GB2533401A

GB2533401A - Testing rig and method

Info

Publication number: GB2533401A
Application number: GB1422744.1A
Authority: GB
Inventors: Barnes Ashley; Lee James; Goodman Edward; Hocking Matthew
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2014-12-19
Filing date: 2014-12-19
Publication date: 2016-06-22

Abstract

A method of measuring the tackiness of a pre-preg tape includes pressing the tape against a test surface, applying a shear load to the tape and measuring the shear load applied to the tape. A test rig 50 for this purpose may comprise test portion 52 and sliding portion 56 where the shear force is applied by moving the sliding portion away from the test portion. The test portion may be a floating bed supported on a plurality of load cells while the sliding portion may include a clamp configured in the form of a pivoting arm 58 to secure the tape to the surface. An automated fibre placement head may be arranged to lay the tape on the test surfaces and the force, speed and acceleration at which this is achieved may be monitored. A heat mat and heat sensors may also be incorporated.

Description

Testing Rig and Method

Technical Field

The present disclosure concerns a test method and/or a rig for measuring the tack strength of a pre-preg tape for use in forming a composite component.

Background

A conventional method of manufacturing a composite component is to use prepreg plies; i.e. reinforcement fibres pre-impregnated with a resin matrix. The plies can be laid on top of each other to create a laminate. Plies have traditionally been laid by hand, but for certain applications the plies can be laid using an automated fibre placement (AFP) machine (AFP may alternatively be referred to as automated tape laying ATL).

When plies are laid using AFP, the plies are formed using tape. Tape for the AFP process is provided with backing paper in a roll, and may also be referred to as a tow when used in AFP. The tape is laid using a head of the AFP machine. The head removes the backing paper and lays the tape on a substrate. The head generally includes a compaction roller that is used to press the tape against the substrate. The tape bonds to the substrate due to the tackiness of the tape. Accordingly, it is important that the tackiness of the tape is selected such that it can be detached from the backing paper but is strong enough that the plies remain bonded together.

To ensure that the tape correctly bonds to the substrate it is important to understand the tackiness of the tape so that the AFP parameters can be adjusted accordingly.

Statements of the disclosure

A first aspect of the disclosure provides a method of measuring the tackiness of a pre-preg tape. The method includes laying and pressing a length of tape against a test surface. A shear load is applied to the laid tape; and the applied shear load is measured.

The method of the first aspect can provide a measurement output that can be more easily related to the parameters used to lay the tape, in particular if the tape is laid using an automated fibre placement method.

The shear load applied to the tape may be a fixed predetermined load or alternatively the shear load applied may be varied, for example progressively increased or increased in step changes.

The test surface may include a test portion and a sliding portion. The method may comprise clamping the tape to the sliding portion. The method may further comprise moving the sliding portion relative to the test portion so as to apply a shear load to the tape.

The sliding portion may be moved using a pneumatic or hydraulic arrangement. Alternatively, the sliding portion may be operated by a mechanical drive system.

The tape may be clamped to the sliding portion using an arm that contacts the tape on an exposed surface of the tape. For example, a surface of the tape opposite the surface of the tape that contacts the test surface.

The arm may be configured to pivot about a fixed axis.

The shear load may be applied to the tape at one end of the tape.

The shear load may be applied to the tape in a longitudinal direction of the tape. The shear load may be measured directly or indirectly. In the case of indirect measurement, the reaction force to the shear load may be measured.

A force transducer (e.g. load cell) may be provided to measure the shear load applied to the tape.

An automated fibre placement (AFP) head may be used to lay and press the tape against the test surface.

The tape laying head may include a dispenser for laying the tape on the test surface and removing the backing paper. The tape laying head may include a compaction roller for pressing the tape against the test surface.

The method may include measuring the force applied to press the tape against the test surface, e.g. the force applied by the AFP head. The method may include measuring the drag force or tension (e.g. tow tension) applied to the tape by the AFP head.

The method may include measuring the speed and/or the acceleration at which the tape is laid and pressed against the test surface.

The method may include the step of measuring the temperature of the test surface and/or the temperature of the tape during and/or after being applied to the test surface.

The method may include heating the test surface.

The method may include measuring the pressure footprint applied by the automated fibre placement head.

