Effects of aging process and testing temperature on the open-hole compressive properties of a carbon fiber composite

Abstract

The properties of T800 carbon fiber–epoxy composite specimens with a hole were studied in terms of mass change, scanning electron microscopy, glass transition temperature (T _g), heat-resistant temperature, Fourier-transform infrared (FTIR) spectroscopy, open-hole compressive strength at different temperatures, and stereomicroscopic observations after being subjected to hygrothermal aging and thermal-oxidative aging processes. FTIR spectra indicated that after hygrothermal aging at 70°C and 85% relative humidity (RH), chemical aging did not occur, whereas after thermal-oxidative aging at 190°C, the specimens exhibited chemical aging. The unaged specimens had a T _g of 229°C and an extreme heat-resistant temperature T _gmod of 184°C; after hygrothermal aging, the specimens had a T _g and T _gmod of 207°C and 143°C, respectively; and after thermal-oxidative aging, the specimens had a T _g and T _gmod of 252°C and 215°C, respectively. The effects of temperature on open-hole compressive strength were evaluated at room temperature of 23°C, 50°C, 100°C, 150°C, and 200°C. The compressive strengths of the specimens decreased after aging and with the increasing test temperature. At the highest test temperature, the unaged specimens, hygrothermal-aged, and thermal-oxidative-aged specimens retained over 73.7%, 65.5%, and 67.9%, respectively, of their compressive strength. Thus, the T800 carbon fiber–epoxy composite evaluated in this study exhibited good resistance to the effects of aging and high temperature. These results should be beneficial to the understanding of the long-term performance of composites.

Keywords

T800 carbon fiber–epoxy composite hygrothermal aging thermal-oxidative aging open-hole compressive strength glass transition temperature extreme heat-resistant temperature

Introduction

Carbon fiber-reinforced resin matrix composites exhibit an advantageously high specific strength ratio, stiffness, specific modulus, and fatigue resistance, as well as good extreme temperature resistance, impact resistance, and vibration damping performance, so they are widely used in aerospace vehicles as a high-performance composite material.^1

–5 The wet and hot environments to which these composite materials are exposed during usage in such applications are important causes of aging and inevitably result in a reduction in performance. Therefore, it is important to study and understand the change in the properties and behaviors of composites due to hygrothermal aging and thermal-oxidative aging.^6
–8

Furthermore, holes are often provided in composite structures for attachment and installation purposes, cutting the fibers and introducing serious stress concentrations at the hole edges.^9,10 Accordingly, the capacity of a composite structure to resist a compression load, which is the most common type of structural load, can be seriously reduced by the introduction of holes.^11,12 As a result, scholars have conducted a great deal of research into the performance of composite compression members with open holes.^13
–15 Research into the effects of holes in aged composites on compressive strength has, however, largely been limited to consistent test temperatures, neglecting the potentially major influencing factor such as loading temperature and loading conditions on the compressive strength of composites.^16
–18

The changes in the properties of composites with and without holes subjected to hygrothermal aging and thermal-oxidative aging have been studied extensively. Dao et al.¹⁹ studied the effect of long-term hot/wet aging under different temperatures and humidities on carbon fiber–epoxy composite. They observed that chemical changes appeared significant on the material surface and that the absorption of water reduced the glass transition temperature (T _g) of the carbon fiber composite. Ray²⁰ investigated the shear strength of carbon–epoxy and glass–epoxy composites after exposure to different hygrothermal temperatures, determining that hygrothermal aging influenced the moisture uptake kinetics and mechanical properties of the material and that the higher the hygrothermal aging temperature, the lower the interfacial adhesion within the material. Furthermore, as the hygrothermal aging temperature increased, the interlaminar shear strength of the material decreased. Kubota et al.²¹ studied the long-term compressive strength stability of carbon fiber-reinforced polyimide on exposure to high temperatures. They found that the composites maintained excellent compressive strength at temperatures of 240°C and 270°C but began to degrade at a temperature of 300°C due to the decrease in the transverse shear moduli of the surface plies.

