METHOD FOR EVALUATING BINDING STRENGTH OF MECHANICAL COMPOSITE PIPE FIELD OF THE INVENTION [00011 The invention relates to the field of the technology for evaluating the mechanical performance, and more particularly to a method for evaluating a bonding strength of a mechanical composite pipe. BACKGROUND OF TIIE INVENTION [0002] The liner pipe and the base pipe of a mechanical composite pipe are bonded together by means of the relative deformation thereof. No metallurgical bonding interface is fonned between the liner pipe and the base pipe. The bonding of the liner pipe and base pipe is maintained primarily by a radial residual stress of the base pipe on the liner pipe. Thus, the bonding strength of the mechanical composite pipe decides the service environment thereof [0003] Typical indexes for evaluating the bonding strength of the mechanical composite pipe include axial shear separation strength and radial clamping force. The axial shear separation strength refers to an interfacial shear stress in the axial direction when relative slide occurs between the base pipe and the liner pipe under the force of an external load. The radial clamping force refers to a radial compression residual stress acting on an outer surface of the liner pipe after the base pipe and the liner pipe are re-bonded. [0004] To evaluate the above two indexes, a destructive sampling means is generally used. The destructive sampling means include: a residual stress release method for measuring the radial clamping force, and an axial compression or an axial tension method for 1 RECElVED~ TIME 29. APR. 19:02 PRINJT TIME 29. APR. 19:33 measuring the axial shear strength. The residual stress release method is a method for calculating the hoop residual stress of the composite pipe by measuring the variation of the axial strain and the hoop strain of the liner pipe before and after the removal of the base pipe. The axial extension or axial compression method is a method for measuring a maximum axial shear stress by extending or compressing the liner pipe and the base pipe to cause relative slide. [0005] The above two measuring methods have three drawbacks. First, the two evaluating methods belong to the destructive testing, and the testing cost is high. Second; the testing methods are troublesome; and the testing speed is low, it generally takes two or three days to evaluate the bonding strength of the composite pipe by using the residual stress method or the axial extension or axial compression method. Third, the sampling can be achieved only at two ends of the composite pipe. The testing has a large error, and the reliability of the testing result is low. SUMMARY OF THE INVENTION [0006] In view of the above-described problems, it is one objective of the invention to provide a method for evaluating a bonding strength of a mechanical composite pipe. The method solves the problems in the prior arts that the destructive test is required, the test has a large testing eror, high production costs, low efficiency, and is unable to be conducted on-line. [0007] Technical scheme of the invention is as follows: a method for evaluating a bonding strength of a mechanical composite pipe, the method comprising the following steps: [00081 1) selecting a standard piece of the mechanical composite pipe having the same material and the same specification as the mechanical composite pipe to be tested has and 2 RECEIVED TIME 29. APR. 19 :0 2 PRINT TIME 29. APR. 19 :3 3 having a bonding strength satisfying evaluating requirements; [0009] 2) exerting an excitation force on the standard piece of the mechanical composite pipe obtained from step 1) by a certain method; recording an excitation force signal; real time gathering an acceleration signal at specific points; analyzing and processing obtained signals; and acquiring values of modal paramctcrs of the standard piece of the mechanical composite pipe; [0010] 3) using the same operations in step 2), exerting the same excitation on the mechanical composite pipe to be tested; real time gathering an acceleration signal thereof at coiresponding specific points; analyzing and processing obtained signals; and acqu irng values of the same modal parameters of the mechanical composite pipe to be tested; and [00111 4) comparing the values of the modal parameters of the standard piece of the mechanical composite pipe obtained in step 2) with the values of the modal parameters of the mechanical composite pipe to be tested obtained in step 3), and detennining whether the mechanical composite pipe to be tested is qualified according to a comparison result. [0012] The standard piece of the mechanical composite pipe in step 1) is specifically selected as follows: [0013] 1.1) providing a base pipe and a liner pipe having the same material, the same outer diameter, the same wall thickness, and the same length as the mechanical composite pipe to be tested