A second aspect of the disclosure provides a pre-preg tape tack measurement rig. The rig comprises a test surface against which the pre-preg tape can be pressed. The rig further comprises a force application arrangement for applying a shear force to a pre-preg tape; and a measurement arrangement for measuring said applied shear force.

The test surface may include a test portion and a sliding portion. The sliding portion may be configured to move relative to the test portion.

The force application arrangement may comprise a clamp configured to clamp a pre-preg tape against the surface of the sliding portion.

The clamp may comprise an arm pivotable about an axis and operable to hold the tape in position against the sliding portion. The arm may be pneumatically, hydraulically or mechanically operated.

The arm may be provided in the region of the sliding portion of the test surface.

The rig may comprise a drive for moving the sliding portion relative to the test portion. For example, the drive may be a mechanical drive, a pneumatic drive or a hydraulic drive. The drive may take the form of a ram. For example, the rig may comprise a pneumatic ram configured to slide the sliding portion relative to the test portion of the test surface.

The test portion may be a floating bed. The floating bed may alternatively be referred to as an instrumented portion. For example, the test portion may be instrumented to measure forces applied to the test portion. The test portion may be undamped.

The test portion may be supported on a plurality of force measurement devices, for example a plurality of force transducers, e.g. load cells.

The force measurement devices may be positioned to measure the load, speed and/or acceleration at which the tape is pressed on to the test surface. The force measurement devices may be arranged to measure a force normal to the test surface.

Optionally, the force measurement devices may be provided off-centre to the test surface. For example, optionally the test surface is square or rectangular and in such examples a force measurement device may be provided at a position corresponding to one or more, e.g. each of, the corners of the test surface. Provision of the force measurement devices in off-centre locations aids in measuring the pressure applied to the tape and/or the movement of the pressure applied to the tape whilst the tape is pressed against the test surface.

The measurement arrangement may be configured to indirectly measure the applied shear load, for example the measurement arrangement may be configured to measure the reaction to the applied shear load.

A force transducer (e.g. load cell) is provided and arranged to measure the shear load applied to the tape.

The force transducer may be positioned at a location spaced from arm. For example, the force transducer may be positioned in a central region of the test portion.

The test surface of the rig may be flat. The test surface may be provided in a supporting frame. The supporting frame may be provided with a plurality of stabilising legs. Alternatively the frame may be mounted directly to an AFP machine. Optionally, the frame may be equipped with an actuator configured to change the angle of the test surface. When force transducers are provided, the force transducers may be mounted to the frame.

The rig may be instrumented tooling shaped to define the final shape of a component intended to be manufactured with the pre-preg tapes.

The rig may comprise a pressure mat. The rig may comprise heat sensors.

A third aspect of the disclosure provides a pre-preg tape tack measurement arrangement comprising the rig according to the second aspect, and an automated fibre placement head arranged to lay pre-preg tape on the test surface.

The rig of the second aspect and/or the arrangement of the third aspect may be used in performing the method of the first aspect.

The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects of the invention may be applied mutatis mutandis to any other aspect of the invention.

Description of the drawings

Embodiments of the invention will now be described by way of example only, with reference to the Figures, in which: Figure 1 is a sectional side view of a gas turbine engine; Figure 2 is a schematic of a fan blade of the gas turbine engine of Figure 1; Figure 3 is a perspective view of the a pre-preg ply tack measurement rig; Figure 4 is a plan view from below a test surface of the rig of Figure 3; Figure 5 is a perspective view of an underside of the rig of Figure 3; Figure 6 is a schematic sectional side view of a test surface of the rig of Figure 3 during a tack strength test; and Figure 7 is a schematic sectional view of a test surface of the rig of Figure 3 and an automated fibre placement head laying a tape on the test surface.

Detailed description

With reference to Figure 1, a gas turbine engine is generally indicated at 10, having a principal and rotational axis 11. The engine 10 comprises, in axial flow series, an air intake 12, a propulsive fan 13, an intermediate pressure compressor 14, a high-pressure compressor 15, combustion equipment 16, a high-pressure turbine 17, and intermediate pressure turbine 18, a low-pressure turbine 19 and an exhaust nozzle 20. A nacelle 21 generally surrounds the engine 10 and defines both the intake 12 and the exhaust nozzle 20.

