Acoustic structural materials and structures

Abstract

The present invention provides an acoustic material that functions as a structural material while achieving lightweight construction, and a structure equipped therewith. [Solution] The underwater acoustic structural material 1 has a sound-absorbing layer A that absorbs sound waves, and comprises a surface portion 2 that absorbs sound waves in water, and a back portion 4 joined to the back of the surface portion 2. The back portion 4 has two plate-shaped members 41 and 42 made of fiber-reinforced plastic, and a reflective layer 43 made of a bubble-dispersed viscoelastic material or a porous structure viscoelastic material sandwiched between the two plate-shaped members 41 and 42. The characteristic acoustic impedance value of the surface portion 2 is 0.5 to 0.9 times the characteristic acoustic impedance value of water, and the characteristic acoustic impedance value of the reflective layer 43 is 0.2 to 0.4 times the characteristic acoustic impedance value of water.

Description

Technical Field

[0001] The present disclosure relates to an acoustic material having a function as a structural material and a structure including the same. Background Art

[0002] Conventionally, acoustic materials such as sound absorbing materials that absorb sound waves and sound insulating materials that block sound waves have been known. For example, Patent Document 1 discloses a sound insulating plate which is a plate-shaped sound insulating material.

[0003] The sound insulating plate of Patent Document 1 includes a sound insulating material main body made of a rubber elastic body having a recess formed on one side surface, and a cover member that covers the one side surface of the sound insulating material main body. The cover member has rubber layers disposed on both side surfaces and a fiber-reinforced resin layer disposed between the rubber layers, and the shape of the cover member is maintained by the fiber-reinforced resin layer even after aging. Prior Art Literature Patent Literature

[0004] Patent Literature 1 Japanese Unexamined Patent Publication No. 2001-166779 Summary of Invention Problem to be Solved by Invention

[0005] Generally, a plate-shaped acoustic material is attached to a frame or a face material of a structure, or fastened with bolts, nuts, or the like. When rationalizing this method, the acoustic material itself does not have the function or strength as a structural material. Simply combining a metal structural face material to provide the acoustic material with strength as a structural material inevitably increases weight and reduces sound absorption performance.

[0006] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a technique for achieving weight reduction of an acoustic material having a function as a structural material and a structure using the same. Means for Solving the Problem

[0007] To solve the above problems, an acoustic structural material according to one aspect of this disclosure is: A surface portion having a sound-absorbing layer that absorbs sound waves, It comprises a back portion joined to the back of the surface portion, The rear portion is characterized by having two plate-like members made of fiber-reinforced plastic and a reflective layer sandwiched between the two plate-like members.

[0008] Furthermore, a structure relating to one aspect of this disclosure is, Frame members and The present invention is characterized by comprising the acoustic structural material coupled to the frame member. [Effects of the Invention]

[0009] According to this disclosure, it is possible to achieve weight reduction of acoustic materials that have the function of structural materials and structures that use them. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a cross-sectional view of an acoustic structural material according to one embodiment of the present disclosure. [Figure 2] Figure 2 is a cross-sectional view of an acoustic structural material according to a modified example in which the surface portion consists of multiple sound-absorbing layers. [Figure 3] Figure 3 shows an example of how acoustic structural materials are used as components of a structure. [Figure 4] Figure 4 shows an example of how conventional acoustic materials are used as structural components. [Modes for carrying out the invention]

[0011] Next, embodiments of the present disclosure will be described with reference to the drawings. Figure 1 is a cross-sectional view of an acoustic structural material 1 according to one aspect of the present disclosure. The acoustic structural material 1 shown in Figure 1 is a plate-shaped member that combines the functions of an acoustic material and a structural material. Acoustic materials refer to sound-absorbing materials that absorb sound waves and sound-insulating materials that block sound waves, and the acoustic structural material 1 according to the present disclosure has the functions of both a sound-absorbing material and a sound-insulating material. Structural materials are members that become components (structural materials) of structures such as buildings, ship hulls, car bodies, and aircraft bodies. Since structural materials are subjected to loads, they are required to have higher strength and bending rigidity compared to non-structural members.

[0012] The acoustic structural material 1 is made up of a laminated surface portion 2 and a back portion 4. The back portion 4 is joined to the back of the surface portion 2, and the surface portion 2 and the back portion 4 are integrated. The surface portion 2 is visible on the surface of the acoustic structural material 1, and the back portion 4 is visible on the back.

