CN104897478A - Method of determining sampling time in accelerated storage test of NEPE (nitrate ester plasticized polyether) propellant - Google Patents

Abstract

The invention discloses a method of determining sampling time in accelerated storage test of NEPE (nitrate ester plasticized polyether) propellant and aims to solve the problems that sampling is only made by experience for the prior accelerated storage test of the NEPE propellant, the consumption of chemicals is high and test samples are unable to be accurately sampled. The method includes: acquiring dynamic chemical characteristics by means of dynamic mechanical analysis, indirectly recognizing the information about changes in chemical properties of an accelerated storage sample for the NEPE propellant, and determining the sampling time of a tensile strength change sample for the accelerated storage test of the NEPE propellant. The method has the advantages that adding more drugs is never required in the accelerated storage test of the NEPE propellant, the defect that sampling cannot be accurately made in the accelerated storage test is overcome, and the method is suitable for the determination of the sampling time in the accelerated storage test of the NEPE propellant.

Description

A kind of method determining NEPE propellant accelerated storage test sample time

Technical field

The invention belongs to explosive wastewater technical field, relate generally to NEPE propellant accelerated storage test, particularly relate to and adopt dynamic mechanical analysis technology to obtain Dynamic mechanical property amount, identify NEPE propellant accelerated storage sample mechanical property change information, determine the NEPE propellant accelerated storage test tensile strength change sample sampling time.

Technical background

The Polyether propellants (NEPE propellant) of nitrate plasticising is the solid propellant of new generation that the U.S. grew up the end of the seventies in last century, the beginning of the eighties, this propellant adopts pouring technology preparation, combining the advantage of double base propellant and composite propellant, is the novel propellant of current energy characteristics and excellent in mechanical performance.NEPE propellant take superpolymer as the compound substance of matrix, its cementing agent is prepolymer and the polyisocyanates reactant of terminal hydroxy group ether, and plastifier is nitroglycerine and 1,2, the mixture of 4-BTTN, filler is ammonium perchlorate, ammonal, aluminium powder etc.In long storage process, can there is physics, chemical change slowly in NEPE propellant component, causes security respectively, mechanical property changes, affect the storage life of solid propellant rocket.

Chinese scholars has carried out large quantity research to the ageing properties of NEPE, for taking tensile strength as inefficacy parameter NEPE propellant formulation, the failure mechanism of its accelerated storage process is the superpolymer network system generation degradation reaction in NEPE propellant, crosslinking degree reduces, propellant general performance is that static limit mechanics tensile strength reduces, the feature of the mechanical property decline of powder charge.

Be sealed in engine due to during powder charge long storage periods, main environmental stress is temperature, usually adopts high temperature accelerated storage test to estimate the storage life of propellant.When high temperature accelerated storage test, at a set temperature, multiple sample is put into accelerated storage test baking oven simultaneously and carries out accelerated storage test, i.e. aging test, test sample is taken out in different digestion time, obtain the aging sample of the different aging degree of depth, and carry out static mechanical property test, obtain the Changing Pattern of the tensile strength under different aging temperature with digestion time.But in aging test process, mainly there is following defect: the sample time of (one) aging sample only judges by rule of thumb, interval is too short, properties of sample change is not remarkable, interval is long, aged samples performance change is too fast, and sampling inequality causes aging sample can not accurate description ageing properties Changing Pattern; (2) static mechanical property tested for tensile strength is destructive test, can not duplicate measurements, can by the appropriate mode increasing test specimen amount for improving the uneven problem of above-mentioned sampling, but because propellant is flammable and explosive substance, accelerated test sample size should strictly control, can not excess, thus the mode being difficult to increase sample size solves the problem, in addition, for high value material, increase sample size and also just add experimentation cost; (3) science is determined to the sample time of NEPE propellant accelerated storage test, can only by virtue of experience judge, lack economy, safely and effectively method and process of the test is monitored.

Summary of the invention

This patent overcomes the deficiency of background technology, provide a kind of dynamic thermal machinery analyses technology that adopts and obtain Dynamic mechanical property amount, and according to the rate of change of characteristic quantity, indirect identification propellant accelerated storage aging sample mechanical property change information, determines the method for NEPE propellant accelerated storage test tensile strength change sample sampling time.

