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A micromechanics approach for damage modeling of polymer matrix composite

A micromechanics approach for damage modeling of polymer

matrix composites

E.J.Barbero

a,*

,G.F.Abdelal b ,A.Caceres

Mechanical and Aerospace Engineering,315Engineering Science Building,West Virginia University,Morgantown,WV 26505,USA

National Authority for Remote Sensing and Space Science,Giza,Egypt

Department of Civil Engineering,University of Puerto Rico at Mayag €u ez,Mayag €u ez,PR 00681-9041,Puerto Rico

Available online 25March 2004

Abstract

A new model for damage evolution in polymer matrix composites is presented.The model is based on a combination of two

constituent-level models and an interphase model.This approach reduces the number of empirical parameters since the two con-stituent-level models are formulated for isotropic materials,namely ?ber and matrix.Decomposition of the state variables down to the micro-scale is accomplished by micromechanics.Phenomenological damage evolution models are then postulated for each constituent.Determination of material parameters is made from available experimental data.The required experimental data can be obtained with standard https://www.wendangku.net/doc/5712008615.html,parison between model predictions and additional experimental data is presented.ó2004Elsevier Ltd.All rights reserved.

Keywords:Damage mechanics;Micromechanics;Composites;Stress concentration;Strain concentration;Periodic microstructure

1.Introduction

Using classical laminate theory and other similar approaches,polymer matrix composites (PMC)are routinely analyzed by assembling laminae response into laminate response models [8].The laminate-level re-sponse to external loads is then decomposed into lami-nae responses.That is,the point stress and strains on each homogeneous orthotropic lamina are found.When this approach is applied to modeling of damage,the major shortcoming is the large number of material constants required to represent the equivalent ortho-tropic material [4–6,22].There are only few material systems for which the whole set of sti?ness and strength values are available from experimental data.Each new ?ber/matrix combination requires a lengthy and expen-sive material characterization e?ort.The data are scar-cer with regards to damage evolution.

Advances in micromechanics allow us to predict lamina-scale sti?ness from constituent (?ber,matrix)properties.Some micromechanical models [15,23]make it possible to decompose the lamina-scale state variables

(e.g.,stress,strain,damage)into their components in each of the constituents.Therefore,damage evolution models and failure criteria can be formulated at the constituent-level.The model proposed herein accounts for di?erent initiation,evolution,and failure of the two main constituents (?ber and matrix)and,with the addition of an interphase model,it accounts for other e?ects not captured by the constituent models.Loss of transverse isotropy at the lamina-level due to damage can be predicted [12].The material parameters are determined by modeling standard material tests and adjusting individual material parameters to reproduce the observed material response.Then,model predictions for independent test conditions are compared with their corresponding test data.

In laminate analysis,each lamina is considered as a homogeneous material.The characteristic length of a material element over which the stress and strains do not change rapidly is the lamina thickness.The ?ber diam-eter,?ber spacing,and dimensions of micro-cracks are much smaller than the lamina thickness.Therefore,?ber breaks,matrix crazes and micro-cracks can be analyzed as distributed damage.Since damage of the ?ber phase contributes only to loss of sti?ness and strength in the ?ber direction,the characteristic length of the ?ber phase is of the order of the ?ber length,supporting the

Corresponding author.Fax:+1-304-2936689.

E-mail address:ebarbero@https://www.wendangku.net/doc/5712008615.html, (E.J.Barbero).

doi:10.1016/https://www.wendangku.net/doc/5712008615.html,pstruct.2004.02.001

Composite Structures 67(2005)

427–436

assumption that?ber breaks can be modeled as distrib-uted damage[19,29].In tensile loading normal to the ?bers,matrix cracks grow along the?ber length and can exceed the lamina thickness,which seems to invalidate the assumption of distributed damage.But if that hap-pens to a unidirectional lamina,such cracks lead to immediate failure.However,if such cracks grow in a laminate,their growth is controlled by the adjacent laminae and thus can be thought of distributed damage in the context of the laminate,not the lamina where they occur.In other words,transverse cracks can be still be accounted for by a CDM model in a lamina provided such lamina is part of a laminate,which is the practical case virtually all the time.An alternative option would be to formulate the damage model completely at the lamina level[4,5,21].Such approach requires a more extensive database of lamina strength values.In this work,it was decided to use the constituent-level approach because of the basic nature of the strength data required,namely ?ber strength,Weibull dispersion,and so on.

