Patent Publication Number: US-2022212449-A1

Title: Transparent composite body panels with localized structural reinforcements for motor vehicles

Description:
INTRODUCTION 
     The present disclosure relates generally to body panels for motor vehicles. More specifically, aspects of this disclosure relate to transparent roof panels for moonroof and panoramic roof assemblies of motor vehicles. 
     Most current production motor vehicles, such as the modern-day automobile, are erected on a rigid vehicle body—either as a body-on-frame or a unibody construction—with an interior passenger compartment that seats and safeguards the vehicle occupants. In automotive applications, driver-side and passenger-side door assemblies are movably mounted to port and starboard flanks of the vehicle body to provide controlled access to the passenger compartment and to provide lateral visibility through accompanying door windows. A rear window or back glass seals off, yet provides visibility through, a rearward end of the passenger compartment. Mounted between the forward A-pillars of the vehicle body is a windshield that provides an aerodynamically formed window through which the driver views the roadway while preventing unwanted ingress of wind, rain, and debris. Modern windshields, side and rear windows, and glass panel roofs are generally formed as a laminated glass construction composed of a multilayer assembly with a plastic interlayer, typically of polyvinyl butyral (PVB) or ethylene-vinyl acetate (EVA), which is laminated between two or more curved sheets of tempered glass. 
     SUMMARY 
     Presented herein are multilayer composite panels for motor vehicles, methods for making and methods for using such panels, and motor vehicles equipped with transparent composite roof panels having selectively located reinforcement features. By way of example, a structural transparent composite roof with localized opaque reinforcement sections is presented, e.g., for a panoramic “glass roof” automobile. The transparent composite roof panel may be a laminated sandwich construction with three or more layers, including: one or more scratch-resistant exterior layers; one or more thermoplastic or thermoset fiber reinforced polymer (FRP) layers; one or more optical bond layers; one or more infrared (IR) reflective layers; one or more solid-state, light absorbing sunshade layers; one or more electrically insulating low-k coating layers; and/or one or more chemically strengthened or soda-lime glass layers. The sequential order, individual and collective thicknesses, and respective contents of the layers may be varied depending, for example, on the intended application of the multilayer composite panel. 
     The structural integrity and transparency level of the composite panel may be controlled by the contents and composition of reinforcing fibers incorporated into the FRP layer(s) of the panel&#39;s multilayer construction. Load-bearing aspects of a transparent composite roof, for example, may be dictated by the local and directional application of high-volume-fraction fibers in a prefabricated fiber-weave mat (preform), a multidirectional pre-impregnated (prepreg) layup, or unidirectionally applied fiber tows, which is derived by load path optimization through finite element control. The transparent composite roof may be a tripartite laminate that consists essentially of three layers, or may consist essentially of five layers, nine layers, ten layers, or eleven layers. The foregoing composite panels help to improve occupant visibility while increasing occupant-perceived spaciousness without compromising the roof&#39;s structural integrity or increasing gross vehicle weight (GVW). 
     For vehicular roof applications, the vehicle body may be fabricated with an optimized roof support structure to provide subjacent support for the transparent composite roof panel. The roof support structure is composed of longitudinally elongated, laterally spaced roof side rails and laterally elongated, longitudinally spaced front and rear roof headers. Opposing ends of the roof headers are mounted to inboard surfaces of the roof side rails to cooperatively define a roof window frame with a central opening. The roof panel is securely mounted onto the roof window frame to cover the central opening. Traditional cross-car reinforcement bows located between the front and rear roof headers may be eliminated from the roof support structure and replaced by the localized FRP reinforcement sections within the laminate composite roof panel. The high-volume-fraction fibers may be arranged within the multilayer laminate composite such that each internal, localized FRP reinforcement is isolated to a diamond lattice-shaped plan-view region, a U-shaped plan-view region, and other plan-view profiles containing symmetrical, asymmetrical, simple, and complex shapes and patterns. These plan-view regions have at least two longitudinally elongated side rail segments that are interconnected by one or more transversely oriented crossmember segments. 
     Aspects of this disclosure are directed to sandwich-type multilayer composite panel structures, including methods for manufacturing and methods for utilizing such panel structures. In an example, a multilayer body panel for a motor vehicle is fabricated with at least one exterior layer that is formed, in whole or in part, from an optically transparent, rigid material. At least one bonding layer is attached, either directly or indirectly, to the exterior layer and is formed, in whole or in part, from a transparent adhesive material. The multilayer body panel also includes at least one structural reinforcement layer that is attached, directly or indirectly, to the bonding layer(s) and the exterior layer(s). The structural reinforcement layer includes a fiber-reinforced polymer material. The multilayer body panel has a plan-view profile with a length and width defining a plan-view area. The individual layers of the body panel may extend substantially the entire length and width of the body panel. In contrast, the fibers within each structural reinforcement layer are confined to one or more discrete regions within the plan area of the panel. Disclosed panel structures may be incorporated into any logically relevant component of a motor vehicle and may be utilized for automotive and non-automotive applications alike. 
     Additional aspects of this disclosure are directed to motor vehicles equipped with transparent composite panels having selectively located reinforcement features. As used herein, the terms “vehicle” and “motor vehicle” may be used interchangeably and synonymously to include any relevant vehicle platform, such as passenger vehicles (ICE, BEV, REV, FEV, fuel cell, fully and partially autonomous, etc.), commercial vehicles, industrial vehicles, tracked vehicles, off-road and all-terrain vehicles (ATV), motorcycles, farm equipment, watercraft, aircraft, electric bicycles (“ebikes”), etc. In an example, a motor vehicle includes a vehicle body with a passenger compartment, multiple road wheels mounted to the vehicle body, and other standard original equipment. A prime mover, which may be in the nature of an engine assembly (e.g., for internal combustion engine (ICE) powertrains), an electric traction motor (e.g., for full-electric vehicle (FEV) powertrains), or both an engine assembly and a traction motor (e.g., for hybrid electric vehicle (HEV) powertrains), selectively drives one or more of the road wheels to thereby propel the vehicle. 
     Continuing with the discussion of the above example, the vehicle also includes a multilayer body panel that is mounted on the vehicle body and covers at least a portion of the passenger compartment. The multilayer body panel includes an exterior layer that includes a transparent rigid material, and a bonding layer that is attached to the exterior layer and includes a transparent adhesive material. A structural reinforcement layer, which is attached to the bonding and exterior layers, includes a fiber-reinforced polymer material. The multilayer body panel has a plan-view profile with a plan area; the individual layers extend substantially the entire length and width of the plan area, whereas the fibers in the structural reinforcement layer are localized to a discrete region within the plan area. 
