Patent Publication Number: US-2009233537-A1

Title: Air baffle and calculation method of deformational stress thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 097109156 filed in Taiwan, R.O.C. on Mar. 14, 2008, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to an air baffle, in particular, to an air baffle having a second-order deformation and a calculation method of a deformational stress thereof. 
     2. Related Art 
     In order to satisfy consumers&#39; demands for higher data processing speed of computer systems so as to achieve booting various programs in a very short time, persons in this art usually increase the precision of the chips to improve the processing speed and the development of multiplex operation. Along with the advancement of the processing speed of the computer systems, in the trend of miniaturization of the electronic devices, the problem of high heat generation of the computer devices inevitably occurs. 
     If the thermal cannot be dissipated in time, the over high temperature may severely influence the stability and efficiency of operation of the chips or electronic processing units, and even reduce the service life or damage the computer devices. Therefore, how to quickly dissipate the thermal generated by the operation processing units is in need of solution urgently. 
     For a 1U blade server, when the memory unit in the server is operating, the ventilation of the thermal dissipation airflow flow is unsatisfactory due to the limited space inside the server. Thus, the memory unit may be overheated, leading to a low performance or even damage. 
     As shown in  FIGS. 1 and 2 , in order to solve the thermal dissipating problem in the 1U server, an air baffle  10  supported on the bottom of the circuit board  22  is mounted on a back plate  21  of a server  20 . The conventional air baffle  10  includes a fixed section  11 , a connecting section  12 , a bent section  13 , and an urging section  14 . The connecting section  12 , the bent section  13 , and the urging section  14  successively extends from the two opposite lateral sides of the fixed section  11 . The fixed section  11  is fixed on the back plate  21 , the urging section  14  bears the circuit board  22 , and the connecting section  12  and the bent section  13  provide an elastic deformation range of the air baffle  10 , such that a memory unit (not shown) may be accommodated in the space of the server  20 . 
     Since the air baffle must have elasticity so as to restore its original state after being deformed under a pressure, the selection of size and material of the air baffle must take the condition that the stress of the deformed air baffle cannot exceed the yield stress of the selected material into account, so as to ensure the deformation mode of the air baffle is an elastic deformation mode, and prevent the permanent deformation of the air baffle. 
       FIGS. 3 and 4  show analysis results of elasticity and plasticity simulation of a finite element of a stainless steel (model No. SUS301) and Ti alloy. It is known from  FIG. 3  that after the air baffle made of the conventional stainless steel SUS301 is compressed, the deformational stress exerted on the connecting section has exceeded the yield stress (the yield stress is 965 MPa) of stainless steel SUS301. As shown in  FIG. 4 , even if the air baffle is made of Ti alloy (the yield stress of the Ti alloy is 1140 MPa), the problem of the permanent deformation generated after the air baffle is compressed cannot be solved, and the air baffle can merely be compressed downwardly for 18.4 mm. Thus, the formed space is insufficient for accommodating the memory unit. 
     The conventional air baffle is usually in the form of a first-order arm. Even if the Ti alloy having a higher yield stress is adopted, the problem that the deformational stress of the air baffle easily exceeds the yield stress of the material thus further causing a permanent deformation of the air baffle cannot be solved. Therefore, how to design the air baffle kept in an elastic deformation mode is in need of solution urgently. 
     SUMMARY OF THE INVENTION 
     In view of the above problem, the present invention provides an air baffle and a calculation method of a deformational stress thereof, so as to solve the problem that the elastic deformation range of the first-order arm type air baffle cannot meet the requirement in use of the server, and the deformational stress may cause a permanent deformation of the air baffle caused by the relative increasing of deformation in the conventional art. 
     The air baffle of the present invention has elasticity and is disposed in an electronic device. The air baffle is capable of being elastically deformed under a pressure exerted by an article. The air baffle includes a fixed section and at least one deformable section extending from a lateral side of the fixed section. The deformable section is arc-shaped and has a second-order deformation. A deformational stress of the deformable section is calculated using 
     
       
         
           
             
               σ 
               = 
               
                 
                   
                     FR 
                      
                     
                       ( 
                       
                         sin 
                          
                         
                             
                         
                          
                         θ 
                       
                       ) 
                     
                   
                    
                   t 
                 
                 
                   2 
                    
                   I 
                 
               
             