Due to the long storage that powder charge is under airtight condition, main environmental stress is temperature.Under long storage environment temperature and under high temperature accelerated test condition, the failure mechanism of NEPE propellant is due to superpolymer network system generation degradation reaction in accelerated storage process, crosslinking degree reduces, cause static mechanical tensile strength to reduce, thus its dominant failure mode is that static mechanical tensile strength reduces.Certain correlationship is there is between tensile strength and Dynamic mechanical property amount, thus the technical issues that need to address of the present invention are: by the change of Dynamic mechanical property amount in dynamic thermal machinery analyses technical monitoring NEPE propellant travelling charge ageing process, quantitative acquisition NEPE Propellant aging sample Dynamic mechanical property amount change information, thus identify the change of NEPE propellant tensile strength, determine the NEPE propellant accelerated storage test tensile strength change sample sampling time.

1 dynamic thermomechanical obtains ageing process Dynamic mechanical property amount:

(1) dynamic mechanical and characteristic quantity

The dynamic mechanical parameter of superpolymer is relevant with the mechanical state (glassy state, elastomeric state and viscous state etc.) of macromolecule aggregation state in material (crystalline state, amorphous state, liquid crystal etc.) and material.The mechanical property of superpolymer is the reflection of molecular motion state in essence, glass transition, crystallization, the orientation of superpolymer, be cross-linked, the structure change such as to be separated is all closely related with the change of molecular motion state, this change is not only reflected in limit mechanical property, again can be sensitive be reflected on dynamic mechanical.Dynamic thermal machinery analyses DMA (Dynamic Mechamic Analysis) is a kind of means of research Polymer Structure---molecular motion---performance.Can measure by continuous print within the scope of very wide frequency f (or angular frequency) or temperature T, (dynamically) mechanical property change of material and the relation of time can be obtained fast and accurately, thus abundant viscoelasticity information can be obtained in the short period of time, as storage modulus E ', loss modulus E ", storage compliance J ', loss compliance J ", losstangenttanδ, complex modulus E ^*, complex compliance J ^*deng the data of dynamic mechanical, important information can be provided for studying high molecular molecular structure.

For superpolymer and this kind of typical viscoelastic material of compound substance thereof, all above-mentioned performance parameters are all relevant with environmental factor (as humidity, medium) with temperature, frequency, time, stress (or strain).Study the change of dynamic mechanical with temperature, frequency, lifting/lowering temperature speed, strain/stress level etc. of viscoelastic material, the much information about material structure and molecular motion can be disclosed, theoretical research and practical application are all had very important significance.

(2) Dynamic mechanical property amount and tensile strength correlativity

The tensile test of viscoelastic material measures the relation of deformation under material non-vibration load and temperature at a certain temperature with under certain loading speed, performance when material fracture occurs or destroys is called static limit mechanical property, comprising tensile strength, extensibility etc.Different loading speed and temperature have different static limit mechanical properties, for having viscoelastic macromolecular material, stretch at different temperature and loading speed, compressions etc. are tested the various intensity obtained and all can be superposed with certain shift factor along time shaft and strain rate axle with strain, form stress-strain principal curve, be time-temperature superposition principle (TTS), utilize time-temperature superposition principle, at different temperatures with the DMTA frequency spectrum within the scope of certain frequency, by certain displacement, DMTA frequency spectrum under being superimposed as given reference temperature in broad frequency range---be called principal curve or build-up curve.WLF equation then describes shift factor α _twith temperature difference (T-T _s) between relation:

${\mathrm{loga}}_T=\frac{C_1(T_S-T)}{C_2+T_S-T}---\left(1\right)$

Wherein, α _t– shift factor; T _s– reference temperature, K or DEG C; T – temperature, K or DEG C; C ₁and C ₂for empirical constant.

For viscoelastic material, in certain temperature range, dynamic mechanical also meets WLF equation (1 formula), carries out the corresponding principal curve of superimposed acquisition by flat shift factor.Now, WLF equation a _tshift factor mainly reflects and determines the segment friction factor of all allosteric rearrangement speed or the relation of mobility and temperature.

