PMI foam cores find further applications

PMI foam cores find further applications

PMI foam cores find further applications Composite sandwich applications Hermann foam T structures ranging F. Seibert and some from trains of R...

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PMI foam cores find further applications Composite


applications Hermann foam



ranging F. Seibert

and some

from trains of Rijhm

of its current

he first generation of polymethacrylimide (PMI) foams, marketed



[email protected] , was invented


on PMI core materials

and ships to automotive



and aerospace the properties

tradename 29 years ago.

specification. To date the foam has received 154 specifications worldwide, covering aerospace, ship and railcar manufacturing, as well as antenna and radome applications.




to complex


PM1 foams have a crosslinked, 100% closed cellular structure. The uniform material distribution throughout the cell walls gives excellent structural stability and a high level of mechanical strength. The imide groups in the chemical structure guarantee good performance at high temperatures. The entire manufacturing process is free of chlorofluorocarbons (CFCs) and halogens. Core shaping is very easy and can be realized with standard




PM1 foams

largest potential weight optimized with foam cores.



for manufacturing sandwich structures The payload fakings of the Delta II satellite launch vehicle are made using PM/ in a

The payload


the Delta vehicle


II satellite

are made

high performance grade

and of


using the PMI WF

in a co-curing

technique. PM1 foams also offer superior behaviour at elevated temperatures, which means that structural integrity of a sandwich structure can be maintained over a wide temperature range. It must be concluded that only the family of PM1 foams




the most


PMI offers










A comparison









of specific The



PM/ foam

strength/ has




can serve as a reliable sandwich core material at temperatures above 130°C. A significant decrease in performance first sets in at 180°C.

Creep compression


In addition to physical properties, the suitability of foam cores for particular manufacturing processes is interesting. While the sandwich cures, the foam core must withstand a combination of heat and pressure loads for a specified period of time. In this respect, creep compression resistance is the key factor that determines the reliability and reproducibility of sandwich component manufacture. Rohm carried out a series of tests to evaluate some typical foams.



of PMI


As a result of their superior to-weight

the interstage



honeycombs, ten times higher feed rates can be achieved. PM1 foams can also be

cessfully introduced in an aerospace programme and received its first aerospace


used in


wood cutting

Only three years later, PM1 foam was suc-



are being

launch vehicles

The payload fairings and the interstage section of the Delta II satellite launch vehicle are made using the high performance PM1 WF grade in a co-curing technique. These large components measuring 3 m in diameter and 9 m and 6 m in 0034-3617/00/$ Elsevier

- see front matter 0 2000 Science Ltd. A// rights reserved.

PM/ foam cores find further


The thermoforming behaviour

of PMI meant

core shaping work could be drastically


The new concept also marks a milestone in the manufacturing of railcars in Japan as it was the first time Japanese authorities ever allowed the use of composite structures. The composite solution is also likely to be used for the 700 Shinkansen

series as well as for the

Japanese MAGLEV railcar. length; are co-cured at 180°C. The foam core fully supports the prepreg during the curing step and, because of its excellent creep compression resistance, guarantees perfect consolidation of the laminate plus a smooth surface. Compared to the aluminium honeycomb cored version initially developed, the new manufacturing method is significantly cheaper. The cost reduction has two main origins. The conventional technique with the aluminium honeycomb demands a number of individual cure cycles, whereas the PM1 version is co-cured using only a single tool. In addition, because the PM1 foam fully supports the prepreg any dimpling effects at the surface are avoided. The prepreg layers are perfectly consolidated during the cure and therefore a high buckling resistance can be achieved with a reduced number of prepreg layers. In view of the significant cost savings potential, the PM1 foam manufacturing method has also been implemented for Boeing’s Delta III and Delta IV programmes. Mitsubishi Heavy Industries also uses the PM1 co-curing technology to manufacture the interstage section of its HIIA launch vehicle. Japanese high speed train Superior strength-to-weight ratio and high creep resistance were the deciding factors in choosing a PM1 foam core for

the front end of the E4 Shinkansen highspeed train operated by Eastern Japanese Railway. The impressive carbon fibrel epoxy resin skinned component, measuring approximately 5 m in length, is also manufactured by the cost effective single-step co-curing process. No other sandwich foam core with the very low density of 52 kg/m3 can offer the creep compression resistance required to withstand the high temperature and pressure loads associated with autoclaving. The PM1 core also contributed to significant cost savings as compared with the initial hand-shaped aluminium design, the favourable thermoforming behaviour of PM1 meant core shaping work could be drastically reduced.


of the

specific shear properties.

Dynamic shear modulus versus temperature.

Antenna systems Besides high mechanical



high temperature capabilities a special PM1 grade called HF, which shows excellent dielectric properties, is available. This, in combination with low weight and high strength, makes this particular foam the ideal dielectric to support or space electronic antenna devices. The above properties have also led to the use of PM1 foams in the manufacture of aircraft radomes. The thermoformability allows the realisation of complex and even double curved shapes. The foam shows very good impact resistance, whereas other foams do not pass the most common rain erosion test - they simply turn to dust. Helicopter engine cowling Besides the successful use of PM1 foam cores in the in-mould pressing technology for the manufacture of high performance helicopter rotor blades the new PM1 XT grade has opened up a new field of helicopter applications. Most recently 1 EUROCOPTER qualified the product for the manufacture of hat stringer stiffened engine cowlings for the Tiger helicopter. This part is co-cured using bismaleimide (BMI) prepregs. The new XT foam is the only rigid sandwich foam core to provide the required creep compression resistance to withstand the cure cycle. The components are post-cured at 230°C for nine hours to fully exploit the





PMI foam cores find further


density. Two different types - one in a density of 52 kg/m3, the other 75 kg/m3are available. The elongation properties are as follows : 51 FX Tensile elongation(%) Elongation in shear (%)

9 25

71 FX 9 12

The FX grade also offers excellent fatigue





example, crosslinked PVC foams and PEI foam in similar densities. A series of fourpoint bending tests carried out at the Aachen, University of


Germany, showed the superior performance of the new, more ductile PMI. Although PM1 foams have been in existence for almost 30 years now, they

properties of the BMI skins. It is the first time that a foam cored sandwich component could be manufactured in the one step co-curing process.

Car body structure The Italian company Modena Design, a performance manufacturer of high sports cars, used a PM1 cored sandwich structure to realise the car body structure of the ZONDA and to meet the requirements regarding light weight and high stiffness. The foam cored front sections contribute to a much better crash behaviour of the car. A similar construction using PM1 foam is used in the current Ferrari Formula 1 race cars.

New grades The existing product range of seven different grades has recently been widened by two new grades. The first, Rohacell XT, shows outstanding heat distortion temperature and excellent creep compression resistance. It completes the existing product line towards the very high temperature range. This particular sandwich foam core material is compatible with BMI prepregs cocuring at temperatures of up to 190°C and pressures of up to 0.7 MPa. Post curing temperatures



Ja n u a ry

2 000

of up to 235°C can be applied to exploit the Tg potential of the BMI matrix. The second new grade, Rohacell FX, combines ductility with suitability for exposure to and processing at high temperatures. The mechanical properties of this foam compare very well with those of a crosslinked PVC foam of similar

cannot be considered ‘old’ materials. PM1 foams have been successfully introduced into many different fields of application including sporting goods, xray tables, wind turbine blades, antennas and radomes, stealth applications, railway and ship building, automotive applications and aerospace. New developments are on their way to meet the growing demands of the dynamic comW posite industry.