Soutis²² researched the effect of hot and wet environments on the compressive and in-plane shear responses of carbon fiber–epoxy composite laminates and provided theoretically based predictions of the associated open-hole compressive strengths. Their results indicated that hot and wet conditions reduced the strength of the material, leading to through-the-thickness fiber microbuckling as the effects of temperature and environmental conditions reduced the matrix strength and weakened the interface between plies. Xu et al.²³ investigated the behavior of epoxy resin composites subjected to hygrothermal aging and thermal-oxidative aging, determining that hygrothermal aging caused physical aging, whereas thermal-oxidative aging caused both physical aging and chemical aging. Furthermore, they found that the samples subjected to hygrothermal aging exhibited a more serious decrease in open-hole compressive strength due to matrix swelling and plasticization.

The study of the open-hole compression performance of composite materials under wet and hot environments is an important part of the evaluation of their mechanical properties. Indeed, structural safety in wet and hot environments has become a key objective of the composite structure behavior verification.²⁴ Accordingly, in this study, tests were conducted on T800 carbon fiber–epoxy composite specimens equipped with a hole to determine the effects of hygrothermal aging and thermal-oxidative aging on the physical properties and behavior of the material was observed when loaded in compression under different temperatures. The aging behavior was studied by analyzing the change in mass, surface morphology, dynamic mechanical properties, and infrared spectra of the composite specimens. Open-hole compression tests were then conducted at room temperature of 23°C, 50°C, 100°C, 150°C, and 200°C to study the effects of testing temperature on the compressive strengths of the aged composites. By determining the open-hole compressive strengths of an aged composite under different temperatures, this study makes a meaningful contribution to the body of knowledge by providing basic reference data for the application of such composites in the aviation field, where they are often exposed to harsh environments, and provides a basis for further practical engineering-oriented research into the long-term behavior of composite materials.

Experimental procedures

Specimen preparation

The Liaoning Key Laboratory of Advanced Polymer Matrix Composites at Shenyang Aerospace University provided the T800 carbon fiber–epoxy resin composite laminate specimens, and the composite laminates were fabricated by prepreg. The carbon fiber is a domestic T800 and the basic in-plane stiffness and strength of the T800 carbon fiber–epoxy resin composite laminate under tensile and compressive loading are presented in Table 1.

Table 1.

Stiffness and strength properties of the T800 carbon fiber–epoxy laminate.

E_11T (GPa)	E_22T (GPa)	G_{12 T} (GPa)	$σ_{11 T}$ (MPa)	$σ_{22 T}$ (MPa)	$τ_{12}$ (MPa)
146	10.2	5.5	2500	45	75
E_11C (GPa)	E_22C (GPa)	$υ_{12}$	$σ_{11 C}$ (MPa)	$σ_{22 C}$ (MPa)
112	6.8	0.32	1450	238

The standard specimens evaluated in this study were 300 × 36 × 3.36 mm³ with 0.14-mm thick layers in a symmetrically balanced stacking sequence of (+45°/0°/−45°/90°)_{3 s} in accordance with ASTM D6484/D6484M-2014.²⁵ They were cured in an autoclave at 150°C for 2 h, 180°C for 2 h, and then postcured at 200°C for 5 h. A Φ6-mm round hole was then drilled in the center of each specimen using a composite engraving and milling machine with a special diamond drill bit, and then the edges of each hole were finely sanded to ensure that they were smooth and free of burrs. A specimen diagram is shown in Figure 1.

An SM-J3B-700 water-immersed ultrasonic C-scanning testing machine produced by the Beijing Institute of Aeronautical Materials was used for nondestructive testing to identify manufacturing defects (such as delaminations, internal cracks, and so on) in the cured prepreg panels and in the completed composite specimens with round holes. The SM-J3B-700 scanned on three axes at an ambient temperature of 20–30°C with a scanning accuracy of 0.05 mm. Only specimens that were qualified by the C-scanning test were subjected to the aging tests.