     For any of the disclosed panels, methods, and vehicles, a reflector layer may be attached directly to one side of a bonding layer. The reflector layer is formed, in whole or in part, from an IR-reflective material. The IR-reflective material may include a metallic material (e.g., particulate silver (Ag), gold (Au), copper (Cu), aluminum (Al), etc.) and/or a dielectric material (e.g., TiO 2 , Sift, etc.). As a further option, a sunshade layer may be attached directly to one side of a bonding layer, e.g., opposite that of the reflector layer. The sunshade layer is formed, in whole or in part, from a solid-state, visible (VIS) light and IR-light absorbing material. The light absorbing material may include an electrochromic polymer-dispersed liquid crystal (PDLC) material and/or an indium tin oxide (ITO) based electrochromic material. The transparent rigid material of the exterior layer(s) may include a scratch-resistant hard coat, whereas the transparent adhesive material of the bonding layer(s) may include an ethylene-vinyl acetate or polyvinyl butyral optical bonding agent. As yet a further option, the FRP material of the structural reinforcement layer(s) may include a fiber-weave preform entrained within a thermoset or thermoplastic matrix. 
     For any of the disclosed panels, methods, and vehicles, an optional low-k layer may be attached, e.g., indirectly by a bonding layer, to the sunshade layer. The low-k layer is formed, in whole or in part, from a dielectric material with a relatively small dielectric constant (e.g., small relative to the dielectric constant of silicon dioxide). Optionally, the multilayer composite panel may include a second bonding layer that is attached, directly or indirectly, to the low-k layer, and a second reflector layer that is attached, directly or indirectly, to the second bonding layer. An optional second structural reinforcement layer with the FRP material may be attached, directly or indirectly, to the second reflector layer. This additional structural reinforcement layer is localized to the same discrete region(s) within the plan area. 
     For any of the disclosed panels, methods, and vehicles, the multilayer composite panel may consist essentially of eleven layers that are stacked sequentially as: an exterior layer, a structural reinforcement layer, a bonding layer, a reflector layer, another bonding layer, a sunshade layer, yet another bonding layer, another reflector layer, a low-k layer, an additional bonding layer, and another structural reinforcement layer. A bonding layer and/or a reflector layer may be removed from the foregoing assembly to form 9-layer and 10-layer configurations. A multilayer composite panel may consist essentially of ten layers that are stacked sequentially as: an exterior layer, a reflector layer, a bonding layer, a sunshade layer, a structural reinforcement layer, another bonding layer, another reflector layer, yet another bonding layer, a low-k layer, and another exterior layer. 
     For any of the disclosed systems, methods, and vehicles, the multilayer composite panel may consist essentially of three layers (glass-FRP-glass) or may consist essentially of five layers (glass-bond-FRP-bond-glass). For five-layer constructions, the first bonding layer is attached directly to and sandwiched between the first exterior layer and the structural reinforcement layer. In this instance, the multilayer composite panel includes a second exterior layer material and a second bonding layer that is attached directly to and sandwiched between the second exterior layer and the structural reinforcement layer. For the three-layer and five-layer configurations, the transparent rigid material of the two exterior layers includes a chemically strengthened glass or a soda-lime glass, the transparent adhesive material of the two bonding layers includes an EVA or PVB-based optical bonding agent, and the FRP material of the center reinforcement layer includes a fiber-weave preform entrained within a thermoset or thermoplastic matrix. 
     The above summary does not represent every embodiment or every aspect of this disclosure. Rather, the above features and advantages, and other features and attendant advantages of this disclosure, will be readily apparent from the following detailed description of illustrative examples and modes for carrying out the present disclosure when taken in connection with the accompanying drawings and the appended claims. Moreover, this disclosure expressly includes any and all combinations and subcombinations of the elements and features presented above and below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevated, perspective-view illustration of a representative motor vehicle with an example of a multilayer transparent composite roof panel with internal FRP reinforcements in accordance with aspects of the present disclosure. 
         FIG. 2  is a schematic, side-view illustration of a select section of a representative 11-layer laminated transparent composite roof panel with localized FRP reinforcements in accord with aspects of the disclosed concepts. 
         FIG. 3  is a schematic, side-view illustration of a select section of a representative 10-layer laminated transparent composite roof panel with localized FRP reinforcements in accord with aspects of the disclosed concepts. 
         FIG. 4  is a schematic, side-view illustration of a select section of a representative 5-layer laminated transparent composite roof panel with localized FRP reinforcements in accord with aspects of the disclosed concepts. 
         FIG. 5  is a schematic, side-view illustration of a select section of a representative 3-layer laminated transparent composite roof panel with localized FRP reinforcements in accord with aspects of the disclosed concepts. 
         FIGS. 6-13  are elevated, perspective-view illustrations of representative vehicle roof assemblies highlighting various representative plan-view profiles for the localized FRP reinforcements of transparent composite roof panels in accord with aspects of the disclosed concepts. 
     
    
    
     Representative embodiments of this disclosure are shown by way of non-limiting example in the drawings and are described in additional detail below. It should be understood, however, that the novel aspects of this disclosure are not limited to the particular forms illustrated in the above-enumerated drawings. Rather, the disclosure is to cover all modifications, equivalents, combinations, subcombinations, permutations, groupings, and alternatives falling within the scope of this disclosure as encompassed, for instance, by the appended claims. 
     DETAILED DESCRIPTION 
     This disclosure is susceptible of embodiment in many different forms. Representative examples of the disclosure are shown in the drawings and herein described in detail with the understanding that these embodiments are provided as an exemplification of the disclosed principles, not limitations of the broad aspects of the disclosure. To that end, elements and limitations that are described, for example, in the Abstract, Introduction, Summary, Description of the Drawings, and Detailed Description sections, but not explicitly set forth in the claims, should not be incorporated into the claims, singly or collectively, by implication, inference, or otherwise. Moreover, the drawings discussed herein may not be to scale and are provided purely for instructional purposes. Thus, the specific and relative dimensions shown in the Figures are not to be construed as limiting. 
