3/4/2021 1 ME-305 (Machine Design II) Ch # 9 Permanent Joints – Welding – Brazing – Soldering – Cementing – Gluing • Welding is widely used in fabrication • As a replacement for bolted and riveted joints • Use for repairing ME-305 (Machine Design II) Types of Welding • Electric Arc welding – Shielded Metal Arc (SMAW) or Stick – Metal Inert Gas (MIG) – Tungsten Inert Gas (TIG) – Flux-cored Arc (FCAW) – etc. • Gas welding – Oxy-Acetylene – Oxy-Gasoline – Butane-Propane – etc. • Thermit welding
Transcript
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ME-305 (M
achine Design II)
Ch # 9
Permanent Joints– Welding
– Brazing
– Soldering
– Cementing
– Gluing
• Welding is widely used in fabrication
• As a replacement for bolted and riveted joints
• Use for repairing
ME-305 (M
achine Design II)
Types of Welding
• Electric Arc welding– Shielded Metal Arc (SMAW) or Stick
– Metal Inert Gas (MIG)
– Tungsten Inert Gas (TIG)
– Flux-cored Arc (FCAW)
– etc.
• Gas welding– Oxy-Acetylene
– Oxy-Gasoline
– Butane-Propane
– etc.
• Thermit welding
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ME-305 (M
achine Design II)
Types of Welded Joints
1. Lap or Fillet
2. Butt
ME-305 (M
achine Design II)
9-1 Welding Symbols
• The most common
• Representation on manufacturing drawings
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ME-305 (M
achine Design II)
9-1 Welding Symbols…
ME-305 (M
achine Design II)
9-1 Welding Symbols…
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ME-305 (M
achine Design II)
9-2 Butt and Fillet Welds
• The Normal Stress in the Butt jointdue to tension or compression loading
𝜎𝐹ℎ𝑙
→ 9.1
• The average Shear Stress in the Butt joint
𝜏𝐹ℎ𝑙
→ 9.2
• h is the throat length
ME-305 (M
achine Design II)
9-2 Butt and Fillet Welds…
• The Shear Stress in Transverse Fillet Weld is
𝜏𝐹𝑡𝑙
→ 1
• The Normal Stress in the Transvers Fillet Weld is
𝜎𝐹𝑡𝑙
→ 2
• Where 𝐹 𝐹𝑐𝑜𝑠𝜃𝐹 𝐹𝑠𝑖𝑛𝜃
• t is the throat thickness
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ME-305 (M
achine Design II)
9-2 Butt and Fillet Welds…
• t is calculated using sines law𝑡
𝑠𝑖𝑛45ℎ
𝑠𝑖𝑛 180 45 𝜃ℎ
𝑠𝑖𝑛 135 𝜃2ℎ
𝑐𝑜𝑠𝜃 𝑠𝑖𝑛𝜃• From which
𝑡ℎ
𝑐𝑜𝑠𝜃 sin 𝜃• Put for Fs and t in (1) to get
𝜏𝐹ℎ𝑙
𝑠𝑖𝑛𝜃𝑐𝑜𝑠𝜃 𝑠𝑖𝑛 𝜃 → 𝑑
• Put for Fn and t in (2) to get
𝜎𝐹ℎ𝑙
𝑐𝑜𝑠 𝜃 𝑠𝑖𝑛𝜃𝑐𝑜𝑠𝜃 → 𝑒sin(A − B) = sin A cos B − cos A sin B
ME-305 (M
achine Design II)
9-2 Butt and Fillet Welds…
• The von Mises stress at angle is
• It is found that the largest von Mises stress occurs at an angle 62.5o. Then
𝜏1.196𝐹
ℎ𝑙
σ0.623𝐹
ℎ𝑙
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ME-305 (M
achine Design II)
9-2 Butt and Fillet Welds…
• The Shear Stress in Parallel Fillet Weld is (only shear stress occurs)
𝜏1.414𝐹
ℎ𝑙→ 9.3
ME-305 (M
achine Design II)
9-3 Stresses in Welded Joints in Torsion
• Locate the critical point(s) and label
• Calculate primary shear (A is throat area)
𝜏 → 9.1
• Calculate the secondary shear or torsion
𝜏 → 9.1
• r is the distance from the centroid of the weld group.
• Centroid �̅� and 𝑦 can be determined using Table 9-1
• And J = 0.707hJu
• Ju is taken from Table 9-1
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ME-305 (M
achine Design II)
9-3 Stresses in Welded Joints in Torsion…
ME-305 (M
achine Design II)
Example 9-1
• A 50-kN load is transferred from a welded fitting into a 200-mm steel channel as illustrated in Figure. Estimate the maximum stress in the weld.
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ME-305 (M
achine Design II)
Example 9-1 (Solution)
a) Label the ends and corners of each weld by letter
b) Estimate the primary shear𝜏,
c) Locate the centroid of the weld pattern �̅�
d) Find distances 𝑟e) Find J using Table 9-1
f) Find M
g) Find secondary shear 𝜏,,
h) Find (angle of 𝜏,, along �̅�)
i) Find Shear stresses at all ends and corners
j) Identify the most stress point
ME-305 (M
achine Design II)
• Figure shows a welded joint subject to eccentric loading
• The eccentric load produces a vertical primary stress as
𝜏𝑉𝐴
→ 𝑎
• and a horizontal bending stress as
𝜏𝑀𝑐
𝐼→ 𝑏
• Where 𝑐 and 𝐼 0.707ℎ𝐼
• Iu is taken from Table 9.2
9-4 Stresses in Welded Joints in Bending
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ME-305 (M
achine Design II)• The vertical and
horizontal stress components are vector sum to give the total weld stress
𝜏 𝜏 𝜏
9-4 Stresses in Welded Joints in Bending…
ME-305 (M
achine Design II)
• Also known as Filler rod
• Represented on drawing as
• Written as Exxxx-X, (E7018-X)• E Indicates that this is an electrode
• 70 Indicates how strong this electrode is
when welded, measured in thousands of psi.