             , 
           
         
       
     
     and an allowable radius of curvature of the deformable section. In the equation, σ is the deformational stress of the deformable section, I is a moment of inertia, F is a maximum external force exerted on the deformable section by the article, R is the allowable radius of curvature of the deformable section, θ is an angle formed between two ends of the deformable section and a center of the radius of curvature of the deformable section, and t is a thickness of the air baffle. Based on the above equation, the deformational stress of the deformable section is ensured to be not exceeding a material yield stress of the air baffle. Therefore, the deformation mode of the air baffle of the present invention maintains an elastic deformation mode. 
     The present invention provides a calculation method of the deformational stress of the air baffle, which includes the following steps. Firstly, a material is selected, and a material thickness t and an allowable radius R of curvature are determined, such that the material assumes an arc shape. The angle θ formed between two ends of the arc of the material and the center of the allowable radius of curvature is determined according to the allowable radius R of curvature of the material. Then, the maximum external force F exerted on the material by the article is determined, and the moment of inertia I of the material is calculated. Finally, the deformational stress σ of the material is calculated using 
     
       
         
           
             σ 
             = 
             
               
                 
                   
                     FR 
                      
                     
                       ( 
                       
                         sin 
                          
                         
                             
                         
                          
                         θ 
                       
                       ) 
                     
                   
                    
                   t 
                 
                 
                   2 
                    
                   I 
                 
               
               . 
             
           
         
       
     
     In the present invention, a dynamic deformational stress of the air baffle under a pressure exerted by the article is calculated based on the above equation, and the deformable section of the air baffle is designed to have an arc shape with a second-order deformation, so that the maximum deformational stress of the air baffle will not exceed the material yield stress, thereby preventing the permanent deformation of the air baffle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawings will be provided by the Office upon request and payment of the necessary fee. 
       The present invention will become more fully understood from the detailed description given herein below for illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  is a perspective view of a conventional air baffle; 
         FIG. 2  is a perspective view of a conventional electronic device having the air baffle; 
         FIG. 3  is a schematic view of a simulation test of the conventional air baffle; 
         FIG. 4  is a schematic view of a simulation test of the conventional air baffle; 
         FIG. 5  is a perspective view of an air baffle of the present invention; 
         FIG. 6  is a perspective view of an electronic device having the air baffle of the present invention; 
         FIG. 7  is a flow chart of steps of calculating a deformational stress of the air baffle of the present invention; 
         FIG. 8  is a schematic view of a simulation test of the air baffle of the present invention; and 
         FIG. 9  is a relation diagram of a radius of curvature and a deformational stress of the air baffle of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The air baffle of the present invention is mounted in an electronic device which likes a computer device, such as a desktop computer, a notebook computer, and a server, but not limit to the above-mentioned computer devices. In the following detailed description of the present invention, the server is taken as an example for illustrating the present invention. However, the drawings are merely provided for reference and illustration instead of limiting the present invention. 
     As shown in  FIGS. 5 and 6 , the air baffle  100  of the present invention has elasticity and is mounted in an electronic device  200 . The electronic device  200  has a back plate  210  and an article  220 , the article  220  is placed on the air baffle  100 , and the air baffle  100  may be elastically deformed under a pressure exerted by the article  220 . The article  220  of the present invention is, for example, but is not limited into, a circuit board in the embodiments. 
     The air baffle  100  includes a fixed section  110  and two deformable sections  120  extending from two opposite lateral sides of the fixed section  110 , so that the air baffle  100  of the present invention forms a symmetrical structure. The fixed section  110  has at least one fixing hole  111 , and the back plate  210  of the electronic device  200  has a joining hole  211  corresponding to the fixing hole  111 . A locking member  140  such as a bolt, a latch, and a rivet passes through the fixing hole  111  and is locked in the joining hole  211 , thereby fixing the fixed section  110  on the back plate  210 . 
     Please refer to  FIGS. 5 and 6 , the deformable section  120  of the present invention has a plurality of arms  121  arranged separately. A support piece  130  extends from the other side of the arm  121  opposite to the fixed section  110  so as to support the bottom side of the article  220 . The deformable section  120  is arc-shaped and has a second-order deformation, and a dynamic deformational stress of the deformable section  120  is calculated using the following equation (1), so as to keep the deformational stress of the deformable section  120  not exceeding a material yield stress of the air baffle  100 : 
     
       
         
           
             
               
                 
                   σ 
                   = 
                   
                     
                       
                         FR 
                          
                         
                           ( 
                           
                             sin 
                              
                             
                                 
                             
                              
                             θ 
                           
                           ) 
                         
                       
                        
                       t 
                     
                     
                       2 
                        
                       I 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
         
         
           
             where, σ is a deformational stress of the deformable section  120 , I is a moment of inertia of the deformable section  120 , F is a maximum external force exerted on the deformable section  120  by the article  220 , R is an allowable radius of curvature of the deformable section  120 , θ is an angle formed between two ends of the deformable section  120  and a center of the radius of curvature of the deformable section  120 , and t is a thickness of the air baffle  100 . F in the above equation (1) is a relevant function of the deformation of the deformable section  120 : F=f(Δ), and the equation (1) is deduced from the following equation (2): 
           
         
       
    
     
       
         
           
             
               
                 
                   σ 
                   = 
                   
                     My 
                     I 
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
         
         
           
             where, M is a bending moment of the deformable section  120 , and M=FR sin θ, the values are substituted into equation (2) to obtain the equation (1). 
           