     For purposes of the present detailed description, unless specifically disclaimed: the singular includes the plural and vice versa; the words “and” and “or” shall be both conjunctive and disjunctive; the words “any” and “all” shall both mean “any and all”; and the words “including,” “containing,” “comprising,” “having,” and permutations thereof, shall each mean “including without limitation.” Moreover, words of approximation, such as “about,” “almost,” “substantially,” “generally,” “approximately,” and the like, may each be used herein in the sense of “at, near, or nearly at,” or “within 0-5% of,” or “within acceptable manufacturing tolerances,” or any logical combination thereof, for example. Lastly, directional adjectives and adverbs, such as fore, aft, inboard, outboard, starboard, port, vertical, horizontal, upward, downward, front, back, left, right, etc., may be with respect to a motor vehicle, such as a forward driving direction of a motor vehicle, when the vehicle is operatively oriented on a horizontal driving surface. 
     Referring now to the drawings, wherein like reference numbers refer to like features throughout the several views, there is shown in  FIG. 1  a perspective-view illustration of a representative automobile, which is designated generally at  10  and portrayed herein for purposes of discussion as a sedan-style passenger vehicle. The illustrated automobile  10 —also referred to herein as “motor vehicle” or “vehicle” for short—is merely an exemplary application with which novel features of this disclosure may be practiced. In the same vein, implementation of the present concepts into a panoramic “glass roof” assembly should also be appreciated as an exemplary application of some of the novel concepts disclosed herein. As such, it will be understood that aspects and features of the present disclosure may be applied to other vehicle body panels, may be incorporated into any logically relevant type of motor vehicle, and may be implemented for automotive and non-automotive applications alike. Moreover, only select components of the motor vehicles and body panels are shown and described in additional detail herein. Nevertheless, the vehicles and panels discussed below may include numerous additional and alternative features, and other available peripheral components, for carrying out the various functions of this disclosure. 
     Automobile  10  of  FIG. 1  includes a vehicle body  12  that is erected on a rigid vehicle frame  20 , for example, as either a body-on-frame or a unibody construction in a three-box configuration. Front and rear road wheels  11  are operatively attached to the vehicle frame  20 , e.g., via individual corner assemblies. In order to propel the vehicle, the road wheels  11  are driven by a prime mover  18 , which may be in the nature of an internal combustion engine assembly and/or one or more electric traction motors. Located aft of a front compartment (e.g., engine bay) and forward of a rear compartment (e.g., trunk or battery compartment) is an interior passenger compartment  16  of the vehicle body  10  that seats and safeguards the vehicle occupants. A rigid roof structure  14  generally delimits the upper extent of the passenger compartment  16 , shielding the driver and passengers from rain, snow, ultraviolet (UV) light, and other elements. In accord with the illustrated example, the roof structure  14  is generally composed of laterally spaced roof rails  22  that are interconnected with longitudinally spaced front and rear headers. The roof rails  22  and roof headers cooperatively provide subjacent support for a transparent roof panel  24  (traditional cross-car reinforcement bows may be eliminated from the roof support structure). The roof structure  14 , including the rails  22 , braces, and roof panel  24 , extends over and across the upper boundary of the passenger compartment  16 . As illustrated, the transparent roof panel  24  has a “panoramic” design in that it extends across the entire fore-aft length of the vehicle roof and, thus, provides vehicle occupants with a predominantly unobstructed view through the top of the vehicle  10 . 
     Inset within  FIG. 1  is an enlarged, perspective-view illustration of the vehicle roof structure  14  to provide a more detailed look at the structural transparent composite roof panel  24 . From a plan-view perspective, the composite roof panel  24  has eight substantially transparent sections  26  that are separated by a diamond lattice-shaped reinforcement section  28  that is translucent or opaque. It should be appreciated that the number, shape, size, and arrangement of the transparent sections  26  and opaque/translucent sections  28  may be varied from that which are shown in the drawings without departing from the intended scope of this disclosure. An optional sensor farm  30  may be located at a forward end of the roof structure  14  and, if desired, embedded within the roof panel  24 . The sensor farm  30  may comprise an assortment of sensing devices, including one or more digital cameras, radar transmitters/receivers, LiDAR phased array and laser emitter, rearview mirror camera, etc. An electrical wiring harness  32  for the sensor farm  30  may pass within a high-fiber-fraction region of the composite roof panel  24  to conceal the wires from the occupants and passersby. 
     As will be explained in further detail below, the transparent composite roof panel  24  has a laminated, sandwich-type construction with orthotropic properties and load path optimization enabled by localized FRP reinforcement features. The structural integrity and overall level of optical transparency of the composite panel may be controlled by the contents and arrangement of reinforcing fibers incorporated into the FRP layer or layers of the panel&#39;s multilayer construction. Load path optimization with limited panel transparency may be governed, for example, by an FRP composite layer with: an FRP-layer lateral width of less than approximately 80-100 millimeters (mm) and an FRP-layer total vertical thickness of about 0.25 mm to about 4.75 mm; a local high volume fraction (V f ) of fibers of about 0.5; a reinforcing fiber total width that is less than an average pupillary spacing (e.g., about 52 mm); and an optical transparency of the FRP region(s) of less than about 5%. For at least some embodiments, a total vertical thickness of the laminate composite panel is substantially constant along the length and width of the panel. Likewise, a total vertical thickness of an FRP-composite layer is substantially constant along the length and width of the panel; however, the fibers within the FRP-composite layer are localized to one or more discrete regions and, thus, are not present at every location along the length and width of the panel. 
       FIG. 2  schematically illustrates a first example of a structural transparent composite panel  124  that may be implemented for the vehicle roof panel  24  of  FIG. 1 . In accord with the illustrated example, the composite panel  124  (also referred to herein as “body panel” or “roof panel” for automotive applications) is a multilayer sandwich-type construction composed of at least eleven (11) layers: an uppermost exterior layer  140 ; a pair of structural reinforcement layers  142 A and  142 B; four bonding layers  144 A,  144 B,  144 C and  144 D; a pair of reflector layers  146 A and  146 B; a sunshade layer  148 ; and an insulating low-k layer  150 . In at least some embodiments, all eleven of the foregoing layers are coextensive with and, thus, span substantially the entirety of one another. Alternatively, one or more select layers of disclosed multilayer composite panel structures may take on distinctive shapes, sizes, and/or locations. It should also be noted that any reference to “first”, “second”, “third”, etc., in the specification and claims does not per se act as a serial limitation or a numerical limitation but, instead, may be provided to distinguish between or to more easily identify the various members of a group. 
