Abstract:
An exemplary embodiment providing one or more improvements includes a composite structure of materials that are formed together in a way which gives the composite structure improved yield strength and thermal conduction capabilities.

Description:
RELATED APPLICATIONS 
     The present application claims priority from U.S. Provisional Application Ser. No. 60/683,735, filed on May 24, 2005, U.S. Provisional Application Ser. No. 60/683,764, filed on May 24, 2005, U.S. Provisional Application Ser. No. 60/711,760, filed Aug. 29, 2005 all of which are incorporated herein by reference along with U.S. patent application Ser. No. 11/439,401 which shares the filing date of the present application. 
    
    
     BACKGROUND 
     A composite may be described as a material produced by combining materials differing in composition or form on a macroscopic scale to obtain specific characteristics and properties. In these composites, the constituents retain their identity, can be physically identified, and often exhibit an interface between one another. For instance, a clad metal is a composite that contains two or more layers of different metal that have been bonded together. The bonding may be accomplished by co-rolling, co-extrusion, welding, diffusion bonding, casting, heavy chemical deposition, or heavy electroplating. Clad metals are commonly found on the bottoms of household pots and pans. Copper or aluminum is clad to the stainless steel pan as a way to improve the thermal conduction and de-localize heat from a burner to the entirety of the pan. For a household pan, the cladding process is usually achieved by diffusion bonding, which generally is compressing the two dissimilar metals together with high pressure at high temperatures. 
     While the clad arrangement described above can produce a composite with the physical properties of both metals (i.e. it is a sheet of copper bonded to a sheet of steel). In an application where a high temperature piston applies a high force normal to the copper and steel sheets, the piston would deform the low yield strength copper rather easily, regardless of the thickness of the steel sheet. While the copper is adequate for conducting the heat from the piston, it cannot handle the applied forces without deformation, particularly when at elevated temperature. Most common materials with significant thermal conductivity will either have a low melting point (like aluminum) or a low yield strength (like copper) and cannot be employed for the application of cooling a high temperature piston. While there are non-composite high thermal conductivity, high yield strength exotic materials like Copper Tungsten (CuW) which can be used for this demanding application, they are economically unfeasible for many applications. 
     In some instances, it is necessary or desirable to have a three dimensional composite structure that exhibits a desirable property in one dimension more than in another dimension, while the structure exhibits another desirable proper in another dimension. An example of this would be a three dimensional composite sheet that has a thermal conductivity that is higher in one direction through the sheet and has a high yield or compressive strength in another direction through the sheet. 
     The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon reading of the specification and a study of the drawings. 
     SUMMARY 
     The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements. 
     In general, composites and methods of constructing a three dimensional structure are described which provide for improved characteristics in the structure. A method for producing a three dimensional composite sheet for withstanding a compressive force normal to a major surface of the composite sheet is disclosed. The major surface of the composite sheet is defined by a first and a second dimension of the composite sheet. The composite sheet withstands the compressive force while conducting heat along at least one of the first and the second dimensions of the composite sheet more efficiently than heat is conducted along a third, thickness dimension of the composite sheet. The composite sheet is produced by forming a pattern in a first high yield strength sheet material by removing the first material to a predetermined degree in at least a first selected region of the first material and by forming a complementary pattern in a second high thermal conductivity sheet material. The first material and the second material are combined into the three dimensional composite sheet so that the pattern and the complementary pattern cooperate to cause the first material to primarily withstand the compressive force and the second material to primarily conduct the heat in the composite sheet. 
     In another embodiment, a method is disclosed for producing a composite sheet made from a first material and a second material where the composite sheet has an overall compressive strength that is higher than a compressive strength of the second material and has an overall thermal conductivity that is higher than a thermal conductivity of the first material. The method includes forming the first material in full thickness areas and in reduced thickness areas and forming the second material in the reduced thickness areas of the first material to produce an overall thickness that is substantially the same as the thickness of the full thickness areas. 