         
       
    
     Referring to the flow chart of the steps in  FIG. 7 , the calculation method of the deformational stress of the air baffle of the present invention includes the following steps. Firstly, a material is selected as the material of the air baffle  100  (Step  300 ), so as to determine a material yield stress σ y  of the air baffle  100 . The stainless steel SUS301 is selected for illustration in this embodiment of the present invention. However, persons skilled in the art may adopt other materials for making the air baffle  100 , which is not limited to this embodiment. Then the thickness t of the material is determined (Step  310 ), and the allowable radius R of curvature of the material is determined, such that the deformable section  120  of the air baffle  100  is formed arc-shaped (Step  320 ). The angle θ formed between two ends of the deformable section  120  and a center of the radius of curvature of the deformable section is determined according to the allowable radius R of curvature of the material (Step  330 ). Then, the moment of inertia I of the deformable section  120  is calculated (Step  340 ), and then the maximum external force exerted on the deformable section  120  by the article  220  (for example, a circuit board in this embodiment) in the electronic device  200  is determined (Step  350 ). Finally, the above designed parameters are substituted into the equation (1): 
     
       
         
           
             σ 
             = 
             
               
                 
                   FR 
                    
                   
                     ( 
                     
                       sin 
                        
                       
                           
                       
                        
                       θ 
                     
                     ) 
                   
                 
                  
                 t 
               
               
                 2 
                  
                 I 
               
             
           
         
       
     
     so as to calculate the deformational stress of the deformable section  120  (Step  360 ), thereby ensuring the deformational stress σ of the deformable section  120  not exceeding the yield stress σ y  of the material of the air baffle  100 . 
     It should be noted that, the order of the above Steps  310 ,  320 ,  330 ,  340 , and  350  in the present invention may be changed according to the actual calculation process, and is not limited to the order disclosed in this embodiment. In the present invention, the allowable radius R of curvature of the deformable section  120  is determined, and the deformational stress is calculated using the equation (1), so as to ensure the deformational stress σ of the deformable section  120  not exceeding the material yield stress σ y  of the air baffle  100 . 
     If the deformational stress ay calculated using the equation (1) exceeds the material yield stress σ y , the radius R of curvature of the air baffle  100  is adjusted, so as to prevent the deformational stress σ of the deformable section  120  from exceeding the material yield stress σ y  to cause the permanent deformation of the air baffle  100 . However, the present invention may also adjust other design parameters of the air baffle  100 , such as the maximum external force F exerted on the deformable section  120  by the article  220 , or the thickness t of the air baffle  100 , which is not limited to the adjustment of the radius R of curvature of the deformable section  120 . 
     As shown in  FIGS. 8 and 9 , the stainless steel SUS301 is used in the present invention for making the air baffle  100 . It can be known from the analysis results of elasticity and plasticity simulation that, when the deformable section  120  suffers a continuous force, the arm  121  extends outwardly so as to reduce the suspending distance of the arm  121 . Meanwhile, the deformational stress of the arm  121  is reduced to compensate the increased deformational stress due to the increased deformation of the arm  121  connected to the fixed section  110 . As shown in  FIG. 9 , according to the equation (1), when the minimum allowable radius of curvature of the deformable section  120  is designed to be 30 mm, the maximum deformational stress of the deformable section  120  will not exceed the material yield stress (965 MPa) of stainless steel SUS301. When the pressure exerted on the deformable section  120  by the article  220  is increased, the radius R of curvature of the deformable section  120  is increased accordingly and the angle θ is reduced, and accordingly the deformational stress of the deformable section  120  is reduced according to a sin θ function. Moreover, it is known from  FIG. 9  that, the effective radius of curvature of the deformable section  120  in the present invention is optimally 30 mm to 60 mm, so as to ensure the air baffle  100  in the elastic deformation mode, and prevent the air baffle  100  from producing the permanent deformation (plastic deformation). 
     In the present invention, the dynamic stress variant of the deformed air baffle is calculated using the equation (1), and the deformable section of the air baffle is designed to have an arc shape with a second-order deformation according to the equation (1). Thus, when a force is exerted on the deformable section by the article, the suspending length is reduced with the increase of the deformation, and the maximum deformational stress of the air baffle will not exceed the material yield stress, thereby preventing the permanent deformation of the air baffle.