Title

FAILURE ANALYSIS OF POLYMER FURNITURE COMPONENTS

Date

2013

Objective

To determine the cause of failure of a polymer furniture component.

Photo

Figure 1. Close-up of Sample B – failed sample (cracks circled).

Figure 2. A Specimen showing voids in the material removed from Sample B prior toashing.

Testing Undertaken

FT-IR analysis according to ASTM E 573, using an Alpha Measurement Module byBrukerOptik

Thermal analysis by DSC according to ASTM D 3418, using a DSC Q20 by TA instruments

Ash testing according to the residue on ashing procedure described in ASTM D 2584.

Failure Mode and Recommendations

The failures are due to shrinkage cracking where the polymer undergoes post-moulding shrinkage but is constrained by the metal insert causing the polymer to be placed in tension.  The presence of a high level of filler and the use of PPhomopolymer make the polymer less able to resist these tensile forces so cracking occurs.

The internal voids are moulding defects due to volatiles or shrinkage voids and these lower the material strength of the polymer.

Mould shrinking can be limited by increasing mould temperature, controlling the moulding variables, the thermal history of the moulding (temperature, cooling rate, part thickness and gate dimensions).

Heating the metal inserts close to the mould temperature before moulding removes differences in thermal expansion that can lead to stress build-up at the metal/plastic interface.

Title

TESTING OF REINFORCED FLEXIBLE POLYPROPYLENE (R-PP) GEOMEMBRANE SAMPLES

Date

2013

Objective

Comparative testing of five reinforced flexible polypropylene (R-PP) cover samples

Testing Undertaken

Breaking Strength: Procedure A – Grab Test Method (ASTM D 751)

Trapezoidal Tear (ASTM D 4533)

Carbonyl Index (based on ASTM F2102)

Surface microscopy (photographs for assessing micro-cracking)

Weld Shear (ASTM D 6392)

Ply Adhesion (ASTM D 6636)

Conclusion

ATR FT-IR data indicated that all the used samples had undergone significant oxidation.

Micrograph showed considerable crazing of the exposed samples but no micro-cracking was evident.

Title

TESTING OF REINFORCED FLEXIBLE POLYPROPYLENE (RPP) GEOMEMBRANE SAMPLES

Date

2013

Objective

To conduct comparative testing on three reinforced flexible polypropylene (RPP) cover samples.

Photo

Figure 1. Surface Detail x200 magnification – no surface micro-cracking evident but slight crazing only.

Figure 2. Surface Detail x200 magnification – surface micro-cracking and fissuring evident.

Figure 3. Surface Detail x200 magnification – surface micro-flaking evident.

 Figure 4. Surface Detail x200 magnification – surface crazing/chalking evident.

Figure 5. Surface Detail x200 magnification – surface micro-cracking and flaking evident.

Testing Undertaken

Surface microscopy

Grab Tensile Strength: ASTM D751, Procedure A

Trap Tear Strength: ASTM D4533

HP-OIT: ASTM D5885

IR: ASTM F2102

Surface infra-red analysis and carbonyl index

Conclusion

The sample L was the most degraded (lowest HP-OIT values and lowest mechanical properties, with the black surface showing extensive cracking consistent with its relatively high carbonyl index (0.12). The black side appears to have been subject to chlorine attach leading to destruction of the stabilizers and oxidative embrittlement of the black ply.

Samples L and Ware less degraded than Sample L but still show evidence of oxidation and cracking of the black side and some crazing of the coloured side. Sample U had the highest retained stabiliser levels on the coloured side, the lowest carbonyl index for the coloured side, and the highest retained grab tensile strength and trap tear strength in direction 2.

Title

ASSESSMENT OF AN ELECTROFUSION WELD

Date

2013

Objective

To assess the condition of electrofusion weld assembly samples.

Photo

Figure 1. Mating surfaces of specimen showing some melting of the surfaces (as evidenced by visible ridges)

Figure 2. Socket magnified surface

Figure 3. Pipe magnified surface

Testing Undertaken

Failure analysis

Failure Analysis

The weld failure was most likely caused by the mating surfaces not being hot enough for the materials to meld together.

Title

TENSILE TESTING OF BUTT FUSED HDPE PIPE SAMPLES

Date

2013

Objective

To measure the tensile properties of HDPE pipe samples for qualification or production testing purposes

Photo

Figure 1. Specimen 1 failure mode (ductile break)

Figure 2. Specimen 2 failure mode (ductile break)

Figure 3. Specimen 3 failure mode (ductile break)

Testing Undertaken

Tensile properties testing per ISO 13953:2001(E)

Title

FAILED ELECTROFUSION WELD

Date

2013

Objective

To investigate the cause of a failed Electrofusion weld

Photo

Figure 1. Pipe weld section after extensive cleaning. Some mud remained in weld. Long thing contaminant noticed that had mirror image on the fitting surface.

Figure 2. Weld Area at x200 magnification revealing dirt particles melted into surface of specimen

Testing Undertaken

Failure analysis under microscope

Failure Mode

Although the pipe and fitting were hot enough to melt the polymer, the surfaces were never close enough or clean enough for a proper joint to form.

Title

CRACKING OF 5MM HDPE SHEET LINER IN A SEWER

Date

2012

Objective

To test coupons/retrieved samples to determine the root cause of embrittlementand cracking failures of a 5mm thick HDPE lining sheet installed in a sewer tunnel approximately 4 years ago.

Photo

Figure 1. Observed cracking

Testing Undertaken

DSC Thermal analysis

OIT

Melt flow index

Density determination

Microscopy

Peel testing

Failure Analysis

The 5mm HDPE sheet failed by brittle stress cracking (environmental stress cracking).

The root cause of the cracking was poor material selection as the grade of HDPE used was a homopolymer grade which has excessively high density and high %crystallinity and a marked propensity to undergo stress cracking.

Title

KNEE PAD MATERIAL IDENTIFICATION AND PERFORMANCE TESTING

Date

2013

Objective

To determine the performance properties and possible identity of the materials used in a kneepad sample

Testing Undertaken

FT-IR

DSC

Flexural crack (cyclic fatigue)

Hardness (DurometerShore A)

Conclusion

FT-IR and DSC analysis indicated the kneepad was constructed from LDPE foam with a small amount of EVA. No flex cracking or flex damaged was observed after 1,000,000 oscillations. The kneepad tested had a larger hardness value than the two kneepads previously tested.

Title

DELAMINATION FAILURE OF MULTILAYER PLASTIC LAMINATE PACKAGING

Date

2013

Objective

To investigate the origin of delamination defects (ie. adhesion failure of the top clear coating) of a plastic laminate used in packaging bags for dog food.

Photo

Figure 1a, 1b, 1c, 1d. Photomicroscopy of samples 1, 2, 3 and 4.

Testing Undertaken

Photomicroscopy

FTIR

TOF-SIMS

Failure Analysis

Delamination was associated with the presence of areas of silicone contamination.

Title

PURITY OF NYLON SAMPLES

Date

2013

Objective

To measure the nylon 6,6 content of two samples.

Samples were recycled material. Not supplied with identification/description, identified in report as Green Fibre Mixture and Grey w/ Green Fibre Mixture.

Photo

Testing Undertaken

ASTM D 3418

Thermal properties were tested using Differential scanning calorimetry (DSC),crystallinity was also measured

Conclusion

DSC indicated the green fibrous sample was Nylon 6. Crystallinity measurements of the Grey w/ Green sample indicated it contained Nylon 6