AN INFLUENCE OF SEGMENTED MANDREL ON STRENGTH PROPERTIES OF WOUND MOTOR CASE ICCM-16 PROCEEDINGS

Transcription

1 6 TH INTENATIONAL CONFEENCE ON COMPOSITE MATEIALS AN INFLUENCE OF SEGMENTED MANDEL ON STENGTH POPETIES OF WOUND MOTO CASE ICCM-6 POCEEDINGS A.S.Cherevatsky, G.aykin, M.Shabtai, M.Buyum [A.S.Cherevatsky]: IMI, amat-hasharon,pob 044,Israel Keywords: ilament winding,segmented mandrel,wrinkles,pressure test. Abstract In order to increase the eiciency o the ilament winding manuacturing process o motor case, based on using the washable mandrels, a segmented mandrel was designed and produced. This mandrel is assembled o longitudinal aluminum segments, connected together on both ends o an internal steel shat. Ater winding and curing o the irst case on the segmented mandrel it was ound that the ibers o the upper wound layers on the cylinder part o the case were wrinkled. This paper analyses the possible reasons o the phenomena by numerical simulation o mechanical interaction between mandrel and wet wound ibers. Special tests were perormed to prove the conclusions o simulation. Using the conclusions o simulation, some improvements were realized in mandrel design. As a result, the radial displacement o the segments decreased and iber's wrinkles disappeared. ater winding. An assembly o segmented mandrel is demonstrated on ig.. Fig.. Internal structure o segmented mandrel Structure o Segmented Mandrel Washable mandrels are usually used in the ilament winding manuacturing process o motor cases. An essential disadvantage o washable mandrels is their one cycle lie: or each one new case a new one mandrel should be produced. To increase the eiciency o the ilament winding process o motor case, a segmented mandrel was designed and produced. This mandrel is assembled o longitudinal aluminum segments, connected together on both ends o an internal steel shat, see ig.. Each segment has ew supports on the shat along its length. The ewer the segment supports, the easier the removal procedure o shat Fig.. Assembly o segmented mandrel Phenomenon o Wrinkled Fibers Ater winding and curing o the irst case on the segmented mandrel it was ound that the ibers o the upper wound layers on the cylinder part o the case were wrinkled, see ig.3.

2 ABEL.S.CHEEVATSKY, G.aykin, M.Shabtai, M.Buyum Wrinkles were located in two areas on the cylinder, along the trajectories o the helical wound layers. Each wrinkle was parallel to the longitudinal axis o the case. hardener. The wound mandrel was put into the oven (see ig.4) and heated according to the normal cure procedure. During various stages o cure the mandrel was pulled out rom the oven and checked. The phenomenon o wrinkled ibers was reproduced on the advanced stage o the curing, ig.5. Fig.3. Wrinkles on the external surace o the irst wound case During the pressure test o this case some wrinkled ibers broke locally under relatively low internal pressure, without general ailure o the case. The burst pressure o the case, achieved in this test, was essentially lower than the nominal value o the burst pressure or the same cases, manuactured on washable mandrels. 3 Special Heating Tests In order to investigate a wrinkling phenomenon and to identiy the type o wound layers that wrinkled, two special tests were designed and Fig.4. Mandrel wound without hardener enters the oven perormed. The segmented mandrel was wound by ibers, impregnated with resin only, without Fig.5. Wrinkles on the external surace o the heated case. Heating test Wrinkles were ound in upper hoop wound layers, and were oriented in the direction o helical wound ibers. Second heating test was perormed or same mandrel, wound dierently with ibers impregnated by resin without hardener: all upper hoop layers Fig.6. Wrinkles on the external hoop wound surace o the heated case in the heating test were wound only locally, on a restricted area o the cylinder. On the remaining part o the cylinder the upper wound layer was last helical layer.

