An Evaluation of the Sandwich Beam Compression Test Method for Composites

Abstract

This report evaluates the sandwich beam in four-point bending as a compression test method for advanced composites. To accomplish this evaluation the test method was used to obtain preliminary compressive design data for the temperature range 117 to 589 K (−250 to 600°F) and was analyzed to determine any influence from the honeycomb core on composite mechanical properties. The [08], [908], [(±45)2]s, and [0/±45/90]s laminate orientations were investigated utilizing HTS1/PMR-15 graphite/polyimide composite material. The experimental and analytical results indicated that the test method can be used to obtain compressive elastic constants for graphite/polyimide composites. Elastic data were obtained for a wide temperature range, although many failures were initiated by either load concentrations or top cover debonds. The analysis indicated that the honeycomb core had negligible effects on composite mechanical properties. The top cover carried essentially all the compressive load in the beam test section, and the stress state in the test section of the top cover was essentially uniform and uniaxial.

Evaluation of Compressive Nonlinear Response of Unidirectional Carbon Fiber Reinforced Composites using a Modified Sandwich Beam Specimen in Flexure

“…As reported by Shuart [13], sandwich beam construction in flexure gives a good approximation of a uniaxial stress state in the skin laminate. The following items should be taken into account in the development of the test method:…”

“…Shuart [13] found that sandwich specimens were susceptible to crushing of the honeycomb core or debonding of the skin; although he claimed that this test method provides a good approximation of a uniaxial state of stress if the stiffness of the honeycomb is negligible. Sandwich specimens with unidirectional 08 skins exhibit these unwanted failure modes.…”

“…Contrary to side loaded coupon-type testing, ASTM D 5467 [12] includes a method for measuring compressive strength using a sandwich beam specimen that consists of thin composite skins and a honeycomb core loaded in four-point bending. Shuart [13] found that sandwich specimens were susceptible to crushing of the honeycomb core or debonding of the skin; although he claimed that this test method provides a good approximation of a uniaxial state of stress if the stiffness of the honeycomb is negligible. Sandwich specimens with unidirectional 08 skins exhibit these unwanted failure modes.…”

A Reusable Sandwich Beam Concept for Composite Compression Test

“…ANALYSIS Subjecting the sandwich beam to four-point bending induces a constant moment throughout the test section, which is statically equivalent to a coupled force. This coupled force loads the faces in tension and compression [3]. Most of the load is carried by the faces, but there is a small portion carried by the plexiglass (Figure 3).…”

Design of an improved four point bending test on a sandwich beam for free edge delamination studies

“…7) testing procedures; † or subjecting a honeycomb core sandwich beam with a thin composite skin to four point bending: ASTM D5467(Fig. 8)[23,24,25].…”