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Quality Assurance and Nondestructive Evaluation of Composite Materials

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Presentation on theme: "Quality Assurance and Nondestructive Evaluation of Composite Materials"— Presentation transcript:

1 Quality Assurance and Nondestructive Evaluation of Composite Materials
Student Notes: _____________________________________________________________________

2 Outline, Section 2 Design and Detectability
Manufacturing and Fabrication Testing-NDT In-Service Inspection-NDT Damage Assessment and Repair Inspection Visual Inspection Typical Conditions-Laminates Typical Conditions-Honeycomb Mechanical Methods Measuring composites Tools, UT Thickness, Magnamike Acceptance Criteria Fiberglass and translucent materials, Hot light Inspection Manual and Automated Tap Test Inspecting known damage Foreign Material, Foreign Object Detection, (FOD), Foreign Object Evaluation and/or Elimination (FOE) Student Notes: _____________________________________________________________________

3 Design, Section 2 The strength of any given laminate under a prescribed set of loads is probably best determined by “conducting a test”. However, when many laminates and different loading conditions are being considered, as in a preliminary design study, analysis methods for estimation of laminate strength become desirable. Because the stress distribution throughout the fiber and matrix regions of all the plies of a laminate is quite complex, precise analysis methods are not available. However, reasonable methods do exist which can be used to guide the preliminary design process. Student Notes: _____________________________________________________________________

4 Design, Section 2 Key Design Considerations Material Selection
Processing/Fabrication Methods Structural Considerations Environmental Effects & Protection Sandwich Construction Student Notes: _____________________________________________________________________

5 Design, Section 2 Aircraft Composite Design Process
Determine requirements and loads Select structural configuration Select material, fabric, thickness, style, ply sequence Calculate laminate properties Strength, stiffness, strain to failure, etc Calculate stress induced by loads Go back to 3 if stress × 1.5 >1 Evaluate cost versus weight Go back to 2 if high cost or weight Build & test prototype – final design Student Notes: _____________________________________________________________________

6 Design, Section 2 Design concern example:
With failure rates still high for turbine blades (a Sandia Lab survey of wind energy plants documented rates as high as 20% failure) and down-time costly and bad for business, blade designers and manufacturers have turned to the best practices for designing composites. Student Notes: _____________________________________________________________________

7 Design, Section 2 Select Structural Configuration
Important to have a thorough knowledge of the advantages and disadvantages of the various fabrication / manufacturing techniques Design for Manufacture Usually a specific structural configuration is selected for Ease of construction Low tooling and fabrication costs Lightweight Once the type of composite structure has been selected = preliminary structural sizing of the components and laminates can proceed Using standard structural analytical techniques Together with simple optimization techniques and equations Student Notes: _____________________________________________________________________

8 Design, Section 2 Design and Analysis of Structures
Analysis of composite components is difficult Dynamic loads are especially hard to consider Design tools are less developed than those for conventional materials Testing is still widely used to validate design and analysis models Student Notes: _____________________________________________________________________

9 Design, Section 2 Design concerns of Composites
Environmental degradation of resin dominated properties Notch sensitivity Impact damage Poor through thickness properties Variability Properties not established until manufactured Limited availability of design data Reinforcement incorrectly located Lack of codes and standards Recycling not easy Fire, smoke and toxicity performance Student Notes: _____________________________________________________________________

10 Further design Considerations of Composites
Design, Section 2 Further design Considerations of Composites Textured surfaces Self coloring Integration of parts Economy of scale Molding direct to final dimensions Efficient use of materials Durability Lifetime costing attractive Student Notes: _____________________________________________________________________

11 Design, Section 2 Uses of Fiber/Matrix
Typical aerospace composite manufacturing processes consist of filament winding, fiber placement, pultrusion, tape laying, tape wrapping, press molding, hand layup and resin transfer molding. Student Notes: _____________________________________________________________________ Uses of Fiber/Matrix