3 AN INFLUENCE OF SEGMENTED MANDEL ON STENGTH POPETIES OF WOUND MOTO CASE As it was done in heating test, the wound mandrel was put into the oven and heated according to the normal cure procedure. The phenomenon o wrinkled ibers was reproduced once more on the advanced stage o the curing, on the hoop wound external surace o the case only, see ig.6. Ater cooling the heated mandrel all wrinkles disappeared, wound ibers lined up, as they were beore heating. 4 Mechanical Model o Mandrel/Fibers Interaction Due to the heating tests it was understood, that it is enough to explain the phenomenon as the interaction o heated mandrel with ibers, impregnated by virtual non-curable resin system. In the irst case the wrinkling phenomenon occurred but modiied by using a curable resin system during the winding. To investigate the reason o the wrinkles appearance, the stress-strain state o the wound non cured layers o ibers in interaction with the stressstrain state o the mandrel segments in heating process were analyzed. Symbols: E - Elastic modulus o impregnated ibers s - Fiber cross section area Z - Longitudinal coordinate o mandrel W - Width o wound ibers tow ε - Strain o helical wound ibers - External cylinder radius o mandrel r - External radius o shat L - Length o cylinder on room temperature - Indicates the parameter's value on the heating stage T - Maximum mandrel temperature in the oven above the room temperature - adius o curvature o cylinder in iber direction φ - Winding angle on cylinder T - Fiber tension W - adial displacement o segment under ibers pressure h - Vertical diagonal o elementary rhombus d - Horizontal diagonal o elementary rhombus α - Coeicient o thermal expansion o segment raw material α - Coeicient o thermal expansion o shat raw material The maximal longitudinal expansion o the mandrel's segment should be calculated according to the ormula: ( α ) ( ) L L + T The maximal radial expansion o the mandrel's cylinder should be calculated according to the ormula: ( + α T ) + ( r)( + α T ) ( ) r Tension along the iber is: T E ε s ( 3) where iber strain depends on thermal and mechanical deormations o the segments in the oven. As the result o segments deormation (composed o the longitudinal and radial thermal expansions and radial elastic displacements), the winding angles are changed, and the length o the iber's trajectory is changed also. This change determines the iber's strain. To estimate the change o the winding anglesthe elementary rhombus o the helical wound structure beore heating, see ig. 7,9 should be compared to the same rhombus ater heating, ig. 8,0. The initial winding angle in each station on the cylinder may be calculated rom the elementary rhombus: h tg ϕ ( 4) d Ater heating, the dimensions o the rhombus are deormed: π π ( w) h h ( + T ) d d α and winding angles are changed correspondingly: W tgϕ tgϕ ( + α T ) ( 5) ( 6) ( 7) 3

4 ABEL.S.CHEEVATSKY, G.aykin, M.Shabtai, M.Buyum L φ φ d h Fig. 7 The non-deormed structure o ibers on the cylinder φ φ d Fig. 9 Elementary rhombus o helically wound ibers beore heating h L φ Fig. 8 The deormed structure o ibers. on the cylinder φ <φ Fig. 0 Elementary rhombus o helically wound ibers ater heating Due to these assumption the elongation and strain o the helically wound ibers may be estimated as: ε L + tg ϕ dz 0 0 L 0 The elongation o the mandrel initiates the elongation o ibers, and increases the pressure between ibers and segments o the mandrel. Pressure o one helical wound layer (containing two hal layers wound with ±φ angles) on the cylinder part o the mandrel may be calculated as: q T W Finite elements model was used to describe the elastic radial displacements o the segments under external pressure and maximum temperature, see ig.. L + tg ϕ dz T sin ϕ W + tg ϕ dz ( 9) sin ϕ ( 0) ( 8) The domes area o the mandrel is relatively small in comparison with cylinder length, and radial elastic displacements are absent in this area, according to mandrel design, so we suppose, that the path o the wound ibers on the domes does not change essentially during the heating. 4

5 AN INFLUENCE OF SEGMENTED MANDEL ON STENGTH POPETIES OF WOUND MOTO CASE Fiber tension, ound on the i-stage o iteration process, is used to estimate the ibers pressure on the mandrel, and radial displacement o the segments on the (i+) iteration stage. The maximum (i+) stage pressure on the mandrel is compared with i-stage pressure. Iteration process, should be stopped, when the dierence in the pressure values is within the previously determined tolerance δ, see ig.. Fig. Vertical displacements o the segments o mandrel under external pressure and high temperature According to equation (-0) the radial displacement o the segment depends on the ibers pressure, which is a unction o radial displacement. These closed non-linear system o equations may be solved by the ollowing iteration procedure. Analytical model o ibers behavior during heating o mandrel End o calculations Calculation o ibers pressure on segments Yes FE model or calculation o radial displacements o segments No I pressure dierence between two last calculations smaller then δ Updated calculation o ibers pressure on segments Fig. An iteration process o calculations 5

6 ABEL.S.CHEEVATSKY, G.aykin, M.Shabtai, M.Buyum esults o calculations or designed segmented mandrel: mm MPa ε W max 3.7 q ε ε W max.7 q ε W max.5 q ε W max.35 q ε W max.308 q 0.56 ε W max.804 q 0.77 ε W max.844 q ε W max.8 q ε W max.83 q The value o maximum radial displacement o the mandrel, ound in iteration process, indicates that the ibers o the upper hoop wound layers should be ully loose. So, the wrinkles o the loose hoop wound ibers were ormed in the oven and cured on external surace o the irst wound case. Using the conclusions o stress-strain analysis, some improvements were realized in mandrel design. As a result, the radial displacement o the segments decreased, see ig. 3, and ibers wrinkles disappeared. Fig.3 Vertical displacements o the segments o improved mandrel under external pressure and high temperature 6