CN101655434B - Method for testing Poisson's ratio of linear-viscoelastic material - Google Patents

Abstract

The invention relates to a method for testing Poisson's ratio of a linear-viscoelastic material, which comprises the following steps: placing a nano indentation sample and a tensile sample of a polymer/polymer base composite material in a constant temperature and humidity chamber, heating until the temperature is 5-10 DEG C higher than glass-transition temperature, standing, and cooling at low speed until the temperature is below the glass-transition temperature; placing in a sample chamber for 72h; applying a dynamic nano indentation test to the indentation sample under a constant loading speed or constant load by adopting a glass pressure head, obtaining a curve of indentation depth changed with the time; obtaining indentation shearing creep compliances in two loading modes; applying a constant tensile load to the tensile creep sample on a general tester, obtaining a creep displacement-time curve so as to a tensile compliance; and determining the Poisson's ratio of the linear-viscoelastic material according to the calibration relation of the shearing creep compliances and the tensile creep compliance. The invention provides an accurate and convenient test solution for the ration of the Poisson's ratio of various linear-viscoelastic materials.

Description

A kind of method of testing of linear-viscoelastic material Poisson ratio

Technical field

The present invention relates to a kind of nano impress creep and simple extension creep test combined, the method for test linear-viscoelastic material Poisson ratio belongs to materials mechanics experimental method field.

Background technology

Poisson ratio (μ) is a very important mechanics of materials parameter.At present the method for testing of Poisson ratio is divided into contact and contactless two types.The former mainly contains Mechanical Method and electrical measuring method, and the latter then comprises the acoustic method that utilizes the sound transmission characteristic and the optical means of holographic interferometry or moir etc.In numerous Poisson ratio test methods, Mechanical Method is because of simple to operate, convenient widely utilization.Wherein apply tensile load on the test specimen, based on the Poisson ratio standardization of material Mechanical Method testing elastic material of the ratio of transversely deforming and linear deformation under the single axial stress state.As far as polymkeric substance, constant outer carry effect down lax the or creep of material can't avoid, its transverse strain response is carried out with linear deformation is often asynchronous.The experimental measurement that is viscoelastic material γ is much complicated than resilient material.Novel test method of Poisson ratio and technology continue to bring out in recent years, like (the Chinese invention patent publication number: CN101063646A), based on the load-relative volume curve of material and diclinic rate computing method (the Chinese invention patent publication number: CN101441151A) etc. of load-strain curve of the plunging through the nonlinear relationship acquisition μ between the distortion of indentation load and impression.But above-mentioned test method is only applicable to the mensuration of resilient material Poisson ratio.Up to now, still there is not the Poisson ratio that suitable Mechanical Method is assessed linear viscoelastic polymer film.

Summary of the invention

The objective of the invention is to the deficiency that exists to prior art, provide a kind of be suitable for linear-viscoelastic polymkeric substance and compound substance Poisson ratio thereof accurately with contact method of testing easily.

Thinking of the present invention is: 1. derive glass formula (Berkovich) pressure head by the continuum mechanics method and be pressed in the linear-viscoelastic polymer process theoretical expression that the material creep compliance changes with compression distance; 2. obtain depth of cup-curve of load under the specific load through nano-hardness tester, can obtain the material Poisson ratio thus with the EVOLUTION EQUATION that is pressed into creep compliance; 3. according to test specimen uniaxial tension creep test, confirm the tensile creep compliance of material; 4. utilize linear material to be pressed into the equivalence principle of creep compliance and its tensile creep compliance, can realize the accurate measurement of linear-viscoelastic material Poisson ratio.

According to the foregoing invention design, the present invention adopts following technical proposals:

A kind of method of testing of linear-viscoelastic material Poisson ratio is used for the sample of processing with polymkeric substance and compound substance thereof is tested, and it is characterized in that testing procedure is following:

A. with polymkeric substance or polymer matrix composite nano impress and tensile sample is put into constant temperature, constant humidity cabinet is heated above 5-10 ℃ of glass transition temperature (Tg), leave standstill 1-2 hour to eliminate its prestress, the speed with 5 ℃/hr is cooled to below the Tg at a slow speed again.Test specimen is to test after 25 ± 0.5 ℃, humidity are to place 72 hours in 50 ± 2% the indoor environment in temperature.

