Methods of testing of small transparent specimens of timber

IS 1708 Part 1-18: Scope - Key Formulas & Tables Summary

The scope covers determination of mechanical characteristics of timber under static bending and impact tests using specified formulae.

Key Formulas (Clause 4.2 & 4.3)

Impact Test Related (Clause 4.3)

IS 1708 Part 1-18: Test Specimen Preparation and Dimensions

Specimen Sizes & Shapes (Clause 2.1)

• Two specimen sizes:
  • Size 1: 5 × 5 cm cross-section, length 20 cm (or 6 cm for shear test)
  • Size 2: 2 × 2 cm cross-section, length 8 cm (or 3 cm for shear test)

Notch and Failure Area

• Notches as per Fig. 1A & 1B to induce failure in radial or tangential surface.
• Failure area:
  • 50 × 20 mm (for 5 × 5 cm specimen)
  • 20 × 10 mm (for 2 × 2 cm specimen)

Additional Specifications

• Specimens must be free of defects.
• Grain slope ≤ 1:20 relative to longitudinal edges.
• End planes must be perpendicular to specimen length.
• Notches are designed to produce shear failure on specified surface areas.

Summary Table

This ensures standardized specimen preparation for consistent shear testing results.

IS 1708 Part 1-18: Test Procedures & Loading Rates

Key Specifications for Rate of Loading (Clause 3.2):

• The movable head of the testing machine must move at a constant rate during the test.
• Typical rates specified:
  • 2.5 mm/min until maximum load (for both sizes).
  • Alternative rates mentioned: 0.4 mm/min and 0.6 mm/min (context-dependent).

Summary Table of Loading Rates:

Important Notes:

• The load must be applied continuously and smoothly to avoid shock loading.
• The rate ensures uniform stress application and accurate measurement of strength.
• Data recording should be synchronized with the displacement and load to capture peak values.

flowchart LR
    Start[Test Setup] --> LoadApplied[Apply Load]
    LoadApplied --> MovableHead[Movable Head moves at constant rate]
    MovableHead --> MaxLoadReached{Max Load reached?}
    MaxLoadReached -- No --> ContinueLoading[Continue at constant rate]
    MaxLoadReached -- Yes --> RecordData[Record Load & Displacement]
    RecordData --> End[Test Complete]

This ensures compliance with IS 1708 Part 1-18 for consistent and reliable test results.

IS 1708 Part 1-18: Recording of Data and Calculations

Key Specifications:

• Loading rate: 6 mm/min constant travel of machine head (Clause 3.2).
• Failure recording: According to appearance/development per Fig. 2 (Clause 3.4).

Important Formulas (Clause 4.2):

Parameters:

• (P) = Load at limit of proportionality (kg)
• (P') = Maximum load (kg)
• (l) = Span length (cm)
• (b) = Breadth of specimen (cm)
• (h) = Depth of specimen (cm)
• (\Delta) = Deflection at load (P) (cm)
• (C) = Area constant (kg·cm)
• (A, A', A'') = Areas under load-deflection curve up to LP, max load, and final

Specific Gravity Determination (IS 1708 Part 1-18)

Key Formulas:

1. Specific Gravity at Test Condition: [ \text{Specific Gravity} = \frac{W_1}{V_1} ]

   • (W_1) = weight of test specimen (g)
   • (V_1) = volume of test specimen (cm³)

2. Adjusted Specific Gravity (considering moisture content): [ \text{Adjusted Specific Gravity} = \frac{W_1}{V_1} \times \frac{100}{100 + m} ]

   • (m) = moisture content (%) of specimen

3. Oven Dry Specific Gravity: [ \text{Oven Dry Specific Gravity} = \frac{W_o}{V_o} ]

   • (W_o) = oven dry weight (g)
   • (V_o) = oven dry volume (cm³)

Specimen Dimensions (Clause 2.2):

• For specific gravity test:
  • Cross-section: 5 x 5 cm, Length: 15 cm
  • Or Cross-section: 2 x 2 cm, Length: 6 cm
  • If rectangular specimens unavailable: volume ≈ 10 cm³

Notes:

• Standard Specific Gravity: Adjusted specific gravity for green specimens (above fibre saturation point).
• Dry Specific Gravity: Specific gravity of dry specimens.

flowchart TD
    A[Specimen Preparation] --> B{Specimen Size?}
    B -->|Rectangular| C[Use 5x5x15 cm or 2x2x6 cm]
    B -->|Irregular| D[Take ~10 cm³ volume specimen]
    C & D --> E[Measure Weight (W1) and Volume (V1)]
    E --> F[Calculate Specific Gravity = W1/V1]
    F --> G{Moisture Content Known?}
    G -->|Yes| H[Adjusted Specific Gravity = (W1/V1)*(100/(100+m))]
    G -->|No| I[Use Specific Gravity at Test]
    H & I --> J{Oven Dry Required?}
    J -->|Yes| K[

IS 1708 Part 1-18: Static Bending Strength Tests Summary

Specimen Dimensions (Clause 2.1)

• 5 x 5 cm cross-section, 75 cm length, or
• 2 x 2 cm cross-section, 30 cm length
• Grain slope ≤ 1:20, defect-free specimens.