12 Design, Section 2 Summary of Composite Manufacturing Processes
Student Notes: _____________________________________________________________________

13 Design, Section 2 Student Notes:
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14 Design, Section 2 PREPREG PRODUCTION PROCESS Pultrusion Student Notes:
_____________________________________________________________________ Pultrusion

15 Design, Section 2 Student Notes:
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16 Production Inspection, Section 2
NDE Techniques for Detecting Defects in Composite Materials Student Notes: _____________________________________________________________________ 1. Filament winding 5. Tape wrapping 2. Fiber placement 6. Press molding 3. Pultrusion 7. Hand layout 4. Tape laying 8. Resin transfer molding

17 Detection, Section 2 Failure modes
Composites tend to fail in a different way to metals Failure modes Brittle fibres in a ductile matrix Sudden brittle failure – no elasticity Crazing and matrix cracking may occur Unseen failure may initiate in the laminate Hence fear due to BVID in carbon fiber structures Inter laminar disbonding and damage Student Notes: _____________________________________________________________________

18 Detection, Section 2 Student Notes: _____________________________________________________________________ This figure illustrates the interrelationship between key factors involved in the concept of inspection reliability. A detailed discussion in these issues falls outside the scope of this overall view. Pertinent information can be found elsewhere /1/. However, while some traditional notions shown may seem self-explanatory for inspection practitioners other, wide or closely related with the trends of NDT-reliability improvements, deserve to be outlined. /1/V. Schmitz, K.J. Langenberg, W. Kappes, M. Kröning: "Inspection procedure assessment using modeling capabilities" Nuclear Engineering and Design,

19 Detection, Section 2 Student Notes: _____________________________________________________________________ With the new developed modeling algorithms, practically the whole NDT testing technique can be covered. The NDT modeling systems developed under the logo of CAI (Computer Aided Inspection) are a combination of modeling the geometry and material response of the inspected component together with the testing techniques and its scanning parameters.

20 Detection, Section 2 Student Notes: _____________________________________________________________________ Accurate NDE methods are considered a necessity to ensure aircraft airworthiness and passenger safety. Traditionally, tap tests and a few ultrasonic-based inspection methods have been used to inspect composite aircraft structures.

21 Detection, Section 2 Categories of Damage & Defect Considerations for
Primary Composite Aircraft Structures Student Notes: _____________________________________________________________________

22 Detection, Section 2 A test program, called “Composite Flaw Detection Experiments”, was undertaken at the Federal Aviation Administration (FAA) Airworthiness Assurance NDI Validation Center (AANC), operated by Sandia National Laboratories. A large number of test panels, representing the detrimental conditions of construction on aircraft, were inspected using a wide array of NDE techniques. Forty-four Nomex honeycomb core panels with either carbon/epoxy or fiberglass/epoxy skins were manufactured, with flaws ranging from 0.2 in² to 3 in² (1.29 cm² to cm²). F The panels were shipped to airlines, third-party maintenance depots, aircraft manufacturers and NDE developer labs around the world. Industry-wide data was generated to quantify how well current inspection techniques are able to reliably find flaws in composite honeycomb structure. [Roach, 2010] The program developed Probability of Detection (PoD) curves for various laminates and NDE techniques. Results from the “round-robin” detection study are shown. Student Notes: _____________________________________________________________________

23 Detection, Section 2 The reliability of inspection techniques may be understood and quantified in probabilistic terms. Broadly speaking the inspection reliability is defined as the probability of not overlooking an existing defect (probability of detection, POD) and correct sizing the defect. Whatever simple this definition may appear, it encompasses many complex issues ranging from the specification of the nature of defects to influencing factors related with the inspection instrumentation, product nature, the involved human factor and the available expertise for inspection data processing and assessing. Student Notes: _____________________________________________________________________

24 Detection, Section 2 Typical reference standard and/or probability of detection sample Student Notes: _____________________________________________________________________