     In another embodiment, a three dimensional composite sheet is disclosed having a major surface defined by a first and a second dimension of the composite sheet and a thickness defined by a third dimension of the composite sheet. The composite sheet having a first material and a second material which combine to give the composite sheet an overall compressive strength that is higher than a compressive strength of the second material and an overall thermal conductivity that is higher than a thermal conductivity of the first material. The composite sheet including a first sheet material area of the composite sheet surface which is defined by at least a portion of a first sheet material for primarily withstanding the compressive force substantially normal to the composite sheet surface and a second sheet material area of the composite sheet surface which is defined by at least a portion of the second sheet material for primarily conducting the heat along the at least one of the first and second dimensions of the composite sheet. 
     In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following descriptions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a composite sheet which incorporates the present disclosure. 
         FIG. 2  is an enlarged partial cross section view of the composite sheet taken along line  2 - 2  shown in Fig. I. 
         FIG. 3  is an enlarged partial cut-away view of the composite sheet taken from area  3  shown in  FIG. 1 . 
         FIG. 4  is a view of another composite sheet which incorporates the present disclosure. 
         FIG. 5  is a perspective view of a material sheet used in the composite sheet shown in  FIG. 4 . 
         FIG. 6  is an enlarged detail view of the material sheet taken from area  6  shown in  FIG. 5 . 
         FIG. 7  is an enlarged partial cross section view of the material sheet shown in  FIG. 5  shown in a facing relationship along with another material sheet used in the composite sheet shown in  FIG. 4 . 
         FIG. 8  is an enlarged partial cross section view of the composite sheet taken along line  8 - 8  shown in  FIG. 4 . 
         FIG. 9  is a view of yet another composite sheet which incorporates the present disclosure. 
         FIG. 10  is a perspective view of a material sheet used in the composite sheet shown in  FIG. 9 . 
         FIG. 11  is an enlarged detail view of the material sheet taken from area  11  shown in  FIG. 10 . 
         FIG. 12  is an enlarged partial cross section view of the material sheet shown in  FIG. 10  shown in a facing relationship along with another material sheet used in the composite sheet shown in  FIG. 9 . 
         FIG. 13  is an enlarged partial cross section view of the composite sheet taken along line  13 - 13  shown in  FIG. 9   
         FIG. 14  is a plan view of still another composite sheet which incorporates the present disclosure. 
         FIG. 15  is a perspective view of material sheets used in the composite sheet shown in  FIG. 14 , with the material sheets shown in a facing relationship. 
         FIG. 16  is an enlarged partial view of the material sheets taken from area  16  shown in  FIG. 15 . 
         FIG. 17  is an enlarged partial cross section view of the material sheets taken along line  17 - 17  shown in  FIG. 15 . 
         FIG. 18  is an enlarged partial cross section view of the composite sheet taken along line  18 - 18  shown in  FIG. 14 . 
         FIG. 19  is a perspective view of material sheets which combine into another composite sheet according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     A composite sheet  30  according to the present disclosure is shown in  FIGS. 1-3 .  FIG. 1  shows composite sheet  30  in a plan view,  FIG. 2  shows partial cross section view of composite sheet  30  and  FIG. 3  shows a detail of composite sheet  30 . Composite sheet  30  includes a base material sheet  32  ( FIG. 2 ) of a first material that is patterned with traces  34  and  36  of a second material. The base sheet  32  includes an upper surface  38  with upper recesses  40  that are separated by upper crowns  42  and a lower surface  44  with lower recesses  46  that are separated by lower crowns  48 . In the example shown in  FIG. 2 , traces  34  of the second material fill upper recesses  40  to the point where a generally planar surface  50  is created on the upper side of composite sheet  30 , and traces  36  fill lower recesses  46  to the point where a generally planar surface  52  is created on the lower side of composite sheet  30 . 
     In composite sheet  30 , base sheet  32  is constructed from stainless steel. Stainless steel has a high yield or compressive strength which allows composite sheet  30  to withstand high compressive forces such as the compressive force applied normal to the upper and lower surfaces  50  and  52  represented by arrows  54 . The stainless steel of base sheet  32  is the primary structure for withstanding the compressive and other physical forces on the composite sheet  30  provided that the force is distributed across a sufficiently broad area of the surface of the sheet. Base sheet  32  can also be constructed of any other suitable material that has a high compressive strength. 