The gas turbine engine 10 works in the conventional manner so that air entering the intake 12 is accelerated by the fan 13 to produce two air flows: a first air flow into the intermediate pressure compressor 14 and a second air flow which passes through a bypass duct 22 to provide propulsive thrust. The intermediate pressure compressor 14 compresses the air flow directed into it before delivering that air to the high pressure compressor 15 where further compression takes place.

The compressed air exhausted from the high-pressure compressor 15 is directed into the combustion equipment 16 where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines 17, 18, 19 before being exhausted through the nozzle 20 to provide additional propulsive thrust. The high 17, intermediate 18 and low 19 pressure turbines drive respectively the high pressure compressor 15, intermediate pressure compressor 14 and fan 13, each by suitable interconnecting shaft.

The fan includes a plurality of fan blades 30 mounted around a hub. Referring to Figure 2, the blades 30 each comprise an aerofoil portion or core 32 having a leading edge 34, a trailing edge 36, a concave pressure surface 38 extending from the leading edge to the trailing edge and a convex suction surface (not shown) extending from the leading edge to the trailing edge. The fan blade has a root 42 via which the blade can be connected to the hub. The fan blade has a tip 46 at an opposing end to the root. The fan blade may also have an integral platform 44 which may be hollow or ribbed for out of plane bending stiffness. The fan blade includes a metallic leading edge covering the leading edge of the core and extending along a portion of the pressure surface and suction surface of the core. The fan blade also includes a metallic trailing edge covering the trailing edge of the core and extending along a portion of the pressure surface and the suction surface of the core. The core 32 is made from a composite material.

Many of the components of a gas turbine engine may be made from a composite material, but currently the fan blades 30 and the fan casing (indicated at 28 in Figure 1) are more generally made from a composite material. As will be appreciated by the person skilled in the art, the method and rig described in this disclosure may be used in the process of manufacturing any composite component, with fan blades and casing being mere examples of such components.

An exemplary method of manufacturing a composite component is to use an automated fibre placement (AFP) machine. In such a method, pre-preg tape (i.e. tape made from reinforcement fibres pre-impregnated with a resin matrix) with backing paper is provided on a roll or a reel. The AFP machine has a head that lays the tape onto the surface of a mould or a substrate, and at the same time removes the backing paper from the tape. The AFP machine head often includes a compaction roller that presses the tape against the substrate so as to increase the adherence between the tape and the substrate. The tape forms plies that are laid up on top of each other so as to form a laminate. As desired additional process steps then may be carried out before the laminate is cured.

A factor affecting the strength of the final laminate is how well the tape has bonded to the rest of the substrate (i.e. the other tapes defining the composite component). Tackiness is understood in the art to be a measurement indicative of the adhesive strength between plies (or tapes as is the case here) before the composite is cured. Different tapes have a different tackiness, and factors such as age of the thermoset pre-preg, can affect tackiness so it is often not possible to know how best to configure an AFP machine so as to achieve the desired strength between plies. . For example, once the tackiness of a given pre-preg tape is known, it can be possible to select appropriate parameters for the AFP machine to ensure improved adhesion between tapes. Parameters that may be varied include, by way of example only, the speed at which tape is laid, the force applied by the compaction roller, the material of the compaction roller and/or the temperature of the tape, roller and/or test surface.

Various tests have been suggested in the literature for testing tackiness. Examples of such tests include applying a force normal to the tape to try to pull or peel the tape from a surface. Although these tests give an indicator of tackiness, they do not use AFP parameters to lay the tape and the testing method is not a good representation of the tack strength required. However, the present disclosure proposes a rig and test method that can use AFP parameters as an input to the test, and measures tack strength in a direction more representative of the required strength direction.

Referring to Figures 3 to 5, firstly a pre-preg ply tack measurement rig will be described. The rig is indicated generally at 50 and includes a test surface 52. In the present embodiment the test surface is a flat rectangular surface, but in alternative embodiments the surface may take any suitable shape and may be non-planar, for example the rig may take the form of instrumented tooling. The test surface 52 includes a test portion, which in this embodiment is a floating bed 54, and a sliding portion 56.