Key Formulas (Clause 4.2)

• P = load at limit of proportionality (kg)
• P' = maximum load (kg)
• l = span length (cm)
• b = breadth (cm)
• h = depth (cm)
• δ = deflection at P (cm)
• C = energy per unit area under load-deflection curve (kg·cm)

Impact Bending Strength Test (IS 1708 Part 1-18)

Specimen Dimensions (Clause 2.1)

• Size 1: 5 × 5 cm cross-section, 75 cm length
• Size 2: 2 × 2 cm cross-section, 30 cm length
• Grain slope ≤ 1:20 parallel to edges.

Test Setup (Clause 3.1)

• Span:
  • 70 cm for 5 × 5 × 75 cm
  • 28 cm for 2 × 2 × 30 cm
• Hammer weight:
  • 25 kg (large specimen)
  • 1.5 kg (small specimen)
• Hammer face radius: 75 cm (large), 30 mm (small).
• Impact on tangential surface near heartwood.
• For stronger species, double hammer weight and height.

Key Formulas (Clause 4.2)

Where:

• ( P ) = load at limit of

Key Formulas for Compressive Strength Tests (IS 1708 Parts 1-18)

1. Compressive Stress Calculations (Clause 4.1)

2. Compression Parallel to Grain (Clause 4.2)

Key Formulas & Specifications for Tensile Strength Tests (IS 1708 Parts 1-18)

1. Tensile Strength Parallel to Grain (IS 1708 Part 12)

• P = Load at proportional limit (kg)
• P' = Maximum load (kg)
• A = Cross-sectional area (cm²)
• L = Gauge length between extensometer points (cm)
• Δ = Elongation at proportional limit (cm)

2. Tensile Strength Perpendicular to Grain (IS 1708 Part 13)

• P, P' = Load at proportional limit, max load (kg)
• l = Span length (cm)
• b = Breadth (cm)
• h = Depth (cm)
• Δ = Deflection at proportional limit (cm)

3. Horizontal Shear Stress (IS 1708 Part 5 & 6)

Shear and Cleavage Strength Tests as per IS 1708 (Parts 1-18)

1. Shear Strength Test (IS 1708 Part 15 & 11)

• Specimen size:
  • 5 x 5 cm cross-section, 6 cm length or
  • 2 x 2 cm cross-section, 3 cm length.
• Notching: On one end to induce shear failure on radial or tangential plane.
• Test Setup:
  • Specimen supported by cross bar with edges vertical.
  • Shearing tool rests on the notch.
  • Shearing direction parallel to grain.
• Formula for Maximum Shearing Stress (MSS):
  [ MSS = \frac{P_{max}}{A} ]
  Where:
  (P_{max}) = Maximum load at failure (kg or N)
  (A) = Shear area (cm² or mm²)

2. Cleavage Strength Test (IS 1708 Part 14)

• Specimen: With drilled holes (Ø 4 mm) as per Fig. 1.
• Formula for Cleavage Resistance:
  [ \text{Cleavage Resistance (kg/cm)} = \frac{P_{max}}{b} ]
  Where:
  (P_{max}) = Maximum load at failure (kg or N)
  (b) = Width of the specimen (cm)

Summary Table

flowchart LR
    A[Specimen Preparation] --> B[Notching / Drilled Holes]
    B --> C[Setup on Testing Rig]
    C --> D{Apply Load

IS 1708 Part 10: Hardness Testing of Timber (Static Indentation)

Key Specifications:

• Indentation Tool: Steel ball or hemispherical steel bar, diameter = 1.128 cm.
• Indentation Depth: Standard depth = 0.564 cm.
• Load: Load in kg required to penetrate to the specified depth is recorded.
• Surfaces Tested: Tangential, radial, and end surfaces.
• Hardness Values:
  • Average of two penetrations on one surface or one penetration on both ends.
  • Side hardness = average of radial and tangential hardness.