B. adopting semi-cone angle is that glass formula (Berkovich) pressure head of θ is implemented F under the constant load to the impression sample _n(t)=P ₀, P in the formula ₀Dynamic nano indentation test for the load size obtain compression distance h (t) change curve of t in time in view of the above, and then linear-viscoelastic material is pressed into shear creep compliance J _s(t) in time evolution is:

$J_s\left(t\right)=\frac{{4h}^2\left(t\right)}{{\mathrm{<figure-callout\; id="0"\; label="P"\; filenames="H2009101957334E00011.png,H2009101957334E00012.png"\; state="\{\{state\}\}">P</figure-callout>}}_0\mathrm{\&pi;}(1-\mathrm{\&mu;})c\tan \mathrm{\&theta;}};$

C. on universal testing-machine (UTM) applies constant stretch load F to the tensile creep sample _t, obtain creeping displacement-time curve l (t)-t, the tensile creep compliance J of sample _t(t) can get thus.Promptly

F in the formula _tFor imposed load big

Little, l0 is the gauge length of sample, and S is that sample cross is long-pending.

D. based on the test findings of above-mentioned dynamic nano impress and tensile creep, and according to compliance in shear J _s(t) with body (stretching) compliance J _t(t) conversion relation:

Linear-viscoelastic material Poisson ratio (μ) can be by following formula:

$\mathrm{\&mu;}=\sqrt{1-\frac{{2h}^2\left(t\right)}{J_t\left(t\right){\mathrm{<figure-callout\; id="0"\; label="P"\; filenames="H2009101957334E00011.png,H2009101957334E00012.png"\; state="\{\{state\}\}">P</figure-callout>}}_0\mathrm{\&pi;}c\tan \mathrm{\&theta;}}}.$

The present invention compared with prior art; Its outstanding substantive distinguishing features and remarkable advantage are: existing Mechanical Method, electrical measuring method, optical method and acoustic method etc. all can't be measured the Poisson ratio of nontransparent polymkeric substance and composite material film thereof; And the present invention is based on strict continuum mechanics theory and method, what can be all kinds of linear-viscoelastic material Poisson ratios quantitatively provides accurately, tests easily solution.

Description of drawings

Fig. 1 is load-time curve in polymethylmethacrylate (PMMA) the nano impress process.

Fig. 2 is compression distance-time curve in polymethylmethacrylate (PMMA) the nano impress process.

Fig. 3 is polymethylmethacrylate (PMMA) tensile creep compliance change curve in time.

Fig. 4 is load-time curve in polycarbonate (PC) the nano impress process.

Fig. 5 is compression distance-time curve in polycarbonate (PC) the nano impress process.

Fig. 6 is polycarbonate (PC) tensile creep compliance change curve in time.

Embodiment

It is existing that details are as follows with specific embodiment of the present invention:

Embodiment 1

1. polymethylmethacrylate (PMMA) being processed physical dimension (the wide x of long x is thick) respectively is: the nano impress sample of 8mm * 8mm * 1mm and the tensile sample of 200mm * 10mm * 1mm; 2. test specimen being put into temperature is 110 ℃ constant temperature, constant humidity cabinet, leaves standstill 2 hours to eliminate its prestress, and the speed with 5 ℃/hr is cooled to below the room temperature at a slow speed again.Test specimen is to test after 25 ± 0.5 ℃, humidity are to place 72 hours in 50 ± 2% the indoor environment in temperature; 3. through Hysitron-Tribo Indentation nano-hardness tester; Adopting semi-cone angle is that 70.32 ° glass formula (Berkovich) pressure head is implemented the dynamic nano indentation test of constant load as shown in Figure 1 to the impression sample, obtains compression distance (h (the t)) change curve of (t) (like Fig. 2) in time in view of the above; 4. on the Zwick/Roell universal testing-machine, tensile sample is applied the creep test under the constant stretch loading, according to creeping displacement-time test curve (l (t)-t), the tensile creep compliance (J of calculating gained sample _t(t)) as shown in Figure 3; 5. according to the calculating formula (1) of above-mentioned dead load pattern lower linear viscoelastic material Poisson ratio, can get PMMA Poisson ratio (μ).In the time scale of nano indentation test (less than 300 seconds), because of μ change in time minimum, so desirable its mean value 0.22 is as the Poisson ratio of PMMA.

