Direct measurement of axial compressive strength of carbon fibers using multifilament method

Abstract

To measuring the compressive strength of carbon fibers accurately and effectively, a specially designed fixture was applied for directly measuring axial compressive strength of carbon fibers using T800HB‐12 K multifilament. Influence of adhesive thickness and specimen length on the testing results was investigated. Adhesive of epoxy effectively transferred compressive stress from the fixture to the specimen and provided enough support of multifilament rod from bending during compressive load. Typical shear failure for multifilament rod was realized for T800HB‐12 K carbon fibers during compression testing using the purposely designed fixture at adhesive thickness of 0.101–0.110 mm and test length of 2.0–3.0 mm. Compressive strength of about 2700 MPa with variation coefficient of 8% was obtained for T800HB‐12 K carbon fibers. The fixture and method established were capable for characterizing axial compressive strength of 1–24 K carbon fibers.

Effects of anisotropy and off‐axis angle on buckling behavior of carbon/epoxy Z‐pin under axial pressure

“…Since the tensile modulus E t is often substituted into the Euler formula to predict the axial buckling load of single carbon fiber [14][15][16][17][18][19][20] or composite strands [20][21][22][23] under axial compression, the theoretical deviation caused by the neglect of compression modulus E c and shear modulus G 12 is discussed. In order to intuitively reflect the instability performance of Z-pins with different aspect ratios λ, the buckling loads are substituted into Equation ( 2) and converted into the apparent bending modulus E f_ap .…”

“…The Euler formula is widely used at home and abroad to predict and analyze the axial compression performance of single carbon fiber [14][15][16][17][18][19][20] and composite strands. [20][21][22][23] Its application is mainly divided into the following two aspects. (1) Strength test of small length-diameter ratio pressure bar.…”

“…(1) Strength test of small length-diameter ratio pressure bar. [14][15][16][17][18][19][20][21]23 The Euler formula was used to predict the critical instability aspect ratio, shorten the length of the pressure bar, and ensure the compression failure of the sample. (2) Buckling test of pressure bar with large length-diameter ratio.…”

“…Its application is mainly divided into the following two aspects. (1) Strength test of small length‐diameter ratio pressure bar 14–21,23 . The Euler formula was used to predict the critical instability aspect ratio, shorten the length of the pressure bar, and ensure the compression failure of the sample.…”

“…The theoretical deviation caused by the neglect of compression modulus and shear modulus is unknown and leads to the following two problems. First, scholars have differing views on selecting Young's modulus 14–23 . According to the works of References 14–18,20–23, they directly substituted the tensile modulus into the Euler formula because it was easy to obtain or measure.…”