Specification for Medium Strength Aircraft Plywood

IS 709: Scope - Key Formulas, Tables & Specifications

Scope: Covers aircraft plywood manufacture, specifying timber species, dimensions, tolerances, and test methods.

1. Timber Species (Clause 3.1, Table 1)

Other species allowed if performance criteria are met.

2. Shear Strength Formula (Clause 1.3, Table B-1)

[ f_s = \frac{2 \times P}{t \times w} ]

• ( f_s ) = Shear strength (kg/cm²)
• ( P ) = Ultimate load (kg)
• ( t ) = Thickness of plywood (cm)
• ( w ) = Width of specimen (cm)

3. Loading Block Sizes for Shear Test

4. Mandrel Diameter for Bending Test (Clause 2.1, Table 3)

This summary covers timber selection, test procedures, and dimensional standards for aircraft plywood per IS 709.

IS 709: Key Definitions & Specifications

1. Definitions (Clause 2.1)

   • Definitions are as per IS 707:1968 (Timber and plywood glossary & terms).

2. Timber Species for Aircraft Plywood (Clause 3.1, Table 1)

   Botanical Name	Trade Name	Abbreviation for Marking
   Dysoxylum malabaricum Bedd	White cedar	WCE
   Palaquium ellipticum (Dalz.) Engler	Pali	PAL

   • Other species (e.g., rosewood, teak, walnut) may be used if performance meets the standard.

3. Bending Test Mandrel Diameter (Clause A-2.1, Table 3)

   Plywood Thickness (mm)	Mandrel Diameter (mm)
   1.0	100
   1.5	150
   2.0	200
   2.5	250
   3.0	300
   3.5	350
   4.0	400
   4-5	450
   5.0	500

Summary Diagram: Bending Test Setup

graph LR
A[Plywood Sample] --> B[Bending over Mandrel]
B --> C{Mandrel Diameter}
C -->|Depends on Thickness| D[Plywood Thickness]

Note: Mandrel diameter = 100 × plywood thickness (in mm), e.g., 2 mm thick plywood → 200 mm mandrel diameter.

This ensures consistent bending tests per IS 709 requirements.

IS 709: Key Formulas, Tables & Specifications for Materials

Timber Species for Aircraft Plywood (Clause 3.1, Table 1)

Note: Other species (e.g., rosewood, teak, walnut) may be used if performance meets the standard.

Shear Strength Formula (Clause 1.3)

[ f_s = \frac{2 \times P}{t \times w} ]

• (f_s) = Shear strength (kg/cm²)
• (P) = Ultimate load (kg)
• (t) = Thickness of plywood (cm)
• (w) = Width of specimen (cm)

Loading Block Sizes for Shear Test (mm)

Mechanical Properties of Plywood (Clause 7.1.6, Table 1)

Thickness Options (Clause 1.0)

• Available thicknesses: 1.0 mm to 10.0 mm in 0.5 mm increments (e.g., 1.0, 1.5, 2.0 ... 10.0 mm)
• Custom sizes allowed by agreement.

This summary helps in selecting timber, testing shear strength, and understanding mechanical properties per IS 709 for aircraft plywood.

IS 709 Veneer Quality & Defects Summary

Key Specifications (Clauses 4.1.8 - 4.1.10)

• Face Veneers (4.1.9):

  • No open defects: insect holes, splits, pitch pockets.
  • No large, loose, or dead knots.
  • Small live knots allowed ≤ 6 mm diameter.
  • Dead knots sum ≤ 10 mm diameter per 1000 cm³.

• Defects Not Allowed in Veneers (4.1.8):

  • Discolouration due to sap stain.
  • Ingrown bark.
  • Birds eye.
  • Filling and inlaying.

• Core Veneers (4.1.10):

  • Some defects permissible (not detailed here, refer to full clause).

• Inspection (10.2):

  • Each veneer inspected individually for compliance.

Quick Reference Table for Face Veneer Defects

Notes:

• Veneer quality is critical for appearance and structural integrity.
• Adherence to these limits ensures durability and aesthetic standards.
• For core veneers, minor defects may be acceptable (refer IS 709 Clause 4.1.10).

flowchart TD
    A[Veneer Inspection] --> B{Face Veneer?}
    B -- Yes --> C[Check defects per 4.1.8 & 4.1.9]
    B -- No --> D[Core Veneer: Check per 4.1.10]
    C --> E{Defects found?}
    E -- No --> F[Pass Quality]
    E -- Yes --> G[Reject or Rework]
    D --> E

This ensures

IS 709: Size and Thickness of Boards (Plywood)

1. Board Sizes (Clause 5.1)

Standard rectangular plywood board sizes (cm):

2. Thickness and Tolerances (Clause 5.2 & 5.3)

• Thickness is the average of 10+ random measurements.
• For thickness < 6 mm: ±10% tolerance.
• For thickness ≥ 6 mm: ±5% tolerance.

