关注：

1) 应力计算：加应变， 计算应力(剪切应力+主应力)

2) 应力测试的方法：   氢脆、氦脆效应的研究

分享是一种美德，更是一种快乐

constr_cell_relax.F

cat  constr_cell_relax.F
!-----------------------------------------------------------------------
!
! At present, VASP does not allow to relax the cellshape selectively
! i.e. for instance only cell relaxation in x direction.
! To be more precisse, this behaviour can not be achived via the INCAR
! or POSCAR file.
! However, it is possible to set selected components of the stress tensor
! to zero.
! The most conveninent position to do this is the routines
! CONSTR_CELL_RELAX  (constraint cell relaxation).
! FCELL contains the forces on the basis vectors.
! These forces are used to modify the basis vectors according
! to the following equations:
!
!      A_OLD(1:3,1:3)=A(1:3,1:3) ! F90 style
!      DO J=1,3
!      DO I=1,3
!      DO K=1,3
!        A(I,J)=A(I,J) + FCELL(I,K)*A_OLD(K,J)*STEP_SIZE
!      ENDDO
!      ENDDO
!      ENDDO
! where A holds the basis vectors (in cartesian coordinates).
!
!-----------------------------------------------------------------------

     SUBROUTINE CONSTR_CELL_RELAX(FCELL)
     USE prec
     REAL(q) FCELL(3,3)

!     just one simple example
!     relaxation in x directions only
!      SAVE=FCELL(1,1)
!      FCELL=0   ! F90 style: set the whole array to zero
!      FCELL(1,1)=SAVE

     RETURN
     END SUBROUTINE

应力测试的方法：   氢脆、氦脆效应的研究

2008-Hydrogen Embrittlementof Metals

This fundamentaldifference in the phase diagrams results in a fundamental difference in thehydrogen damage processes. When the hydrogen content of aluminumor steel exceeds the solubility limit hydrogen gas bubbles should precipitate in the metal lattice,leading to hydrogen induced blistering or cracking.

In contrast,when the hydrogen content of zirconium, titanium, uranium and other hydrideforming metals exceeds the solubility limit, metalhydrides precipitate. The hydrides are typically low density, brittlecompounds whose presence degrades the ductility of the alloy.

Additionally,applied and/or residual stresses may interactwith the stresses associated with the volume expansion of the low densityhydride phase and effect the orientation and distribution of the hydrideprecipitates.

正文-氢损伤的N种表现-hydrogen embrittlement

 The four forms of hydrogen damage discussed previously

 (blistering, 

cracking from precipitation of internal hydrogen,

hydrogen attack ,

and crackingfrom hydride formation)

can be qualitatively understood by consideringthe influence of a phase transformation

(precipitation of a hydrogen gas bubble,t

he production of an insoluble gaseous product or the precipitation of ahydride) on the mechanical properties.

An understandingof the fifth form of hydrogen damage (hydrogen embrittlement)is much more elusive even though the first published papers on the subject werepublished over a century ago.

Early workdemonstrated that the susceptibility of mild steels to hydrogen embrittlementduring a tensile test is dependent on the testtemperature and strain rate, Figure 19.

Other workshowed that hydrogen embrittlement could occur whenthe applied stress level was below the yield strength of the material.

In this case thehydrogen embrittlement process is similar to thedelayed failure hydride embrittlement in titanium and zirconium welds,except that no hydride phase is formed. In fact, the term delayed failureoriginated from descriptions of hydrogen embrittlement in steels. Qualitatively delayed failure hydrogen embrittlement involves  the following generalized processes:

1) Hydrogen isintroduced into the component during manufacture (or service).

2) The absorbedhydrogen atom is too large to fit comfortably in the interstitial sites in the metal lattice and because of its mobility will migrateto extraordinary sites where the lattice is dilated【扩大的，膨胀的】.

3) The extraordinary sites in an unstressed componentare randomly distributed throughout the material and consist primarily ofinclusions, precipitates, dislocation tangles, grain boundaries and other suchmicrostructural features. The hydrogen is therefore distributed in amacroscopically random fashion and the local accumulations do not produce localfractures. This lack of hydrogen induced damage will persist until thecomponent is placed in service.

4) The serviceinduced loads will result in concentrated stresses which produce localized, macroscopicregions of lattice dilation. For example, the region immediately below a threadroot of a loaded bolt. Hydrogen will then migrate tothis region of lattice dilation.

