燃料电池电堆内部应力分布的模拟和压敏纸测量：介电材料和边框材料的应用、膜干湿对应力的影响［设计因素其三］Simulation and in situ measurement of stress distribution in a polymer electrolyte membrane fuel cell stack

Javier de la Cruz

Ulises Cano

Tatiana Romero

Abstract

A critical parameter for PEM fuel cell＇s electric contact is the nominal clamping pressure． Predicting the mechanical behavior of all components in a fuel cell stack is a very complex task due to the diversity of materials properties． Prior to the integration of a 3 kW PEMFC power plant， a numerical simulation was performed in order to obtain the mechanical stress distribution for two of the most pressure sensitive components of the stack： the membrane， and the graphite plates． The stress distribution of the above mentioned components was numerically simulated by finite element analysis and the stress magnitude for the membrane was confirmed using pressure films． Stress values were found within the elastic zone which guarantees mechanical integrity of fuel cell components． These low stress levels particularly for the membrane will allow prolonging the life and integrity of the fuel cell stack according to its design specifications．

Fig． 1． Fuel Cell： 3D Model and prototype built （see Fig． 2 for detailed description of components of a unit cell）．

Fig． 2． Single cell assembly components．

Fig． 3． Single cell assembly using pressure films．

Fig． 4． （a） Anode graphite plate stress distribution， anode side． （b） Anode graphite plate stress distribution， current collector side． （c） Cathode graphite plate stress distribution， anode side． （d） Cathode graphite plate stress distribution， current collector side．

Fig． 5． Membrane： （a） Cathode side， （b） Anode side．

这里应力最大的位置

red spots with 30 MPa， close to the yield limit for bare membranes使用的数据是Nafion211／Nafion212的官方干态数据。

为了缓解应力，使用了拉伸强度为80MPa的Sub－Gasket和拉伸强度为200MPa的介电材料。

The tensile strength of the semi rigid material （80 MPa， enhances the membrane＇s， preventing permanent damage on the membrane＇s area that receives the highest pressure from compression．

Besides， the presence of this sub－gasket reduces enormously the
possibility of thinness or rips in those areas where the membrane is
under higher stress due to shear stress caused by the graphite
plates＇ grooves．

Another benefit from this sub－gasket is its contribution
to the membrane＇s dimensional stability， reducing swelling
and contraction of the membrane＇s edge due to hydration cycles
during regular fuel cell duty．

Table 1 Mechanical properties of elements．

Table 2 Test information．

Fig． 6． Stress distribution： （a） Outside side of upper end plate， （b） Inner side of upper end plate， （c） Outside side of bottom end plate．

Fig． 7． Dry membrane： low pressure film．

Fig． 8． Super low pressure film： （a） （b） Dry membrane， （c） （d） Wet membrane．

湿膜压缩应力分布很少有文献涉及，膜吸湿后对压缩应力分布的影响需要定量。

Conclusion

In this work， mechanical properties of a fuel cell＇s components
were used for determining the compression distribution by finite
element analysis in a 3 kW PEMFC stack with a nominal clamping
pressure of 20 psi．

0．14MPa，这个压强并不大。但是原文中不是这个意思。

Each bolt of this assembly had applied a torque of 20 PSI， this
torque is equivalent to a force of 2468 N over eachwasher （stainless
steel）．

The numerical simulation and experimental tests performed for this work， confirmed that the design and nominal torque are within the safe mechanical limits for the membranes and metal and graphite plates， preventing permanent deformation even in the two most extreme water content conditions． Results from experimental tests， confirmed the simulation＇s results， highlighting the importance of using a semi rigid sub－gasket to protect the border of the MEA， the most mechanically stressed zone found．

The analysis showed that gas inlet and outlet zones， as well as areas
of the membrane in contact with rigid components require special
considerations during design to avoid stress concentration． The use
of materials to dissipate the load stress and protect sensitive materials
can be an alternative to maintain the integrity of the fuel cell
stack and prologue its lifetime．