2.Damage model

The overall damage model is based on the combina-tion of damage models for?ber,matrix,and interphase [2,32–35].All three damage models are based on the concepts of continuous damage mechanics[20].For each phase,damage is represented by a state variable,in the form of a second-order damage tensor D ij,or by its complement the integrity tensor X ij?d ijàD ij.To pre-serve the symmetry of the e?ective stress tensor,a fourth-order damage-e?ect tensor is used to compute the e?ective stress from the damaged one.The damage-e?ect tensor M is univocally determined in terms of the sec-ond-order damage tensor D.Since tension,compression, and shear have di?erent e?ects on damage,crack closure coe?cients(0

r ij?M ijkl r kl

M ijkl?f ijkl h r kl i

1àD ij

f ijkl hàr kl i

1àc n D ij

I ijklàf ijkl

1àc s D ii

e1T

where f ijkl?1if i?j?k?l?1,zero otherwise,and <>is the McAuley bracket.

The analysis uses three con?gurations:e?ectiveerT, partially damagede~rTand damagederT.In the e?ective con?guration,the undamaged portion of?ber and ma-trix carry the load.In the partially damaged con?gura-tion,the?ber and matrix have distributed damage but the interphase damage is not present.In the damaged con?guration,all the damage is present.The three con?gurations are illustrated in Fig.1,starting with damaged on the right,partially damaged at the center,and e?ective on the left.These con?gurations are similar to those proposed in[32–35].The model is phenome-nological and damage is assumed to be distributed. Therefore,the model cannot predict microscopic fea-tures such as crack spacing[16,25,27,28,30].All forms of damage are homogenized and their e?ect is felt on the reduced sti?ness only.

Mapping between con?gurations is accomplished by the appropriate damage e?ect tensor,M L from damaged to partially damaged(due to interphase damage-e?ects), M f and M m from partially damaged to e?ective for?ber and matrix phases,respectively.The total damage-e?ect tensor M that accounts for the combined e?ect of?ber, matrix,and interphase damage is given by

M ijrs?ec f M f

ijkl

B f

kluv

tc m M m

ijkl

B m

kluv

TM L

uvrs

e2TAt each con?guration,mapping between phases (?ber,matrix,and interphase)is accomplished by micromechanics using the stress and strain concentra-tion tensors,B and A,respectively,according to

r r?B r:r;B r?C r:A r:Cà1

e r?A r:e;A r?Càf:B r:C

e3T

where r r indicates the stress in the phase r?f,m,l,and r is the stress in the homogenized material.In this work, these tensors represent the mapping of average stress and strains,which are averaged over the individual phases.The sti?ness tensor C of one con?guration(say damaged)is obtained in terms of the sti?ness C of the precursor con?guration(say virgin)by using the energy equivalence principle[20],as

C?Mà1:C:Mà1e4TEq.(3)account for the stress redistribution between the ?ber and the matrix that must take place when

both

428 E.J.Barbero et al./Composite Structures67(2005)427–436

phases undergo damage at di?erent rates.Stress redis-tribution also takes place at the macro-level(among laminae)as a result of updating the lamina sti?ness tensor C according to Eq.(4).

The stress and strain concentration tensors are ob-tained using[23]in the e?ective con?guration.Then,the concentration tensors in the partially damaged con?g-uration are computed as

e A f??v m Màm A m Aà

f Màftv f I à1

e A m?1

v m

?Iàv f e A f

I ijkl?1

ed ik d jltd il d jkT

e5T

Similar equations are used to compute the concen-tration tensors in the damaged con?guration in terms of the same in the partially damaged one.Also for each con?guration,the sti?ness tensor of the homogenized material is computed by C?v f C f A ftv m C m A m,where v f and v m are the?ber and matrix volume fractions of the current con?guration.The volume fractions in the damaged con?guration are those determined during fabrication of the composite.The volume fractions in the e?ective con?guration are di?erent that those in the damaged con?guration because the e?ective con?gura-tion deals with the volume of undamaged?ber and matrix,both of which are di?erent from the original volumes of?ber and matrix of the as-produced com-posite.The?ber and matrix volume fractions in the e?ective con?guration are computed by taking into ac-count the amount of damaged volume in the?ber and matrix phases[2,11],as follows

v r?

v re1àD r

v fe1àD f

Ttv me1àD m

D r

eq ?eD r

D r

T1=2

e6T

3.Damage evolution

A damage surface is assumed to limit the space of thermodynamic forces Y for which no damage occurs,as follows geY;cT?