[0013] The surface portion 2 has a sound-absorbing function that absorbs sound waves and attenuates reflected waves. The constituent materials and structure of the surface portion 2 are preferably selected according to the manner in which the acoustic structural material 1 is used. The acoustic structural material 1 according to this disclosure is intended for use in water, and the surface portion 2 is made of a bubble-dispersed viscoelastic material and has the function of absorbing sound waves and attenuating reflected waves in water. The bubble-dispersed viscoelastic material is a viscoelastic material such as rubber or rubber-like resin in which a large number of fine bubbles are dispersed substantially uniformly inside. The bubble-dispersed viscoelastic material may be a foam. Alternatively, the surface portion 2 may be made of a porous structure viscoelastic material. The thickness of the surface portion 2 is preferably about 1 / 4 to 1 / 16 of the wavelength of the highest frequency in the frequency band to be attenuated. The index value K0 (K0 = inherent acoustic impedance value of surface portion 2 / inherent acoustic impedance value of water), which is expressed with respect to the inherent acoustic impedance value of water, is preferably 0.5 or more and 0.9 or less.

[0014] As shown in Figure 2, the surface portion 2 may have a laminated structure consisting of two or more types of sound-absorbing layers A with different intrinsic acoustic impedance values. Here, n is a real number, and the larger the value of n, the closer it is to the back portion 4. In the example shown in Figure 2, n=3. For example, the intrinsic acoustic impedance value of the first sound-absorbing layer A1 is greater than the intrinsic acoustic impedance value of the nth sound-absorbing layer An. Furthermore, the index value K1 (K1 = intrinsic acoustic impedance value of the first sound-absorbing layer A1 / intrinsic acoustic impedance value of water), expressed with respect to the intrinsic acoustic impedance value of water, is preferably between 0.5 and 0.9. Similarly, the index value Kn (Kn = intrinsic acoustic impedance value of the nth sound-absorbing layer An / intrinsic acoustic impedance value of water), expressed with respect to the intrinsic acoustic impedance value of water, is preferably between 0.5 and 0.9. In other words, the difference in the inherent acoustic impedance values ​​between the first sound-absorbing layer A1 on the surface and water is small enough to suppress sound wave reflection, while the difference in inherent acoustic impedance values ​​between the nth sound-absorbing layer An and water is larger. For example, if the index value K1 is 0.9, then the index value Kn is 0.7. Furthermore, the index value Kn-1 of the (n-1)th sound-absorbing layer An-1 is greater than the index value Kn of the nth sound-absorbing layer An. Here, the index value Kn-1 is the inherent acoustic impedance value of the (n-1)th sound-absorbing layer An-1 / the inherent acoustic impedance value of water. Since the inherent acoustic impedance value is expressed as the density of the medium × the speed of sound in the medium, the density of the surface 2 is greater than the density of water, and the density of the (n-1)th sound-absorbing layer An-1 is greater than the density of the nth sound-absorbing layer An.

[0015] Returning to Figure 1, the back portion 4 serves as a base for supporting the front portion 2, providing the acoustic structural material 1 with structural strength and bending rigidity. The back portion 4 also has a sound absorption function that absorbs sound waves, and a sound insulation function that blocks and reflects sound waves. The back portion 4 is made up of a first FRP plate 41, a reflective layer 43, and a second FRP plate 42, laminated in this order. The first FRP plate 41, the reflective layer 43, and the second FRP plate 42 are joined together to form an integrated structure. For example, the first FRP plate 41 and the reflective layer 43, and the reflective layer 43 and the second FRP plate 42 may be joined by adhesive. The first FRP plate 41 is joined to the front portion 2. For example, the first FRP plate 41 and the front portion 2 may be joined by adhesive.

[0016] The first FRP plate 41 and the second FRP plate 42 are plate-shaped members made of fiber-reinforced plastics (FRP). Fiber-reinforced plastics are reinforced plastics whose strength is improved by compounding fibers such as glass fibers, resin fibers, and carbon fibers with epoxy resins or phenolic resins. Fiber-reinforced plastics have a higher specific strength than metal materials and can be made lighter. The individual thicknesses of the first FRP plate 41 and the second FRP plate 42 are preferably about 1 / 4 to 1 / 16 of the wavelength of the highest frequency in the frequency band to be attenuated.