     The structural transparent composite panel  124  may consist essentially of the eleven illustrated layers, ordered from top-to-bottom in the sequence that is presented in  FIG. 2 . In this instance, additional features and layers may be incorporated into the composite panel  124  so long as any such additions do not materially affect the load-path optimization and optical transparency characteristics of the multilayer construction. It is further contemplated that the composite panel  124  may comprise greater or fewer layers than the eleven layers enumerated above. As an example, one or both of the reflector layers  146 A,  146 B may be removed, one or more of the bonding layers  144 A- 144 D may be removed; and/or the exterior layer  140  may be removed. Examples of additional or alternative layers may include, singly, collectively, or in any combination, a window heat strip (“defroster”) layer, an anti-glare layer, chemically strengthened or soda-lime glass layers, a second exterior layer located opposite the uppermost exterior layer  140  to act as a lowermost layer, etc. It should be noted that use of the term “layer” in the description and claims is inclusive of but does not necessarily require that a particular segment of the composite construction be a continuous sheet or otherwise span the entirety of the panel. 
     With continuing reference to  FIG. 2 , the uppermost exterior layer  140  and the second structural reinforcement layer  142 B are positioned in parallel spaced arrangement as the outermost layers of the composite panel  124 , thus sandwiching therebetween the remaining nine panel layers. According to the illustrated architecture, the first structural reinforcement layer  142 A is sandwiched between and attached directly to the uppermost exterior layer  140  and the first bonding layer  144 A. In the same vein, the first reflector layer  146 A is sandwiched between and attached directly to the first and second bonding layers  144 A,  144 B, whereas the sunshade layer  148  is sandwiched between and attached directly to the second and third bonding layers  144 B,  144 C. The second reflector layer  146 B is sandwiched between and attached directly to the third bonding layer  144 C and the low-k layer  150 . The low-k layer  150  is adhered to the inside surface of the second structural reinforcement layer  142 B via the fourth bonding layer  144 D. In an 11-layer configuration, the composite panel  124  may have a total thickness of about 1.5 mm to about 15.5 mm or, in at least some embodiments, about 2.25 mm to about 12 mm. It is envisioned that the order of the illustrated layers may be modified from that which is shown in the drawings without departing from the intended scope of the present disclosure. 
     To provide functional UV and scratch protection, the uppermost exterior layer  140  of the composite panel  124  may be formed, in whole or in part, from a rigid yet transparent material. This transparent, rigid material may include a wear-resistant and scratch-resistant hard coating with a thickness ranging from a few microns to about 0.1 mm. In a more specific example, the exterior layer  140  is a silicone hard coat with a film encased between a poly(methyl methacrylate) (PMMA) sheet and a transparent polycarbonate (PC) sheet. Alternatively, the uppermost exterior layer  140  is a clear coat film that provides an optically transparent, scratch-resistant “Class A” surface. 
     Four optical bonding layers  144 A- 144 D function to operatively connect the individual layers of the 11-layer composite panel  124  to one another without impeding the optical characteristics of the panel  124 . Each bonding layer  144 A- 144 D may be formed, in whole or in part, from a transparent adhesive material offering at least about 75-90% transparency, for example. This transparent adhesive material may include a thermoset ethylene-vinyl acetate (EVA) optical bonding agent or a thermoplastic polyvinyl butyral (PVB) optical bonding agent. The bonding layers  144 A- 144 D may each have an individual thickness of about 0.5 mm to about 1 mm or, in at least some embodiments, about 0.8 mm for a total optical bonding thickness of about 3.2 mm or less. One or more of the bonding layers  144 A- 144 D may be integrated within one or more of the structural reinforcement layers  142 A,  142 B. 
     Continuing with the discussion of the structural transparent composite panel  124  of  FIG. 2 , the two reflector layers  146 A,  146 B help to radiation-borne mitigate thermal loading on the passenger compartment  16  and, at the same time, on the occupants of the vehicle  10 . Each reflector layer  146 A,  146 B may be formed, in whole or in part, from an infrared (IR) reflective material offering at least 65-85% reflectance, for example. This IR-reflective material may include a metallic material (e.g., an aluminum, gold, or silver film) and/or a dielectric material (e.g., oxides of titanium, tantalum, zirconium, hafnium, scandium, and niobium). Optional pigments and dyes, such as EPOLIGHT™ notch-absorbing dye, may be used as an additive in a polymeric matrix for the IR-reflective material. The reflector layers  146 A,  146 B may each have an individual thickness of about 75 to about 150 nanometers (nm) or, in at least some embodiments, about 100 nm for a total IR reflector thickness of about 200 nm or less. Each IR reflector layer  146 A,  146 B may be a PET film with a low-emissive, silver-based sputter coating. 
     The center layer of the multilayer composite panel  124  is a sunshade layer  148  that selectively provides maximum light absorption. Sunshade layer  148  of  FIG. 2  may be formed, in whole or in part, from a solid-state, visible (VIS) light absorbing and IR-light absorbing material. This solid-state, light-absorbing material may include an electrochromic polymer-dispersed liquid crystal (PDLC) material and/or an indium tin oxide (ITO) based electrochromic material. PDLCs, for example, are liquid crystal dispersions within a polymer matrix; these films can be switched between an opaque state and a transparent state by applying a suitable alternating current (AC) electric field. The sunshade layer  148  may have a total thickness of about 0.05 mm to about 0.15 mm or, in at least some embodiments, about 0.1 mm. The sunshade layer  148  may be a solid-state EC film (e.g., for visual glare reduction or further IR control) with a vapor barrier. 
     Attached to an interior-facing surface of the second reflector layer  146 B is an optional low-k coating layer  150 , namely an interlayer of transparent dielectric material with a low dielectric constant (e.g., a k value of about 3.6 or less). The low-k layer  150  may function as an insulating dielectric that separates the occupants of the passenger compartment  16  from electrically conductive elements within the composite panel  124 , such as the magnetic field used to operate the sunshade layer  148 . In addition, the low-k layer  150  may help to reduce the amount of heat escaping from a vehicle passenger compartment while remaining sufficiently transparent so as to not degrade the optical transparency of the panel  124 . This low-k layer  150  may have a thickness of about 75 nm to about 125 nm or, in at least some embodiments, about 100 nm. Optional configurations may altogether eliminate the low-k coating layer  150  from the laminate stackup. 