??????????????????

Y:J:Y

??????????????

j H:Y j

àectc0Te7Twhere J and H are second-order tensors of material

coe?cients which are univocally related to the material properties of each phase,c is the hardening parameter in

Y-space,and c

is the damage threshold in Y-space.In this work,an o?-centered surface is used[5]to account for di?erent behavior in tension and compression of each phase.Two two-dimensional views of the g-surface are shown in Fig.2.The second-order tensor Y contains the thermodynamic forces,dual to the damage tensor,in the thermodynamic sense as Y?o w?1o?C:e:e , where the free energy w is given by the sum of the strain energy p plus the damage dissipation potential C,as w?pee;DTtCedT,where d is an intermediate variable such that d d?àl and l is the damage multiplier,ob-tained by satisfying the consistency conditions g?0and d g?0.Based on experimental observations[26,36],it is possible to assume that the damage principal directions coincide with the principal material directions,in which case the damage and integrity tensors become diagonal. With this simpli?cation,it is possible to derive explicit equations relating the thermodynamic forces to the stress components.For example,using contracted notation[8]and a state of plane stress we have

Y1?

C11

C12

r1r2t

C66

Y2?

C22

C12

r1r2t

C66

Y3?0

e8T

Using these explicit equations,the damage surface can be written in stress space,and its shape is the same as that of the Tsai-Wu quadratic failure criterion,but its size is variable as controlled by the magnitudes of the damage threshold c0and hardening parameter c.In summary,Eq.(7)reduces to

g?f ij r i r jtf i r iàectc0T;ei?1;2;...;6Te9TEq.(9)coincides with the Tsai-Wu criterion when

ctc

?1.Since the Tsai-Wu criterion predicts lamina failure in terms of available strength data,it is possible to determine all the coe?cients of the tensors J and H

in Fig.2.Damage surface in thermodynamic force Y-space.

E.J.Barbero et al./Composite Structures67(2005)427–436429

Eq.(7),or f ij and f i in Eq.(9),in terms of available strength data for each phase(see Table1),as described in Section4.The size of the damage surface in Y-space evolves according to the following equation

celT?o w

o d

?c1?1texpeàd=c2T

d d?l o g

o c

?àl

e10T

in terms of two empirical parameters c1and c2to be determined from experiments.The damage multiplier l is found interactively so that the consistency conditions g?0and d g?0are met.That is,after an increment of strain that causes damage,the Y-state must remain on the g?0surface with no further change of that surface ed g?0T.Once the damage surface is reached,damage accumulates along the normal to the damage-?ow sur-face

feY;cT?

??????????????????

Y:J:Y

àectc0Te11T

The magnitude of additional damage is controlled by

the damage multiplier so that(see Fig.3)d D ij?l o f

ij ;

D ij?R

d D ij;X ij?d ijàD ij.A transversely isotopic

lamina may become orthotropic as a result of damage [12],which is allowed in the formulation by virtue of Eq.

(4)using and orthotropic damage tensor D and damage-e?ect tensor M.Also,the model separates damage in the ?ber and matrix,and redistributes the stress into the ?ber and matrix.4.Determination of model parameters

Nine model parameters(three per phase)are neces-

sary to track the evolution of damage.For each phase (?ber,matrix,and interphase),there are two parameters ec1;c2Tin the evolution law Eq.(10)and the damage threshold c0in Eq.(7).The nine parameters are deter-mined by modeling standard material tests for which data are available.The procedure is illustrated using available data for T300/5208(Table1)[14]and LTM45EL-SM unidirectional tape data(Table2)[38]. The intermediate parameters in Tables3and4are computed as explained in Section 5.The following procedure is used to adjust the nine damage parameters for each material.

First,a longitudinal tensile test(ASTM D3039[3])is simulated.The?ber parametersec f

;c f

Tare adjusted so that at failure the?ber stress equals the?ber strength F ft and the?ber damage equals the known value D ft?1àexpeà1=mT,where m is the Weibull modulus [19,29],which is available[18,24,31](Tables1and2).

Second,a transverse tensile test is simulated[3].The

matrix parametersec m

;c m

Tare adjusted so that at failure the transverse stress equals the known transverse strength of the composite F mt and the matrix damage equals D mt?1=2as estimated by[17](Tables1and2).