25 Least opportunity for detection
Detection, Section 2 Least opportunity for detection Best opportunity for detection Student Notes: _____________________________________________________________________ Probability of Detection (PoD) versus flaw size (diameter in inches) for composite sandwich panels with various skin architectures

26 Detection, Section 2 Aerospace Damage and Repair Inspection Procedures
Methods used in the field for aerospace composite part damage detection, damage characterization, and post-repair inspection are typically less sophisticated than those employed by the OEM for their post-processing inspection. Operators and maintenance organizations use visual inspection as their main technique for initial detection of field damages, unless NDE techniques are specified by the specific maintenance planning manual or aircraft maintenance manual. Once damage is detected visually, other NDE methods are typically used to map the full extent of damage for proper disposition. Student Notes: _____________________________________________________________________

27 Detection, Section 2 In addition to the use of visual inspection to first detect damage, more sophisticated NDE methods are essential to the subsequent damage disposition and repair processes. Many types of damage have both visual and hidden damages. Hidden damage in composites usually covers a larger area than visual indications of damage is most responsible for lost residual strength. It is essential that the proper NDE methods be applied to damage found on aerospace composite structure to map the full extent of the damage, which is needed to determine whether damage is below the Allowable Damage Limit (next slide) or whether repairs are required. Since a disposition of repair size limits also depends on accurate mapping, decisions on whether the repair substantiation database is sufficient also relies on a complete inspection with the proper NDE. Student Notes: _____________________________________________________________________

28 Production Inspection, Section 2
We need a general understanding before we begin our inspection! Can the inspection technique detect the suspected imperfection(s)? Are there reference standards? What is the inspection criteria? What is the minimum detectable vs. minimum rejectable ? Is there a FOE or FOD program required? What is the direction of loading and suspect flaw location? Customer Requirements? What are the qualification and certification requirements? What is the best inspection method? What is the inspection requirement? Student Notes: _____________________________________________________________________ What process was used to fabricate? What is the Material? What type of defects can be produced?

29 Production Inspection, Section 2
Testing: Component, subcomponent, and generic structural tests are performed to verify analysis. Particular component tests may include elements of aerodynamics, vibro acoustic and thermal loading conditions, as well as significant externally applied mechanical loads. Subcomponent tests may be performed for critical areas of the component. Generic tests include flange and stiffened panel tensile tests, damage tolerance tests, and standard temperature effect tensile and compressive coupon tests. Student Notes: _____________________________________________________________________

30 Production Inspection, Section 2
Student Notes: _____________________________________________________________________

31 Production Inspection, Section 2
Planning the inspection points Student Notes: _____________________________________________________________________

32 Production Inspection, Section 2
Quality assurance for composite parts centers on techniques for validating the physical and mechanical properties of a cured composite. However, quality assurance begins long before the end item is tested. A logical approach to quality control follows the fundamentals of composite reaction control: raw material validation reaction control; material characteristics; In process fabrication/handling/tooling effects; cure process control and documentation; Post cure machining. Visual inspection is used to inspect bond lines that are visible in the various bond stages and to detect any visible surface discontinuities and/or delaminations. Mechanical inspection is used to verify design dimensions, acoustics, input resistance, static loads and dynamic loads. Nondestructive evaluation is perhaps the most important inspection technique for determining defects in composites, particularly the defects specified in Table Student Notes: _____________________________________________________________________

33 Production Inspection, Section 2
Typical Process Flow Student Notes: _____________________________________________________________________

34 In-Service Inspection, Section 2
Student Notes: _____________________________________________________________________

35 In-Service & Repair Inspection, Section 2
Student Notes: _____________________________________________________________________

