高温环境下C/C复合材料热膨胀系数测量新技术
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"测量非均匀温度样品的热膨胀系数的新技术"
在本文中，研究者提出了一种用于高温下测量碳/碳复合材料纵向热膨胀系数的新方法。这项技术的创新之处在于它能处理非均匀温度分布的样品，这对于理解和优化高性能材料在极端环境下的性能至关重要。热膨胀系数是材料科学中的一个关键参数，它描述了材料随温度变化时尺寸的变化率。
测量原理主要基于热膨胀系数与温度的关系。当材料受热时，其长度会随温度的升高而增加，这一变化可以通过精确的测量设备来探测。该装置主要包括以下几个部分：
1. 高温环境室：这个组件提供了一个可控的高温环境，使样品能够达到稳定的高温状态，这对于模拟实际应用中的工作条件至关重要。
2. 加热电源电路：通过恒定的电流对样品进行电阻加热，使其达到所需的高温。
3. 高速测温仪：通常为红外测温仪，用于实时监测样品表面的温度分布。由于热传导会导致样品表面的温度不均匀，因此需要高速测温仪来捕捉这种复杂的变化。
4. 激光扫描系统：激光扫描系统用于精确测量样品的长度变化，通过激光束的反射或干涉效应，可以非接触地获取样品的微小尺寸变化。
在实验过程中，样品被电阻加热到稳态的高温，然后通过两个高精度的高速测温仪监测其表面温度。由于热传导，样品表面的温度分布通常是不均匀的，这使得传统的热膨胀系数测量方法难以适用。然而，通过激光扫描系统，可以克服这一难题，计算出整个样品的平均热膨胀系数。
文章指出，计算方法是基于热膨胀系数与温度的依赖关系推导出来的。这可能涉及到线性或非线性的温度-膨胀模型，具体取决于材料的性质。通过对不同位置的温度和长度变化数据进行整合，可以得出考虑了非均匀温度效应的热膨胀系数。
这项工作为高温条件下复杂温度分布材料的热膨胀系数测量提供了新的途径，对于航空航天、能源和汽车等领域的材料研发具有深远的影响。通过改进和优化这种技术，我们可以更准确地评估材料在高温环境下的性能，从而为新材料的设计和应用提供关键的理论支持。
September 10, 2008 / Vol. 6, No. 9 / CHINESE OPTICS LETTERS 669
Measurement of thermal expansion coefficient of
nonuniform temperature specimen
Jingmin Dai (
µµµ
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)
1
, Chunsuo Xin (
"""
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)
1
, and Xiaowa He (
ÛÛÛ
)
2
1
Department of Automation Measurement and Control, Harbin Institute of Technology, Harbin 150001
2
Aerospace Research Institute of Materials and Processing Technology, Beijing 100076
Received February 29, 2008
A new technique is developed to measure the longitudinal thermal expansion coefficient of C/C composite
material at high temperature. The measuring principle and components of the apparatus are described
in detail. The calculation method is derived from the temperature dependence of the thermal expansion
coefficient. The apparatus mainly consists of a high temperature environmental chamber, a power circuit of
heating, two high-speed pyrometers, and a laser scanning system. A long solid specimen is resistively heated
to a steady high-temperature state by a steady electrical current. The temperature profile of the specimen
surface is not uniform because of the thermal conduction and radiation. The temperature profile and the
total expansion are measured with a high-speed scanning pyrometer and a laser slit scanning measuring
system, respectively. The thermal expansion coefficient in a wide temperature range (1000 − 3800 K) of
the specimen can therefore be obtained. The perfect consistency between the present and previous results
justifies the validity of this technique.
OCIS codes: 120.0120, 120.4570, 000.6850, 120.6780.
doi: 10.3788/COL20080609.0669.
In the past decades, most of the accurate measurements
of thermal expansion coefficients at temperatures above
1100 K generally rely on the steady-state techniques
such as push-rod dilatometry, X-ray diffractometry, and
optical comparator methods. The measuring precision
of the steady- state techniques mainly depends on the
degree of keeping uniform temperature of the specimen,
which is hard to realize because of thermal conduction
at ends, especially at high temperature
[1]
. The problem
of nonuniform temperature profile restricts the applica -
tion of those methods at ultra high temperature. With
the rise of pulse heating method and the development of
modern electronics, Righini et al. proposed a new idea
to measure the thermophysical properties by an assumed
function of thermalphysical properties and temperature
according to the rules of ther malphysical varying with
temper atures
[2]
. Moreover, this method was applied to
the measurement of thermal expansion coefficient of a
sp e cimen with a nonuniform temperature pr ofile based
on the apparatus of pulse experiment and a high-speed
scanning pyrometer
[3]
. However, the temperature profile
of the specimen must be measured as quickly as possi-
ble in the transient-state technique in order to minimize
the influence of temperature fluctuation. Based on the
advantages of the steady-state method and the Righini’s
calculation theory of nonuniform temperature profile,
the present paper describes an integration method for
the measurement of thermal expansion coefficient up to
ultra high temperature. The requirement of mea suring
the thermal expansion coefficient of a C/C composite
material can be satisfied with this method.
A method for thermal expansion measurements of a
sp e cimen with nonuniform temperature profile was suc-
cessfully developed
[4]
. Righini assumed that the expan-
sion function in the temperature range of interest may
be represented by a n n th order polynomial constrained
by a reference temperature T
0
f (T ) =
∆L (T )
L (T
0
)
= a
1
(T − T
0
) + a
2
(T − T
0
)
2
+ · · ·
+a
n
(T − T
0
)
n
, (1)
where L (T
0
) is the length of the specimen at T
0
, ∆L (T )
is experimental total e xpansion associated with a partic-
ular temperature profile, a nd T is the ex periment tem-
perature of the spe cimen.
If the experimental temper atures are measured in po-
sitions z
1
, z
2
, · · · , z
M
with equal intervals, the specimen
may be considered as composed of M segments with
equal length of S. These segments are marked as l
i
(i = 1, 2, · · · , M) and the corresponding le ngth at tem-
perature T
0
may be any sizes and they are not necessarily
equal. The relations of these quantities can be expressed
with the following eq uations:
L (T
0
) =
M
X
i=1
l
i
, L (T ) =
M
X
i=1
S = M · S. (2)
The sp e cimen may have an arbitrary temperature dis-
tribution. An overdetermined system may be got if p
profiles are measured (p > n)
∆L
1
= a
1
M
1
P
i=1
l
1i
(T
0
) (T
∗
1i
− T
0
) + · · ·
+a
n
M
1
P
i=1
l
1i
(T
0
) (T
∗
1i
− T
0
)
n
.
.
.
∆L
p
= a
1
M
1
P
i=1
l
pi
(T
0
)
T
∗
pi
− T
0
+ · · ·
+a
n
M
1
P
i=1
l
pi
(T
0
)
T
∗
pi
− T
0
n
, (3)
1671-7694/2008/090669-04
c
2008 Chinese Optics Letters
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