When thehydrogen concentration in that localized region reachesa critical level, a crack will nucleate andpropagate through the region that has the high hydrogen concentration.

(Thetime required for this event to occur will depend on the metallurgicalcondition of the material, temperature of exposure, hydrogen content in thematerial and the magnitude of the stress concentration.The mechanism by which the hydrogen induced cracksnucleate and propagate remains a subject for scientific debate but this paperwill assume that hydrogen lowers the strength of the various microscopicinterfaces in the material and facilitates dislocationnucleation at the crack tip.)

5) The cracknucleation and/or extension process relieves thestresses and associated lattice dilationin the cracked region and moves the region of high stress and lattice dilationto a zone immediately below the new crack tip.

6) Hydrogen willrelocate to the newly dilated zone and the crack nucleation/propagation processwill repeat until either the crack reaches a critical size and the componentfractures or the stresses acting on the component have decreased to the pointthat a critical hydrogen concentration cannot be reached in the region oflattice dilation.

实验方面大牛：

段慧玲 

北京大学力学与工程科学系、系主任、长江学者特聘教授，国家杰出青年科学基金获得者。

弹性力学；非均质材料力学 ；流固耦合力学

http://www2.coe.pku.edu.cn/subpaget.asp?id=76

http://www2.coe.pku.edu.cn/faculty/duanhuiling/web/menu/publications.html

http://www2.coe.pku.edu.cn/faculty/duanhuiling/web/menu/group.html

北大教授段慧玲：要把钱给真正能做事的学者

http://mp.weixin.qq.com/s?__biz=MjM5MDAyMzQyMQ==&mid=204333819&idx=2&sn=1e3e45e589e0c2671f3a658f6fd4a12b&3rd=MzA3MDU4NTYzMw==&scene=6#rd

http://baike.baidu.com/link?url=NF70PXpUL03fy0xNEuJZ94J2cNXmpM0VZRMi3KzIMGsKJdiBXRuWixXyq6d0aEMZofAWsgn04pV99Ynkn8UnChl1q7nqKvkRPJ25PGr3AdW

来源：中国科学报

萧杨

近年来，科技体制改革不断深化。在国家层面，从之前的每个部委都掌握一定科研经费，变成了统一的“大平台”机制；在研究经费方面，从之前的直接经费、间接经费不分家，到目前基金委实行加大间接经费比例的“新政”，我国的科研经费管理体制不断有新的探索。

      日前在接受《中国科学报》记者采访时，北京大学工学院力学与工程科学系系主任、教育部“长江学者”特聘教授段慧玲对我国科研经费、基础研究等发表了看法。她认为，目前我国的基础研究经费不断增加，但更为重要的，应当是“基础研究要把钱给真正能做事的人，而且要有宽松的环境”。

     长期以来，我国科研经费拨款中一直存在“重设备，轻人头”的趋势。也就是说，大部分科研经费都用来购买各种昂贵的设备，但用于支付科研人员的劳务费、培养博士的人员费等却少得可怜，这一现象一直为科学家诟病。

    段慧玲指出，在国外，科研经费基本上都是用来养人的。“比如说我拿了50万美元的钱，可能有30万美元或者更多是用来招博士生或者博士后。我的项目申请就注明招博士后，这个博士后3年的工资就要花掉几十万。”

       具体而言，目前中国的科研经费中，劳务费基本只能占到10%，“这点钱基本上连学生的助学金都没法发。科研项目中有那么多钱在那儿放着，也需要很多人，但因为很多经费不能花在人身上，我们招不了博士后。”段慧玲指出，从这点来说，基金委在这方面的探索值得肯定，有了间接经费之后，增加了人员费的比例，方便科研人员招收博士后。

“在科研经费管理方面，国外一般都是把规则制定好了，大家去遵守。科研人员可以有更简单的生活，全部精力用来从事教学和科研。”段慧玲认为，国内在这一方面仍须加强。

段慧玲认为，目前基础研究的投入已较多。“中国的问题是，所有大学都想变成综合性大学，都想大量招本科生。应该有一些技术类的大学培养专门的人才，中国的制造业为什么这么差？一个原因就是没有技术工人。”她说。

段慧玲进一步指出，大学应该有明确的定位，并不是说所有的大学都要去搞基础研究，去做创新。现在的大学培养机制，导致很多博士毕业后根本不想做学术，只是把学历当敲门砖。因此，基础研究要把钱给真正愿意静下心来做学术的人。

分享是一种美德，更是一种快乐