3. Dimensional Tolerances (Clause 5.3)

Summary

• Boards come in standard sizes with strict length/width tolerances.
• Thickness varies from 1 mm to 10 mm with specified tolerances.
• Thickness measured as average of multiple points

IS 709: Manufacture and Treatment of Plywood Boards

1. Treatment of Boards (Clause 4.6)

• Immediately after pressing and while hot, boards are dipped for 2 minutes in:
  • 2% sodium pentachlorophenate solution in water, or
  • 2% pentachlorophenol solution in a suitable organic solvent (room temp).
• Boards are then allowed to dry.
• Note: Sodium pentachlorophenate may precipitate on acidification; concentration must be periodically checked.

2. Shear Strength Formula (Clause 1.3)

[ f_s = \frac{2 \times P}{t \times w} ]

Where:

• ( f_s ) = shear strength (kg/cm²)
• ( P ) = ultimate load (kg)
• ( t ) = thickness of plywood (cm)
• ( w ) = width of specimen (cm)

3. Loading Block Sizes for Shear Test (mm)

4. Mandrel Diameter for Bending Test (Clause 2.1, Table 3)

5. Marking Requirements (Clause 3.1)

• Veneer species abbreviation
• Date of manufacture
• Thickness of board
• Batch number and press-load number

flowchart TD
    A[Pressing of Boards] --> B[Dip in 2% Solution (2

IS 709 - Testing Requirements Summary

1. Bending Test (Clause 2.1 & Appendix A)

• Mandrel Diameter to Veneer Thickness Ratio (Table 3):

2. Sampling (Clause 9.1)

• Number of samples per batch (Table 2):

3. Shear Strength Formula (Clause 1.3)

[ f_s = \frac{2 \times P}{t \times w} ]

Where:

• (f_s) = shear strength (kg/cm²)
• (P) = ultimate load (kg)
• (t) = thickness of plywood (cm)
• (w) = width of specimen (cm)

4. Shear Test Setup

• Load applied axially at ~455 kg/min on compression table.
• Loading block sizes (mm):

Visual: Bending Test Setup (Mandrel and Specimen)

flowchart LR
    A[Plywood Specimen] --> B(Mandrel)
    B --> C{B

IS 709 - Marking and Identification of Aircraft Plywood (Clause 8.1 & 3.1)

Each plywood board must be legibly stamped on one side with:

• Manufacturer's name or trade-mark
• IS standard number (IS 709)
• Veneer species abbreviation (from Table 1, Clause 3.1)
• Date of manufacture
• Thickness of board (in mm)
• Batch number and press-load number

Table 1: Timber Species & Abbreviations for Marking

Additional Notes:

• Other timber species may be used if performance meets the standard.
• Marking ensures traceability and quality control.
• Thickness and batch details help in identifying production specifics.

flowchart LR
    A[Board] --> B[Stamped Side]
    B --> C[Manufacturer Name]
    B --> D[IS Standard No. (709)]
    B --> E[Veneer Species Abbreviation]
    B --> F[Date of Manufacture]
    B --> G[Thickness]
    B --> H[Batch & Press-load No.]

This marking system ensures quality assurance and traceability in aircraft plywood production per IS 709.

IS 709 Sampling Key Points

Sampling of Boards (Clause 9.1 & Table 2)

• Samples must be drawn randomly from each batch.
• Number of samples depends on batch size:

• Clause 9.1.1: If any boards in the batch have joints, samples must include boards with joints.

Tendered Samples (Clause 10.1)

• Manufacturer submits six 3-ply boards of any size for each plywood type and thickness.
• These are for type tests by the purchaser.

flowchart TD
    A[Batch of Boards] --> B{Batch Size?}
    B -->|<50| C[Select 2 Samples]
    B -->|51-100| D[Select 4 Samples]
    B -->|101-200| E[Select 5 Samples]
    B -->|201-250| F[Select 6 Samples]
    B -->|251-500| G[Select 7 Samples]
    C & D & E & F & G --> H{Boards with Joints?}
    H -->|Yes| I[Include Jointed Boards in Samples]
    H -->|No| J[Random Samples]

This ensures representative sampling per IS 709 for quality control and testing.

IS 709 - Inspection Key Points

1. Inspection of Veneers (Clause 10.2)

• Each veneer sheet is inspected individually.
• Must conform to requirements under Clause 4 (quality, dimensions, defects).

2. Specimen Bending (Clause 2.2)

• Specimens bent to a parallel-sided 'U' shape at specified radius.
• Bent once in one direction and then reversed without tension side support.