Next,adjust the interphase parametersec L

;c L

Tto minimize any discrepancies between the shape of the shear stress-strain plot and the corresponding experi-mental data of a unidirectional lamina(see Section5.3). This is illustrated in Figs.4and5.The error is measured by the v2statistical measure of the di?erence between the predicted values p i and the experimental values e i

v2?

ep2

àe2

e i

e12T

The values obtained are shown in Tables5and6.The model is then used to predict the response of other laminates.The predictions are then compared in Section 7against experimental data that was not used to adjust the model parameters.

Table1

Material properties for T300-5208

Property Fiber Matrix Lamina Modulus,E(GPa)230 4.6–

Poisson’s ratio m0.220.380.284

Initial volume

fraction

0.60.4–

F t,(GPa) 3.6540.0586 1.550(longitudinal) F c,(GPa) 1.0960.1876 1.096(longitudinal) Critical D t0.1051610.50.105161

Critical D c0.1109450.50.110945

F6,(GPa)––0.08616

G12,(GPa)104.545 1.667 5.090

Weibull

dispersion m

0.89–

–

Table2

Material properties for LTM45EL-SM

Property Fiber Matrix Lamina

Modulus,E(GPa)235 2.9–

Poisson’s ratio m0.20.380.3

Initial volume

fraction

0.50.5–

F t,(GPa) 3.6540.0281 1.330(longitudinal)

F c,(GPa) 1.1730.0945 1.173(longitudinal)

Critical D t0.1051610.50.105161

Critical D c0.1109450.50.110945

F6,(GPa)––0.0745

G12,(GPa)96.3110.760 4.0

Weibull dispersion m0.89––

430 E.J.Barbero et al./Composite Structures67(2005)427–436

5.Determination of intermediate constants

The coe?cients in the second-order tensors J and H are intermediate constants introduced in order to write the damage surface in a concise form.They are not adjustable parameters.The values of the constants are determined univocally in terms of available sti?ness and strength material properties.The relationship between the coe?cients in J and H and the material properties is established in this section.Since the principal directions of damage in each phase is assumed to coincide with the material directions of the lamina,the tensors J and H are diagonal.5.1.Intermediate constants for the matrix

Since the matrix is isotropic,J33?J22?J11and H33?H22?H11.The values of J11and H11for the ma-trix are obtained by writing Eq.(7)for the case of tensile and compressive failure of the matrix as

??????

J11

p C

??????????????????????????

j H11j

C11

v u

u t

??????

J11

p C

??????????????????????????

j H11j

C11

v u

u t

e13T

Table3

Intermediate coe?cients in terms of properties in Table1

Parameter Fiber Matrix Interphase

H10.263003·10à130.214158·10à130.147130·10à10

H2?H30.263003·10à130.214158·10à130.731900·10à13

J11)0.142753·10à5)0.616990·10à6)0.313700·10à4

J22?J33)0.142753·10à5)0.616990·10à60.129691·10à8

Table4

Intermediate coe?cients in terms of properties in Table2

Parameter Fiber Matrix Interphase

H1)0.1947072329e)4)0.7727031701e)6)0.1056696052e)6

H2?H3)0.1947072329e)4)0.7727031701e)60.4920883693e)2

J110.2332145379e)120.1863544484e)130.3816379041e)15

J22?J330.2332145379e)120.1863544484e)130.9059230378e)8

E.J.Barbero et al./Composite Structures67(2005)427–436431

where F t?F mt,F c?F mc are the tensile and compressive strength of the matrix,respectively,X mt and X mc are the critical values of integrity at failure.For a brittle matrix, X mt?X mc?0:5[17].

5.2.Intermediate constants for the?ber

Although anisotropic?bers are allowed by the model, it is more practical to assume that the?bers are isotro-pic.Then J33?J22?J11and H33?H22?H11.The val-ues of J11and H11for the?bers are obtained using Eq.

(13)setting F t?F ft,F c?F fc for the case of tensile and compressive failure of the?ber.In the case of?bers,the tensile strength of?ber F ft,can be reached by subjecting a composite to longitudinal tensile loading but the compressive strength of?bers cannot be reached since the?bers buckle?rst.Therefore,F fc corresponds to the compressive strength of the composite.The critical values of integrity for tensile behavior of the?bers is limited by the number of unbroken?bers at failure according to the weakest link model[19,29];that is X ft?expeà1=mTor about0.894for?ber Weibull dis-persion m?8:9[18].For compression,the critical integrity corresponds to the number of unbuckled?bers carrying load at the onset of kink-band formation,with can be approximated as

X fc?erf

a cr

???

e14T

where erf is the error function,a cr is the?ber angle at failure,and K is the standard deviation of?ber mis-alignment[8–10,37].Using data from the literature [7,13,14,21],Eq.(14)yields X fc?0:9for all the materi-als considered in this work.

