The injection moulding process is a well-known manufacturing process in the automotive industry for producing plastic injection moulds from plastic materials. The material is fed into a heated barrel, mixed, and forced into a mould cavity by a reciprocating screw or a ram injector, where the injection moulded part cools and hardens to the configuration of the mould cavity. The injection moulding process presents several advantages in terms of recurring cost, lead time and parts repetitivity. On the other hand, injection plastics present low stiffness properties and the required clamping force to close the mould increases with the part surface or size and the injection pressure.
Assuming the previous state of the art, the Trimmable Horizontal Stabilizer (THS) tips are selected as potential application of this technology in the aerospace industry due to their low structural responsibility and relative small size. The objective of this work is to study the structural performance of a THS tip part made of injection thermoplastic materials reinforced with short fibers, manufactured in one-shot by means of injection moulding process. Furthermore, this study aims to identify which type of configuration or architecture is more efficient in terms of weight for different aircraft size, taking into account the structural requirements. Additionally, in order to assess the scale factor, Single Aile (SA) and Long Range (LR) are taken as reference of different size aircrafts.
Three different configurations for the SA and LR THS tips, made of injection thermoplastic materials reinforced with short fibers, were studied in this work:
SA THS tip (see Figure 1) is a metallic sheet construction comprised of the following parts:
The tip is joined to the THS torsion box and leading edge by means of countersunk rivets.
LR THS tip is a metallic typical box construction made up by spars and ribs to which the external skin panels are fastened to, comprising the following parts (see Figure 2):
Upper and lower tip skin panels are fastened to the torsion box and leading edge by means of a single row or removable screws and nuts.
These configurations consisted of a single part forming the tip skin and integrating different internal elements or not, as shown in Figure 3 were studied.
As preliminary approach, these tips are supposed to be manufactured in one-shot by injection moulding process and attached to the torsion box and leading edge by the same fastener system as the reference, in order to ensure the interchangeability with current design.
As baseline, the external surface was protected against Lightning Strike events by means of Expanded Copper Foil (ECF) also integrated during the injection process.
The tips were loaded under a variable pressure distribution along its own chord and span. Two different type of load cases based on SA and LR THS tips envelopes were evaluated depending on the failure modes, phenomena and design details to be considered
Maximum values of ultimate load pressures for the critical load cases were considered in order to demontrace compliance to static strength
Cruise airloads were taken into account to demonstrate that the maximum deflection of the tip did not exceed the aerodynamic tolerances for external surfaces under cruise condition (according to the programme Technical Design Directives).
Maximum values of limit load pressure for cruise condition were taken from the pressure curve at box and tip joint span sections provided by the aerodynamic department.
Material selected for the different tip configurations made by injection moulding process was a high performance Short Carbon Fiber Thermoplastic.
Material was considered as isotropic for the preliminary analysis in this work.
The following hypotheses were made in order to simplify the calculations and reduce the number of uncertainties on the whole process:
Detailed Finite Element Models (DFEM) were created for each of the configurations showed in Figure 3. THS Tips are categorized as structure D and structure C for the SA and LR respectively. Taking into account this categorization, the following failure modes, phenomena and design details were considered:
Figure 4 shows the results associated with SA proposals. The aerodynamic stiffness/deflection criteria was found as sizing driver, defining the thicknesses for each alternative.
For the LR configuration, Figure 5 illustrates the results. The aerodynamic stiffness/deflection criteria was, as in SA case, the sizing driver.
Tips are one of the most impacted areas by lightning strike attachments with long hang-on. The protection philosophy used for the composite tip of the torsion box in the standard LR THS was applied, i.e., Expanded Copper Foil (ECF). Further improved solutions as metallization or solid copper foil were under development.
Weight estimations were performed for SA and LR THS Tips Note that the weight estimations of the new sized configurations were FEM weights, while the reference tips weights were the real ones. Additionally, it must be remarked that only static sizing FEM weights were considered. Reinforcement at stringer feet, extra thickness due to demoulding angles and other extra weight should be added due to design and manufacturing requirements.
Tendencies of the weight impact for the different configurations under study as per Figure 3 are indicated in Table 1 for SA and LR
|SA Weight Impact
|LR Weight Impact
|4 Intergrated Ribs
Initial manufacturing studies were performed during the project.
After finishing the first engineering activities, some manufacturing studies and flow simulations were developed in order to assess the injection process (see Figure 6). Some results from this research were the following ones:
An initial material coupon test campaign in order to have a first assessment on the joint behavior of this material type is in process, mainly bearing and pull-trough coupons.
In addition fatigue un-notched coupons are being tested under different types of loading and stress profile.
SA and LR THS Tips analyses offer the following conclusions:
As way forward, the following activities are defined:
The previous project was included in the project FACTORIA, funded by the Ministerio de Economía y Competitividad, by means of the Centro Tecnológico Industrial (CDTI), in the Strategic Programme CIEN 2016.
 Internal References. Confidential.
Published on 29/04/18
Accepted on 29/04/18
Submitted on 29/04/18
Volume 02 - Comunicaciones Matcomp17 (2018), Issue Num. 2 - Aplicaciones y compuestos multifuncionales, 2018
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