For commaterial, in identical temperature range, it is consistent that the shift factor-temperature relation obtained with the modulus principal curve of DMA and the stress-strain principal curve of limit mechanical property obtain, therefore, there is correlativity in DMA dynamic mechanical modulus and limit mechanical property (tensile strength).

Mechanical relaxation measures stress to increase in time and the phenomenon decayed when constant strain, and for viscoelastic material, its Relaxation Modulus E (t) is:

E(t)＝σ(t)/ε ₀(2)

In formula, σ (t) is stress relaxation intensity, is the function of time t; ε ₀for determining strain.

Meanwhile, also can define strain rate modulus F (t) (corresponding to tension, crush test) is

F(t)＝σ(t)/ε (3)

ε is strain.Pass between E (t) and F (t) is:

E(t)＝F(t)[1+d logF(t)/d l og(t)] (4)

Approximation relation is there is between dynamic mechanical storage modulus and static mechanical property Relaxation Modulus E (t)

$E\left(0.48t\right)\≈E^{\′}\left(\mathrm{\ω}\right){|}_{\mathrm{\ω}=\frac{1}{t}}---\left(5\right)$

E'(ω) be equivalent to when angular frequency is ω=1/t value

According to the theory that failure envelope and test method have nothing to do, determining strain stress _bunder, stress relaxation is to σ _btime, material will destroy.Therefore, in the moment of material damage, in formula (4), the differential term on the right equals zero.Namely

E(t)＝F(t)＝σ _b(t)/ε ₀(6)

σ _band ε ₀be respectively ultimate strength and the constant strain of tension (or resistance to compression).Meanwhile, (5) formula can change into:

$E\left(t\right)=E^{\′}\left(\frac{\mathrm{\ω}}{0.48}\right)$

$\left(7\right)$

Therefore, in certain temperature range, following relationship can be set, namely

E(t)≈kE'(ω) (8)

In formula: k is constant.

Because elastic contractile force is proportional to absolute temperature, so the stress of material damage moment all should be multiplied by T _s/ T is as conversion amount, and simultaneous formula (6) and formula (8) simultaneously, has following formula to set up:

${\mathrm{kE}}^{\′}\left(\mathrm{\ω}\right)=\frac{{\mathrm{\σ}}_b\left(t\right)T_s}{{\mathrm{\ϵ}}_{0}T}---\left(9\right)$

According to Time-temperature equivalence principle, at a certain reference temperature T _sunder, corresponding dynamic storage modulus reference frequency ω must be there is _swith reference time t _s, they are also set up for formula (9).

${\mathrm{kE}}^{\′}\left({\mathrm{\ω}}_s\right)=\frac{{\mathrm{\σ}}_b\left(t_s\right)T_s}{{\mathrm{\ϵ}}_0{T}_s}---\left(10\right)$

The corresponding relation formula that formula (9) obtains dynamic storage modulus and ultimate strength divided by formula (10) is:

$\frac{E^{\′}\left({\mathrm{\ω}}_s\right)}{E^{\′}\left(\mathrm{\ω}\right)}=\frac{{\mathrm{\σ}}_b\left(t_s\right)T}{{\mathrm{\σ}}_b\left(t\right)T_s}---\left(11\right)$

For selected reference temperature T _s, corresponding dynamic storage modulus reference frequency ω _sreference time t _sunder, the ultimate strength of arbitrary temp can be obtained by dynamic storage modulus E ' (ω) according to (11) formula, therefore in ageing process, the rate of change of different time E ' (ω) also reflects the rate of change of ultimate strength, can be used for predicting the sample interval of aging test.

The change of dynamic storage modulus E ' along with the conversion of the Dynamic mechanical property amounts such as loss modulus E ", storage compliance J ', loss compliance J ", losstangenttanδ, selects the most significant variable of change to compare as characteristic parameter equally in process of the test.