5.3.Intermediate constants for the interphase

The e?ects of interphase damage are accounted for at the lamina level.Since a lamina is initially a transversely isotropic material,J33?J22and H33?H22.The inter-mediate constants J11and H11can be found by consid-ering the tensile and compressive tests of a unidirectional lamina.Therefore,using Eq.(13)with F t?F1t,F c?F1c being the tensile and compressive strength of the lamina,respectively,X t and X c are the critical values of integrity at failure.For tensile behavior X t?0:1[19,29]and for compression X c?0:9[9].The values of J22and H22are found as follows.

Let the?ber-reinforced lamina be subjected to a transverse uniaxial load,so that the only stress compo-nent di?erent from zero is r2.The expression of the damage surface can be written in terms of the tensile failure strength of the material in the transverse direc-tion.Then,the component J22can be derived as a function of H2as

J22?1à

????????????????

j H2j

C22

F2t

C22

F2t

!à2

e15T

where the parameter X2t is the critical value of the integrity component X2for tensile loading in the trans-verse direction.Since brittle fracture of the matrix controls the transverse tension strength of a lamina,the limiting value of the component X2of the integrity tensor can be found using the brittle loose bundle model [17],which yields X2t?0:5.

Next,let us consider the?ber-reinforced lamina subject to a state of inplane shear,so that the only stress component di?erent from zero is r6.In this case Eq.(6), in terms of the inplane shear strength of the lamina F6, reduces to

Table5

Damage parameters for T300-5208

Parameter Fiber Matrix Interphase

C1 1.0 1.0 1.0

C2)1.1·105)4.2·106)1.5

c0)6.5 2.00.0

Table6

Damage parameters for LTM45EL-SM

Parameter Fiber Matrix Interphase

c1111

c2)5e2)6.2e6)1.5

c0)6.5 1.750

432 E.J.Barbero et al./Composite Structures67(2005)427–436

???????????????????

J11 X4

1s t

J22

2C66

1s X2

??????????????????????????????????????

2C66

v u

u t

?ec?tc0T?1e16Twhere X1s and X2s are the critical values of the integrity component X1,X2for a state of inplane shear stress. Since the shear response of a?ber-reinforced lamina along material principal directions is independent of the sign of the shear stress,the coe?cient of the linear term in Eq.(16)must be zero,leading to the relationship

H2?àX2

H1?àr s H1;r s?

e17T

Then,the component J22can be written as a function of the parameter r s using Eq.(15).Hence,Eq.(16) becomes

??????????????????????

J11r s k s t

J22 k s r s

2C66 k s F2

?1;k s?X2

e18T

Finally,Eq.(18)can be solved to obtain the value of the parameter r s,which is then used to compute J22and H2. Experimental evidence reveals a highly nonlinear behavior for a?ber-reinforced lamina subject to inplane shear.Writing the shear stress-strain law in the damaged and undamaged con?gurations we have

r6?2G12X1X2e6?2G12e6

X1X2

e19T

Calling G?

12the value of the unloading(damaged)shear

modulus just prior to failure,and G12to the virgin shear modulus,we have

k s?X2

1s X2

?G?

=G12e20T

Thus,only the critical value of the product of the integrity parameters in shear can be determined and not their individual values.This is a consequence of the assumption that the principal directions of the second-order damage tensor D remain aligned with the material principal directions over the entire life of the material. Under these conditions,shear damage is interpreted as a combination of longitudinal and transverse matrix cracks,which is supported by experimental observations [26,36].However,as experimentally observed,most of the damage is in the form of?ber-matrix debonding along the?bers,resulting in D2s>D1s,and from Eq.

(17)we obtain a restriction on the value of r s,namely 0

6.Finite element implementation

The damage model was implemented as a user material subroutine(UMAT)into Abaqus[1].The model updates the stress,damage,and sti?ness at each Gauss point as a function of the increment of strain D e provided by Abaqus.If D e is too large,it is subdivided inside the UMAT to achieve convergence at the end of the De interval before returning to Abaqus.