3. Shear Strength Test (Clause 1.3 & Table B-1)

• Assembly placed on compression table; load applied axially at ~455 kg/min.
• Shear strength formula:

[ f_s = \frac{2 \times P}{t \times w} ]

Where:

• ( f_s ) = Shear strength (kg/cm²)
• ( P ) = Ultimate load (kg)
• ( t ) = Thickness of plywood (cm)
• ( w ) = Width of specimen (cm)

4. Loading Block Sizes (mm)

5. Board Inspection (Clause 10.2.2)

• Inspect for warp freedom.
• Conformity to Clauses 5 & 6.
• Tests as per Clauses 7.1.1 to 7.1.5 (physical, mechanical properties).

flowchart TD
    A[Veneer Inspection] --> B{Conform to Clause 4?}
    B -- Yes --> C[Pass]
    B -- No --> D[Reject]
    E[Specimen Bending] --> F[Bend to 'U' shape]
    F --> G[Bend forward and reverse]
    H[Shear Test] --> I[Apply load @ 455 kg/min]
    I --> J[Calculate shear strength fs]
    J --> K[Use fs = 2P / (t w)]
    L[Board Inspection] --> M{Warp free?}
    M -- Yes --> N[Tests 7.1.1 to 7

IS 709: Determination of Bending Properties of Plywood

Key Specifications & Formulas

1. Static Bending Strength (Clause 7.1.6)

• Test: 3 specimens per direction (parallel & perpendicular to face veneer grain) per IS 1734 (Part II):1983.
• Required values from Table 1:

2. Bending Test Mandrel Diameter (Clause 2.1, Table 3)

• Mandrel diameter depends on plywood thickness to avoid fracture/separation:

3. Test Procedure (Appendix A, Clause 7.1.4)

• Plywood ≤ 5 mm thickness must bend around the mandrel diameter without fracture or ply separation.

Summary Diagram of Bending Test Setup

flowchart LR
    A[Plywood Specimen] --> B[Bending around Mandrel]
    B --> C{No fracture or ply separation?}
    C -- Yes --> D[Pass Bending Test]
    C -- No --> E[Fail Bending Test]

Note:

• MOE and MOR values ensure plywood strength and stiffness in both grain directions.
• Mandrel bending test ensures flexibility and ply bonding quality.

IS 709: Determination of Shear Strength (Clause 7.1.5.2 & Appendix B)

• Shear Strength is evaluated per Appendix B (Clause 7.1.5.2).
• At least two specimens are tested from each board (Clause 7.1.5.1).
• The shear strength is based on the maximum load at failure divided by the shear area.

Key Formula:

[ f_v = \frac{P_{max}}{A_s} ]

Where:

• ( f_v ) = Shear strength (N/mm²)
• ( P_{max} ) = Maximum load at failure (N)
• ( A_s ) = Shear area (mm²), typically the cross-sectional area resisting shear

Typical Shear Area Calculation:

• For rectangular cross-section:
  [ A_s = b \times d ]
  where ( b ) = width, ( d ) = thickness of the specimen.

Testing Notes:

• Specimens are loaded in shear until failure.
• The average of at least two specimens is taken for design values.
• Appendix B provides detailed test setup and specimen dimensions.

flowchart LR
    A[Select Board] --> B[Prepare 2+ Specimens]
    B --> C[Apply Shear Load]
    C --> D[Record Max Load \(P_{max}\)]
    D --> E[Calculate Shear Strength \(f_v = P_{max}/A_s\)]
    E --> F[Determine Average Shear Strength]

Summary: Shear strength is experimentally determined as max load divided by shear area, averaging multiple specimens per IS 709 Appendix B.

IS 709: Additional Test Procedures Key Points

1. Bending Test (Clause 2.1, Table 3)

• Mandrel diameter is proportional to veneer thickness.
• Specimens bent to a parallel-sided 'U' shape without tension side support.
• Bend once forward, then reverse (Clause 2.2).

2. Edge Straightness & Squareness (Annex A, Clause 5.3)

• Procedure involves visual and dimensional checks for edge alignment and squareness.
• Use straight edges and squares to verify tolerances.

3. Shear Strength (Clause 7.1.5.2, Appendix B)

• Shear strength determined by standardized shear tests on specimens.
• Follow specified loading and support conditions as per Clause 7.1.5.2.

flowchart TD
    A[Plywood Specimen] --> B[Bending Test]
    B --> C{Mandrel Diameter}
    C -->|Based on Thickness| D[Refer Table 3]
    B --> E[Bend 'U' Shape Twice]
    A --> F[Edge Straightness Test]
    A --> G[Shear Strength Test]

Summary: Use Table 3 for mandrel sizing, bend specimens twice in opposite directions, check edges for straightness/squareness per Annex A, and perform shear strength tests as per Clause 7.1.5.2.