Effect of an open hole on static strength and its temperature dependence

This section discusses the ratio of static OH strength to static NH strength and its temperature dependence, where this ratio is calculated from the mean strength based on the test results in Table2 or Fig. 3. Since the cross section of OH specimens was equal to that of NH specimens and the static strength was represented by the net section stress in this study, the experimental results are directly comparable.

Table 5 shows the ratios of the mean OH strength SUO to the mean NH strength SUN, where SUO is represented by the net section stress, calculated from the data at RT and 150°C.


r = UO (3)

‘ notch


This table indicates that an open hole greatly reduces static strength for both tensile and compressive loading...


Detailed discussion of test results

1.1 Fiber-dominant strength, matrix-dominant strength, and failure modes

As described above, static tensile strength and tension fatigue strength are predominantly fiber-dominant, and static compressive strength and compression and tension-compression fatigue strengths are matrix-dominant. This section discusses the fiber-dominant and matrix-dominant characteristics of static and fatigue strengths based on observations of specimen failure and failure modes. The mechanical properties of carbon fibers are considered to be constant over the range from RT to 215°C. Moreover, since no signs of fatigue damage were found in the fibers themselves, any fatigue strength reduction of carbon fibers can be left out of consideration...


Tension-compression fatigue strength

Fig. 6 shows the static OHC strength and S-N relationship obtained from tension – compression fatigue tests for R=-1 at RT and 150°C. Since compression load repetition greatly influences fatigue life in tension-compression fatigue tests, as described later, static OHC strength was plotted at N=1 as in the case of compression fatigue. According to the S – N lines at RT and 150°C and the Ъ values in Table 4, Smax apparently decreases with increasing N. Moreover, there is an apparent difference between the two S-N relationships at RT and 150°C, as was the case in the compression fatigue tests. The tension-compression fatigue strength is strongly dependent on temperature and the number of load cycles, as in the compression fatigue tests.

Furthermore, these S-N lines pass fairly above their...


Compression fatigue strength

Fig. 5 presents the static OHC strength and S-N relationships obtained from compression fatigue tests for R=10 at RT and 150°C. From the two S-N lines in this figure and the Ъ or Ъ/a values in Table 4, compression fatigue strength Smin at RT and 150°C drops considerably with the increase in the number of load cycles N. Moreover, there is a clear difference between the two S-N lines at RT and 150°C. However, as N becomes larger, the difference between the lines tends to decrease.

The values of intersection a in Table 4 are very close to the highest values of static compressive strength plotted at N=1 for the RT and 150°C conditions, and higher than their mean in Table 2...


Fatigue strength of OH specimens

Let us examine S-N (stress-life) relationships on semi-logarithmic graph paper based on net section stress, placing the maximum stress Smax on the ordinate and the logarithm of fatigue life logN on the abscissa, where N is the number of load cycles to failure. In compression fatigue, the minimum stress Smin is used instead of Smax on the ordinate. If N is assumed to be an independent variable on the S-N diagram, Smax will be a dependent variable and can be regarded as fatigue strength. OH static strength is plotted as Smax at N=1 to compare it with fatigue strength. An S-N relationship is assumed to be linear on semi-logarithmic graph paper. The S-N line approximating only S-N data is determined by the least-squares method.

The S-N equation is represented by

Smax = a – b • log N (2)



Static strength of NH and OH specimens

Fig. 3 shows non-hole tensile (NHT) strength, non-hole compressive (NHC) strength, open – hole tensile (OHT) strength, and open-hole compressive (OHC) strength at RT and high temperatures, where OH strength is represented by net section stress, as described above. Since these tests were carried out to determine their temperature dependence, only a few specimens were tested for each case, as shown in Table 1. The relationship between static strength and temperature is represented by a solid line, which connects the mean strength at every test temperature. When there is only one test result, this value is taken as the mean. NHT strength at 150°C is slightly lower than that at RT. Although this fact is strongly influenced by the lowest value measured at 150°C (Fig...


. Test results

Table 2 presents the numerical data of static strength Su and its mean Su, while Table 3 presents fatigue life data. These data were systematically obtained as described above and are expected to be used for the reference or comparison data for conventional CF/BMI composite materials and new CF/BMI materials recently developed for low-cost and out-of­autoclave manufacturing such as those produced by a VaRTM (Vacuum assisted Resin Transfer Molding) method.



Temp. (°C)

Strength Su


Mean Su (MPa)



RT (23)

1016, 1060, 1116, 1126



871, 1000, 1033



RT (23)

834, 884, 899






651, 652, 659










RT (23)

704, 724




Material, specimens and testing procedures

The prepreg system used is a combination of G40-800 CF and 5260 toughened BMI resin made by CYTEC Co. The lamination has a quasi-isotropic (QI) stacking sequence, 32 plies [45/0/-45/90]^. The nominal thickness of 4.29 mm (0.134 mm x 32) was used in calculating stress on specimens. Laminate panels were cured in an autoclave at 190°C for two hours at a pressure of 6.0 kgf/cm2 and post-cured at 215°C for four hours in an air-circulating oven. All panels were cured at the same time.

(c) Common specimen for OHT and OHC static and fatigue tests Fig. 1. Specimen configurations for static and fatigue tests (mm)

Fig. 1 (a) and (b) illustrate specimen configurations for NH tensile and compressive static tests. Fig...


G40-800/5260 Carbon Fiber/Bismaleimide Composite Material: High Temperature Characteristics of Static and Fatigue Strengths

Toshiyuki Shimokawa1, Yoshiaki Kakuta2 and Takenori Aiyama3 formerly Tokyo Metropolitan Institute of Technology, 2Japan Aerospace Exploration Agency, 3Toyota Motor Corporation Japan

1. Introduction

A lot of polymer composite materials are being used in the structures of civil transport aircraft currently under development, such as the Boeing 787, Airbus A350, and Bombardier C Series. Their percentages of structural weight are announced at 50%, 53% and 46%, respectively. However, mostly carbon fiber/epoxy (CF/Ep) systems are being introduced into their primary structures and they are only being introduced in environments where they are not expected to encounter high temperature...


Lightweight Unfolded Composite Materials Acquiring Stability of the Shape due to Factors of Space Environment

Laricheva V. P.

Branch of FSUE "Karpov Institute of Physical Chemistry"

Obninsk, Kaluga Region, Russia

1. Introduction

In this article it is discussed the compact-packed materials, which acquire rigidity under the exposure to ionizing radiation. The prepreg materials, additionally curable under the irradiation exposure, can be used for the fabrication of large-size products (for example, supporting constructions of the large space antennas of space transport vehicles and aircrafts, protective shields of spacecraft and shielding constructions on the lunar surface); they can be transformed in the space environment and acquire rigidity (stability of form) under the influence of space factors (UV radiation, vacuum)...