Embodiment 2

1. polycarbonate (PC) being processed physical dimension (the wide x of long x is thick) respectively is: the nano impress sample of 8mm * 8mm * 0.5mm and the tensile sample of 150mm * 10mm * 0.5mm; 2. test specimen being put into temperature is 150 ℃ constant temperature, constant humidity cabinet, leaves standstill 1 hour to eliminate its prestress, and the speed with 5 ℃/hr is cooled to below the room temperature at a slow speed again.Test specimen is to test after 25 ± 0.5 ℃, humidity are to place 72 hours in 50 ± 2% the indoor environment in temperature; 3. through Hysitron-Tribo Indentation nano-hardness tester; Adopting semi-cone angle is that 70.32 ° glass formula (Berkovich) pressure head is implemented the dynamic nano indentation test of permanent loading speed as shown in Figure 4 to the impression sample, obtains compression distance (h (the t)) change curve of (t) (like Fig. 5) in time in view of the above; 4. on the Zwick/Roell universal testing-machine, tensile sample is applied the creep test under the constant stretch loading, according to creeping displacement-time test curve (l (t)-t), the tensile creep compliance (J of calculating gained sample _t(t)) as shown in Figure 6; 5. according to the calculating formula (2) of above-mentioned dead load pattern lower linear viscoelastic material Poisson ratio, can get the PC Poisson ratio.Because of in the time scale of nano indentation test (less than 300 seconds), μ changes also minimum in time, gets its mean value: 0.32 is the Poisson ratio of PC.

Above-mentioned PMMA, two kinds of samples of PC are respectively 0.24 and 0.34 by the material Poisson ratio that traditional electrical measuring method obtains; Differ all less than 10% with the inventive method test figure; This shows and of the present inventionly combine based on nano impress creep and simple extension creep test; In the time scale of nano indentation test (less than 300 seconds), the method for testing of linear-viscoelastic material Poisson ratio has higher precision.

Claims (1)

1. the method for testing of a linear-viscoelastic material Poisson ratio is characterized in that its testing procedure is following:

A. with polymkeric substance or polymer matrix composite nano impress and tensile sample is put into constant temperature, constant humidity cabinet is heated above glass transition temperature 5-10 ℃; Leave standstill 1-2 hour to eliminate its prestress, be cooled to below the glass transition temperature at a slow speed with 5 degrees centigrade/hour speed again; Sample is to test after 25 ± 0.5 ℃, humidity are to place 72 hours in 50 ± 2% the indoor environment in temperature;

B. adopting semi-cone angle is that the glass formula pressure head of θ is implemented the dynamic nano indentation test under the constant load to the impression sample, and constant load is F _n(t)=P ₀, P in the formula ₀Be the load size, obtain compression distance h (t) curve over time, and then linear-viscoelastic material be pressed into shear creep compliance J _s(t) in time evolution is:

$J_s\left(t\right)=\frac{{4h}^2\left(t\right)}{P_0\mathrm{\&pi;}(1-\mathrm{\&mu;})c\tan \mathrm{\&theta;}};$

C. on universal testing-machine, the tensile creep sample is applied constant stretch load F _t, obtain creeping displacement-time curve l (t)-t, the tensile creep compliance J of sample _t(t) be:

F in the formula _tBe imposed load size, l ₀Be the gauge length of sample, S is that sample cross is long-pending;

D. according to shear creep compliance J _s(t) with tensile creep compliance J _t(t) conversion relation:

Linear-viscoelastic material Poisson ratio μ can be confirmed by following formula:

$\mathrm{\&mu;}=\sqrt{1-\frac{{2h}^2\left(t\right)}{J_t\left(t\right)P_0\mathrm{\&pi;}c\tan \mathrm{\&theta;}}}.$

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