1. INVESTIGATION OF JOINTS IN 3D SPACER FABRIC COMPOSITES
By-
Vishnupriya
Mtech(Aero) B
Supervised by-
Prof. R. Santhanakrishnan
Department of Aero Engg.
HITS

2. OBJECTIVE
To design a 3D spacer fabric composite by simple hand layup technique.
Join them in different methods and conduct mechanical tests on them.
To evaluate the results analytically and mathematically and compare with the experimental results.
To determine the optimum joining method for the material.

3. 3D SPACER FABRIC COMPOSITE
Complex 3D constructions made of two separate fabric layers connected vertically with pile yarns or fabric layers.
The fabric surfaces are strongly connected to each other by the vertical pile fibers which are interwoven with the skins.
The conventional spacer fabrics composed of two surface layers bound with pile yarns are generally manufactured using weaving and knitting technologies.

4. The interstitial space of the construction can be filled up with foams to provide synergistic support with vertical piles.
The 3-D spacer fabric can provide good skin- core debonding resistance, excellent durability and superior integrity.
These products have broad application prospects:automobile, locomotive, aerospace, marine, windmills, building and other industries.

6. JOINTS
Airframe applications of composite material structures have been investigated for a number of years.
Airframe weight reductions of about 40 percent are obtained.
Weight savings from increased strength and stiffness could be easily offset by weight losses resulting from inefficient joining of these materials.
Joints of structure members are one of most difficult objects to design.
Common ways of part linkages in such composite structures are: bolt, resin bonding or combination of both.

7. BONDED JOINT TYPES

8. BOLTED JOINT TYPES

9. COMBINED JOINT

10. MATERIAL SELECTION Glass fiber cloth : 7 MIL E GLASS
E-glass – Alumino borosilicate glass
Plain weave flat sheet
Fiber orientation 0/90
Fiber dia: mm
High strength to weight ratio

11. Resin: ARALDITE GY 257 Resistant to chemicals
Resistance to crystallization
Gel Time : mins
Very good processing properties
Good mechanical performances
Good surface penetration
Low viscosity: mPa.s at 250 c
Low Density: 1.15 g/cm3

12. Hardener : ARADUR 2963 CH
Light yellow clear liquid with amine-like odour
Density: Kg/m3
Boiling point is more than C
Flash point: C
Kinematic viscosity: mPa.s
Mixing ratio :100 parts by weight of the resin and 45 parts by weight of the hardener

13. PREPARATION OF SPECIMEN

14. STEP 1: PREPARATION OF PANELS
Measure the weight of fiber cloth
Measure resin equal to weight of fiber cloth
Take hardener equal to 45% of weight of resin
Mix resin & hardener together and stir continuously
Place the fabric on the mould and pour the mixture over it
Roll the fabric gently against pile direction and spread mixture evenly
Allow the specimen to dry and harden
Cut the specimen as per ASTM standards

15. Weighing spacer fiber cloth
Measuring resin and hardener

16. Pouring resin-hardener mixture
Placing the fabric on mould
Pouring resin-hardener mixture

17. Rolling for even spread of mixture
Drying and hardening

18. STEP 2: JOINING THE PANELS
Panel I : Bolted Single Cover Butt Joint
Type of Joint selected: Single Cover Butt Joint
Determine the number of bolts and the pattern required for the joint: 4 bolts per panel
Based on the number of bolts and design, calculate the appropriate spacing between the fasteners: 2mm,1mm
Mark the points on the specimen to be drilled.

19. Drill holes of required diameter on the panel: 5mm
Similarly drill holes on the cover plate: 10
Place the cover over the panels placed butt to butt and fasten them together by nuts and bolts
Tighten the nuts and bolts such that the plates are joined tightly.

21. Panel II: Combined Joint Single Cover Butt Joint
Type of Joint selected: Single Cover Butt Joint
Determine the number of bolts and the pattern required for the joint: 2 bolts per panel
Based on the number of bolts and design, calculate the appropriate spacing between the fasteners: 2mm
Mark the points on the specimen to be drilled.
Drill holes of required diameter on the panel: 5mm
Similarly drill holes on the cover plate: 4

22. Apply the resin and hardener mixture on the cover plate.
Now place the cover over the panels placed butt to butt and fasten them by the nuts and bolts
Tighten the nuts and bolts such that the plates are joined tightly and let the specimen dry.

23. Panel III: Resin Bonded Joint
Cut strip of the spacer fabric of equal weight as the two panels combined.
In ratio of 100:45, measure the resin and hardener and mix the together.
Apply the mixture on the fabric strip and wrap the strip on the joint tightly.
Let the set up to dry and harden to form a strong joint.

24. EXPERIMENTAL TESTING AND ANALYSIS

25. Tensile tests were carried out on manufactured specimens.
To observe the behaviour of the specimen joints under tensile loads.
Thus, to obtain the tensile strength of the specimens under consideration.
Results were compared to determine the best joint type.