The constant temperature aging test of 2 travelling charges and tensile strength mechanics sample

Adopt safety-type constant temperature (water-bath) baking oven to carry out aging test, debugged water-bath baking oven, choosing uniform temperature is aging exploration condition.NEPE propellant block medicine is made 120mm × 25mm × 10mm rectangle test piece, be one group with every 6, be packaged in plastic-aluminum sample bag, choosing wherein one group of sample is the baking oven that retinue sample is placed in temperature constant in advance, after five days, powder charge sample is placed in baking oven, the time put in record; In process of the test, automatically record oven temperature by supervisory system, retinue sample is with whole ageing process.Take out powder charge sample at the different time of aging test process, obtain different aging degree of depth powder charge aging sample.

In accelerated test process, at set intervals, take out retinue sample, the DMA performance measurement test piece of 120mm × 10mm face cutting 35mm × 1.5mm × 10mm of a slice rectangle test piece wherein, and carry out DMA test, be fixed Dynamic mechanical property amount variation with temperature rule under frequency, when the rate of change difference of the Dynamic mechanical property parameter that this and front primary sample obtain meets or exceeds a certain particular value, then using the sample time of this retinue sample digestion time as powder charge aging sample.Residue retinue sample is still packaged in former aluminium plastic bag, continues to carry out accelerated storage test together with all the other powder charge samples.

Tensile test piece sample time in 3 Dynamic mechanical property quantitative change rate determination ageing processes:

(a) Dynamic mechanical property weight testing method

(1) NEPE propellant is in ageing process, and the main ultimate strength of investigation is tensile strength.Along with the continuity of test period, take out the retinue sample being placed in baking oven in advance, cutting DMA sample is to be measured, proceeds aging test after residue retinue sample is still packaged in former aluminium plastic bag.

(2) dynamic thermal machinery analyses (DMA) uses TA ARES G2 type flow graph.According to TA ARES G2 type flow graph DMA performance test methods, adopt torsional mode test fixture, the DMA test piece prepared is placed in test fixture, measure in-90 ~ 90 DEG C of temperature ranges, under fixed frequency (1Hz), storage modulus E', the loss modulus E of the aging sample of the different aging degree of depth " and the temperature variant rule of dissipation factor tan δ.

B () contrast is determined to change more significant dynamic mechanical variation characteristic parameter.

Retinue aging sample and the propellant original sample of the different aging degree of depth are compared, obtain the Dynamic mechanical property parameter and rate of change thereof that are changed significantly, and compare with last time aging sample of accompanying, and then identify the change of powder charge aging sample tensile strength, determine powder charge aging sample sample time.

Beneficial effect of the present invention is embodied in following several respects:

(1) the present invention proposes by difference aging degree of depth propellant Dynamic mechanical property quantitative change rate, determine the NEPE propellant accelerated storage test tensile strength change sample sampling time, avoid sample interval in sampling process too intensive or too loose, for powder charge aging sample provides the foundation of science sample time.

(2) the present invention is under the prerequisite not increasing sampling spot, and available minimum sample size carries out accelerated storage test, decreases in accelerated storage test owing to sampling the uneven dose waste caused.

(3) the present invention adopts the mode of retinue sample to be changed by the tensile strength of Dynamic mechanical property parameter identification aging sample, retinue sample dosage is less, can monitor whole aging test process by less dose, and DMA test dosage is little simultaneously, economy, safety.

Accompanying drawing explanation

Dissipation factor-the temperature variation of the aging sample of the different aging degree of depth of Fig. 1 NEPE propellant

(0: original sample, 1-5: aging different time sample)

Dissipation factor-temperature variation before and after the accelerated deterioration of Fig. 2 NEPE propellant

(0: original sample; The retinue aging sample of 1: aging three days; The retinue aging sample of 2: aging six days)

Embodiment

(1) constant temperature accelerated aging test

1. powder charge sample sealing, the sealing of retinue sample

NEPE propellant block medicine is made 120mm × 25mm × 10mm rectangle test piece, every 6 is one group, is packaged in plastic-aluminum sample bag, get wherein one group as retinue sample.