Eight-node solid elements are used for the analysis. The layered structure inside the element is described in the standard Abaqus way[1].Only nine empirical parameters are used to de?ne the damage behavior of the material.These are c1,c2,and c0,for?ber,matrix, and interphase(Table5).They are entered as parame-ters to the UMAT.The model,as implemented in the UMAT,calculates forty-two state variables internally. These are:

Nine components of the damage tensors;three for each phase.

Nine components of the thermodynamic force ten-sors,three for each phase.

Twelve components of the stress tensors,six for?ber and six for matrix.

Three values of the damage surface g for?ber, matrix,and interphase.

Three values of hardening c for?ber,matrix,and interphase.

Three?ags to indicate if the damage surface has been reached.

The problem is discretized in the usual way.Appro-priate boundary conditions are applied on the discreti-zation to simulate the strain?eld of the material tests used for validation.

https://www.wendangku.net/doc/5712008615.html,parison with experimental data

The damage parameters for T300/5208and LTM45EL-SM were determined in Section4using ?ber and matrix properties,and a limited number of lamina properties.Several laminates are analyzed next by using the ABAQUS implementation of the damage model.

First,consider LTM45EL-SM,where SM stands for standard modulus?bers[38].Comparison of predicted and experimental results for an inplane shear test of[0/ 90]s is shown in https://www.wendangku.net/doc/5712008615.html,parison of predicted and experimental results for an axial loading test of[45/)45]s is shown in Fig.7.

E.J.Barbero et al./Composite Structures67(2005)427–436433

Next,for T300/5208,comparison of predicted and experimental results for an inplane shear test of[0/90]2s is shown in https://www.wendangku.net/doc/5712008615.html,parison of predicted and experimental results for an axial loading test of[45/ )45]2s is shown in Fig.9.

The damage model can be used to predict the stress in the?ber and the matrix,as shown in Fig.10for Fiberite M40/949carbon/epoxy unidirectional composite.The material properties are available in[36].8.Conclusions

The proposed model utilizes nine damage parameters, which need to be adjusted with experimental data.Only experimental data available in he literature is needed. No especial tests are required beyond those commonly performed to characterize polymer matrix composites. The orthotropic nature of damage in polymer matrix composites is accounted for.Stress,damage,and de-graded sti?ness of each constituent are predicted. Damage induces stress redistribution.The model ac-counts for stress redistribution among the constituents

434 E.J.Barbero et al./Composite Structures67(2005)427–436

and among the laminae.Implementation of the model into Abaqus allows for analysis of complex structures but its current implementation is computationally expensive.Further work is envisioned to reduce the computational expense.

Acknowledgements

The?nancial support of the Federal Railroad Administration through grant#DT-FR-53-94-G-00039 is gratefully acknowledged.References

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英语选修六课文翻译Unit5 The power of nature An exciting job的课文原文和翻译

AN EXCITING JOB I have the greatest job in the world. I travel to unusual places and work alongside people from all over the world. Sometimes working outdoors, sometimes in an office, sometimes using scientific equipment and sometimes meeting local people and tourists, I am never bored. Although my job is occasionally dangerous, I don't mind because danger excites me and makes me feel alive. However, the most important thing about my job is that I help protect ordinary people from one of the most powerful forces on earth - the volcano. I was appointed as a volcanologist working for the Hawaiian V olcano Observatory (HVO) twenty years ago. My job is collecting information for a database about Mount Kilauea, which is one of the most active volcanoes in Hawaii. Having collected and evaluated the information, I help other scientists to predict where lava from the volcano will flow next and how fast. Our work has saved many lives because people in the path of the lava can be warned to leave their houses. Unfortunately, we cannot move their homes out of the way, and many houses have been covered with lava or burned to the ground. When boiling rock erupts from a volcano and crashes back to earth, it causes less damage than you might imagine. This is because no one lives near the top of Mount Kilauea, where the rocks fall. The lava that flows slowly like a wave down the mountain causes far more damage because it