The floating bed portion 54 is supported by force transducers, in this case four load cells 60 are provided, one at each corner of the floating bed portion. In the present example, the floating bed portion is made from metal, for example aluminium, and has a thickness such that the floating bed does not bend under the forces applied when a tape is pressed against the test surface. The floating bed portion is undamped.

The sliding portion 56 of the test surface 52 is positioned adjacent the floating bed portion 54 and at one end thereof. The sliding portion is supported on a block 62 provided on rails 64 so as to permit the block and therefore the sliding portion to slide in a longitudinal direction of the rig 50. A pneumatic ram 65 is provided to slide the block along the rails.

An arm 58 is provided in a region of the sliding portion 56 of the rig. The arm is mounted off-centre, i.e. towards one longitudinal side of the rig 50. The arm is arranged so as to be pivotable about an axis 66. The arm is pneumatically operated via a cylinder 59 so as to pivot about the axis 66 and to move perpendicular to the plane of the test surface so as to move towards the test surface 52 to clamp a tape between the arm and the sliding portion of the test surface.

A force transducer or load cell 68 is provided in the region of the floating bed 54 and arranged so as to measure shear force. In the present embodiment the force transducer 68 is provided in a central region of the floating bed, but may be provided in any suitable location in the region of the floating bed.

In the present embodiment, the rig also includes a heat mat 70. The heat mat is positioned and arranged to heat the test surface 52. During an AFP process it is common to heat the tooling on which the tape is laid, so use of the heat mat aids in replicating the condition of the tape during a production process.

The rig 50 may optionally include a temperature sensor, such as a pyrometer. The temperature sensor may be used to measure the temperature of the test surface and/or the temperature of the tape when the tape is laid on the test surface. Further optionally, the rig may include a pressure mat which can be used to measure the pressure and pressure distribution (or footprint) applied during the process of pressing the tape against the test surface.

In the present embodiment the rig 50 is provided in the form of a table. The table may be portable for use with different AFP machines. The table includes a frame and supporting legs, with the test surface being provided in a region defined by the frame. The load cells 60 and 68 are connected to the floating bed and to the frame.

A method of measuring pre-preg ply tack and characterising various parameters of a composite manufacturing process will now be described with reference to the rig 50, but as will be appreciated by the person skilled in the ad, it may be possible to implement this method using an alternative rig to the rig 50 shown in Figures 3 to 5.

To measure the tackiness of pre-preg tape, firstly a strip of tape 72 is pressed on to the test surface 52 of the rig. The tape can pressed on to the rig by hand, or the ply may be applied to the test surface of the rig using the head of an AFP machine (as discussed later). During the process of laying the tape 72 on the test surface, the arm is pivoted to a position where it is clear from the region where the tape is laid, e.g. clear from the path of the AFP head. Once the tape 72 has been laid on the test surface 52 (i.e. laid on the test portion 54 and the sliding portion 56), the arm 58 is pivoted to a position over the tape 72 and the arm is moved towards the test surface 52 so as to clamp the tape 72 between the arm and the sliding portion 56 of the test surface 52.

Once the tape 72 is clamped to the sliding portion 56, the pneumatic ram 65 is operated to apply a desired load to the block 62 so as to move the sliding portion 56 away from the floating bed portion 54 of the test surface 52. Due to the tape 72 being clamped to the sliding portion 56, movement of the sliding portion applies a shear load F to the tape urging the tape to move in the direction of travel of the sliding portion. The adherence between the tape and the floating bed portion of the test surface due to the tackiness of the tape will resist movement of the tape in the direction of the applied shear load F. The reaction force R of the tape to the applied shear force F is measured using load cell 68. The magnitude of the resultant force indicates the magnitude of the shear force. A plot of the shear force and the maximum shear force before failure and around the time of the failure can be interpreted to indicate the strength of adhesion between the tape and the test surface.

This method of testing tackiness or tack strength of a tape is advantageous because it is more directly related to the a strength direction that can be affected by the parameters of an AFP machine, and therefore provides improved information about the tackiness of a tape and the way in which the manufacturing process can be changed to adapt for the properties of a given tape.