36 In-Service & Repair Inspection, Section 2
REPAIR OPTIONS When a composite structure sustains damage in service one of three levels of repair must be employed. Cosmetic repair In this case inspection has determined that the damage has not affected the structural integrity of the component. A cosmetic repair is carried out to protect and decorate the surface. This will not involve the use of reinforcing materials. Temporary or interim repairs It is often the case in service, that small areas of damage are detected which in themselves do not threaten the integrity or mechanical properties of the component as a whole. However if left unrepaired they may lead to further rapid propagation of the damage through moisture ingress and fatigue. Simple patch type repairs can be carried out, with the minimum of preparation, to protect the component until it can be taken out of service for a proper structural repair. Temporary repairs should be subject to regular inspection. Structural repair If the damage has weakened the structure through fibre fracture, delamination or disbonding the repair will involve replacement of the damage fibre reinforcement, and core in sandwich structures, to restore the original mechanical properties. Since a bonded-on repair constitutes a discontinuity of the original plies, and therefore a stress raiser, structural repair schemes normally require extra plies to be provided in the repair area. If the damaged area is very small it can be questionable whether a structural repair, requiring removal of a substantial amount of the structure in damage removal and preparation, is preferable to a cosmetic repair. Student Notes: _____________________________________________________________________

37 In-Service & Repair Inspection, Section 2
Student Notes: _____________________________________________________________________

38 In-Service & Repair Inspection, Section 2
Student Notes: _____________________________________________________________________

39 In-Service & Repair Inspection, Section 2
Typical Damage Most damage to fiber reinforced composites is a result of low velocity and sometimes high velocity impact. In metals the energy is dissipated through elastic and plastic deformations and still retains a good deal of structural integrity. While in fiber reinforced material the damage is usually more extensive than that seen on the surface. Student Notes: _____________________________________________________________________

40 In-Service & Repair Inspection, Section 2
Student Notes: _____________________________________________________________________

41 In-Service & Repair Inspection, Section 2
Patch repair The thickness of the original laminate is made up with filler plies and the repair materials are bonded to the surface of the laminate. Advantages Quick and simple to do Requires minimum preparation Disadvantages A repaired laminate is thicker and heavier than the original Very careful surface preparation is needed for good adhesion Student Notes: _____________________________________________________________________

42 In-Service & Repair Inspection, Section 2
Sample Damage Tolerance Criteria Impact Student Notes: _____________________________________________________________________

43 Nondestructive Inspection, Section 2
Most Common Production Inspection Method Ultrasonic inspection is used to detect flaws in a wide variety materials, and composites. It can be performed using portable battery-operated equipment, enabling parts to be inspected while still installed. An ultrasonic testing (UT) instrument typically includes a pulser/receiver unit and a display device. The pulser/receiver unit includes a transducer probe which converts an electrical signal into a high frequency sound wave and then sends that wave into the structure being tested. A defect in the structure, such as a crack, will cause a density change in the material and will reflect sound waves back to the transducer probe. The transducer converts the received sound waves (vibrations) into an electrical signal which is then analyzed and shown on the UT display device. Student Notes: _____________________________________________________________________

44 Nondestructive Inspection, Section 2
Student Notes: _____________________________________________________________________

45 Nondestructive Inspection, Section 2
Student Notes: _____________________________________________________________________

46 Nondestructive Inspection, Section 2
Ultrasonic techniques Student Notes: _____________________________________________________________________

47 Nondestructive Inspection, Section 2
Ultrasonic techniques Student Notes: _____________________________________________________________________

48 Nondestructive Inspection, Section 2
Ultrasonic pulse echo technique Student Notes: _____________________________________________________________________

49 Nondestructive Inspection, Section 2
Ultrasonic pulse echo technique Student Notes: _____________________________________________________________________

50 Nondestructive Inspection, Section 2
Student Notes: _____________________________________________________________________

51 Nondestructive Inspection, Section 2
Common production inspection Student Notes: _____________________________________________________________________