     Disposed at opposing top and bottom sides of the composite panel  124  of  FIG. 2  are outer and inner structural reinforcement layers  142 A,  142 B, respectively, that govern the panel&#39;s structural rigidity and local transparency level. Each reinforcement layer  142 A,  142 B is formed, in whole or in part, as a fiber reinforced polymer (FRP) composite with a fiber filler embedded within a polymer matrix. For instance, the FRP material may include a fiber-weave preform that is entrained within a thermoset or thermoplastic matrix to collectively provide localized opacity or a layer-level transparency of no more than about 5-20%, for example. FRP fibrous materials may be composed of carbon fibers, glass fibers, aramid fibers, basalt fibers, and/or any other suitable reinforcing fiber, which may be arranged unidirectionally, bidirectionally, or multi-directionally. The fiber composition may be woven or compacted, and subsequently cut into a generally flat mat or roving. The FRP composite material may optionally contain one or more additives and a protective hard coating. These structural reinforcement layers  142 A,  142 B may each have an individual thickness of about 1 mm to about 3 mm or, in at least some embodiments, about 2 mm for a total FRP composite thickness of about 4 mm or less. There are possibilities where an embedded glass fiber may act as a structural reinforcement while also having high transparency (e.g., up to 80% transparent in some cases). 
     Fiber spacing and orientation within each FRP composite layer may be used to tailor the level of optical transparency of the composite panel  124 . By way of non-limiting example, an FRP structure with a high fiber volume fraction results in a lower overall optical transparency, whereas an FRP structure with a lower fiber volume fraction results in a greater overall transparency. Utilizing a local high volume fraction of about 0.5 with a total width that is less than an average fiber pupillary spacing (e.g., about 50-100 mm), the structural reinforcement layers  142 A,  142 B may achieve an optical transparency of less than 5%. Moreover, the composite matrix material may be selected to affect a desired level of transparency. For instance, a PMMA matrix would provide greater optical transparency as compared to a thermoset resin matrix that would offer significantly less transparency. 
     Additives may be incorporated into the structural reinforcement layers  142 A,  142 B to minimize or otherwise eliminate UV degradation of the fiber reinforced composite matrix. Ultraviolet absorbers act as a type of light stabilizer that functions by competing with the chromophores to absorb UV radiation. Absorbers change harmful UV radiation into harmless infrared radiation or heat that is dissipated through the polymer matrix. Some examples of UV absorbers include, but are certainly not limited to, carbon black, rutile titanium oxide, hydroxybenzophenone, hydroxyphenylbenzotriazole, oxanilides for polyamides, benzophenones for PVC, and benzotriazoles and hydroxyphenyltriazines for polycarbonate. Other additives that help to prevent UV degradation include quenchers, which are used to return excited states of chromophores to ground states by an energy transfer process. Nickel quenchers are a commercially available type used in film production. As an alternative to quenchers, Hindered Amine Light Stabilizers (HALS) are long-term thermal stabilizers that act by trapping free radicals formed during the photo-oxidation of a plastic material and thus limiting the photodegradation process. Absorbers, quenchers, and HALS all function by different mechanisms; as such, they may be combined into synergistic UV absorbing additives. For example, benzotriazoles may be combined with HALS to protect pigmented systems from fading and color changes. 
     The reinforcement layers  142 A,  142 B function as localized opaque or translucent reinforcements for the transparent composite panel  124 . In particular, the composite panel  124  has a plan-view profile—represented in  FIG. 2  via plan-view arrow A PV —with a plan area defined by the panel&#39;s transverse width and fore-aft length. As used herein, the term “plan view” may be defined to include a 2-dimensional view (e.g., an orthographic projection) of a 3-dimensional object as seen from vertically above. With collective reference to the inset view of  FIG. 1  and the side view of  FIG. 2 , the exterior layer  140 , bonding layers  144 A- 144 D, reflector layers  146 A,  146 B, sunshade layer  148 , and low-k layer  150  all extend substantially the entire length and width of the plan area and, thus are coterminous with the plan-view profile of the composite panel  124 . The structural reinforcement layers  142 A,  142 B, on the other hand, are localized to one or more discrete regions within the panel&#39;s plan-view area (e.g., reinforcement section  28  of  FIG. 1 ). In other words, the reinforcement layers  142 A,  142 B do not extend the entire length and/or the entire width of the plan area; rather, each reinforcement layer  142 A,  142 B is delimited to a specific area or specific areas of the panel structure. According to the example portrayed in  FIG. 1 , each of the reinforcement layers  142 A,  142 B may take on a diamond-shaped lattice pattern. This lattice pattern may be complementary with an optimized roof rail support structure of a vehicle body that provides subjacent support to the composite panel when operatively mounted onto the vehicle. It is envisioned that the reinforcement layers  142 A,  142 B take on alternative shapes, sizes, and locations, including other desired shapes and patterns, as described below with reference to  FIGS. 6-13 . 
     Turning next to  FIG. 3 , there is shown a second example of a structural transparent composite panel  224  that may be utilized, for example, as a vehicle body or roof panel. Although differing in appearance, it is envisioned that any of the features and options described above with reference to the composite panel  124  of  FIG. 2  can be incorporated, singly or in any combination, into the composite panels  224 ,  324  and  424  of  FIGS. 3-5 , and vice versa. In accord with the illustrated example, the composite panel  224  is a multilayer sandwich-type construction composed of at least ten (10) layers: uppermost and lowermost exterior layers  240 A and  240 B, respectively; a central structural reinforcement layer  242 ; three bonding layers  244 A,  244 B and  244 C; a pair of reflector layers  246 A and  246 B; a sunshade layer  248 ; and a low-k layer  250 . Each of the foregoing layers may take on any of the characteristics described above with respect to its corresponding layer(s) in  FIG. 2 . Similar to the architecture of  FIG. 2 , all 10 of the above-itemized layers are coextensive with one another, having substantially the same length and width. However, the fibers contained in the structural reinforcement layer  242  are localized to one or more select regions and, thus, have a distinct shape and distinct measurements as compared to the composite layers. 