     While base sheet  32  primarily withstands physical forces on the composite sheet  30 , traces  34  and  36  are primarily responsible for conducting heat through and along composite sheet  30 . Traces  34  and  36  in composite sheet  30  shown in  FIGS. 1 and 2  are constructed from copper, although any other suitable material with high thermal conductivity could also be used. Copper has a relatively low yield or compressive strength, especially in comparison to stainless steel, on the other hand, stainless steel does not have as high a thermal conductivity as copper does. Therefore, since composite sheet  30  includes base sheet  32  of stainless steel and traces  34  and  36  of copper, composite sheet  30  has a yield strength, in one direction of interest, that is higher than the yield strength of copper and has a thermal conductivity that is higher than the thermal conductivity of stainless steel in another direction of interest. 
     Base sheet  32  is etched, machined or otherwise formed with upper and lower recesses  40  and  46 . Traces  34  and  36  are filled with the secondary material through a process of electroplating, co-rolling, pressing, diffusion bonding or another suitable process. After base sheet  32  is formed, base sheet  32  is left with the full thickness sections of the crowns  42  and  48  and relatively thin reduced sections  56  between crowns  42  and  48 . 
     Composite sheet  30  is structurally reinforced against distortion along the reduced sections  56  by arranging upper and lower crowns  42  and  48  in a pattern with respect to one another as shown in the example in  FIG. 3  where dashed lines represent lower crowns  48 . In a portion of the pattern, crowns  42  and  48  are aligned in a parallel manner with respect to one another (FIGS. I and  2 ) to extend through the full thickness of the composite sheet  30 . In the pattern shown in  FIG. 3 , another portion of upper crowns  42  are positioned at an angle with respect to lower crowns  48  shown in dashed lines, the angle in this instance is about  90  degrees. Positioning the upper and lower crowns  42  and  48  at an angle with respect to one another prevents reduced sections  56  from defining a straight line through the entire composite sheet  30  along which the sheet could bend. In the pattern shown in  FIG. 3  upper surface  50  is represented by solid lines and lower surface  52  is represented by dashed lines. In the portion where upper and lower crowns  42  and  48  run in parallel the dashed lines are not shown since lower crowns  48  are below upper crowns  42 . On the other hand, in the portion where upper crowns  42  are angled with respect to lower crowns  48 , the lower crowns can be seen as dashed lines. Full thickness areas  53  are defined where upper crowns  42  cross lower crowns  48 ; partial thickness areas  55  are defined where upper crowns  42  cross lower traces  36 ; partial thickness areas  57  are defined where upper traces  34  cross lower crowns  48 ; and reduced thickness areas  59  are defined where upper traces  34  cross lower traces  36 . 
     The pattern shown in  FIG. 3  is structurally reinforced against distortion because bending or deformation along one of the reduced sections  56  of the base sheet  32  would also require bending multiple crowns  42  and  48  as well. 
     Another composite sheet  60  according to the present disclosure is shown in  FIGS. 4-8 .  FIG. 4  shows a plan view of composite sheet  60 ;  FIG. 5  shows a perspective view of a lower sheet  74  of composite sheet  60 ;  FIG. 6  shows a detail of lower sheet  74 ;  FIG. 7  shows upper and lower sheets  72  and  74  of composite sheet  60 ; and  FIG. 8  shows a partial cross section view of composite sheet  60 . Composite sheet  60  is constructed of upper and lower material sheets  62  and  64  ( FIG. 7 ) into which are etched, machined, stamped or otherwise formed a pattern ( FIGS. 5 and 6 ). The pattern in sheets  62  and  64  are complementary so that when sheet  62  is inverted with respect to sheet  64  as shown in  FIG. 7 , sheets  62  and  64  fit together to form composite sheet  60  as detailed in  FIG. 8 . When sheets  62  and  64  are combined into composite sheet  60 , the composite sheet has generally planar upper and lower surfaces  66  and  68  ( FIG. 8 ). 
     The pattern shown in  FIGS. 5 and 6  with respect to sheet  64  is the generally the same as for sheet  62 . Sheet  64  includes full thickness portions  70 , reduced thickness portions  72  and holes  74  and sheet  62  ( FIG. 7 ) includes full thickness portions  76 , reduced thickness portions  78  and holes  80 . As shown in  FIG. 7 , inverting sheet  62  with respect to sheet  64  allows full thickness portions  70  of upper sheet  64  to be aligned with holes  80  of lower sheet  64  and full thickness portions  76  of lower sheet  64  to be aligned with holes  74 . 