Hygrothermal aging

The specimens were placed in a Shanghai Yiheng Scientific Instrument Co. LHS-100CH constant temperature and humidity chamber in which the temperature was 70°C and the relative humidity was 85% for 40 days to provide hygrothermal aging. The resulting moisture absorption process was measured in accordance with the ASTM D5229-2014 standard test method for moisture absorption properties and equilibrium conditioning of polymer matrix composite materials.²⁶ The change in mass of each specimen was determined by weighing every day with ALC-210.4 analytical balance of Sartorius Scientific Instruments Co., Ltd (Beijing, China), and the moisture absorption was then determined by

M_{t} = \frac{m_{t} - m_{0}}{m_{0}} \times 100 %

where M_t (%) is the moisture absorption rate at time t, m_t (g) is the weight at time t, and m ₀ (g) is the weight before the hygrothermal aging test.

Thermal-oxidative aging

Using the artificial accelerated thermal-oxidative aging test method according to the T _g of the unaged specimens, determined as described in “Dynamic mechanical analysis” section,^27,28 thermal-oxidative aging was conducted in a DHG-9140A electrothermal constant temperature blast drying oven (Shanghai Linpin Instrument Stock Co., Ltd, Shanghai, China) at 190°C for 40 days. The change in mass was determined by weighing every day with the ALC-210.4 analytical balance of Sartorius Scientific Instruments Co., Ltd (Beijing, China), and the mass-loss rate was then calculated by

M_{loss} = \frac{W_{0} - W_{t}}{W_{0}} \times 100 %

where M _loss (%) is the mass loss rate, W ₀ (g) is the mass before aging, and W_t (g) is the mass at time t.

SEM observations

The observation surface of each specimen was sprayed with gold under vacuum and then observed before and after the aging processes using a Hitachi (Japan) SU3500 scanning electron microscope (SEM).

Dynamic mechanical analysis

Dynamic mechanical analysis (DMA) of the specimens was conducted using a DMA Q800 dynamic mechanical thermal analyzer in the single cantilever beam mode according to the ASTM D7028-2007 standard.²⁹ The frequency was 1 Hz, and the heating rate was 5°C min⁻¹.

FTIR analysis

A Fourier-transform infrared (FTIR) spectrum analysis was conducted using a spectrum 100 FTIR spectrometer (PerkinElmer Instruments Co., Ltd, Shanghai, China ) with a spectral range of 600–4000 cm⁻¹ at a resolution of 4 cm⁻¹.

Open-hole compressive strength tests

After 40 days of exposure to the aging environments, the specimens were subjected to open-hole compressive strength tests at room temperature of 23°C, 50°C, 100°C, 150°C, and 200°C. The tests were conducted using an Instron 5982 testing machine, with an antistability fixture providing boundary support, at a loading rate of 2 mm min⁻¹ in accordance with ASTM D6484/D6484M-2014.²⁵ The test results reported in this article are the average of five specimen tests.

Fracture morphology

Finally, a stereomicroscope was used to observe the fracture morphologies of the specimens following the compression tests.

Results and discussion

Mass change analysis

The weighing data were processed according to equations (1) and (2) to generate the moisture absorption and mass loss curves shown in Figure 2.