     The structural transparent composite panel  224  may consist essentially of the ten illustrated layers, ordered from top-to-bottom in the sequence that is presented in  FIG. 3 . The uppermost and lowermost exterior layers  240 A,  240 B are positioned in parallel spaced arrangement as the outermost layers of the composite panel  224 , thus sandwiching therebetween the remaining eight panel layers. According to the illustrated architecture, the first reflector layer  246 A is sandwiched between and attached directly to the uppermost exterior layer  240 A and the first bonding layer  244 A. The sunshade layer  248  is sandwiched between and attached directly to the first bonding layer  244 A and an outward-facing surface of the central structural reinforcement layer  242 . The second reflector layer  246 B is adhered to an inward-facing surface of the central structural reinforcement layer  242  via the second bonding layer  244 B and to an outward-facing surface of the low-k layer  250  via the third bonding layer  244 C. The low-k layer  250  is sandwiched between and attached directly to the lowermost exterior layer  240 B and the third bonding layer  244 C. 
       FIG. 4  presents a third non-limiting example of a structural transparent composite panel  324  that may be utilized as a body panel or roof panel for an automobile, such as vehicle  10  of  FIG. 1 . As mentioned above, the composite panel  324  may include any of the features and options described above and below with respect to the other representative composite panels  124 ,  224 ,  424 , and vice versa. In this example, the composite panel  324  is a multilayer sandwich-type construction composed of at least five (5) layers: uppermost and lowermost exterior layers  340 A and  340 B, respectively; a central structural reinforcement layer  342 ; and two bonding layers  344 A and  344 B each bonding a respective face of the central structural reinforcement layer  342  to a respective one of the exterior layers  340 A and  340 B. 
     Central structural reinforcement layer  342  may have a thickness of about 1 mm to about 6 mm or, for at least some configurations, about 2-4 mm, and may comprise an FRP composite structure with a dry fabric core or, alternatively, a multidirectional pre-impregnated (prepreg) layup. Each exterior layer  340 A and  340 B may be a chemically strengthened glass or a soda-lime glass layer with an individual thickness of about 0.5 mm to about 2.1 mm, which results in a total glass thickness of about 1.0 mm to about 2.2 mm and a total panel thickness of about 5 mm to about 9.8 mm. The structural reinforcement, exterior, and bonding layers may be coextensive with one another and with the panel  324 . The fibers contained in the structural reinforcement layer  342 , however, are localized to one or more select regions. The structural transparent composite panel  324  may consist essentially of the five illustrated layers, ordered from top-to-bottom in the sequence that is presented in  FIG. 4 . 
     With reference next to  FIG. 5 , there is shown a fourth non-limiting example of a structural transparent composite panel  424  that may be utilized, for example, as a body panel or roof panel for an automobile. In this example, the composite panel  424  is a multilayer sandwich-type construction composed of at least three (3) layers: uppermost and lowermost exterior layers  440 A and  440 B, respectively; and a central structural reinforcement layer  442  sandwiched between and attached directly to the exterior layers  440 A and  440 B. Similar to the architecture of  FIG. 4 , each exterior layer  440 A and  440 B of  FIG. 5  may include a chemically strengthened glass, a tempered glass, a soda-lime glass, an alkali-aluminosilicate sheet glass, etc., with an individual thickness of about 0.7 mm to about 2.1 mm, which results in a total glass thickness of about 1.4 mm to about 2.2 mm and a total panel thickness of about 3.4 mm to about 8.2 mm. The individual layers may be coextensive with one another and the panel, whereas the fibers in the structural reinforcement layer is localized to one or more select regions. The structural transparent composite panel  424  may consist essentially of the three illustrated layers, ordered from top-to-bottom in the sequence that is presented in  FIG. 5 . 
     For any of the disclosed panels, vehicles, and methods, a structurally reinforcing FRP layer fiber may employ any suitable fiber type, including: carbon fiber, glass fiber, basalt fiber, Kevlar fiber, ultra-high molecular weight polyethylene fibers, spider silk fibers, polypropylene fibers, boron fibers, or any combination thereof. As yet a further option, the fiber volume fraction may locally be high, such that it resembles a structural composite (e.g., with local fiber volume fraction up to 70 vol %), yet globally may be less than 1 vol % of the entire structure. Fiber orientation may be constructed using unidirectional fiber tows, spread tows, tapes, unidirectional fabrics using tow placement methods, or any combination thereof. It is also possible to weave fabrics using traditional woven or non-crimp fabrics, such as plain, twill, harness satins, quasi-isotropic layups, etc. 
     For any of the disclosed panels, vehicles, and methods, it may be desirable to remove the low k-layer/coating from the multilayer laminate composite structure. As yet a further option, disclosed FRP layers may be constructed as a fiber-reinforced composite with a polycarbonate matrix, and with a PMMA layer (e.g., with UV absorbers and/or UV stabilizers) coated with a Silicone Hard Coat (e.g., for scratch resistance). Alternatively, the fiber-reinforced composite may be fibers within an acrylic matrix (e.g., with UV stabilizers and/or UV absorbers) which then has a hard coat. Optionally, the fiber-reinforced composite may employ a polycarbonate, nylon, or acrylic matrix without a hard coat. 
       FIGS. 6-13  are enlarged, perspective-view illustrations of representative vehicle roof assemblies employing respective structural transparent composite roof panels with distinctive localized reinforcement sections. As described above, each multilayer body panel includes one or more structural reinforcement layers that are fabricated, in whole or in part, from a high fiber volume fraction FRP material. Each structural reinforcement layer confines the fibers contained therein to a predefined topography in order to define a discrete plan-view region within the laminate stackup&#39;s plan-view profile. In so doing, these composite roof panels act as load-bearing structures with orthotropic properties and maximized “panoramic” optical transparency. While differing in appearance, any of the features and options described with reference to the composite roof panel  524  of  FIG. 6  can be incorporated, singly or in any combination, into the composite roof panels  624 ,  724 ,  824 ,  924 ,  1024 ,  1124  and  1224  of  FIGS. 7-13 , and vice versa. In the same vein, each of the multilayer laminated roof panel constructions illustrated in  FIGS. 6-13  may take on any of the structural transparent composite panel constructions illustrated in and described with respect to  FIGS. 2-5 . 