Referring now to Figure 7, as mentioned previously the tape 72 can be applied to the test surface using the head 74 of an AFP machine. The head includes a dispenser that dispenses tape onto the test surface and removes the backing paper from the tape. The head also includes a compaction roller 76 that compacts the tape; pressing the tape against the test surface 52. The load cells 60 provided in the corners of the floating bed of the rig 50 measure the compaction force applied by the roller and the output from the load cells 60 can be used to calculate the tension in the tape (often referred to as tow tension when referring to the process of laying a tape on a substrate). The load cell 68 may be used during the process of laying the tape to measure the shear force or drag applied to the tape by the roller, and also the shear force that may cause a tow to slip during the AFP process. The load cells 60 in the corners of the rig may be used to estimate speed and/or acceleration of the tape laying process.

When the tape is laid using an AFP machine, the rig 50 can be used to measure the properties of a given AFP machine, which can be used, by way of example only, to verify AFP machine performance, to compare AFP machines, compare roller types, and/or provide input information into the tack strength test by providing parameters such as the force at which the tape is attached to the test rig, the speed at which the tape is laid and/or the acceleration at which the tape is laid.

It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

The described rig uses load cells to measure the applied forces, but as will be appreciated by a person skilled in the art, any type of force transducer or force measurement device may be used e.g. a dynamometer. The speed and/or acceleration may be estimated using the read out from the force measurement device, or alternatively a speed measurement device may be used, by way of example only a laser system may be used.

In the described examples the tape is applied to the test surface using the head of an AFP machine because this allows the AFP process variables to be easily adjusted, but in alternative examples the tape may be applied to the test surface using alternative methods, e.g. by hand.

Claims

Claims 1. A method of measuring the tackiness of a pre-preg tape, the method including: laying and pressing a length of tape against a test surface; applying a shear load to the laid tape; and measuring the shear load applied to the tape.
2. The method according to claim 1, wherein the test surface includes a test portion and a sliding portion, and wherein the method comprises the step of clamping the tape to the sliding portion and moving the sliding portion relative to the test portion so as to apply the shear load to the tape.
3. The method according to claim 2, wherein the tape is clamped to the sliding portion using an arm that contacts the tape on an exposed surface of the tape.
4. The method according to any one of the previous claims, wherein a force transducer is provided to measure the shear load applied to the tape.
5. The method according to any one of the previous claims, wherein an automated fibre placement head is used to lay and press the tape against the test surface.
6. The method according to claim 5, including measuring the force applied by the head to press the tape against the test surface.
7. The method according to claim 5 or 6, including measuring the speed and/or the acceleration at which the tape is laid and pressed against the test surface.
8. A pre-preg tape tack measurement rig comprising: a test surface against which the pre-preg tape can be pressed; a force application arrangement for applying a shear force to a pre-preg tape; and a measurement arrangement for measuring the shear force applied to the pre-preg tape.
9. The rig according to claim 8, wherein the test surface includes a test portion and a sliding portion, the sliding portion being configured to move relative to the test portion.
10. The rig according to claim 9, wherein the force application arrangement comprises a clamp configured to clamp a pre-preg tape against the surface of the sliding portion.
11. The rig according to claim 10, wherein the clamp comprises an arm pivotable about an axis and operable to hold the tape in position against the sliding portion.
12. The rig according to any one of claims 9 to 11, comprising a pneumatic ram configured to slide the sliding portion relative to the test portion.
13. The rig according to any one of claims 9 to 12, wherein the test portion is a floating bed.
14. The rig according to claim 13, wherein the test portion is supported on a plurality of load cells.
15. The rig according to any one of claims 8 to 14, wherein a force transducer is provided and arranged to measure the shear force applied to the tape.
16. The rig according to any one of claims 8 to 15, wherein the test surface of the rig is flat.
17. The rig according to any one of claims 8 to 15, wherein the rig is instrumented tooling shaped to define the final shape of a component intended to be manufactured with the pre-preg tapes.
18. The rig according to any one of claims 8 to 17, wherein the rig comprises a heat mat for heating the test surface.
19. The rig according to any one of claims 8 to 18, wherein the rig comprises heat sensors.
20. A pre-preg ply tack measurement arrangement comprising the rig according to any one of claims 8 to 19, and an automated fibre placement head arranged to lay pre-preg tape on the test surface.
21. A method and/or rig substantially as described herein with reference to and as illustrated in Figures 3 to 7 of the accompanying drawings.