It can be seen in Figure 2 that in the initial stage of aging, both mass change rates increase sharply before gradually stabilizing in later stages. Hygrothermal aging first occurs as the moisture enters voids inside the composite material, readily infiltrating defects, such as bubbles and cracks in the initial stage of aging, rapidly increasing the mass. As aging progresses, these volumes become filled and the specimen reaches the saturation stage, indicating, in this case, an equilibrium moisture absorption rate of only about 0.73%.³⁰ Thermal-oxidative aging occurs in the initial stages with the evaporation of the moisture inside the composite specimen and the volatilization of low-molecular-weight substances on the surface, causing a sharp increase in the mass loss rate. With time, the specimen may undergo continued thermal aging and oxidation, but as all low-molecular-weight substances have already volatilized, the mass loss rate gradually stabilizes.²³

SEM analysis

As shown in Figure 3(a), massive areas of resin surround the fibers on the surface of the unaged composite. After hygrothermal aging, shown in Figure 3(b), the surface of the composite became smooth and some of the resin had shed. This may be because during hygrothermal aging, the resin expands with moisture absorption, but as the carbon fiber does not absorb moisture, the interface bond between the fiber and the resin weakens, destroying the surface of the composite specimen and deteriorating its mechanical properties.³¹ After thermal-oxidative aging, shown in Figure 3(c), voids and matrix cracks are present on the surface of the composite. As the thermal expansion coefficient of the fibers and the resin does not match, shrinkage stress is generated under prolonged exposure to high temperatures, causing these cracks at the interface between the materials and thus allowing oxygen to readily enter the material. This may accelerate the rate of thermal oxidation, leading to a decline in mechanical performance,³² as further discussed in “Open-hole compressive strength tests” section.

DMA analysis

The T _g is the temperature corresponding to the peak of the tan δ curve of a material, so it represents the highest temperature at which the composite remains rigid. The temperature at which the storage modulus drops rapidly is generally regarded as the extreme heat-resistant temperature (T _gmod) of the composite, at which the material can be used for a short period of time, but for long-term use, the temperature should be lower than T _gmod.³³

Figure 4(a) shows that the storage modulus and tan δ peak of the composite are lower after aging, this is possibly because the aging process destroys the van der Waals forces and hydrogen bonds between the molecules, resulting in a decrease in the force between macromolecular chains. This weakening allows these molecular chains to move, eventually causing the observed decline in the storage modulus of the composite.²⁰ The physical aging that may occur causes the bonds between molecules to become denser, increasing the cross-linking and eventually leading to a gradual decrease in loss of storage modulus.²³ After thermal-oxidative aging, the tan δ peak of the composite can be observed to be narrower because thermal aging at 190°C can cause both physical and chemical aging.

The unaged composite had a T _g of 229°C and a T _gmod of 184°C. After hygrothermal aging, the composite had a T _g of 207°C and a T _gmod of 143°C because the plasticization of the epoxy resin matrix of the composite material as it absorbed moisture from the hot and humid environment caused the interface properties to degrade.³⁴ After thermal-oxidative aging, the composite had a T _g of 252°C and a T _gmod of 215°C, both increased by the higher aging temperature of 190°C, which may accelerate the physical aging and postcure rate of the material.³⁵ The tan δ peak for the thermal-oxidative aged composite can be accordingly observed in Figure 4(b) to shift toward a higher temperature.³¹ This indicates that the T800 carbon fiber–epoxy composite material evaluated in this study has good resistance to aging.

FTIR analysis

As can be observed in Figure 5, the infrared spectrum of the composite after hygrothermal aging is basically the same as that of the unaged composite, except that the OH stretching vibration absorption peak near 3369 cm⁻¹ is higher due to the moisture absorbed by the specimen in the hot and humid environment. There is no change in the peak positions on the spectrum in other locations, and no new characteristic peaks are generated. This indicates that the composite material did not occur chemical aging during the hygrothermal aging process, no new substances were formed, and no chemical reactions occurred.³¹