52 Visual Inspection, Section 2
Visual inspection can be a quite powerful and often under-rated technique for detecting damage in composite structures. Even low-energy impacts may leave a slight marring, paint scrape, or faint surface blemish on a part. A slight wave or ripple on the surface may indicate an underlying delamination or disbond. A light spot or "whitish" area on a fiberglass part may indicate trapped air, a resin-lean or fractured area, or a delamination. Visual inspection is the first line of inspection in both manufacturing and damage assessment. Student Notes: _____________________________________________________________________

53 Visual Inspection (tap test), Section 2
Tap Testing Tap Testing is a quick, inexpensive method for detecting hidden damage. It is especially useful for finding delaminations and disbonds in thin-skin structures or near the surface of a thick composite part. Tap testing is probably the most common inspection technique other than visual. By tapping gently on the surface of a composite part, one can often hear a change in sound from a clear sharp tone to a dull thud. By tapping back and forth over the area in question, and making a small mark at the point where the tone just begins to change, it is possible to outline large, irregularly-shaped areas of delaminations or disbonds. However, there are many limitations to tap testing, including: Not good for deep damage. Requires knowledge of the underlying structural detail of the part. Not very effective in quantifying the degree or depth of damage. Cannot locate very small defects. Student Notes: _____________________________________________________________________

54 Visual Inspection, Section 2
Visual inspection is probably the most widely used of all the nondestructive tests. It is simple, easy to apply, quickly carried out and usually low in cost. Good eyesight and illumination are required. Reliability is likely to be improved significantly if undertaken by experts. It is beneficial if inspectors regularly inspect composite components. No formal NDT qualifications are required. Visual inspection has the following advantages and limitations: doorframe Cracking of window frame Student Notes: _____________________________________________________________________

55 Visual Inspection, Section 2
Student Notes: _____________________________________________________________________

56 Visual Inspection, Section 2
Visual Inspection is important, how it is applied is critical! Inspectors quotes or excuses?: What should be done? What would you do? “…if the inspection needs to be conducted during a particularly windy evening, I will have to place my cherry picker at a greater than the normal distance in order to avoid an impact to the aircraft, which will be moving due to the wind. However from such a distance I might not be able to detect all the existing defects. “… if the sun is shining very brightly into my eyes and I am trying to inspect the rudder I might miss something during that particular inspection” Student Notes: _____________________________________________________________________

57 Visual Inspection, Section 2
Visual inspection refers to the simple examination of a component for defects using the human eye. The term enhanced visual inspection is used where the inspection is aided by artificial tools, such as closed circuit TV cameras, special lighting systems, endoscopes and automated defect recognition tools Visual inspection is the most common form of inspection for composites and other materials systems. Increasingly digital cameras, CCTV or video cameras are used either for monitoring or to provide a permanent record of the inspection. Visual inspection is widely used for inspection of composite parts, particularly after manufacture. It is an accepted and useful part of quality control. There are established standards such as ASTM D 2563 The chief advantages of visual inspection are its speed, simplicity and ability to detect a variety of flaws. Coverage may be limited. Speed is usually but not always faster than NDE methods. Student Notes: _____________________________________________________________________

58 Visual Inspection, Section 2
Advantages of Visual Inspection Simple Usually fast Widely used Accepted standards e.g. ASTM D2563 Can pick up a range of defects Good for obvious manufacturing flaws Embedded flaws in GRP can be detected by backlighting Does not need NDT qualified inspector Can be enhanced by backlighting e.g. GRP chemical vessels Can be applied to complex parts where access for NDE is restricted Student Notes: _____________________________________________________________________

59 Visual Inspection, Section 2
Limitations of Visual Inspection Subjective Only see if defects are surface evident Lighting conditions critical Requires line of sight Limited applicability to painted components Backlighting not possible for CFRP Embedded defects may not be evident, e.g disbonds Reliability limited Unlikely to be sufficient, unless supported by NDE for higher integrity components Affected by surface condition Student Notes: _____________________________________________________________________

