“…In order to avoid local out-of-plane wrinkling in the recess area (which could interfere with the study) a [(90, 45 2 , −45 2 , 90, 0 2 ) 2 ] s lay-up was used, which previously has been proven not to wrinkle on this geometry. 16–18 This lay-up is partly co-stacked which is not favorable for avoiding squeeze flow 3,15 in the zero-degree fiber direction in the radius area. Figure 6.Double-curved spar geometry.…”
Section: Experimental Studymentioning
confidence: 99%
“…In order to avoid local out-of-plane wrinkling in the recess area (which could interfere with the study) a [(90, 45 2 , À45 2 , 90, 0 2 ) 2 ] s lay-up was used, which previously has been proven not to wrinkle on this geometry. [16][17][18] This lay-up is partly co-stacked which is not favorable for avoiding squeeze flow 3,15 in the zerodegree fiber direction in the radius area. As in the previous study, the steel sheet sandwich including the lay-up was heated in a dedicated oven to an even 65 C. After heat-up the steel sheet sandwich was placed on the cooled (-22 C) aluminum tool block and then the forming surface was covered with PU rubber.…”
Section: Forming Of Double Curved Spar Using Tailored Temperature Varmentioning
In this article, tailored temperature zones are used to obtain improved quality during rapid, high pressure forming of multi-stacked unidirectional prepreg. Particularly in aerospace applications, commonly used forming processes for multi-stacked unidirectional prepreg are often considered a bottleneck in production since the forming cycle requires both heating and cooling ramps and consequently takes long time—often about 1 h. It is possible to speed up the process by using elevated pressure and temperature. However, higher pressure and temperature also increase the influence of pressure gradient-driven, in-plane material movement (squeeze flow). This typically appears as radius thinning when forming a C-spar geometry on a male mold. Decrease of lay-up temperature will decrease radius thinning, but due to obstructed interply slippage, instead bending-induced wrinkles appear on the spar flange. In this article, tailored temperatures at the radius and in the flange area are introduced by using a hot lay-up and a cold mold. The results show that temperature differences of 6℃–10℃ between the radius area and the flange edge of the lay-up decreases radius thinning while still avoiding bending-induced wrinkles. Except from the radius temperature also the stacking sequence and the choice of prepreg system showed a significant influence on the radius thinning.
“…In order to avoid local out-of-plane wrinkling in the recess area (which could interfere with the study) a [(90, 45 2 , −45 2 , 90, 0 2 ) 2 ] s lay-up was used, which previously has been proven not to wrinkle on this geometry. 16–18 This lay-up is partly co-stacked which is not favorable for avoiding squeeze flow 3,15 in the zero-degree fiber direction in the radius area. Figure 6.Double-curved spar geometry.…”
Section: Experimental Studymentioning
confidence: 99%
“…In order to avoid local out-of-plane wrinkling in the recess area (which could interfere with the study) a [(90, 45 2 , À45 2 , 90, 0 2 ) 2 ] s lay-up was used, which previously has been proven not to wrinkle on this geometry. [16][17][18] This lay-up is partly co-stacked which is not favorable for avoiding squeeze flow 3,15 in the zerodegree fiber direction in the radius area. As in the previous study, the steel sheet sandwich including the lay-up was heated in a dedicated oven to an even 65 C. After heat-up the steel sheet sandwich was placed on the cooled (-22 C) aluminum tool block and then the forming surface was covered with PU rubber.…”
Section: Forming Of Double Curved Spar Using Tailored Temperature Varmentioning
In this article, tailored temperature zones are used to obtain improved quality during rapid, high pressure forming of multi-stacked unidirectional prepreg. Particularly in aerospace applications, commonly used forming processes for multi-stacked unidirectional prepreg are often considered a bottleneck in production since the forming cycle requires both heating and cooling ramps and consequently takes long time—often about 1 h. It is possible to speed up the process by using elevated pressure and temperature. However, higher pressure and temperature also increase the influence of pressure gradient-driven, in-plane material movement (squeeze flow). This typically appears as radius thinning when forming a C-spar geometry on a male mold. Decrease of lay-up temperature will decrease radius thinning, but due to obstructed interply slippage, instead bending-induced wrinkles appear on the spar flange. In this article, tailored temperatures at the radius and in the flange area are introduced by using a hot lay-up and a cold mold. The results show that temperature differences of 6℃–10℃ between the radius area and the flange edge of the lay-up decreases radius thinning while still avoiding bending-induced wrinkles. Except from the radius temperature also the stacking sequence and the choice of prepreg system showed a significant influence on the radius thinning.
“…Kulkarni et al [8] and Hassan [3] summarised numerous sources of fibre waviness. Some were inherent in the laminated composite: the stacking sequence [9,10], the difference of thermal expansion coefficients between the fibres and the matrix [11], the critical limb length [12], the inter-ply shear stress or the through-thickness compaction [13,14]. Other works have focused on the wrinkling sources in relation with the interactions between the part and the mould: the difference of thermal expansion coefficients [15,16], the proportion of 0 • plies and the size of the corner radius of the mould [17].…”
“…These methods are, however, computationally expensive due to the number of elements required to simulate wrinkle-scale deformations [16]. Recently, Johnson et al [27] proposed a Compatibility Index, a rapid analytical metric for laminate formability based upon the scalar products of eigenvectors representing low-energy deformation modes of adjacent plies, achieving excellent correlation with experimental forming trials. This method provides a suitable means of accounting for wrinkle formation within stacking sequence optimisation, which is not currently achievable using less efficient methods.…”
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