复合材料长期热氧老化失效机制解析

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本文主要探讨了复合材料在长期储存过程中面临的热氧老化失效机理。热氧老化是一种常见的材料降解过程，特别是在航空航天、汽车工业等应用广泛的高性能复合材料中，由于暴露于高温和氧气环境中，材料的性能会逐渐衰退。《复合材料科学与技术》杂志在1998年3月的一篇文章中详细阐述了这一现象，由Tom Tsotsis和Shaw M. Lee两位作者合作完成，他们的研究着重于揭示了复合材料在经历长时间热氧交互作用后所出现的失效模式及其背后的根本原因。研究指出，热氧老化可能导致复合材料中的聚合物基体和增强纤维之间的界面劣化，包括键合强度下降、裂纹扩展以及材料微观结构的改变，如氧化、交联和碳化等。这些变化会导致材料的机械性能，如拉伸强度、模量和断裂韧性降低，从而影响其整体结构的稳定性。文章引用的 Impact Factor（IF）为3.57，表明该研究具有较高的学术影响力，已被引用37次，阅读量达到了65次。 Tsotsis在Boeing公司和Hexcel Composites担任职务，他们的研究不仅基于理论分析，还可能结合实验室实验数据，提供了对实际工程应用有指导意义的实践性见解。文中提到的研究过程包括数据收集、模型建立和实验验证，最终目的是为了找到延缓或抑制复合材料热氧老化的方法，以提高其使用寿命和可靠性。文章的出版商Elsevier Science Ltd.强调了版权信息和定价，并声明所有权利归版权所有者所有。这篇论文的DOI（Digital Object Identifier）为10.1016/S0266-3538(97)00123-1，读者可以通过这个链接获取全文，或者在1998年11月20日之前访问Tom Tsotsis的个人资料获取更多相关信息。这篇文章深入剖析了复合材料在长期热氧老化条件下的失效机制，对于理解这类材料的耐久性、优化设计和改进防护策略具有重要意义。对于任何从事复合材料研究或应用的人来说，理解和掌握这些失效机理是至关重要的。

T. K. Tsotsis, S. hf. Lee

exhibited severe surface erosion, delamination, and easy

ply separation by peeling. A large-scale series of aging

experiments by Kerr and Haskins tested [O”], and [O’!

* 45”ls carbon- and boron-reinforced epoxy coupons

exposed to elevated temperatures and various air pres-

sures for up to 50000 h. Different air pressures were

used to simulate the relatively low air pressure encoun-

tered at altitudes used for supersonic operation and to

examine the degradation rate which is known2m5 to

increase with increasing air (oxygen) pressure. They

noted that edge cracking and severe property degrada-

tion did indeed occur at longer time for lower air pressure.

Bowles et al.h observed similar behavior for PMR-1%

based composites with severe surface degradation in the

form of transverse surface cracks which reduced

strength and provided pathways for deeper oxygen

penetration into the polymer matrix. Most of the stu-

dies, such as those mentioned, focused mainly on fiber-

dominated tensile property degradation and did not

examine the individual contributions of fiber. matrix

and interface.

There have also been some studies reported in the lit-

erature addressing the degradation kinematics and

mechanisms of long-term aging. Several thermogravi-

metric (TGA) methods

’ I0 for determining useful life-

times for polymers by use of kinetic models of weight

loss have been proposed. Using the method of Flynn

and Wall,’ Lee and Levi” found a significant increase in

activation energy of thermal degradation of an epoxy

resin when the temperature was increased from 100 to

200°C. The work by Grayson and Fry’” employed a

similar method to determine a ‘map’ to determine usage

temperatures and lifetimes of several polymers. Rose ct

al.” combined TGA and spectroscopic techniques to

study the degradation of an epoxy resin; they showed

the degradation mechanism to be a dehydration reac-

tion at temperatures causing less than 5% weight loss.

In a later study, Rose rt af.13 used invariant kinetic

parameters to evaluate the heat resistance of epoxy

resins. Most of the studies mentioned used TGA tech-

niques to determine weight loss rates of polymers with

temperatures. Such an approach can be subject to error

as pointed out by Arnold et a1.14 and MacCallum,‘S

with the possibility of mass transfer effects influencing

kinetic data.

Recently, Hipp et al.” performed accelerated tests to

determine a methodology for selecting candidate

composite materials (K3B polyimide and cyanate ester

reinforced with carbon fibers) for HSCT applications.

Weight loss measurements were used to construct models

to predict accelerated aging conditions. In a similar

study, Pederson et al.”

measured the effects of iso-

thermal aging on the development of cracks and found

that a BMI system showed much greater cracking and

more weight loss than the Avimid K. Nam and Seferis’s

concluded from their study on a carbon/bismaleimide

(BMI) composite that because thermo-oxidative stability

is related to the diffusion of oxygen, it is also affected by

material anisotropy and thus should be considered as a

tensorial quantity instead of a scalar quantity such as

weight loss in bulk resins. Tsotsis” pointed out the

unreliable nature of kinetic data alone to reflect com-

posite performance and concluded, for the same reason,

that the glass transition temperature, r,, is a poor indi-

cator of thermo-oxidative stability. The work of Laius

rt al.‘” studied the role of molecular structures on ther-

mal degradation of polyimides. They concluded that the

stability of the molecules was due qualitatively to the

differences in intramolecular interactions and not the

stability of the molecular backbone. McManus and

Cunningham2’

recently developed a qualitative model

for the environmental degradation of composites by

coupling diffusion and reaction mechanisms with

mechanical degradation.

Although certain understandings about the effects of

aging on mechanical properties have been reached in the

past, the exact mechanisms controlling such degrada-

tion are still not well understood. From the standpoint

of predicting long-term performance, a clearer under-

standing of the roles of the fiber, matrix and interface at

the material level is needed in order to address general

laminate performance. Clearly, weight loss and T, var-

iations alone do not directly reflect different mechanisms

controlling mechanical property degradation. Different

composite properties being dominated by fiber, matrix,

interface. or a combination, will vary in different ways

with aging. However, mechanical property degradation

is by no means unrelated to molecular structural chan-

ges which may be manifested as weight loss or T, var-

iations. It simply means that these molecular changes

affect the various material variables (mechanical and

physical) in different ways.

This paper reports on a study of long-term thermo-

oxidative aging of composites related to the other work

of Tsotsis.‘9,22 In the previous workI data were pre-

sented for the effect of thermo-oxidative aging on the

thermal, fracture and compressive properties two car-

bon-reinforced epoxy composite systems. In the com-

panion paper to the present work,22 additional data are

presented to gain deeper insights into the general char-

acteristics of resin-dominated versus fiber-dominated

property degradation.

It should be clearly pointed out that the two materials

studied here were chosen purely as model systems for

the purpose of establishing a meaningful methodology

for characterizing thermo-oxidative aging of polymeric

composites. The materials were not designed to be used

at the aging temperature (177°C). Indeed, because of

this, their property degradation as a consequence of

aging was significant in allowing the degradation

mechanisms to be clearly identified in the study. Thus

the mechanisms found would reflect the relative effects

of degradation on composite properties, even at lower

aging temperatures with, of course, lower degradation

rates. Such relative effects can then justify the necessary

tests to be performed on composites aged at the desired

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