60 Visual Inspection, Section 2
Hidden damage is the greatest issue, including manufacturing defects. (for example, a low velocity impact, which normally wouldn’t cause much damage may cause a sandwich structure to disbond between the skin and core due to poor adhesion during manufacture. If this disbond is the only damage, there may be no visible trace of it from the surface.). Reliance on just visual inspection is not recommended for higher integrity components. Student Notes: _____________________________________________________________________

61 Visual Inspection, Section 2
The best quality of visual inspection for transparent/translucent composite materials is where access is possible from both sides with backlighting. In this case internal defects such as delaminations, fabrication defects and cracking may be seen. CFRP composites are not transparent to light. The effectiveness will depend on wall thickness, resin type and coating. It is increasingly common practice to paint GRP vessels and pipes for aesthetic reasons, which makes backlit inspection impracticable. If access is limited to one side then only surface apparent or obvious defects will be seen. Users often have great confidence in visual inspection, which belies the limited data available on actual reliability. Enhanced visual inspection is widely used in airframe components; here large areas need to be inspected. Identifiable defects include, delamination, cracks, localised (thickness) deformation, impact damage, poor wetting of fibres, inclusion, air entrapments, excessive adhesive in joints (reducing internal diameter), environmental effects (e.g. UV, erosion) and wear damage. Student Notes: _____________________________________________________________________

62 Visual Inspection, Section 2
Radome – Bird Strike Typical Repairs Inboard Flying Panel – partial separation Student Notes: _____________________________________________________________________

63 Visual Inspection, Section 2
subsequent inspection – severed spar and skin - aircraft grounded probable cause – upstream access cover separation/impact Student Notes: _____________________________________________________________________ Same defect, visual results, digital radiography and thermographic

64 Visual Inspection, Section 2
Know your criteria/nomenclature for inspection reporting per your customer requirements A dent is a damaged area which is pushed in or out, with respect to its usual contour. There is no cross-sectional area change in the material; edges are smooth. Flaking is defined as the delamination and possible loss of the outside ply in a localized area. Flaking occurs at the part edge or at a cutout, and is caused by trimming, drilling, or edge impact. Student Notes: _____________________________________________________________________ An impact mark is a damage of any size that results in a cross-sectional area change and was caused by impact. A mark that was caused by impact may have additional damage below the surface of the outside plies. Impact marks can also occur at an edge. Examples of visual criteria based on a typical Aerospace Company.

65 Visual Inspection, Section 2
Procedures There are well established procedures and standards for visual inspection of composite components. The standards also generally include acceptance criteria. This includes: ASTM standard D2563 Standard practice for classifying visual defects in glass-reinforced plastic laminate parts Specific procedures are used in different industries dependent on the integrity level required and the defect types that are likely to impair performance in that type of composite structure. For example the European Space Agency has it's own standards for visual inspection of space components. ASTM standard D 2563 defines critical areas where more stringent criteria may be required. Four Levels of acceptance are allowed, defined by the user with reference to the part drawing, dependent on required component integrity. Defects are categorized in terms of allowable defects and repairable defects. A library of photographic images is included giving examples of the main defect types. Student Notes: _____________________________________________________________________

66 Visual Inspection, Section 2
CFRP Structure which effect Maintainability Student Notes: _____________________________________________________________________

67 Visual Inspection, Section 2
BVID Small damages which may not be found during heavy maintenance general visual inspections using typical lighting conditions from a distance of five (5) feet Typical dent depth – 0.01 to 0.02 inches (OML) Dent depth relaxation must be accounted for Student Notes: _____________________________________________________________________

68 Visual Inspection, Section 2
Criteria Requirements for Visible Damage Airframe must support design limit loads without failure. No detrimental damage growth during fatigue cycling representative of the structure’s inspection interval. One missed inspection is assumed (two interval requirement) Validated by testing Airframe must be able to support residual strength loads until the damage is found and repaired. Student Notes: _____________________________________________________________________

