What accelerated weathering testing can and cannot predict
Laboratory weathering compresses years into weeks by intensifying specific stresses. It ranks materials and confirms mechanisms reliably; converting its hours into calendar years is where it gets misused.
Premature or expected? Rating exposure against service life
All outdoor plastics degrade eventually, so degradation alone establishes nothing. The question is whether it happened faster than the material, as specified and as installed, should have allowed.
The carbonyl index and how far the degradation has gone
Photooxidation is measurable rather than merely visible. Depth-profiling oxidation from the exposed surface inward turns a faded, chalky part into a quantified degradation front.
Degraded before it was moulded: regrind, heat and residence time
A part can be measurably brittle while the resin certificate reads entirely normal. Thermal history in the barrel, moisture at the hopper and regrind content all degrade material before the tool sees it.
Design defect or moulding defect? Ask the population
A defect built into the geometry appears in every part from the tool. A process defect varies between lots and cavities. How failures distribute across a production population separates the two.
Weld lines: the plane a moulded part was always going to break on
Where two melt fronts meet, the polymer never fully re-entangles. That plane is weaker than the material around it, its location is predictable, and it is a recurring source of field cracking.
Reproducing stress cracking: what bent-strip testing proves
Reproducing a stress-cracking failure under controlled conditions is the most persuasive evidence available in these matters — provided the test conditions are defensible and the limits are stated.
Where the stress came from in a stress-cracking failure
ESC cannot happen without sustained tensile stress, and that stress is often nowhere in the design load case. Moulded-in stress, assembly stress and service load each leave a different trace.
ESC or chemical attack? The polymer itself answers it
Environmental stress cracking and chemical attack look alike on a broken part and separate cleanly in the laboratory. The discriminator is whether the polymer's chemistry changed at all.
Was the delamination stable, or was it growing?
A flaw that sat unchanged for years and one that was propagating toward a critical size support very different conclusions. What fracture toughness testing and free-edge geometry establish about growth.
Manufacturing or in service? Reading delamination geometry
A delamination introduced in the autoclave and one introduced by an impact look similar on a report and different in cross-section. What void content, distribution and damage shape each establish.
Barely visible impact damage and what visual inspection misses
A dropped tool can cost a laminate a large fraction of its compression strength and leave almost nothing on the surface. Why BVID defeats visual inspection, and what actually finds it.
Bonds that fail years after they passed qualification
A joint that met every acceptance test and released after years in service points to durability rather than initial strength. How moisture works into a bondline, and what distinguishes ageing from a latent defect.
Surface preparation and the records that prove it happened
Surface preparation determines whether a bond achieves real adhesion, and it becomes invisible the moment the joint closes. What documentation, exemplars and contact-angle data can establish after the fact.
Classifying a bond fracture: adhesive, cohesive or substrate
Where a bonded joint separates is the first and most consequential observation in the investigation. ASTM D5573 gives the vocabulary, and the percentages usually decide which party the inquiry moves toward.
Proving chemical degradation, not just detecting a chemical
Identifying the chemical on a failed part and proving it caused the failure are two separate tasks. What FTIR, thermal analysis, molecular weight and controlled exposure each establish.
The gap between a compatibility chart and a service condition
Chemical resistance data is generated at one concentration, one temperature and no applied stress. Most compatibility disputes live in the distance between that test and the part in service.
Solvation, hydrolysis, oxidation: three different failures
Chemical attack is not one process. Solvation, extraction, hydrolysis and oxidation are chemically distinct, leave different signatures, and each implies a different exposure history.