After thermal-oxidative aging, the peak positions on the infrared spectrum are attenuated in Figure 5, and new peaks have been formed, indicating that chemical aging occurred.³⁶ During thermal-oxidative aging, the high-temperature exposure causes the evaporation of water in the specimen, resulting in the observed disappearance of the OH stretching vibration absorption peak near 3369 cm⁻¹. Due to the thermal aging effect, the =C–H stretching vibration absorption peak at 821 cm⁻¹, the C–O–C stretching vibration absorption peak at 1239 cm⁻¹, and the C=C stretching vibration absorption peaks on the benzene ring skeleton at 1505 and 1590 cm⁻¹ are all gradually reduced.³⁷ Thermal-oxidative aging also causes the C–O bonds to break, resulting in the disappearance of the C–O stretching vibration absorption peak at 1182 cm⁻¹. It is also possible that the presence of oxygen in the hot environment reacts with the resin matrix to form a new carbonyl group, resulting in the new carbonyl peak that appears at 1540 cm⁻¹.²³

Open-hole compressive strength tests

The open-hole compressive strengths of the specimens under different test temperatures are shown in Figure 6 and given in Table 2.

Table 2.

Open-hole compressive strengths of composite specimens at different test temperatures after aging under different processes.

Aging process	Test temperature (°C)	Compressive strength (MPa)	Strength retention (%)	Standard deviation (%)	Coefficient of variation (%)
Unaged	23	293	100.0	11.39	3.89
	50	270	92.2	10.43	3.87
	100	266	90.8	9.68	3.72
	150	248	84.6	13.05	5.26
	200	216	73.7	11.30	5.22
Hygrothermal	23	279	95.2	10.49	3.76
	50	254	86.7	13.69	5.38
	100	240	81.9	11.31	4.71
	150	221	75.4	16.85	7.63
	200	192	65.5	13.16	6.84
Thermal-oxidative	23	282	96.2	13.20	4.69
	50	263	89.8	13.87	5.27
	100	251	85.7	12.67	5.04
	150	230	78.5	14.72	6.41
	200	199	67.9	17.51	8.79

It can be seen from the figure that after either hygrothermal or thermal-oxidative aging, the open-hole compressive strengths of the specimens gradually decrease with the increase in the test temperature. The open-hole compressive strengths of the unaged specimens decrease less with increasing test temperature than those of the specimens aged in hygrothermal or thermal-oxidative environments. In all cases, after 100°C, the open-hole compressive strengths of the specimens decrease considerably. This may be because the polymer has a certain mechanical strength in the glass state, but as the temperature increases, the strength of the increasingly near-glass transition region decreases, resulting in degradation of the composite material performance.¹¹

By comparing the open-hole compressive strengths of the composite specimens at the same test temperature after exposure to different aging processes, it can be observed that the specimens exposed to hygrothermal aging exhibit more marked degradation in strength than those exposed to thermal-oxidative aging. The main reason for this trend may be that the compressive strength of a composite material is greatly affected by the properties of its matrix material. As discussed in terms of surface morphology in “SEM analysis” section, during the hygrothermal aging process, the infiltration of water has a plasticizing effect on the resin matrix, lowering its strength and resulting in a decrease in the strength of the composite material.^11,38 Additionally, the entry of moisture into the interface between the carbon fibers and the resin in the composite laminates destroys the interface, causing the load to be borne by either the matrix or fibers, but not shared between them, resulting in a further decrease in compressive strength,³⁹ as demonstrated by the fracture morphology observations in “Fracture morphology” section.

It can be seen from Table 2 that for unaged specimens, the open-hole compressive strength remains above 73.7% for all test temperatures; after hygrothermal aging, the open-hole compressive strength remains above 65.5% for all test temperatures; and after thermal-oxidative aging, the open-hole compressive strength remains above 67.9% for all test temperatures. Clearly, the hot and humid environment has a significant effect on the open-hole compressive strength of the composite material, but the retained strengths of the composite material specimens remained high after exposure to either aging process, indicating that the T800 carbon fiber–epoxy resin composite evaluated in this study provides good resistance to high temperatures.

Fracture morphology

The side profiles of the specimens were observed using a stereomicroscope and are shown in Figure 7.