[0017] The reflective layer 43 has the function of absorbing sound waves and attenuating reflected waves. The reflective layer 43 according to this disclosure is made of a bubble-dispersed viscoelastic material or a porous structure viscoelastic material, similar to the surface 2. The thickness of the reflective layer 43 is preferably about 1 / 16 to 1 / 32 of the wavelength of the highest frequency in the frequency band to be attenuated. In other words, the thickness of the reflective layer 43 is about the same as or smaller than that of the surface 2. The index value KR (KR = reflective layer 43's reflective impedance value / water's reflective impedance value), which expresses the reflective layer 43's inherent acoustic impedance value relative to the water's inherent acoustic impedance value, is preferably 0.2 or more and 0.4 or less. In other words, the reflective layer 43's inherent acoustic impedance value is smaller than the surface 2's inherent acoustic impedance value. In other words, the density of the reflective layer 43 is smaller than the density of water, and the density of the reflective layer 43 is smaller than the density of the surface 2.

[0018] The back surface portion 4 is lighter in weight than an FRP plate of the same thickness because the reflective layer 43 is interposed between the first FRP plate 41 and the second FRP plate 42. In this way, the back surface portion 4 achieves the thickness required to provide the bending strength demanded of the back surface portion 4 with a lighter weight structure.

[0019] Here, the acoustic function of the acoustic structural material 1 having the above configuration will be described. Sound waves are incident from the outside onto the surface portion 2, which is the surface of the acoustic structural material 1. Part of the sound waves incident on the surface portion 2 is absorbed by the surface portion 2, another part is reflected by the surface portion 2, and the remainder transmits through the surface portion 2. The first FRP plate 41 and the second FRP plate 42 of the back surface portion 4 reflect sound waves while absorbing them. Part of the sound wave that has transmitted through the surface portion 2 is reflected by the first FRP plate 41 and absorbed again by the surface portion 2, and the remainder enters the back surface portion 4. Part of the sound wave that has entered the back surface portion 4 is reflected by the first FRP plate 41 and the second FRP plate 42, remains between the first FRP plate 41 and the second FRP plate 42, and is absorbed by the reflective layer 43. In this way, the back surface portion 4 absorbs the incoming sound waves and suppresses the transmission of sound waves to the back side of the acoustic structural material 1. Due to the transmission suppression and reflection of sound waves by the back surface portion 4, sound wave attenuation based on phase difference is also achieved.

[0020] Next, application examples of the acoustic structural material 1 will be described. FIG. 3 is a diagram showing an installation example of the acoustic structural material 1. In the example shown in FIG. 3, the acoustic structural material 1 is used as a structure 10 that forms the surface of a structure. The structure 10 includes a frame member 5 serving as a framework, and the acoustic structural material 1 is attached to the frame member 5. The acoustic structural material 1 is arranged such that the second FRP plate 42 of the back surface portion 4 forming the back side of the acoustic structural material 1 is in contact with the frame member 5.

[0021] Figure 4 shows a conventional acoustic material 101 as an element of a structure. In the conventional example shown in Figure 4, the structural body 10A comprising a frame member 5 and a metal panel 102, the metal panel 102 being fixed to the frame member 5 and the acoustic material 101 being bonded to the metal panel 102. Compared with such a conventional combination of metal panel 102 and acoustic material 101, the acoustic structural material 1 according to this disclosure has equivalent or greater strength and bending rigidity, while the structural body 10 can be made lighter by omitting the metal panel 102.

[0022] [Summary] As explained above, the acoustic structural material 1 relating to this disclosure is A surface portion 2 having a sound-absorbing layer that absorbs sound waves, It comprises a back portion 4 joined to the back of the front portion 2, The back portion 4 is characterized by having two plate-like members made of fiber-reinforced plastic (first FRP plate 41, second FRP plate 42) and a reflective layer 43 sandwiched between the two plate-like members 41 and 42.