have, and assembling the base pipe and the liner pipe in coaxial to obtain a mechanical composite pipe before standardization; [00141 1.2) standardization [00151 1.2.1) initial loading [0016] disposing sealing devices on two ends of the composite pipe obtained in step 1.1), and attaching an axial strain gauge and a hoop strain gauge at a middle point position 3 RECEIVED TIME 29. APR 19:02 PRINT TIME 29. APR. 19:33 right above an outer part of the base pipe; [0017] injecting water into an inner cavity of the liner pipe, controlling an injection speed equivalent to an increase of 0.0110.005 magapascal per min of a hydrostatic pressure in the liner pipe, and dynamically gathering and recording a hoop strain C, and an axial strain F 2 of the base pipe: and [0018] calculating a real time hoop stress or of an inner surface of the base pipe according to the hoop strain C and the axial strain ; stopping water injection and unloading water when o7 U d'Htmw, ;calculating a hoop residual stress 0e according to a hoop stress F and an axial stress E of the base pipe after unloading water; and obtaining a meuhanical composite pipe afler standardization if Ia andard a e 1.5o ta, d,,d is satisfied, in which, - is a preset minimum hoop stress value, or otherwise, conducting step 1.2.2); [0019] 1.2.2) repeated loading [0020] injecting water into the inner cavity of the liner pipe again, controlling the injection speed equivalent to the increase of 0.01+0.005 magapascal per min of the hydrostatic pressure in the liner pipe; unloading water after one minute of water injection gathering the hoop stress E and the axial stress F of the base pipe after unloading water and calculating the hoop residual stress de; and obtaining the mechanical composite pipe after standardization when o,..,d,,d : de < 1.50-,,, t d, is satisfied, or otherwise, repeating step 1.2.2) until (j-8- aldrd ! do :! 1.5 (T; lundard is satisfied; and [0021] 1.2.3) removing the scaling devices disposed at two ends of the mechanical composite pipe after standardization, and obtaining the standard piece of the mechanical 4 RECEIVED TIME 29 APR. 19:02 PRINT TIME 29, APR. 19:33 composite pipe. [0022] The modal parameter is a natural frequency 6 Step 2) specifically comprises: horizontally disposing the standard piece of the mechanical composite pipe having a length of I obtained in step 1) on two V-grooves; regulating positions of the two V-grooves to vertically align an external end face of a supporting part of each of the two V-grooves with each external end face of the composite pipe, respectively; disposing an acceleration sensor at the middle point position right above the outer part of the base pipe; exerting an excitation force on the base pipe by an excitation device; controlling a horizontal distance between a position for exerting excitation and the acceleration sensor within a range of between / /10 and 71/10; connecting both the acceleration sensor and the excitation device to a computer via a dynamic signal acquisition device; conducting frequency response analysis by the computer according to the real time acceleration signal and the excitation force signal gathered by the dynamic signal acquisition device; and obtaining the natural frequency O,,tnd,,d of the standard piece of the mechanical composite device by recognition of the modal parameter. [00231 Step 3) comprises: adopting the same method of step 2) to obtain a natural frequency co of the mechanical composite pipe to be tested. [0024] Step 4) comprises: comparing the natural frequency w. of the mechanical composite pipe to be tested obtained in step 3) with the natural frequency ,,, of the standard piece of the mechanical composite device obtained in step 2); and determining the bonding strength of the mechanical composite pipe to be tested is qualified if C0s1m71mg : Cstandar , or otherwise, determining the bonding strength of the mechanical composite pipe to be tested is not qualified. [0025] The modal parameter is a damping '. Step 2) specifically comprises: 5 RECEIVED TIME 29. APR. 19:02 PRINT TIME 29. APR. 19:33 horizontally disposing the standard piece of the mechanical composite pipe having the length of I obtained in step 1) on the two V-grooves; regulating positions of the two V-grooves to vertically align the external end face of the supporting part of each of the two V-grooves with each external end face of the composite pipe, respectively; disposing the acceleration sensor at the middle point position right above the outer part of the base pipe; exciting an excitation force on the base pipe by the excitation device; controlling the horizontal distance between the position for exerting excitation and the acceleration sensor within the range of between 1 /10 and 71 /10; connecting both the acceleration sensors and the excitation device to the computer via the dynamic signal acquisition device; conducting