69 Visual Inspection, Section 2
Sample Damage Tolerance Criteria Impact Student Notes: _____________________________________________________________________

70 Visual Inspection, Section 2
Sample Damage Tolerance Criteria Impact Student Notes: _____________________________________________________________________

71 Visual Inspection, Section 2
CFRP structures must meet same lightning strike regulatory requirements as Aluminum structures Boeing 787 structures are designed, by requirement, to resist economic levels of lightning strike Student Notes: _____________________________________________________________________

72 Thickness Inspection-Magna-Mike, Section 2
Hall Effect thickness gages like the Olympus Magna-Mike 8600 are small, lightweight instruments designed to make fast, accurate, and repeatable measurements of non-magnetic materials such as plastics, glass, composites, aluminum, and titanium. The first commercial instruments of this type were introduced in the 1980s and they are now widely used in a number of industries. Wall thickness is measured by placing a small steel target (ball, disk, or wire) on one side of the test piece and the magnetic probe on the opposite side. The Magna-Mike precisely measures the distance between the probe tip and the target, which corresponds to the thickness of the wall. Student Notes: _____________________________________________________________________

73 Thickness Inspection-Magna-Mike, Section 2
Hall Effect gages can potentially measure any non-magnetic material whose geometry permits placing a probe tip on one side of a wall and a small target like a steel ball on the other, up to a maximum thickness of approximately 1 inch or 25 mm. Materials that can be measured include all types of plastics and composites, aluminum, titanium, and other nonferrous metals, glass, wood and paper products, and certain nonmagnetic stainless steel alloys. Measurement accuracy can be as close as +/- 1% of wall thickness and is typically +/- 3% or better. Important measurement applications include: Plastic bottles and packaging Molded plastic parts like containers and tanks Air bag tear seams Small diameter plastic and nonmagnetic metal tubing Glass containers and scientific glassware Aluminum beverage cans Paper and foam food containers Machined metal parts (except magnetic steel and iron) Plywood and particle board Aerospace parts including turbine blades 2. How Hall Effect gages work Student Notes: _____________________________________________________________________

74 Thickness Inspection-Magna-Mike, Section 2
A Hall Effect sensor is a specialized electronic semiconductor which responds to changes in a magnetic field by varying a voltage that appears across its surface as a current passes through it. A detailed explanation of the physics behind the Hall Effect can be found here: en.wikipedia.org/wiki/Hall_Effect. When a Hall Effect sensor is used for thickness gaging, it is incorporated in a small probe along with a strong magnet that creates a magnetic field around the sensor. A target such as a small steel ball bends the magnetic field generated by the probe magnet, with the bending effect increasing as the target comes closer. As the test piece thickness and thus the distance between the target and the probe changes, the voltage across the Hall Effect sensor also varies in a predictable way. Once the instrument has been calibrated for a particular probe and target, these voltage changes can be converted to thickness readings through a software algorithm that utilizes an established calibration curve. It is important to remember that what Hall Effect gages actually measure is the distance between the probe tip and the target, and thus they measure wall thickness indirectly. For accurate thickness measurements, the operator must insure that the probe and the target are properly aligned with each other and positioned in close contact with the test piece. 3. Probes and targets Student Notes: _____________________________________________________________________

75 Thickness Inspection-Magna-Mike, Section 2
Calibration: Hall Effect instruments must be calibrated before use, using the same probe and target that will be employed for measurements. This is done by taking readings with no target, with the target touching the probe (zero thickness), and at two or more reference thicknesses. This permits the instrument to generate a calibration table that plots voltage changes versus thickness. The calibration matches each target being used to an internal lookup table from the unit's memory. The calibration also measures the two extremes of the target's possible locations (Ball On and Ball Off) and assigns these endpoints to the lookup table. Additional calibration points at known thicknesses are used to fine-tune the table for best accuracy. During operation, calibration should be verified whenever probe orientation or environmental temperature changes. Probe orientation: Because the Magna-Mike 8600 measures thickness by monitoring small changes in a magnetic field, its calibration process includes an automatic compensation for the effects of the earth's magnetic field. Most commonly, the probe is held at a constant orientation, vertically in a stand. However in cases where the probe is used at a different orientation (such as being held horizontally), or when the orientation is changing as in scanning the outside of a curved part, calibration must be updated. In the Magna-Mike 8600, the Q-Cal function is used to make this correction. This is especially important when measuring near the maximum specified thickness for each target type. Simply remove the target and press the Q-Cal key while the probe is held at the desired orientation. Student Notes: _____________________________________________________________________