     Looking first at  FIG. 6 , an example of a vehicle roof structure  514  is shown that employs a structural transparent composite roof panel  524  with selectively located internal reinforcement features for increased structural integrity and improved optical transparency. The two layers of the multilayer composite roof panel  524  that are most readily visible in this particular view are the transparent yet rigid uppermost exterior layer  540  and the outermost (or lone) FRP structural reinforcement layer  542 . Designated generally at  528  is a discrete plan-view region that is defined by the fibers contained in the structural reinforcement layer  540  within the composite panel&#39;s plan-view profile. Similar to the reinforcement section  28  of  FIG. 1 , for example, the plan-view region  528  of  FIG. 6  is translucent or opaque and arranged in a diamond lattice-shaped pattern that demarcates numerous substantially transparent sections extending vertically through the roof panel  524 . In this particular example, the plan-view region  528  is generally composed of assorted intersecting rails and crossmembers, including a pair of laterally spaced side rails  560  and  562  that extend along the fore-aft length of the multilayer body panel  524 . Three transverse crossmembers  564 ,  566  and  568  extend between and connect the side rails  560 ,  562 . As will become apparent from the discussion of  FIGS. 6-13 , the number, shape, size, and arrangement of the side rails and crossmembers may be varied from that which are shown in the drawings. 
     Port and starboard side rails  560  and  562  of the plan-view region  528  are generally parallel to each other and respectively located at opposing left and right sides of the multilayer composite roof panel  524 . The representative side rails  560 ,  562  of  FIG. 6  have elongated, curvilinear shapes (in both plan view and side view; shown as mirrored images of each other) that extend substantially the entire fore-aft length of the roof panel  524 . Each of the three crossmembers  564 ,  566 ,  568  is obliquely angled with respect to the side rails  560 ,  562  e.g., projecting at an angle of about 15-85 degrees from one or both rails. The first and second crossmembers  564 ,  566  intersect at the center of the composite roof panel  524  to define an X-shaped pattern. Contrastingly, a third crossmember  568  is longitudinally spaced from the other crossmembers  564 ,  566  and located proximate the aft end of the panel  524 . The third crossmember  568  includes a left hand-side (first) angled crossmember section  568 A and a right hand-side (second) angled crossmember section  568 B that project from respective ones of the side rails  560 ,  562  and intersect at the center of the composite roof panel  524  to define a V-shaped pattern. Forward-projecting port and starboard angled extensions  570  and  572 , respectively, protrude at oblique angles from the side rails  560 ,  562 , and terminate at the forward end of the panel  524 . While not individually labelled, the plan-view region  528  of the structural reinforcement layer(s)  542  includes assorted other branches, extensions, and angled crossmember segments. 
       FIG. 7  illustrates another example of a vehicle roof structure  614  that employs a structural transparent composite roof panel  624  that is fabricated with selectively located internal reinforcement features to provision increased structural integrity and improved optical transparency. Similar to the view of  FIG. 6 , the uppermost exterior layer  640  and the outermost structural reinforcement layer  642  are most readily visible in the view of  FIG. 7 . The fibers contained in the structural reinforcement layer  640  defines a discrete plan-view region  628  within the composite panel&#39;s plan-view profile. The plan-view region  628  of  FIG. 7  is translucent or opaque and arranged in a pentagonal pattern that demarcates numerous substantially transparent sections extending vertically through the roof panel  624 . Comparable to the example of  FIG. 6 , the plan-view region  628  of  FIG. 7  includes a pair of laterally spaced side rails  660  and  662  that extend along the fore-aft length of the multilayer roof panel  624 . Three transverse crossmembers  664 ,  666  and  668  extend between and connect the two side rails  660 ,  662 . In an alternative configuration, the third crossmember  668  may be eliminated from the reinforcement structure&#39;s topography and, optionally, replaced with a single crossmember section (e.g., a left hand-side angled crossmember section  668 A) that may be shifted towards the aft end of the roof panel  624 . 
     Driver-side and passenger-side rails  660  and  662 , respectively, of the plan-view region  628  are generally parallel to each other and respectively located at opposing left (port) and right (starboard) sides of the multilayer composite roof panel  624 . Both representative side rails  660 ,  662  have elongated, curvilinear shapes, which are shown as mirrored images of each other in  FIG. 7 , that extends substantially the entire fore-aft length of the roof panel  624 . The lateral width of each rail  660 ,  662  varies along the fore-aft length of the panel  624 . Forward edges of the rails  660 ,  662  may originate at and adjoin the vehicle&#39;s front windshield, whereas rearward edges of the rails  660 ,  662  may terminate at and adjoin the vehicle&#39;s rear glass. 
     With continuing reference to  FIG. 7 , the first crossmember  664  is located proximate the forward end of the composite roof panel  624  and has a generally U-shaped plan-view profile that extends substantially the entire width of the panel  624 . Located between the first and third crossmembers  664 ,  668  is a second crossmember  666  that is substantially orthogonal to the side rails  660 ,  662 . This crossmember  666  has an elongated, rectilinear shape that extends substantially the entire width of the composite roof panel  624 . Unlike the second crossmember  666 , the third crossmember  668  is obliquely angled with respect to the side rails  660 ,  662 . The third crossmember  668  is longitudinally spaced from both the first and second crossmembers  664 ,  666 , localized to a central region of the panel  524  topography. Similar to crossmember  568 , the third crossmember  668  of  FIG. 7  includes a left hand-side (first) angled crossmember section  668 A and a right hand-side (second) angled crossmember section  668 B that project from respective ones of the side rails  660 ,  662  and intersect along a longitudinal centerline of the composite roof panel  624  to define a V-shaped pattern. Arched crossmember extensions  670  and  672  protrude at oblique angles from the side rails  660 ,  662 , and intersect with all three crossmembers  664 ,  666 ,  668 . While not expressly labelled or described, the plan-view region  628  may include additional rails, branches, extensions, crossmembers and crossmember segments. 
       FIG. 8  illustrates another example of a vehicle roof structure  714  that employs a structural transparent composite roof panel  724 , which is fabricated with selectively located internal reinforcement features. As with all of the multilayer composite panels described hereinabove, the roof panel  724  of  FIG. 8  includes at least one exterior layer  740  and at least one structural reinforcement layer  742 . Fibers contained in the structural reinforcement layer or layers  740  define a discrete plan-view region (localized topology)  728  within the plan-view profile of the composite roof panel  724 . In this instance, the plan-view region  728  is translucent or opaque and arranged in a U-shaped pattern superposed with a triangular crossmember arrangement. Plan-view region  728  of  FIG. 8  separates four substantially transparent sections that extend through the roof panel  724 . 