     Reduced thickness portions  72  and  78  are reduced in thickness relative to full thickness portions  70  and  76 , respectively, and are reduced only on one side so that the reduced thickness portion of the upper sheet defines a portion of upper surface  66  and the reduced thickness portion of the lower sheet defines a portion of lower surface  68 . In addition, when sheets  62  and  64  are aligned as shown in  FIG. 7 , reduced thickness portions  72  of upper sheet  62  are aligned with reduced thickness portions  78  of lower sheet  64  to combine into a thickness that is generally equal to the thickness of full thickness portions  70  and  76 . 
     When sheets  62  and  64  are combined into composite sheet  60  as shown in  FIG. 8 , full thickness portions  70  and  76  extend the entire distance between upper surface  66  and lower surface  68  of composite sheet  60 . In this example upper sheet  62  is formed from stainless steel and full thickness portions  70  of upper sheet  62  provide a high compressive strength to resist compressive forces, represented by arrows  82 , normal to surfaces  66  and  68  of composite sheet  60  and applied across a sufficiently broad area. Lower sheet  64  in this example is formed from copper so that full and reduced thickness portions  76  and  78  of lower sheet  64  provides a high thermal conductivity characteristic to composite sheet  60 . Lower surface  68  of composite sheet  60  is primarily defined by full and reduced thickness portions  76  and  78  of lower sheet  64  with a relatively lesser area defined by full thickness portions  70  of upper sheet  62 . Because of this, heat is more efficiently conducted into lower surface  68  of composite sheet  60  due to the relatively larger exposed surface area and configuration of lower sheet  64  at surface  68 . 
     Yet another composite sheet  90  according to the present disclosure is shown in  FIGS. 9-13 .  FIG. 9  is a plan view of composite sheet  90 ;  FIG. 10  is a perspective view of a lower sheet  94  of composite sheet  90 ;  FIG. 11  is a detail view of lower sheet  94 ;  FIG. 12  shows upper and lower sheets  92  and  94  of composite sheet  90 ; and  FIG. 13  is a partial cross section view of composite sheet  90 . Composite sheet  90  is constructed of upper and lower material sheets  92  and  94  into which are etched, machined, stamped or otherwise formed a pattern. The pattern in the sheets  92  and  94  are also complementary so that when the sheet  92  is inverted with respect to sheet  94  as shown in  FIG. 12 , the sheets  92  and  94  fit together to form the composite sheet  90  as detailed in  FIG. 13 . When the sheets  92  and  94  are combined into the composite sheet  90 , the composite sheet  90  has generally planar upper and lower surfaces  96  and  98  ( FIG. 13 ). 
     The pattern of the lower sheet  94  shown in  FIGS. 10 and 11  is generally the same as for upper sheet  92 . Sheet  94  includes full thickness portions  100 , reduced thickness portions  102  and holes  104 , and sheet  92  ( FIG. 12 ) includes full thickness portions  106 , reduced thickness portions  108  and defines holes  110 . In this instance of composite sheet  90 , full thickness portions  100  and  106  of sheets  92  and  94  have a more elongated shape than full thickness portions  70  and  76  of composite sheet  60  ( FIG. 5 ). Holes  104  and  110  of sheets  92  and  94  are also more elongated so that full thickness portions  100  and  106  fit within holes  110  and  104 , respectively. Reduced thickness portions  102  and  108  are positioned at the perimeter of sheets  92  and  94  in the example shown in  FIGS. 9-13 . 
     As shown in  FIG. 12 , positioning sheet  92  inverted with respect to sheet  94  allows full thickness portions  100  of sheet  94  to align with holes  110  of sheet  92  and full thickness portions  106  of sheet  92  to align with holes  104  of sheet  94  for combining sheets  92  and  94  into composite sheet  90  shown in  FIG. 13 . Full thickness portions  100  and  106  are immediately adjacent to one another and extend between upper surface  96  and lower surface  98  in an alternating manner across the upper and lower surfaces. Sheet  92  is formed from stainless steel or other high yield strength material and full thickness portions  106  of sheet  92  resist compressive forces represented by arrows  112  for a sufficiently wide area of force application. 