frequency response analysis by the computer according to the real time acceleration signal and the excitation force signal gathered by the dynamic signal acquisition device; and obtaining the damping of the standard piece of the mechanical composite device by recognition of the modal parameter. [00261 Step 3) comprises: adopting the same operations in step 2) to obtain a damping of the mechanical composite pipe to be tested. [0027] Step 4) comprises: companng the damping # of the mechanical composite pipe to be tested obtained in step 3) with the natural frequency (,udrd of the standard piece of the mechanical composite device obtained in step 2); and determining the bonding strength of the mechanical composite pipe to be tested is qualified if . or otherwise, determining the bonding strength of the mechanical composite pipe to be tested is not qualified. [0028] The modal parameter is transfer rate q. Step 2) specifically comprises: horizontally disposing the standard piece of the mechanical composite pipe having the length of I obtained in step 1) on the two V-grooves; regulating positions of the two 6 RECEIVED TIME 29. APR. 19:02 PRINT TIME 29. APR. 19:33 V-grooves to vertically align the external end face of the supporting part of each of the two V-grooves with each external end face of the composite pipe, respectively. Disposing a first acceleration sensor at a position A of an opening right above an inner part of the liner pipe, and disposing a second acceleration sensor at a position B of the middle point right above the outer part of [he base pipe; exerting excitation on the base pipe by the excitation device; connecting both the acceleration sensors and the excitation device to the computer via the dynamic signal acquisition device; analyzing the obtained signals by the computer to obtain a time domain signal a(t) at the position A and a time domain signal b(t) at the position B; conducting Fourier transfonn to obtain A(t) and B(t) dividing A() by BQ) to obtain a transfer rate ;/ ,tndard ofthe acceleration at the position A in relative to the acceleration at the position B, in which, 0 ! dord 1 [0029] Step 3) comprises: adopting the same operations of step 2) to obtain a transfer rate of the mechanical composite pipe to be tested. 100301 Step 4) comprises: comparing the transfer rate ?h of the mechanical composite pipe to be tested obtained in step 3) with the transfer rate gt,,Tidq,, of the standard piece of the mechanical composite device obtained in step 2); and determining the bonding strength of the mechanical composite pipe to be tested is qualified if min-png aldaer , or otherwise, determining the bonding strength of the mechanical composite pipe to be tested is not qualified. [00311 Advantages according to embodiments of the invention are summarized as follows: [00321 1. Excitations are excited on the selected standard piece of the mechanical composite pipe and the mechanical composite pipe to be tested, respectively, to obtain the 7 RECEIVED TIME 29. APR. 19:02 PRINT TIME 29. APR. 19:33 modal parameters are; and the model parameters are compared to know whether the mechanical composite pipe to be tested is qualified. Thus, the invention does not require pipe destruction, thereby lowering the testing cost. [0033] 2. The method of the invention is simple and reasonable, it is proved from extensive experiments that the method of the invention has small testing errors and reliable results for each modal parameter. [0034] 3. The method of the invention is simple and accessible and has high testing efficiency. It requires no more than one minute to test one composite pipe, so that the on line real time testing of the bonding strength of the composite pipe can be realized. Furthermore, the method of the invention is superior to the sampling method in that it decreases the testing error; and comparing with the residual stress method and the axial compression or the axial tension method in the prior art, the method of tie invention has high testing accuracy. BRIEF DESCRIPTION OF THE DRAWINGS [0035] FIG. 1 is a structure diagram of a mechanical composite pipe of the invention; [0036] FIG. 2 is a structure diagram of a vibration model having two degrees of freedom of a mechanical composite pipe of the method of the invention; and [0037] FIG. 3 is a structure diagram of a mechanical composite pipe exerted with excitation by using the method of the invention. DETAILED DESCRIPTION OF THE EMBODIMENTS [0038] For further illustrating the invention, experiments detailing a method for evaluating a bonding strength of a mechanical composite pipe are described hereinbelow 8 RECEIVED TIME 29.APR. 19:02 PRINT TIME 29. APR. 19:33 combined with the drawings. [0039] As shown in FIG. 1, a mechanical composite pipe 1 comprises a base pipe 2 and a liner pipe 3 disposed inside the base pipe 2. Example 1 [0040] A method for evaluating a bonding