26. Test Setup
Universal Testing Machine

27. Mounting Specimen on UTM and application of tensile load

28. Graphical Results for the tests
8 bolt- Single Cover Butt Joint
Gauge Length:170 mm
Thickness: mm
Width: 60 mm
Gauge Peak Load: 6.60 kN
Max C.H Travel:19.7 mm
Tensile Strength: 8.14N/mm2

29. 4 bolt- resin Single Cover Butt Joint
Gauge Length: 170 mm
Width: 60mm
Thickness: mm
Gauge Peak Load: 4.7 kN
Max C.H Travel: 9.1 mm
Tensile Strength: N/mm2

30. Adhesive Bonded Joint Gauge Length: 185mm Width: 60 mm
Thickness : mm
Gauge Peak Load: 2.76 kN
Max. C.H Travel: 5.0 mm
Tensile Strength: 3.29 kN/ mm2

31. 8.14 3.29 Specifications 4 Bolted Joint 8 Bolted Joint Resin Joint
Peak Load(kN)
4.7
6.60
2.76
Max. CH Travel(mm)
9.1
19.7
5.0
Load at Break(kN)
.90
.65 1
CH Travel at break(mm)
10.50 21
5.85
Tensile Strength(N/mm2)
5.80
8.14
3.29

32. INFERENCE
On comparison of graphs from tensile test of specimen it is observed that the 8 bolt joint exhibited maximum tensile strength and resistance to failure .
The combined joint of resin and bolts in specimen II showed lower tensile strength as compared to specimen I.
The resin bonded butt joint had the weakest joint of 3 joints.

33. ANALYTICAL RESULTS

34. FORMULAE USED
Strength of plate between bolt holes in tension = σat x (p – d) x t
Bolt Value = Smaller of bearing strength and shearing strength of rivet
Bearing Strength of bolt = σ pf x d x t
Shearing strength of bolt = τvf x (π/4) x d2
Strength of joint per pitch = smaller of:
(i) the strength of plate between bolt holes in and
(ii) rivet value
Strength of plate per pitch = σat x p x t
Efficiency of Joint = Strength of joint per pitch x 100
Strength of plate per pitch
Where,
σat – allowable tensile stress in an axially loaded tension member
σpf – allowable bolt stress in member
τvf - allowable shear stress in bolts
p - pitch
d- effective diameter of bolt

35. MATHEMATICAL RESULTS FOR BOLTED JOINT
Strength of joint per pitch = 3.32kN
Strength of Plate per pitch = 3.24kN
Max. strength of joint per pitch length = 6.6kN
Efficiency of joint= 67.5%
For 4 bolt, strength of joint= 3.32kN ≈ 4.7kN
For 8 bolt, strength of joint= 6.64kN ≈ 6.60kN

36. COMPUTATIONAL RESULTS

37. ADHESIVE TOOLKIT
It is a unique web based resource of Material Metro Systems (UK)
Provides information required for organisation of relevant material related to adhesives and adhesive bonding.
Stress Analysis module of package used to calculate stress in resin bonded joint.

38. Input Data Loading Condition: Axial Axial Load Value:4000N
Temperature Difference: 0oC
Adherend Material: Fibre Glass/ Epoxy56
Tensile Modulus of the adherend material:40000MPa
Linear coefficient of thermal expansion: 40E-6/K
Type of adhesive material: Epoxy ( Vantico, Ardalite 2011)
Shear Modulus: 555MPa
Elastic Shear Stress Limit of Adhesive: 12MPa
Adherend thickness: 13.5mm
Adhering Length: 60mm
Adhesive Thickness: 1mm
Outer and Inner thickness of material: 13.5 mm

40. CONCLUSIONS
On a weight-efficiency basis, bonded joints were found to be superior to bolted joints. Also,the donot have stress concentrations.
Therefore, they are recommended for permanent- joint applications.
For stronger joints mechanical fasteners are a better option especially parts that require frequent assembling and disassembling.
The combination joints gives the properties of both bolted joints as well as bonded joints.

41. SCOPE OF FUTURE WORK
Similar tests can be conducted on other joints too such as types of lap joints.
Analysis of failure modes of joints to reveal the fracture mechanics aspect of the joint.
FEA on joints to investigate the fracture mechanical behaviour.
Analysis of test data mathematically and semi- empirically.
Use of composite mechanical fasteners instead of metal bolts for same experiment.

42. Determination of fatigue life of the specimen by cyclic load application.
Computational study using ABAQUS and ADINA.
Study of influence of mechanical properties of adhesives on stress distributions.
Estimating strain by microstrain technique to obtain optimum performance of adhesive bonded joints.

43. BIBILOGRAPHY
J.C. Velosa, R. Fangueiro, F.W. J. van Hattum, F. Soutinho, S. Marques, “ Development of Reinforced Composite Sandwich Panels Based on 3D Fabrics”,Budapest, Hungary, June 2010.
Achim Menges, “Integral Computational Design for Composite Spacer Fabric Structures”, Stuttgart University, Germany.
D.M. Hoyt, Steve Ward, “Composite Bonded Joints Analysis, Data, and Substantiation”, Seattle, WA, June 2004.
Diren Mecit, Arzu Marmarali, “Application of spacer fabrics in composite production”, Ege University, Izmir, Turkey, 2012.
Ahmet Refah Torun, “Advanced manufacturing technology for 3D profiled woven performs”, Technischen Universität Dresden,2011.

44. O. M. Lehman,A. V. Hawley, “Investigation of Joints in Advanced Fibrous Composites for Aircraft Structures”, June 1969.
Suranga Gunawardana, “Predicition of failure initiation of adhesively bonded joints using mixed mode fracture data”, Witchita State University,
MD Banea, LFM da Silva, “Adhesively bonded joints in composite materials: An Overview”, Instituto de Engenharia Mecânica, Portugal, May 2008.
Min Li , Shaokai Wang , Zuoguang Zhang , Boming Wu, “Effect of Structure on the Mechanical Behaviors of Three-Dimensional Spacer Fabric Composites”, November 2008.
Geon-Woong Lee, Joong Sik Choi, Sang-Soo Lee, Min Park, “Mechanical Properties and Failure Mechanism of the Polymer Composite with 3- Dimensionally Stitched Woven Fabric”, Seoul , Korea, February 2003.
Parabeam 3D Glass Fabrics: mechdir.com/parabeam-3d-glass- fabrics/

45. THANK YOU