     Yet another composite sheet  120  according to the present disclosure is shown in  FIGS. 14-18 .  FIG. 14  is a plan view of composite sheet  120 ;  FIG. 15  is a perspective view of upper and lower material sheets  122  and  124  of composite sheet  120 ;  FIG. 16  is a detail view of upper and lower sheets  122  and  124 ;  FIG. 17  shows a partial cross section view of upper and lower sheets  122  and  124 ; and  FIG. 18  is a partial cross section view of composite sheet  120 . Composite sheet  120  is constructed of upper and lower material sheets  122  and  124  ( FIG. 15 ). Sheet  122  ( FIG. 17 ) includes full thickness portions  126 , reduced thickness portions  128  and holes  130 , and sheet  124  includes full thickness portions  132 , reduced thickness portions  134  and define holes  136 . Sheet  122  is formed into the pattern shown in  FIGS. 15-18  by starting with a sheet of high yield strength material, such as stainless steel, with a thickness that is equal to the reduced thickness portions  128  of sheet  122  and folding over sections of the sheet of material against itself by stamping or otherwise forming the material. Folding the sections of the sheet creates full thickness portions  126  where the material is folded over against itself, and creates holes  130  where the material is displaced during the folding process. The sheets  122  and  124  are combined into composite sheet  120 , composite sheet  120  has generally planar upper and lower surfaces  121  and  123  ( FIG. 13 ). 
     Sheet  124  is formed in a manner similar to that of sheet  122 , except the material is a high thermal conductivity material such as copper, and holes  136  are created by folding material from the holes  136  over to create the full thickness portions  132 . After the patterns are formed into sheets  122  and  124 , the sheets are positioned as shown in  FIG. 17  and then combined as shown in  FIG. 18  into the composite sheet  120 . As before, the full thickness portions  126  of the steel have a high yield strength that resists compressive and other forces represented in this instance by arrows  138  when such forces are applied over an appropriate surface area. 
     Another composite sheet  140  according to the present description is shown in  FIG. 19 . In this instance composite sheet  140  is formed by combining a high yield strength material sheet  142  with a high thermal conductivity material sheet  144  which have complementary shapes. Sheet  142  defines a hole  146  in which a heat pickup portion  148  of sheet  144  fits. When sheets  142  and  144  are combined, heat pickup portion  148  is positioned in hole  146  and the combination of heat pickup portion  148  and sheet  142  surrounding hole  146  generally define a planar surface of conductive sheet  140 . Sheet  144  also includes a heat sink portion  150  which is sandwiched between sheet  142  and a heat sink  152  in a brake cooling apparatus. A step  154  of sheet  144  transitions between heat pickup portion  148  and heat sink portion  150  of sheet  144 . Step  154  allows heat pickup portion  148  to be positioned in hole  146  of sheet  142  and heat sink portion  150  to be positioned at the surface of sheet  142 . In the embodiment shown in  FIG. 19 , sheets  142  and  144  are connected to one another with rivets  156  which extend through rivet holes  158  and  160 . Heat sink  152  is connected to sheet  144  with braze material  162  that is heated to bond heat sink  152  to sheet  144 . 
     Several embodiments of composite sheets have been shown in which one material with a desirable property is interlaced with another material having a different desirable property to obtain a composite having a combination of both desired properties not achievable with either the primary or secondary material alone. When constructed of high yield strength materials and high thermal conductivity materials, the resulting composite sheet is able to withstand forces that are greater than could be withstood with the high thermal conductivity material when such forces are applied to a portion of the surface area of the composite sheet that includes the high strength material. Additionally, such a composite sheet is also able to conduct heat much more readily than could be accomplished using the high compressive strength material alone. 
     One instance where the composite sheets described herein are useful for resisting compressive forces of a high temperature piston, such as found in disk brake systems. The high yield strength of the composite prevents the composite sheet from deforming under the compressive stress imposed by the piston, even at elevated temperatures. The high thermal conductivity material of the composite sheet moves heat away from the piston. 
     While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.