2. constant temperature accelerated aging test under design temperature

Debug safety-type water-bath baking oven, made its temperature constant at 70 DEG C ± 1 DEG C; Packaged retinue sample is placed in baking oven in advance, after five days, packaged powder charge sample is placed in baking oven, the time put in record; In process of the test, automatically record oven temperature by supervisory system;

3. sample sampling of accompanying is tested

In aging test process, the every other day time, take out retinue sample, after being cooled to room temperature, after the DMA test piece of 120mm × 10mm face cutting 35mm × 1.5mm × 10mm of a slice rectangle test piece wherein, residue sample is still packaged in former aluminium plastic bag, continues to carry out accelerated storage test as retinue sample together with powder charge sample.

(2) acquisition of dynamic mechanically mechanical characteristics amount

Dynamic mechanical is measured and is used TA ARES G2 type flow graph.According to TA ARES G2 type flow graph dynamic mechanically mechanic property test method, adopt torsional mode dynamic mechanical test fixture, the DMA test piece prepared is placed in test fixture, be determined in-90 ~ 90 DEG C of temperature ranges, under fixed frequency (1Hz), storage modulus E', the loss modulus E of the retinue sample of the original and different aging degree of depth " and the Dynamic mechanical property amount variation with temperature rule such as dissipation factor tan δ.

(3) tensile test piece sample time is predicted by Dynamic mechanical property parameter rate of change difference

Under fixed frequency, storage modulus E' reduces gradually with temperature, loss modulus E " and dissipation factor tan δ all first increases rear reduction with temperature; and peak value is there is in glass transition temperature range; thus can select loss modulus E " or the peak change rate of dissipation factor tan δ in glass transition temperature range is to identify the change of tensile strength in NEPE propellant accelerated aging test process, and the characteristic quantity that in choosing the two, rate of change is larger is as the reference quantity of aged samples sample time.This experiment adopts the change of tensile strength in the rate of change identification NEPE Propellant aging process of the test of tan δ peak value, and wherein the Changing Pattern of the retinue aging sample dissipation factor-temperature of the different aging degree of depth as shown in Figure 1.Dynamic mechanical property parameter tan δ peak change rate mathematic(al) representation is:

Wherein tn is current retinue aging sample digestion time, t ₀for original sample, Ts is reference temperature (glass transition temperature that tan δ peak value is corresponding), and tan δ is the peak value of dissipation factor in glass transition temperature range.

Retinue aging sample and the original sample of the different aging degree of depth are compared, and obtain the rate of change of tan δ peak value.Compare when this sub-sampling obtains retinue aging sample and original sample (being only limitted to the determination of the aging sample of powder charge for the first time sample time) or obtains with last sampling time point aging sample of accompanying, the rate of change difference of its Dynamic mechanical property parameter be (2.5 ± 0.2) % time, according to the correlativity of above-mentioned Dynamic mechanical property amount and tensile strength, show that the tensile strength of corresponding propellant also significant change occurs, it is aged samples sample time when thus adopting the retinue aging sample tan δ peak change rate difference of this retinue aging sample and front primary sample point to be (2.5 ± 0.2) %.

When the retinue aging sample tan δ peak change rate difference that this retinue aging sample and front primary sample time point obtain reaches (2.5 ± 0.2) %, record digestion time, and by the digestion time with this aging sample of accompanying, as the sample time of powder charge aging sample.When the retinue aging sample tan δ peak change rate difference that this accompanies aging sample and front primary sample point does not reach (2.5 ± 0.2) %, do not record this digestion time, residue retinue sample continues to be packaged in former aluminium plastic bag, and proceeds aging test together with all the other powder charge samples.When next retinue aging sample takes out, carry out DMA analysis of experiments, duplicate step of laying equal stress on.

Retinue sample is shifted to an earlier date five days in powder charge sample, be placed in the accelerated storage test baking oven that temperature is stable, carry out accelerated storage test, every other day get retinue sample, after the DMA performance test piece of 120mm × 10mm face cutting 35mm × 1.5mm × 10mm of a slice rectangle test piece wherein, carry out DMA analysis of experiments, and continued to be packaged in by residue retinue sample and be placed in baking oven in former aluminium plastic bag and proceed aging test, retinue sample is with the aging test process of whole powder charge sample.