[0023] In the acoustic structural material 1 with the above configuration, the surface portion 2 provides the function of a sound-absorbing material, and the back portion 4 provided on the back of the surface portion 2 provides the function of a structural material. The back portion 4 has a so-called sandwich structure, in which a lightweight reflective layer 43 is sandwiched between a first FRP plate 41 and a second FRP plate 42 to form an integrated structure. Compared to the case in which a metal plate is used as the back portion 4, the back portion 4 having such a sandwich structure can be lighter and have greater bending rigidity. Therefore, according to this disclosure, it is possible to provide an acoustic structural material 1 which is a planar acoustic material that has the strength and bending rigidity of a structural material and achieves weight reduction.

[0024] Furthermore, the back portion 4 functions as both a sound-absorbing and sound-insulating material because sound waves reflected by the first FRP plate 41 and the second FRP plate 42 are absorbed by the reflective layer 43. Therefore, the acoustic structural material 1 has excellent sound-insulating and sound-absorbing functions.

[0025] In the acoustic structural material 1 with the above configuration, the surface portion 2 may have a density greater than that of water.

[0026] In the acoustic structural material 1 with the above configuration, the back portion 4 may have a lower density than the front portion 2.

[0027] This reduces the weight of the rear section 4, which contributes to reducing the weight of the acoustic structural material 1.

[0028] In the acoustic structural material 1 with the above configuration, the surface portion 2 has a structure in which the density changes in a gradient, and in order to realize this structure, it may have a laminated structure of any n sound-absorbing layers A. Here, the closer the sound-absorbing layer A is to the back portion 4, the lower the density. For example, the density of the (n-1) sound-absorbing layer An-1 is greater than the density of the nth sound-absorbing layer An.

[0029] This allows for higher sound absorption performance compared to the case where the surface portion 2 is formed from a single type of sound-absorbing layer A.

[0030] In the acoustic structural material 1 with the above configuration, the surface portion 2 may be made of a bubble-dispersed viscoelastic material or a porous structure viscoelastic material. In this acoustic structural material 1, the surface portion 2 has a (n-1) sound-absorbing layer An-1 and an nth sound-absorbing layer An laminated on the back side of the (n-1) sound-absorbing layer An-1, and the (n-1) sound-absorbing layer An-1 and the nth sound-absorbing layer An have a higher density than water, and the (n-1) sound-absorbing layer An may also have a higher density than the nth sound-absorbing layer An.

[0031] The above-described acoustic structural material 1 is suitable for use in absorbing sound waves underwater. Such an acoustic structural material 1 can be used, for example, as a structural outer material for a ship's hull or an underwater vehicle.

[0032] Furthermore, a structure 10 according to one aspect of this disclosure comprises a frame member 5 and an acoustic structural member 1 coupled to the frame member 5.

[0033] According to the structure 10 with the above configuration, the acoustic structural material 1 combines the functions of a structural material and an acoustic material made of metal, so the structure 10 can be made lighter compared to when the acoustic material and the structural material are separate components.

[0034] The above disclosures are presented for illustrative and explanatory purposes only and are not intended to limit this disclosure to the forms disclosed herein. For example, the features included in this disclosure can be combined with alternative embodiments, configurations, or aspects other than those discussed above. [Explanation of Symbols]

[0035] 1: Acoustic structural material 2: Surface part 4: Back part 5: Frame members 10 :Structure 41: First FRP plate (plate-shaped member) 42: Second FRP plate (plate-shaped member) 43: Reflective layer A: Sound-absorbing layer

Claims

1. A surface portion having a sound-absorbing layer that absorbs sound waves, It comprises a back portion joined to the back of the surface portion, The back portion has two plate-like members made of fiber-reinforced plastic and a reflective layer sandwiched between the two plate-like members. Acoustic structural materials.

2. The aforementioned surface portion has a higher density than water. The acoustic structural material according to claim 1.

3. The surface portion is made of a foam-dispersed viscoelastic material or a porous structure viscoelastic material. The acoustic structural material according to claim 1 or 2.

4. The back portion has a lower density than the front portion. The acoustic structural material according to claim 1.

5. The surface portion has a laminated structure consisting of multiple sound-absorbing layers, with the density of the sound-absorbing layers being lower closer to the back portion. The acoustic structural material according to any one of claims 1 to 3.

6. Frame members and The system comprises an acoustic structural member according to any one of claims 1 to 5, which is coupled to the frame member, structure.

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