From the fracture morphologies of the specimens shown in Figure 7, it can be observed that the failure modes of the open-hole compression test specimens under different test temperatures are basically the same regardless of the aging process. The side profile fractures mainly indicate shear failures accompanied by delamination and buckling characteristics.^23,31,40,41

The unaged specimen shows a small amount of increasing delamination as the test temperature increases, and the fractures are wedge shaped. After hygrothermal aging, the specimens mainly exhibit shear buckling failure. There are also large quantities of delamination at compression fracture under high temperatures after hygrothermal aging. This indicates that the interface properties of the composites have been degraded by exposure to hygrothermal aging. Thus, when the composite material is subjected to compression, the bonds between the laminations and between the carbon fibers and resin are weakened, and extensive delamination phenomena occur. These delamination phenomena become increasingly serious with the increasing test temperature. Finally, the thermal-oxidative aging samples also exhibit layered delamination and include fiber breakage.

Conclusions

This study clarified the effects of test temperature on the properties of T800 carbon fiber–epoxy resin composites after exposure to hygrothermal and thermal-oxidative aging processes. These properties were determined using the results of mass change, SEM, T _g, heat-resistant temperature, FTIR spectroscopy, open-hole compressive strength, and stereomicroscopic observations.

The rate of mass change was observed to increase significantly in the initial stages of aging and then gradually stabilize in the later stages, regardless of the aging process.

Massive bodies of resin were observed by SEM to surrounding the fibers on the surface of the unaged specimen; after hygrothermal aging, the surface of the specimen was smooth and some of the resin had shed; after thermal-oxidative aging, voids and matrix cracking were observed on the surface of the specimen.

The storage modulus and tan δ peak of the composites decreased after either aging process. The unaged specimens had a T _g of 229°C and an extreme heat-resistant temperature T _gmod of 184°C; after hygrothermal aging, the specimens had a T _g of 207°C and a T _gmod of 143°C; after thermal-oxidative aging, the specimens had a T _g of 252°C and a T _gmod of 215°C.

The FTIR analysis indicated that after hygrothermal aging, no new substances were formed and no chemical reactions occurred, this suggested that chemical aging did not occur; after thermal-oxidative aging, the FTIR analysis indicated that chemical aging had occurred.

The higher the temperature, the lower the open-hole compressive strength was observed to be for all the tested specimens. The reduction in the compressive strength of the composite specimens was more pronounced after hygrothermal aging than after thermal-oxidative aging. The open-hole compressive strength of the unaged specimens remained above 73.7% for all evaluated temperatures; after hygrothermal aging, the strength remained above 65.5%; and after thermal-oxidative aging, the strength remained above 67.9%.

Stereomicroscopic observations of the failure modes of the open-hole compression specimens tested under different temperatures were basically the same regardless of the aging process, and the side profile fractures were mainly observed to be shear failures accompanied by delamination and buckling characteristics.

In combination, these test results indicate that the T800 carbon fiber–epoxy resin composite evaluated in this study provides good resistance to high-temperature environments, while retaining its strength to an acceptable degree. These findings are of significance for the design of composite materials to ensure adequate performance in practical engineering applications. They should be of assistance to the design and application of polymer-based fiber-reinforced composites in fields requiring excellent mechanical performance in aggressive environments and useful in understanding the aging behaviors of carbon fiber–epoxy composites.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research was sponsored by the Liaoning Education Department Fund Project (serial no. L201611), the Shenyang Science and Technology Fund Project (serial no. 18-013-0-25), and the Key Laboratory of Fundamental Science for National Defense of Aeronautical Digital Manufacturing Process Fund Project (serial no. SHSYS201802).

ORCID iDs

Yi He

Shaohua Ma

References

Toldy

Szolnoki

Marosi

. Flame retardancy of fibre-reinforced epoxy resin composites for aerospace applications. Polym Degrad Stab 2011; 96(3): 371–376.