     The plan-view region  728  of  FIG. 8  includes or consists essentially of five intersecting segments: first and second side rails  760  and  762  that extend along the fore-aft length of the multilayer body panel  724 ; and three transverse crossmembers  764 ,  766  and  768  that extend the lateral width of the multilayer body panel  724 , sandwiched between and connecting the two side rails  760 ,  762 . The side rails  760  and  762  are generally parallel to each other and respectively located at opposing left and right sides of the multilayer composite roof panel  724 . The first crossmember  764  is located at the forward end of the composite roof panel  724  and has a curvilinear plan-view profile that extends substantially the entire width of the panel  724 . The second crossmember  766  is obliquely angled with respect to the side rails  760 ,  762  and includes first and second angled crossmember sections (not individually labelled) that each projects from a respective side rail  760 ,  762  and intersect to define a V-shaped pattern. The third crossmember  768  is longitudinally spaced from the forward end of the panel  724  and oriented substantially orthogonal to the side rails  760 ,  762 . Alternative configurations may eliminate the third crossmember  768  from the discrete plan-view region  728 , leaving the V-shaped second crossmember  766 . Optionally, both the second and third crossmembers  766 ,  768  may be eliminated, leaving the U-shaped geometry of the first crossmember  764  intersecting with the side rails  760 ,  762 . 
       FIG. 9  illustrates yet another representative vehicle roof structure  814  that employs a structural transparent composite roof panel  824 . The composite roof panel  824  may be structurally equivalent to the composite roof panel  724  of  FIG. 8 , except that roof panel  824  of  FIG. 9  has a fiber-defined, plan-view region  828  that includes or consists essentially of four intersecting segments: first and second side rails  860  and  862  that extend along the fore-aft length of the multilayer body panel  824 ; and two transverse crossmembers  864  and  866  that extend the lateral width of the multilayer body panel  824 , sandwiched between and connecting the two side rails  860 ,  862 . Moreover, side rails  860  and  862  may be identical to side rails  760  and  762 , and crossmember  864  may be identical to crossmember  764 . By way of contrast, however, the second crossmember  866  may have a similar shape, a similar size and/or a similar orientation as the third crossmember  768 , but located closer to the forward end of the panel  824  and the first crossmember  864 . 
       FIG. 10  illustrates one more example of a vehicle roof structure  914  that employs a structural transparent composite roof panel  924 . The composite roof panel  924  of  FIG. 10  has a reinforcement layer with a fiber-defined, plan-view region  928  that includes or consists essentially of eight segments: first and second side rails  960  and  962  that extend along the fore-aft length of the multilayer body panel  924 ; four transverse crossmembers  964 ,  966 ,  968  and  970  that extend the lateral width of the multilayer body panel  924 , sandwiched between and connecting the two side rails  960 ,  962 ; and two rearward-projecting angled extensions  972  and  974  that protrude at oblique angles from the side rails  960 ,  962 , and terminate at the aft end of the panel  924 . Similar to the roof panels  724  and  824 , side rails  960  and  962  of  FIG. 10  may be identical to side rails  760 ,  860  and  762 ,  862  of  FIGS. 8 and 9 . In the same vein, crossmember  964  may be structurally identical to crossmembers  764  and  864 , and crossmember  966  may be structurally identical to crossmember  866 . Third crossmember  968 , on the other hand, is sandwiched between second and fourth crossmembers  966  and  970  and includes two angled crossmember section that project at oblique angles from the side rails  960  and  962  and intersect with crossmember  970  to define a triangular-shaped profile. Angled extensions  972  and  974  also intersect with crossmember  970 , defining an isosceles-trapezoid shaped profile. 
       FIG. 11  illustrates a vehicle roof structure  1014  that employs a structural transparent composite roof panel  1024 . The composite roof panel  1024  of  FIG. 11  has a reinforcement layer with a fiber-defined, plan-view region  1028  that includes or consists essentially of six segments: first and second side rails  1060  and  1062  that extend along the fore-aft length of the multilayer body panel  1024 ; two transverse crossmembers  1064  and  1066  that extend the width of the multilayer body panel  1024 , sandwiched between and connecting the two side rails  1060 ,  1062 ; and two forward-projecting angled extensions  1068  and  1070  that protrude at oblique angles from the side rails  1060 ,  1062 , and terminate at the forward end of the panel  1024 . As noted above, the rails, crossmembers and extensions illustrated in  FIG. 11  may take on any of the features and options described above with respect to the rails, crossmembers and extensions illustrated in  FIGS. 6-10, 12 and 13 . In an alternative configuration, the second crossmember  1066  may be eliminated from the reinforcement structure&#39;s topography  1028 . 
       FIG. 12  illustrates a vehicle roof structure  1114  that employs a structural transparent composite roof panel  1124 . The composite roof panel  1124  of  FIG. 12  has a reinforcement layer with a fiber-defined, plan-view region  1128  that includes or consists essentially of five segments: first and second side rails  1160  and  1162  that extend along the fore-aft length of the multilayer body panel  1124 ; one transverse crossmember  1164  that extends the width of the multilayer body panel  1124  along the forward edge of the panel  1124 , connecting the two side rails  1160 ,  1162 ; and two rearward-projecting angled extensions  1166  and  1168  that extend the entire length of the panel  1124 , protruding at oblique angles from the transverse crossmember  1164 , and terminating at the aft end of the panel  1124 . 
       FIG. 13  illustrates a vehicle roof structure  1214  that employs a structural transparent composite roof panel  1224 . One or more internal reinforcement layer(s) of the composite roof panel  1224  define a plan-view region  1228  that includes or consists essentially of three segments: two laterally spaced, longitudinally elongated side rails  1260  and  1262  that extend the entire fore-aft length of the multilayer body panel  1224 ; and one transverse crossmember  1264  that extends the entire width of the multilayer body panel  1224  along the forward edge of the panel  1224 , connecting the two side rails  1260 ,  1262 . The optional configuration allows for a modified a-pillar design that allows for the expansion of the size of front windshield concomitant with shifting the front header rearward along the fore-aft length of the vehicle body. 
     Aspects of the present disclosure have been described in detail with reference to the illustrated embodiments; those skilled in the art will recognize, however, that many modifications may be made thereto without departing from the scope of the present disclosure. The present disclosure is not limited to the precise construction and compositions disclosed herein; any and all modifications, changes, and variations apparent from the foregoing descriptions are within the scope of the disclosure as defined by the appended claims. Moreover, the present concepts expressly include any and all combinations and subcombinations of the preceding elements and features.