Blast/impact frequency tuning and mitigation

Patent metadata

Field	Value
Publication number	US-9958238-B2
Application number	US-201415036293-A
Country	US
Kind code	B2
Filing date	Nov 14, 2014
Priority date	Nov 14, 2013
Publication date	May 1, 2018
Grant date	May 1, 2018

Abstract

A protective device and method of design to protect against multiple blast and impact events for use in any application in which a delicate target has to be protected. The protective device for mitigating the effects of blast or impact employs a first layer having a first acoustic impedance and a second layer having a second acoustic impedance. The second acoustic impedance is different than the first acoustic impedance. The second layer is proximate to the first layer. The first layer and the second layer are chosen collectively to tune the stress waves from the blast or impact events to one or more specific tuned frequencies. A third layer of a visco-elastic material is employed having a critical damping frequency that matches one or more specific tuned frequencies to dissipate the stress waves of the blast and impact event. The third layer is proximate to the second layer.

First claim

What is claimed is:

1. A protective device for mitigating stress waves resulting from a blast or impact, said protective device comprising:
a first layer having a thickness, h 1 , and having a first acoustic impedance, being made of a linear-elastic material having a first modulus, E 1 , and a first density, ρ 1 ;
a second layer having a second acoustic impedance being made of an elastic material having a second modulus, E 2 and a second density, ρ 2 , said second acoustic impedance being less than said first acoustic impedance such that a ratio of the first acoustic impedance to the second acoustic impedance being expressed as √{square root over (E 1 ρ 1 )}>>√{square root over (E 2 ρ 2 )} and is greater than seventy (70), said second layer being proximate to said first layer along an interface, said first layer and said second layer are collectively configured to tune the stress waves resulting from the blast or impact to a specific tuned frequency of f 1 =√{square root over (E 1 /ρ 1 )}/2h 1 with a portion of the stress wave being reflected back toward the first layer at the interface and a portion of the stress wave at the specific tuned frequency being transmitted through the second layer, the reflected portion of the stress wave being greater than the transmitted portion of the stress wave; and
a third layer being made of a visco-elastic material having a critical damping frequency that matches the specific tuned frequency, said third layer being proximate to said second layer and receiving and dissipating the transmitted portion of the stress wave, the third layer being configured such that a period of the critical damping frequency is substantially equal to a time for the reflected portion of the stress wave to traverse the first layer, with a ratio of an unrelaxed modulus to a relaxed modulus of the third layer being greater than ten (10), and a thickness, h 3 , being greater than five (5) times the wavelength of the tuned stress wave in the third layer so as to ensure significant damping.

2. The protective device according to claim 1 wherein said first layer and said second layer are collectively configured to tune stress waves resulting from the blast or impact to said specific tuned frequency using geometrical parameters.

3. The protective device according to claim 1 wherein said first layer and said second layer are collectively configured to tune stress waves resulting from the blast or impact to said specific tuned frequency using material parameters.

4. The protective device according to claim 1 wherein said first layer and said second layer are collectively configured to allow passage of said specific tuned frequency to said third layer, whereby said specific tuned frequency is visco-elastically dissipated in said third layer.

5. The protective device according to claim 1 wherein said third layer is made of a material sufficient to visco-elastically dissipate a plurality of cycles of the specific tuned frequency.

6. The protective device according to claim 1 wherein said third layer is made of a material sufficient to visco-elastically recover within the time scale of the cyclic loading of the specific tuned frequency.

7. The protective device according to claim 1 wherein a thickness of said third layer is sufficient that the presence of stress wave of said specific tuned frequency substantially decay before passage of said stress wave through said third layer.

8. The protective device according to claim 1 wherein said second layer is joined to said first layer.

9. The protective device according to claim 1 wherein said third layer is joined to said second layer.

10. The protective device according to claim 1 wherein said first layer and said second layer are collectively configured to increase a time scale of the stress waves resulting from the blast or impact.

Assignees

• Univ Michigan Regents

Inventors

• Thouless Michael
• Arruda Ellen M
• Rahimzadeh Tanaz
• Waas Anthony M

Classifications

• B32B15/08

  of synthetic resin · CPC title

• F41H5/04 Primary

  composed of more than one layer {(outerwear resistant to mechanical aggressions A41D31/24; layered products B32B; shaping reinforced articles B29C67/00)} · CPC title

• F42D5/045

  Detonation-wave absorbing or damping means · CPC title

• B32B2307/10

  having particular acoustical properties · CPC title

• B32B2571/00

  Protective equipment · CPC title