Soutis

. Carbon fiber reinforced plastics in aircraft construction. Mat Sci Eng A–Struct 2005; 412(1–2): 171–176.

Khashaba

Khdair

. Open hole compressive elastic and strength analysis of CFRE composites for aerospace applications. Aerosp Sci Technol 2017; 60: 96–107.

Kumar

Reddy

Kumar

, et al. Development and characterization of polymer-ceramic continuous fiber reinforced functionally graded composites for aerospace application. Aerosp Sci Technol 2013; 26: 185–191.

Peng

Shi

Wang

, et al. Effects of three types of T700 carbon fiber on the mechanical properties of their composites with bismaleimide resin. New Carbon Mater 2016; 31(2): 176–181.

Gao

Sun

Gao

, et al. Status and progress of influence of typical aerospace environments on mechanical behavior of polymer matrix composites. Polym Mater Sci Eng 2018; 34(5): 177–182.

Jedidi

Jacquemin

Vautrin

. Accelerated hygrothermal cyclical tests for carbon/epoxy laminates. Compos Part A–Appl Sci Manuf 2006; 37(4): 636–645.

Sun

Zhao

Luo

, et al. Effect of temperature and cyclic hygrothermal aging on the interlaminar shear strength of carbon fiber/bismaleimide (BMI) composite. Mater Design 2011; 32: 4341–4347.

, et al. Tensile failure analysis of composite laminates with a hole. Sci Tech Eng 2018; 18(34): 242–247.

10.

Soutis

Filiou

. Stress distributions around holes in composite laminates subjected to biaxial loading. Appl Compos Mater 1998; 5(6): 365–378.

11.

Hui

Wang

, et al. Study on compress property of composite laminate in the hygrothermal environment. Sci Tech Eng 2016; 16(9): 1671–1815.

12.

Luo

Roy

. Dynamic compressive behavior of unidirectional IM7/5250-4 laminate after thermal oxidation. Compos Sci Technol 2012; 72(2): 159–166.

13.

Liu

Guan

Tan

, et al. Analysis of open-hole compressive CFRP laminates at various temperatures based on a multiscale strategy. Appl Compos Mater 2019; 26: 923–944.

14.

Suemasu

Naito

Gozu

, et al. Damage initiation and growth in composite laminates during open hole compression tests. Adv Compos Mater 2012; 21(3): 209–220.

15.

Tay

Ridha

, et al. Progressive damage modeling of open-hole composite laminates under compression. Compos Struct 2015; 122: 507–517.

16.

Caminero

Lopez-Pedrosa

Pinna

, et al. Damage monitoring and analysis of composite laminates with an open hole and adhesively bonded repairs using digital image correlation. Compos Part B–Eng 2013; 53: 76–91.

17.

García-Moreno

Caminero

Rodríguez

, et al. Effect of thermal ageing on the impact and flexural damage behaviour of carbon fibre-reinforced epoxy laminates. Polymers 2019; 11(1): 80.

18.

García-Moreno

Caminero

Rodríguez

, et al. Effect of thermal ageing on the impact damage resistance and tolerance of carbon-fibre-reinforced epoxy laminates. Polymers 2019, 11(1): 160.

19.

Dao

Hodgkin

Krstina

, et al. Accelerated aging versus realistic aging in aerospace composite materials. V. The effects of hot/wet aging in a structural epoxy composite. J Appl Polym Sci 2006; 115(2): 901–910.

20.

Ray

. Temperature effect during humid ageing on interfaces of glass and carbon fibers reinforced epoxy composites. J Colloid Interf Sci 2006; 298(1): 111–117.

21.

Kubota

Furuta

Aoki

, et al. Long-term thermal stability of carbon fibre-reinforced addition-type polyimide composite in terms of compressive strength. Adv Compos Mater 2019; 28(2): 115–133.

22.