strength of a mechanical composite pipe, the method comprises the following steps: [00411 Step 1): Select a standard piece of the mechanical composite pipe having the same material and (he same specification as the mechanical composite pipe to be tested has and having a bonding strength satisfying evaluating requirements. In other words, the standard piece of the mechanical composite pipe has the same material, the same outer diameter, the same wall thickness, and the same length as the mechanical composite pipe to be tested has. [00421 The standard piece of the mechanical composite pipe in step 1) is specifically selected as follows: [0043] Step 1.1): provide a base pipe and a liner pipe having the same material, the same outer diameter, the same wall thmickess, and the same length as the mechanical composite pipe to be tested has, and assembling the base pipe and the liner pipe in coaxial to obtain a mechanical composite pipe before standardization; [0044] Step 1.2): standardization [0045] Step 1.2.1): initial loading [0046] dispose sealing devices on two ends of the composite pipe obtained in step 1.1), and attach an axial strain gauge and a hoop strain gauge at a middle point position right above an outer part of the base pipe; 9 RECEIVED TIME 29. APR. 19:02 PRINT TIME 29. APR. 19:33 [0047] inject water into an inner cavity of the liner pipe, control an injection speed equivalent to an increase of 0.01+0.005 magapascal per inn of a hydrostatic pressure in the liner pipe, and dynamically gather and record ahoop strain , and an axial strain E of the base pipe; and [0048] calculate a real time hoop stress o, of an inner surface of the base pipe (i2 + r 2 )E according to an equation o, = 2(r + ), in which, r 2 represents an inner 2r 2 (1 - v )e+,J-Yih 2rpeet nne diameter of the base pipe, r, represents an outer diameter of the base pipe, E represents an elastic modulus of the base pipe, and V represents a Poisson's ratio of the base pipe; stop water injection and unload water when a > -,,.dd ; calculate a hoop residual stress a e according to a hoop stress 6 9 and an axial stress ' of the base pipe after unloading water; and obtain a mechanical composite pipe after standardization if Oaat.mdard a 1.Saa,.,daid is satisfied, in which, aatanaard is a preset minimum hoop stress value, or otherwise, conduct step 1.2.2. [0049] step 1.2.2): repeated loading [0050] Inject water into the inner cavity of the liner pipe again, control the injection speed equivalent to the increase of 0.01±0.005 magapascal per min of the hydrostatic pressure in the liner pipe; unload water after one minute of water injection; gather the hoop stress -,g and the axial stress E of the base pipe after unloading water and calculate the hoop residual stress a ; and obtain the mechanical composite pipe after standardization when a 0 9 1.5atandar, is satisfied, or otherwise, repeat step 1.2.2)until a-atandaard - tan a is satisfied; and 10 RECEIVED TIME- 29.APR, 19 : 02 PRINT TIME 29. APR. 19 :3 3 [00511 Step 1.2.3): remove the sealing devices disposed at two ends of the mechanical composite pipe after standardization, and obtain the standard piece of the mechanical composite pipe. [0052] The selection of the standard piece of the mechanical composite pipe in step 1) can be dircctly determined according to the designation of the user to meet different requirements of the users. [0053] Step 2): exert an excitation force on the standard piece of the mechanical composite pipe obtained from step 1) by a certain method; record an excitation force signal; real time gather an acceleration signal at specific points; analytical process obtained signals; and acquire a nature frequency (1,,dar, of the standard piccc of the mechanical composite pipe. [0054] Step 2) is specifically conducted as follows: [0055] As shown in FIG. 3, horizontally dispose the standard piece of the mechanical composite pipe having a length of I obtained in step 1) on two V-grooves 2; and regulate positions of the two V-grooves 2 to vertically align an external end face of a supporting part of each of the two V-grooves 2 with each external end face of the composite pipe, respectively. [0056] Dispose an acceleration sensor 4 at the middle point position right above the outer part of the base pipe, the acceleration sensor 4 has a sensitivity generally being equal to or larger than 100 mv/g. Exert an excitation force on the base pipe by an excitation device 3. Control a horizontal distance between a position for exerting excitation and the acceleration sensor 4 within a range of between 1/10 and 71/10. Connect both the acceleration sensor 4 and the excitation device to a cornputer via a dynamic signal acquisition device (DI-DAS5920). Conduct frequency response analysis by using miodal analysis software (DHMA) in the computer according to the real time acceleration signal 11 RECEIVED TIME 29. APR. 19:02 PRINT