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英语选修六课文翻译第五单元word版本

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英语选修六课文翻译第五单元 reading An exciting job I have the greatest job in the world. travel to unusual places and work alongside people from all over the world sometimes working outdoors sometimes in an office sometimes using scientific equipment and sometimes meeting local people and tourists I am never bored although my job is occasionally dangerous I don't mind because danger excites me and makes me feel alive However the most important thing about my job is that I heIp protect ordinary people from one of the most powerful forces on earth-the volcano. I was appointed as a volcanologist working for the Hawaiian Volcano Observatory (HVO) twenty years ago My job is collecting information for a database about Mount KiLauea which is one of the most active volcanoes in Hawaii Having collected and evaluated the information I help oyher scientists to predict where lava from the path of the lava can be warned to leave their houses Unfortunately we cannot move their homes out of the way and many houses have been covered with lava or burned to the ground. When boiling rock erupts from a volcano and crashes back to earth, it causes less damage than you might imagine. This is because no one lives near the top of Mount Kilauea, where the rocks fall. The lava that flows slowly like a wave down the mountain causes far more damage because it buries everything in its path under the molten rock. However, the eruption itself is really exciting to watch and I shall never forget my first sight of one. It was in the second week after I arrived in Hawaii. Having worked hard all day, I went to bed early. I was fast asleep when suddenly my bed began shaking and I heard a strange sound, like a railway train passing my window. Having experienced quite a few earthquakes in Hawaii already, I didn't take much notice. I was about to go back to sleep when suddenly my bedroom became as bright as day. I ran out of the house into the back garden where I could see Mount Kilauea in the distance. There had been an eruption from the side of the mountain and red hot lava was fountaining hundreds of metres into the air. It was an absolutely fantastic sight. The day after this eruption I was lucky enough to have a much closer look at it. Two other scientists and I were driven up the mountain and dropped as close as possible to the crater that had been formed duing the eruption. Having earlier collected special clothes from the observatory, we put them on before we went any closer. All three of us looked like spacemen. We had white protective suits that covered our whole body, helmets,big boots and special gloves. It was not easy to walk in these suits, but we slowly made our way to the edge of the crater and looked down into the red, boiling centre. The other two climbed down into the crater to collect some lava for later study, but this being my first experience, I stayed at the top and watched them.

人教版英语选修六Unit5 the power of nature(An exciting Job)

高二英语教学设计 Book6 Unit 5 Reading An Exciting Job 1.教学目标（Teaching Goals）: a. To know how to read some words and phrases. b. To grasp and remember the detailed information of the reading material . c. To understand the general idea of the passage. d. To develop some basic reading skills. 2.教学重难点: a.. To understand the general idea of the passage. b. To develop some basic reading skills. Step I Lead-in and Pre-reading Let’s share a movie T: What’s happened in the movie? S: A volcano was erupting. All of them felt frightened/surprised/astonished/scared…… T: What do you think of volcano eruption and what can we do about it? S: A volcano eruption can do great damage to human beings. It seems that we human beings are powerless in front of these natural forces. But it can be predicted and damage can be reduced. T: Who will do this kind of job and what do you think of the job? S: volcanologist. It’s dangerous. T: I think it’s exciting. Ok, this class, let’s learn An Exciting Job. At first, I want to show you the goals of this class Step ⅡPre-reading Let the students take out their papers and check them in groups, and then write their answers on the blackboard (Self-learning) some words and phrases：volcano, erupt, alongside, appoint, equipment, volcanologist, database, evaluate, excite, fantastic, fountain, absolutely, unfortunately, potential, be compared with..., protect...from..., be appointed as, burn to the ground, be about to do sth., make one’s way. Check their answers and then let them lead the reading. Step III Fast-reading 这是一篇记叙文，一位火山学家的自述。作者首先介绍了他的工作性质，说明他热爱该项工作的主要原因是能帮助人们免遭火山袭击。然后，作者介绍了和另外二位科学家一道来到火山口的经历。最后，作者表达了他对自己工作的热情。许多年后，火山对他的吸引力依然不减。 Skimming Ⅰ.Read the passage and answer: (Group4) 1. Does the writer like his job?( Yes.) 2. Where is Mount Kilauea? (It is in Hawaii) 3. What is the volcanologist wearing when getting close to the crater? (He is wearing white protective suits that covered his whole body, helmets, big boots and

Unit5 Reading An Exciting Job(说课稿)