Soutis

. Modelling open hole compressive strength of composite laminates tested in hot wet conditions. Plast Rubber Compos 2009; 38(2–4): 55–60.

23.

, et al. Effects of hygrothermal and thermal-oxidative ageing on the open-hole properties of T800/high-temperature epoxy resin composites with different hole shapes. High Perform Polym 2019. DOI: 10.1177/0954008319860892.

24.

Shen

Yang

. Property requirements of composite systems applicable to aircraft structures. J Mater Eng 2007; 45(S1): 248–252.

25.

American Society for Testing and Materials. ASTM D6484/D6484M-2014 Standard test method for open-hole compressive strength of polymer matrix composite laminates. West Conshohocken: ASTM International, 2014.

26.

American Society for Testing and Materials. ASTM D5229/D5229M-2014 Standard test method for moisture absorption properties and equilibrium conditioning of polymer matrix composite materials. West Conshohocken: ASTM International, 2014.

27.

Jia

, et al. Effects of thermal-oxidative aging on the mechanical properties of open-hole T800 carbon fiber/high temperature epoxy composites. High Perform Polym 2019. DOI: 10.1177/0954008319883691.

28.

Wang

Zhou

, et al. Investigation of the thermal ageing process and mechanism of benzoxazine/bismaleimide/cyanate ester copolymer. High Perform Polym 2018; 31(6): 623–630.

29.

American Society for Testing and Materials. ASTM D 7028/7028M-2007 Standard test method for glass transition temperature (DMA T_g) of polymer matrix composites by dynamic mechanical analysis (DMA). West Conshohocken: ASTM International, 2007.

30.

Sui

, et al. Effects of hygrothermal aging on the thermal-mechanical properties of vinylester resin and its pultruded carbon fiber composites. Polym Compos 2009; 30(10): 1458–1464.

31.

Hui

, et al. Effects of hygrothermal and thermal aging on the low-velocity impact properties of carbon fiber composites. Adv Compos Mater 2019. DOI: 10.1080/09243046.2019.1630054.

32.

Zhang

Zuo

Sun

, et al. Thermal ageing degradation mechanisms on compressive behavior of 3-D braided composites in experimental and numerical study. Compos Struct 2016; 140: 180–191.

33.

Hui

Zhang

, et al. Mechanical properties of carbon fiber/epoxy resin composite after hygrothermal aging. Mater Mech Eng 2016; 40(1): 62–65.

34.

Toscano

Pitarresi

Scafidi

, et al. Water diffusion and swelling stresses in highly crosslinked epoxy matrices. Polym Degrad Stab 2016; 133: 255–263.

35.

Feng

Yang

, et al. High thermally stable thermosetting polyimides derived from a carborane-containing tetramine. High Perform Polym 2019; 31(5): 548–556.

36.

Barbosa

APC

Fulco

APP

Guerra

, et al. Accelerated aging effects on carbon fiber/epoxy composites. Compos Part B–Eng 2017; 110: 298–306.

37.

Meador

MAB

Lowell

Cavano

, et al. On the oxidative degradation of nadic endcapped polyimides: I. Effect of thermocycling on weight loss and crack formation. High Perform Polym 1996; 8(3): 363–379.

38.

Wang

, et al. The hygrothermal aging process and mechanism of the novolac epoxy resin. Compos Part B–Eng 2016; 107: 1–8.

39.

Wang

Chen

Zhou

, et al. Study on hydrothermal properties of carbon fiber composites with multi-frequency dynamic mechanical thermal analysis. J Mater Eng 2006; (S1): 355–359.

40.

Suemasu

Takahashi

Ishikawa

. On failure mechanisms of composite laminates with an open hole subjected to compressive load. Compos Sci Technol 2006; 66(5): 634–641.

41.

Wang

Duan

, et al. Temperature effects on the compression behavior and failure of 3-D MWK glass fabric-reinforced epoxy composites. High Perform Polym 2019; 31(4): 449–461.