Get NEPE propellant original sample and carry out dynamic mechanical analysis, the tan δ peak value obtained under reference temperature is 0.9571, get the accelerated storage retinue sample of three days and carry out dynamic mechanical analysis, obtaining tan δ peak value is 0.9836 (Fig. 2), then itself and original sample compare rate of change, namely rate of change is (0.9836-0.9571)/0.9571=2.77%, compare with primary sample, tan δ peak change rate difference reaches (2.5 ± 0.2) %, in the powder charge sample accelerated storage test carried out subsequently, then take out wherein one group of digestion time is that the powder charge sample of three days is as aging sample first time sampling, and record digestion time, get the accelerated storage retinue sample of six days and carry out dynamic mechanical analysis, obtaining tan δ peak value is 0.9994 (Fig. 2), then itself and original sample compare rate of change, namely tan δ rate of change is (0.9994-0.9571)/0.9571=4.42%, compare with a front sample (i.e. the retinue aging sample of aging three days), tan δ peak change rate difference is 4.42%-2.77%=1.65%, do not reach (2.5 ± 0.2) %, do not record digestion time, retinue sample proceeds accelerated storage test, treats lower sub-sampling.

Claims (6)

1. determine the method for NEPE propellant accelerated storage test sample time, it is characterized in that, comprise the following steps:

A, NEPE propellant block medicine is made 120mm × 25mm × 10mm rectangle test piece, every 6 is one group, is packaged in plastic-aluminum sample bag, and is placed in the baking oven setting temperature and carries out accelerated storage test;

B, accelerated storage test were every 1 ~ 3 day, get the wherein one group of sample in steps A, get same group of test piece later at every turn, and get wherein a slice rectangle test piece, and after the test test piece of cutting 35mm × 1.5mm × 10mm, residue sample is continued to be packaged in former aluminium plastic bag;

C, sample at every turn packaged in step B is continued to put into former baking oven carry out accelerated storage test together with other aging sample;

D, the test test piece of getting in step B are carried out testing and obtaining Dynamic mechanical property amount;

E, the test test piece obtained in step D to be compared with the Dynamic mechanical property amount of original sample, get the more significant characteristic quantity of change as Dynamic mechanical property parameter;

F, calculate adjacent two tests test pieces and original sample and compare, the rate of change of its Dynamic mechanical property parameter, in order to identify that the tensile strength of NEPE Propellant aging sample changes, thus determines the sample time of NEPE propellant accelerated storage test.

2. a kind of method determining NEPE propellant accelerated storage test sample time according to right 1, it is characterized in that, in described steps A, packaged NEPE propellant sample, get wherein one group of retinue sample as accelerated storage test, all the other samples are as aging sample, and getting wherein one group of sample in step B is retinue sample.

3. a kind of method determining NEPE propellant accelerated storage test sample time according to right 1, it is characterized in that, in described steps A, within 5 days, be placed in baking oven in powder charge sample carries out accelerated storage test to retinue sample in advance, and with the whole accelerated storage test process of NEPE propellant.

4. a kind of method determining NEPE propellant accelerated storage test sample time according to right 1, is characterized in that, adopts dynamic mechanical analysis technology to obtain Dynamic mechanical property amount in described step D.

5. a kind of method determining NEPE propellant accelerated storage test sample time according to right 1, it is characterized in that, the Dynamic mechanical property amount obtained in described step D comprises storage modulus E ', loss modulus E ", losstangenttanδ.

6. a kind of method determining NEPE propellant accelerated storage test sample time according to right 1, is characterized in that, in described step F, the determination of NEPE propellant accelerated storage test aging sample sample time comprises the following steps:

G, employing formula,

Wherein characteristic parameter _{tS (tn)}represent this retinue aging sample (tn) characteristic parameter value under reference temperature Ts, calculate the difference of the rate of change of adjacent two retinue aging sample Dynamic mechanical property parameters;

H, when calculating rate of change difference in step G and reaching (2.5 ± 0.2) %, record this retinue aging sample digestion time, and using the digestion time of this time as next powder charge aging sample; When calculating rate of change difference in step G and not reaching (2.5 ± 0.2) %, do not record the digestion time of this time retinue aging sample, step B ~ F in restore one's right profit 1 of laying equal stress on.