar to form 210 is shown in
The interaction between lightwaves incident on an optical fiber and acoustic phonons generates Brillouin scattered light as backscattered light that propagates in the direction opposite to incident lightwaves. Because the phonons decay exponentially, the Brillouin scattered light spectrum is Lorentzian in form. The frequency at which peak power is obtained in the spectrum is shifted about 11 GHz from the incident lightwave frequency at a wavelength of 1.55 μm. This amount of frequency shift is called a Brillouin frequency shift, νB. If longitudinal strain ε occurs in the optical fiber, the Brillouin frequency shift νB changes in proportion to that strain, as shown in
To obtain the distributed strain, that is, distributed νB along an optical fiber, the BOTDR observes the distribution of the Brillouin scattered light spectra along the optical fiber by utilizing the OTDR technique as shown in
Here c is the light velocity in a vacuum and n is the refractive index of the optical fiber. To obtain the spectrum of the Brillouin scattered light, repeated measurements are made, in the manner described above, in which the incident light is slightly changed in relation to the spectrum width. As a result, a large number of power distributions of the Brillouin scattered light are obtained at different frequencies, as shown in
The configuration of the measuring equipment is shown in
Next, by slightly changing the amount of frequency conversion νS in the frequency conversion circuit, for example in 10 MHz increments, and by repeating the measurement the Brillouin scattered light spectra is obtained at any position along the optical fiber. The obtained spectra are then subjected to signal processing and converted to the strain distribution over distance.
The spatial resolution in these measurements, in other words, the distance information included in one item of the strain data at a given position, is decided in the same way as with the OTDR technique, that is, by the pulse width of the incident light. The spatial resolution ΔZ is expressed using a given pulse width τ as shown in Equation 4, where c is the light velocity in a vacuum and n is the refractive index of the optical fiber. At present, the pulse width with this measurement equipment is 10 ns, which corresponds to a spatial resolution of 1 m. The measurement accuracy, which is defined as the maximum variation of the measured strain in a strain-free section is ±0.003%.
Because the BOTDR is capable of measuring continuous strain over the length of the optical fiber, the sensor system of the present invention provides a damage detection system for the vehicle that is light weight and easy to manufacture and implement given that it is integral with the fiber preform that forms a composite vehicle component. As shown in
The foregoing description is illustrative of particular embodiments of the invention, but is not meant to be a limitation upon the practice thereof. The following claims, including all equivalents thereof, are intended to define the scope of the invention.
This application claims priority benefit of U.S. Provisional Application No. 62/889,302 filed 20 Aug. 2019; the contents of which are hereby incorporated by reference.
Number | Date | Country | |
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62889302 | Aug 2019 | US |