Coupon geometries that induce failure in gauge area of composite fatigue test coupons

Patent metadata

Field	Value
Publication number	US-9046450-B2
Application number	US-201313769485-A
Country	US
Kind code	B2
Filing date	Feb 18, 2013
Priority date	Feb 18, 2013
Publication date	Jun 2, 2015
Grant date	Jun 2, 2015

Abstract

A coupon geometry that reliably fails in the gauge area of the coupon during fatigue testing. The propensity to fail at the gauge area is imparted by using a bow-tie-shaped coupon coupled with similarly shaped tabs. The test coupons have a bow-tie-shaped profile with tapered sides that converge as they extend from the opposing ends of the coupon to the gauge area, forming a pair of trapezoidal portions (one the mirror image of the other) connected by the gauge area. These trapezoidal portions of the test coupon include the regions where similarly trapezoidal tabs will be adhered to the front and back of the coupon. The test coupon has a minimum width in the gauge area and a constant thickness, and a height of the gauge area is no greater than 3% of a height of the test coupon.

First claim

The invention claimed is:

1. A test coupon assembly comprising:
a test coupon comprising a multiplicity of plies made of fiber-reinforced plastic material laminated together to form a laminate of constant thickness, said test coupon having a geometry comprising first and second trapezoidal portions connected by a gauge area having a coupon minimum width, said first and second trapezoidal portions and said gauge area forming respective portions of a front face and respective portions of a rear face of the test coupon, each of said front and rear faces having a bow-tie-shaped profile and being parallel to said plies;
first and second tabs adhered to said first trapezoidal portion on respective first portions of said front and rear faces; and
third and fourth tabs adhered to said second trapezoidal portion on respective second portions of said front and rear faces,
wherein each of said first through fourth tabs is made of fiber-reinforced plastic material, each of said first through fourth tabs has a trapezoidal profile, said test coupon has a minimum width in said gauge area and a constant thickness, said first trapezoidal portion comprises first and second straight tapered sides, said second trapezoidal portion comprises third and fourth straight tapered sides, said gauge area comprises first and second radiused sides, said first radiused side is connected to said first and third straight tapered sides, said second radiused side is connected to said second and fourth straight tapered sides, and a height of said first radiused portion is no greater than 3% of a height of the test coupon.

2. The test coupon assembly as recited in claim 1 , wherein said first and second straight tapered sides diverge from each other and said third and fourth straight tapered sides diverge from each other as said first through fourth straight tapered sides extend away from said gauge area.

3. The test coupon assembly as recited in claim 1 , wherein said first and third straight tapered sides are tangent to said first radiused side of said gauge area at respective intersection points of said first and third straight tapered sides with said first radiused side, and said second and fourth straight tapered sides are tangent to said second radiused side of said gauge area at respective intersection points of said second and fourth straight tapered sides with said second radiused side.

4. The test coupon assembly as recited in claim 1 , wherein taper angles of said first through fourth straight tapered sides are equal.

5. The test coupon assembly as recited in claim 4 , wherein the taper angle is in a range of 1 to 10 degrees inclusive.

6. The test coupon assembly as recited in claim 1 , wherein radii of said first and second radiused sides are equal.

Assignees

• Boeing Co

Inventors

• Lee Mitchell J
• Kimball Nicklaus Cummings

Classifications

• G01N2203/0073

  Fatigue · CPC title

• G01N3/60 Primary

  Investigating resistance of materials, e.g. refractory materials, to rapid heat changes {(thermal testing of structures or apparatus G01M99/002)} · CPC title

• G01N3/02 Primary

  Details · CPC title

• G01N3/08

  by applying steady tensile or compressive forces (G01N3/28 takes precedence) · CPC title

• G01L5/0095 Primary

  measuring work or mechanical power · CPC title