Important Formulae (Clause 4.3):

Notes:

• For compressive stress perpendicular to grain, ratio of results for 5x5 cm and 2x2 cm cross-sections = 1.07 (Clause 5.1).
• Hardness is evaluated by static indentation load required for standard penetration.

Summary Diagram of Hardness Test Setup:

flowchart LR
    A[Steel Ball (Ø 1.128 cm)] --> B[Indentation on Timber Surface]
    B -->

Nail and Screw Holding Power
As per IS 1708 (Part 15 & 16) - 1986

Nail Specifications (Clause 3.2, Part 15)

• Length: 50 mm
• Shank Diameter: 2.50 mm
• Type: Bright, galvanized, diamond pointed, plain heads
• Usage: Each nail used only once

Test Specimen & Setup (Clause 1.1 & 4.1)

• Specimen prepared per IS 1708 Part 15
• Testing machine grips timber fixed head & nail/screw movable head
• Load applied to pull out nail/screw recorded

Data Recording (Clause 4.3)

• Record max load to pull out nails/screws on:
  • Radial surface
  • Tangential surface
  • End surface
• Average of radial & tangential = Side value

Test Conditions (Note, Clause 4.3)

• Nails/screws driven in:
  1. Green timber, pulled immediately
  2. Green timber, pulled after drying to 12% moisture
  3. Dry timber (12% moisture), pulled immediately

Typical Holding Power Formula (General Engineering Knowledge)

[ P = F_{max} ]

Where:

• (P) = Nail/Screw holding power (N)
• (F_{max}) = Maximum pull-out load recorded (N)

Summary Table (Example)

flowchart LR
    A[Test Specimen Preparation] --> B[Nail/Screw Driven]
    B --> C[Specimen Mounted on Testing Machine]
    C --> D[Load Applied to Pull Out Nail/Screw]
    D --> E[Max Load Recorded for Radial, Tangential, End Surfaces

IS 1708 Part 16-18: Brittleness Testing (Charpy & Izod Impact)

Specimen Dimensions:

Key Formulas (Clause 4.2):

Notes:

• P =

IS 1708 Part 18 - Torsional Strength Testing of Timber: Key Points

1. Specimen Dimensions (Clause 2.1 & Fig. 1)

• Shape: Cylindrical
• Central length: 220 mm
• Radius:
  • Large size: 25 mm
  • Small size: 12 mm
• End portions for gripping:
  • Length: 40 mm
  • Large size: 30 mm radius
  • Small size: 15 mm radius

2. Test Setup (Clause 3.1)

• Specimen fixed firmly at one end.
• Free to rotate at the other.
• Angular twist measured at the center over a gauge length of 150 mm.

3. Calculation of Torsional Shear Stress and Modulus

• Torsional shear stress, τ:

[ \tau = \frac{T \cdot r}{J} ]

Where:

• (T) = Applied torque (N·mm)

• (r) = Radius of specimen (mm)

• (J = \frac{\pi r^4}{2}) = Polar moment of inertia for circular section (mm⁴)

• Angle of twist, θ:

[ \theta = \frac{T \cdot L}{G \cdot J} ]

Where:

• (L) = Gauge length (mm)
• (G) = Modulus of rigidity (shear modulus) (N/mm²)

4. Data Interpretation (Clause 4.1)

• Plot Torque vs Angular Twist curve.
• Determine proportional limit and maximum load.
• Calculate shear strength at proportional limit and maximum load.

Summary Table of Formulas

Moisture Content Control and Conditioning (IS 1708 Part 1-18)

Key Formulas:

• Moisture Content (%)
  [ \text{Moisture Content} = \frac{W_1 - W_0}{W_0} \times 100 ]
  Where:

  • (W_1) = weight of sample at test (g)
  • (W_0) = oven-dry weight of sample (g)

• Volumetric Shrinkage
  [ \text{Volumetric Shrinkage} = \frac{V_1 - V_T}{V_1} \times 100 ]
  Where:

  • (V_1) = volume at initial (green) condition (cc)
  • (V_T) = volume at dry condition (cc)

Conditioning Specifications:

• Specimens must be air-seasoned until moisture content reaches approximately 12%.
• Weigh and measure specimens periodically with accuracy as per Clause 3.1.
• Oven-dry condition is considered the reference for zero moisture content.

Summary Table:

flowchart LR
    A[Green Specimen] -->|Measure W1, V1| B[Calculate Moisture Content]
    B --> C{Moisture Content > 12%?}
    C -- Yes --> D[Air Seasoning & Periodic Weighing]
    D --> B
    C -- No --> E[Specimen Ready for Testing]

This ensures consistent moisture content for reliable timber testing as per IS 1708.