TIME 29. APR. 19:3 and the excitation force signal gathered by the dynamic signal acquisition device. Obtain the natural frequency os6andar of the standard piece of the mechanical composite device by recognition of the modal parameter. [00571 A selection criteria of the excitation device is that a rubber hammer head is adopted if an estimated nature frequency is less than or equal to 200 Hz, a nylon hammer head is adopted if the estimated nature frequency is between 200 Hz and 500 Hz, and a metal hammer head is adopted if an estimated nature frequency is larger than 500 Hz. [0058] Step 3): use the same operations in step 2), exert the same excitation on the mechanical composite pipe to be tested; real time gather the acceleration signal thereof at corresponding specific points; analytical process obtained signals; and acquire the natural frequency to,, of the mechanical composite pipe to be tested; and [0059] Step 3) is specifically conducted as follows: [0060] Horizontally dispose the standard piece of the mechanical composite pipe having the length of I obtained in step 2) on the two V-grooves; and regulate positions of the two V-grooves to vertically align the external end face of the supporting part of each of the two V-grooves with each external end face of the composite pipe, respectively. [0061] Dispose the acceleration sensor at the middle point position right above the outer part of the base pipe, the acceleration sensor has the sensitivity generally being equal to or larger than 100 mnv/g. Exert an excitation force on the base pipe by an excitation device. The excitation device, and the position, the excitation force, and the way the excitation being exerted are all the same as those of step 2). The position for gathering the acceleration senor is the same as that of step 2). Connect both the acceleration sensor and the excitation device to the computer via the dynamic signal acquisition device. Conduct frequency response analysis by using the computer according to the real time acceleration signal and the excitation force signal gathered by the dynamic signal acquisition device. 12 RECEIVED TIME 29. APR. 19:02 PRINT TIME 29. APR, 19:33 Obtain the natural frequency co ,, of the mechanical composite device to be tested by recognition of the modal parameter. [0062] Step 4): compare the natural frequency co,, of the mechanical composite pipe to be tested obtained in step 3) with the natural frequency a),dr, of the standard piece of the mechanical composite device obtained in step 2); and determine the bonding strength of the mechanical composite pipe to be tested is qualified if ca i ;> costandar, or otherwise, determine the bonding strength of the mechanical composite pipe to be tested is not qualified. Example 2 [0063] In this Example, the modal parameter for evaluating the bonding strength of the composite pipe is a damping ( . In step 2). conduct the frequency response analysis of the acceleration signal and (he excitation force signal to acquire the damping (standard of the standard piece of the mechanical composite pipe. In step 3), conduct the frequency response analysis of the acceleration signal and the excitation force signal of the mechanical composite pipe to be tested to acquire the damping f of the mechanical composite pipe to be tested. Other operations from step 1) to step 3) are the same as those in Example 1. 100641 In step 4), compare the damping f of the mechanical composite pipe to be tested obtained in step 3) with the natural frequency (sanda d of the standard piece of the mechanical composite device obtained in step 2); and determine the bonding strength of the mechanical composite pipe to be tested is qualified if ; , or otherwise, 13 determine the bonding strength of the mechanical composite pipe to be tested is not qualified. [0065] 1. Relation between the bonding strength of the mechanical composite pipe and the normal stiffness of the bonding interface: [0066] According to a fractal model of a nonnal contact stiffness of a rough surface, and providing that the contact surface is isotropic and interaction between asperities of the rough surface can be ignored, then, a dimensionless normal stiffness of the mechanical bonding interface can be expressed as follows: 2-D 2(2-D) DL 2 2 2 -I ' [0067] k = 4,2( -1) 2 2 -a 2 kD [00681 in which, k refers to a nonnal contact stiffness of the dimensionless mechanical bonding surface, A refers to a dimensionless real contact area, D refers to a fractal dimension of the bonding surface, and a* refers to a dimensionless critical contact area. [0069] When plastic deformation occurs on the contact surface, the relation between a normal load and the contact area bctwcen two cylinders arc expressed as follows: [0070] P =3 G"(D-1)g(D)A,2( ) A 2 -a, 2 ]+kpg,(D)A,-a, - D#1.5 [0071] p- G )( /)+3kp( , D-1.5; 3 3 ,, 3 [00721 in which, P refers to a dimensionless nonnal