76 FOD Program, Section 2 Foreign Object Debris and Foreign Object Damage (FOD) Prevention For Aviation Maintenance & Manufacturing Student Notes: _____________________________________________________________________

77 FOD Program, Section 2 Foreign Object Debris (FOD) often causes Foreign Object Damage (FOD). The majority of instances of FOD can be attributed to lack of standards in an organization, personal complacency or disregard for procedures. These may also lead to additional sources of FOD caused by insufficient housekeeping, training or controls deterioration of facilities improper tools and equipment improper or careless maintenance or assembly fatigue and scheduling pressures. Foreign Object Debris (FOD) can come in many different forms and may produce disastrous effects if not identified and corrected. In severe cases, FOD can directly threaten safety of flight crews and integrity of the aircraft. Student Notes: _____________________________________________________________________

78 FOD Program, Section 2 In composites manufacturing, FO is anything e.g. tape, backing material, peel ply, bagging material, etc. utilized in the process that was not intended to be included in the finished part. Material unintended to be in the laminate or bonded assembly may have adverse effects! Foreign Object (FO) or Foreign Object Debris (FOD) – A substance, debris or article alien to an aircraft or system, which would potentially cause damage. Foreign Object Damage (FOD) - Any damage or malfunction attributed to a foreign object that can be expressed in physical or economic terms which may or may not degrade the product’s required safety and/or performance characteristics Critical FO: Foreign objects inadvertently left in areas inside of a component or aircraft from which migration is possible, e.g. through tooling holes, bend relief cutouts, drain holes, intakes, etc., which are probable to cause system or component malfunction or deterioration should the product be put into use. Foreign Object Elimination (FOE): a program or process used to assure a FOD-free product/system. Student Notes: _____________________________________________________________________

79 FOD Program, Section 2 Clean-As-You-Go:
Clean the immediate area when work cannot continue. Clean the immediate area when work debris has the potential to migrate to an out of sight or inaccessible area and cause damage and/or give the appearance of poor workmanship. Clean the immediate area after work is completed and prior to inspection. Clean at the end of each shift. If you drop something or hear something drop - pick it up! Student Notes: _____________________________________________________________________

80 FOD Programs, Section 2 Six Sigma: A comprehensive and proven set of tools and techniques applied in a consistent, systemic fashion to enable to better solve problems and optimize processes in all functional areas. The main focal points of Six Sigma are: Waste Elimination primarily through Lean principles and tools, Variation Reduction through traditional DMAIC tools (Define, Measure, Analyze, Improve, Control), and Growth and Innovation using the tools and principles of DFSS (Design for Six Sigma). Lean Manufacturing: Lean manufacturing is the production of goods using less of everything compared to mass production: less human effort, less manufacturing space, less investment in tools, and less engineering time to develop a new product. 5S: The Japanese mnemonic based process for housekeeping and organizing for efficiency. 5S is a philosophy and a way of organizing and managing the workspace by eliminating waste. Sort Straighten Shine Standardize Sustain Some organizations use 6S with the 6th S being Safety. Student Notes: _____________________________________________________________________

81 Composite Quality Assurance, Section 2
Student Notes: _____________________________________________________________________ Aircraft Programs, OEM’s, Suppliers as well as the individuals who fly every day depend on Quality Assurance Programs


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