• 1 Indicates in what welding positions it can be used.
• 8 Indicates the coating, penetration, and current type used. (See Weld Classification Table)
• X Indicates that there are more requirements. (See Additional Requirements of weld)
- Welding Electrode Classification
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ME-305 (M
achine Design II)• Welding positions
1. Flat, Horizontal, Vertical (up), Overhead
2. Flat, Horizontal
3. Flat, Horizontal, Overhead, Vertical (down)
- Welding Electrode Classification…
ME-305 (M
achine Design II)
• Welding Electrode properties
9-5 The Strength of the Welded Joints
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ME-305 (M
achine Design II)• Minimum fillet weld sizes
Table 9-6 comes here
9-5 The Strength of the Welded Joints…
ME-305 (M
achine Design II)
Example 9-2
• A 12-mm by 50-mm rectangular-cross-section 1015 bar carries a static load of 73 kN. It is welded to a gusset plate with a 10-mm fillet weld 50-mm long on both sides with an E70XX electrode as depicted in Fig. Use the welding code method.a) Is the weld metal strength satisfactory?
b) Is the attachment strength satisfactory?
9-6 Static Loading
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ME-305 (M
achine Design II)Example 9-2 (Soln.)a) Weld metal Strength
• From Table 9-6, allowable force per unit length for a 10mm, E70 electrode is 1025 N/mm of weldment; thus
𝐹 1025 𝑙 1025 50 50 102.5 kN
• Since 102.5 > 73 kN, weld metal is Satisfactory.
b) Attachment Strength (in Shear)
• Sy = 190 MPa (Table A-20), and
• 𝜏 0.4𝑆 0.4 190 76 MPa (Table 9-4)
• The shear stress on the base metal adjacent to the weld is;
𝜏. .
73 MPa
9-6 Static Loading…
Should not exceed 0.40Sy of base metal.
ME-305 (M
achine Design II)
Example 9-2 (Soln.)…• Since 𝜏 𝜏 i.e. 76 >73 MPa, the attachment is
Satisfactory in “shear” near the weldment.
b) Attachment Strength (in Tension)• Sy = 190 MPa (Table A-20), and
• 𝜎 0.6𝑆 0.6 190 114 MPa (Table 9-4)
• The tensile stress on the shank of the attachment is;
𝜎. .
122 Mpa
• Since 𝜎 𝜎 i.e. 114 < 122 MPa, the attachment is Unsatisfactory in “tension” at the shank.
• By changing thickness of the bar from 12 mm to 13 mm will make it Satisfactory.
9-6 Static Loading…
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ME-305 (M
achine Design II)Example 9-4 • Perform an adequacy assessment (by
calculating the f.o.s) of the statically loaded welded cantilever carrying 2.2kN. The cantilever is made of AISI 1018HR steel and welded with a 10-mm fillet weld as shown in the figure. An E6010 electrode was used, and the design factor was 3.0.a) Use the conventional method for the
weld metal.
b) Use the conventional method for the attachment (cantilever) metal.
c) Use a welding code for the weld metal.
9-6 Static Loading…
ME-305 (M
achine Design II)
Example 9-4 (soln.) (a) Adequacy of the Weldment• The weld pattern is “Fillet” and under “Bending”. From
• Since 𝑛 𝑛 i.e. 3.55 3.0, the weld metal is “Adequate”.
9-6 Static Loading…
ME-305 (M
achine Design II)
Example 9-4 (soln.)… (b) Adequacy of the Attachments• Bending stress in the attachment
𝜎⁄
79.2 MPa
• From Table A-20, for 1018 HR steel, 𝑆 220 Mpa
• Factor of Safety
𝑛𝑆𝜎
22079.2
2.78
• Since 𝑛 𝑛 i.e. 2.78 3.0, the attachment is “Not adequate”.
9-6 Static Loading…
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ME-305 (M
achine Design II)Example 9-4 (soln.)… (c) Adequacy of the Weldment (using Welding Code)• From part (a)
𝜏 56.1 Mpa• From Table 9-6, Allowable shear stress on the throat of
E6010 fillet weld is 𝜏 124 MPa, then
𝑛𝜏
𝜏12456.1
2.2 → i
• But 𝜏 is calculated using DE theory and already includes a fos which is
𝑛0.577𝑆
𝜏0.577 345
1241.6 → ii
• The factor of Safety will be (i) multiply by (ii)
𝑛 2.2 1.6 3.53 [Adequate]
9-6 Static Loading…
ME-305 (M
achine Design II)
Example 9-3 • A 1018 HR steel section for the attachment has a cross
section as shown in the Figure and has yield and ultimate tensile strengths of 220 and 400 MPa, respectively. It is statically loaded through the attachment centroid by a load of F = 100 kN. Unsymmetrical weld tracks can compensate for eccentricity such that there is no moment to be resisted by the welds. Specify the weld track lengths l1 and l2 for a 8 mm fillet weld using an E70XX electrode. This is part of a design problem in which the design variables include weld lengths and the fillet leg size.
9-6 Static Loading…
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ME-305 (M
achine Design II)Example 9-6 • The 1018 steel strap of Figure has a repeatedly
applied load of 9 kN (Fa = Fm = 4.5 kN). Determine the fatigue factor of safety of the weldment using Gerber fatigue failure criterion.