force, G' refers a dimensionless fractal roughness parameter, k refers to a coefficient relates to a hardness and a yield strength of a material, & and 9 2 refer to functions of a fractal dimension D. [0073] According to the relation of the normal contact stiffness of the dimensionless 14 RECEIVE[) TIME 29. APR. 19:02 PRINT TIME 29. APR. 19:33 mechanical bonding surface and the dimensionless normal force, it is known that the stiffness of the mechanical bonding interface increases along with the increase of the normal load. [00741 Because the mechanical composite pipe is formed by adopting the underwater blasting technology to make plastic deformation occur in the base pipe and the liner pipe to realize the mechanical attachment, the bonding strength of the mechanical composite pipe relates to the radial residual stress of the interface between the base pipe and the liner pipe, that is, the larger the radial residual stress is, the higher the bonding strength of the composite pipe is. The radial residual stress of the composite pipe is expressed as a=P Ain which, P is the normal force of the bonding surface of the composite pipe, and A is the real contact area of the composite pipe. [0075] In summary, the higher the bonding strength is, [he larger the normal load of the bonding interface is; whereas the larger the normal load of the bonding interface is, the larger the normal stiffness of the bonding interface is; thus, the higher the bonding strength is, the larger the normal stiffness of the bonding interface is. [0076] 2. Relation between the normal stiffness of the bonding interface and the nature frequency of the composite pipe [0077] As the interface between the base pipe and the liner pipe of the mechanical composite pipe is relatively complicate, it is difficult to use a vibration model having an infinite degree of freedom to theoretically analyze the influence of the bonding interface of the base pipe and the liner pipe on the dynamic characteristic of the composite pipe. To dcrcase the difficulty of the analysis, the transverse vibration of the simple supports of the two ends of the composite pipe is simplified into a vibration model having two degrees of freedom. As shown in FIG. 2, mi represents a weight of the base pipe, m, represents a weight of the liner pipe, k 1 , represents a bending stiffness of the composite 15 RECEIVED TIME 29, APR. 19:02 PRINT TIME 29. APR. 19:34 pipe, k, represents an interface stiffness between the base pipe and the liner pipe, c represents an interface damping between the base pipe and the liner pipe, and a represents the nature frequency of the model system. The interface stiffness and the interface damping between the base pipe and the liner pipe are imitated by the spring stiffness and damping element, respectively. [0078] A differential equation of motion is: nz x-c -c xl k+k 2 -kl x]FO [0079] , + 0 mn, -c c x - k k x" 0 [0080] A characteristic equation is: [0081] 2 =0 - 2 k2 - 2, t 2 (k + k )m1 2 + ikA- 2 i ± (k k)m 2 + mA k] - 4m;in 2 k k 2 [0082] So that, d 1ii (k,+,)mmik [(fk)'JmCk ] 2- 4m mlkk2 [0083] When Oi = (k-I- " + i 1c, jV(kl + C ) '2 1-,. 2mn m 2 [0084] Derivate of k, is as follows: [(+ ±c+ )m 2 + n,k 2 ( +m )-2rnni 2 k 1 d0085]2 +dn7+ - ]2 n 2 [0085]-4n k dk 2n),m, [(k, +k2)m 2 + nik 2 ](m + [0086] d > (k, + k, )in 2 + nik 2 k i>0 dk 2 2nz m2 (k, +k2 )n 2 + mk 2 1 k +k2)m2i+msik2+V[(kl+k 2)m2+m lk2 ]-4nmi2C [00871 Similarly, when or - ± ) ± J[ 1 2 16 RECEIVED TIME 29. APR. 19 : 02 PRINT TIME 29. APR. 19 : 34 [0088] Results of derivate of k is: d nm+ m k 1 [0089] 1 2+ >0. dk 1 m 2 (k +k 2 ), +i k, [0090] From the above analysis, it is known that dd / d2 is always larger than zero, and O ' increases with the increase of k. Since k2 represents the nonnal stiffness of the bonding interface of the base pipe and the liner pipe, it is concluded that the larger the normal stiffness of the bonding interface is, the higher the nature frequency is. [0091] 3. Relation between the bonding strength of the mechanical composite pipe and the nature frequency and the damping: [0092] Based on the analysis conclusion of the relation between the bonding strength and the nonnal stiffness of the bonding interface (the higher the bonding strength is, the larger the normal stiffness of the bonding interface is) and the analysis conclusion of the relation between the normal stiffness of the bonding interface and the nature frequency (the larger the normal stiffness of the bonding interface is, the higher the nature frequency is), it is known that the higher bonding strength of the mechanical composite pipe is, the higher natural frequency is. [0093] Meanwhile, as shown in the following Table, the nature frequency and damping of a plurality of the mechanical composite pipes are obtained by using the method of the invention; the bonding strength of the mechanical composite pipes are obtained by using