Unit5 Reading An Exciting Job 说课稿 Liu Baowei Part 1 My understanding of this lesson The analysis of the teaching material:This lesson is a reading passage. It plays a very important part in the English teaching of this unit. It tells us the writer’s exciting job as a volcanologist. From studying the passage, students can know the basic knowledge of volcano, and enjoy the occupation as a volcanologist. So here are my teaching goals: volcanologist 1. Ability goal: Enable the students to learn about the powerful natural force-volcano and the work as a volcanologist. 2. Learning ability goal: Help the students learn how to analyze the way the writer describes his exciting job. 3. Emotional goal: Make the Students love the nature and love their jobs. Learn how to express fear and anxiety Teaching important points: sentence structures 1. I was about to go back to sleep when suddenly my bedroom became as bright as day. 2. Having studied volcanoes now for more than twenty years, I am still amazed at their beauty as well as their potential to cause great damage. Teaching difficult points: 1. Use your own words to retell the text. 2. Discuss the natural disasters and their love to future jobs. Something about the S tudents: 1. The Students have known something about volcano but they don’t know the detailed information. 2. They are lack of vocabulary. 3. They don’t often use English to express themselves and communicate with others.

an exciting job 翻译

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英语选修六课文翻译第五单元

新目标英语七年级下册课文Unit04

新目标英语七年级下册课文Unit04 Coverstion1 A: What does your father do? B: He＇s a reporter. A:Really?That sounds interesting. Coverstion2 A:What does your mother do,Ken? B:She＇s a doctor. A:Really?I want to be a doctor. Coverstion3 A:What does your cousin do? B:You mean my cousin,Mike? A:Yeah,Mike.What does he do? B:He is as shop assistant. 2a,2b Coverstion1 A: Anna,doesyour mother work? B:Yes,she does .She has a new job. A:what does she do? B: Well ,she is as bank clerk,but she wants to be a policewoman. Coverstion2 A:Is that your father here ,Tony?

B:No,he isn't .He's working. B:But it's Saturday night.What does he do? B:He's a waiter Saturday is busy for him. A:Does he like it? B:Yes ,but he really wants to be an actor. Coverstion3 A:Susan,Is that your brother? B:Yes.it is A:What does he do? B:He's a student.He wants to be a doctor. section B , 2a,2b Jenny:So,Betty.what does yor father do? Betty: He's a policeman. Jenny:Do you want to be a policewoman? Betty:Oh,yes.Sometimes it's a little dangerous ,but it's also an exciting job.Jenny, your father is a bank clerk ,right? Jenny:Yes ,he is . Sam:Do you want to be a bank clerk,too? Jenny:No,not really.I want to be a reporter. Sam: Oh,yeah?Why? Jenny:It's very busy,but it's also fun.You meet so many interesting people.What about your father ,Sam. Sam: He's a reporter at the TV station.It's an exciting job,but it's also very difficult.He always has a lot of new things to learn.Iwant to be a reporter ,too

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人教版选修Unit 5 The power of nature阅读课教学设计 Learning aims Knowledge aims: Master the useful words and expressions related to the text. Ability aims: Learn about some disasters that are caused by natural forces, how people feel in dangerous situations. Emotion aims: Learn the ways in which humans protect themselves from natural disasters. Step1 Leading-in 1.Where would you like to spend your holiday? 2.What about a volcano? 3.What about doing such dangerous work as part of your job ? https://www.wendangku.net/doc/5712008615.html, every part of a volcano. Ash cloud/volcanic ash/ Crater/ Lava /Magma chamber 【设计意图】通过图片激发学生兴趣，引出本单元的话题，要求学生通过讨论, 了解火山基本信息，引出火山文化背景，为后面的阅读做铺垫。利用头脑风暴法收集学生对课文内容的预测并板书下来。文内容进行预测，培养学生预测阅读内容的能力。同时通过预测激起进一步探究 Step2. Skimming What’s the main topic of the article?

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Unit1 SectionA 1a Canada, France ,Japan ,the United States ,Australia, Singapore ,the United Kingdom,China 1b Boy1:Where is you pen pal from,Mike? Boy2:He's from Canada. Boy1:Really?My pen pal's from Australia.How about you,Lily?Where's your pen pal from? Girl1:She's from Japan.Where is Tony's pen pal from? Gril2:I think she's from Singapore. 2b 2c Conversation1 A: Where's you pen pal from, John? B: He's from Japan, A:Oh,really?Where does he live? B: Tokyo. Conversation2 A: Where's your pen pal from, Jodie? B: She's from France. A: Oh, she lives in Pairs. Conversation3 A: Andrew, where's your pen pal from? B: She's from France. A: Uh-huh. Where does she live? B: Oh, She lives in Paris.