the shear separation destructive testing method; and it is concluded that the higher the bonding strength of the composite pipe is, the higher the nature frequency is, and the smaller the damping is and that the accuracy of the method for evaluating the bonding strength of mechanical composite pipe of the invention is verified. For a mechanical composite pipe having a specification of 76 x (6+2), the outer diameter of the mechanical composite pipe is 76 mm, the wall thickness of the base pipe is 6 mm, and a wall 17 RECEIVED TIME 29. APR. 19:02 PRINT TIME 29. APR. 19:34 thickness of the liner pipe is 2 mm. For a mechanical composite pipe having a specification of 219 x (14.3+3), the outer diameter of the mechanical composite pipe is 219 mm, the wall thickness of the base pipe is 14.3 mm, and a wall thickness of the liner pipe is 3 mm. Specification Nature Bonding strength Type Length (in) Damping (0') (mm) frequency (Hz) (megapas cal) 1# 5 8.75 3.7c-1 0.012 76 x (6 12) 2# 5 9.25 1.oe-1 0.025 3# 5 10 4.5e-2 0.5 [1 10.68 4.15 8.4-1 0.32 219x 2! 10.68 4.27 6.8-1 0.45 (14.3+3) 3# 10.68 4.33 6.0-1 0.52 Example 3 [0094] In this example, the modal parameter for evaluating the bonding strength of the composite pipe is a transfer rate 71. Operation of step 1) is the same as that of Example 1. 100951 Step 2): exert an excitation force on the standard piece of the mechanical composite pipe obtained from step 1); record the excitation force signal; real time gather the acceleration signal at specific points; analytical process obtained signals; and acquire the transfer rate 17,,w, of the standard piece of the neclianical composite pipe. [0096] Step 2) is specifically conducted as follows: horizontally dispose the standard piece of the mechanical composite pipe having the length of I obtained in step 1) on the two V-grooves; regulate positions of the two V-grooves to vertically align the external 18 RECEIVED TIME 29. APR, 19:02 PRINT TIME 29. APR. 19:34 end face of the supporting part of each of the two V-grooves with each external end face of the composite pipe, respectively. [0097] Dispose a first acceleration sensor at a position A of an opening right above an inner part of the liner pipe, a distance a between the position A and the opening of the liner pipe satisfies O<a 50mm. Dispose a second acceleration sensor at a position B of the middle point right above the outer part of the base pipe. Exert excitation on the base pipe by the excitation device; a position where the excitation is exerted is disposed between 100 mm and 500 mm on a right side of the position B. Connect both the acceleration sensors and the excitation device to the computer via the dynamic signal acquisition device. Analyze the obtained signals by the computer to obtain a time domain signal a(t) at the position A and a time domain signal b(t) at the position B; conduct Fourier transform to obtain A(t) and B(t), and divide A(t) by B(t) to obtain a transfer rate 1 standad of the acceleration at the position A in relation to the acceleration at the position B, in which, 0 q , 1. [0098] Step 3): using the same operation of step 2), exert the same excitation force on the mechanical composite pipe to be tested; real time gather the acceleration signal at specific points; analytical process obtained signals; and acquire the transfer rate Pg of the mechanical composite pipe to be tested, 0 K y, , 1. [0099] Step 4): compare the transfer rate of the mechanical composite pipe to be tested obtained in step 3) with the transfer rate ,,, of the standard piece of the mechanical composite device obtained in step 2); and determine the bonding strength of the mechanical composite pipe to be tested is qualified if , > , , or otherwise, determine the bonding strength of the mechanical composite pipe to be tested is not 19 RECEIVED TIME 29. APR. 19:02 PRINT TIME 29. APR. 19:34 qualified. [0100] In the method of the invention, the transfer rate 17 can also be the modal parameter to evaluate the bonding strength of the composite pipe. Transfer rate and bonding strength of a plurality of mechanical composite pipe are obtained by using the method of the invention and by using the shear destructive testing method in the prior art. It is known from the following table that the higher the bonding strength is, the larger the transfer rate is, and that the accuracy of the method for evaluating the bonding strength of the mechanical composite pipe of the invention is verified. For the mechanical composite pipe having the specification of 89 x (5+2), the outer diameter of the mechanical composite pipe is 89 mm, the wall thickness of the base pipe is 5 mm, and the wall thickness of the liner pipe is 2 mm. Specification (mm) Type Length (m) Transfer rate Bonding strength (megapascal) 1 4.5 0.12 0.01 89 x (5+2) 2# 4.5 0.46 0.21 3ff 4.5 0.58 0.42 20 RECEIVED TIME 29. APR. 19:02 PRINT TIME 29. APR. 19:34