A “Toolbox” for Forensic Engineers

More documents

Recommendations

Info

Failure Due to Manufacturing Faults 157 Figure 5.20 Crack in the middle link of the unbroken keeper. The triangular keeper cracked after 36 h under constant stress. Figure 5.20 illustrates a single crack starting on the tension side of the elastic bend, branching into two just to form the Y shape above the neutral axis. Vickers hardness tests (to HV30) carried out after locally removing the zinc coating gave values of 436 and 449 on the hook and 434 and 444 on the keeper. These indicate a steel having a tensile strength of the order of 1400 MN m –2 , typical of the normal range for springs. Hydrogen is easily picked up during electroplating and causes disastrous effects of delayed cracking if not eliminated immediately after products are removed from the electroplating bath, especially so in the higher strength steels. Most international standards give recommendations for stress relief treatments of formed products prior to electroplating and stipulate baking times and temperatures immediately after the components come out of the plating bath for avoidance of hydrogen embrittlement after electroplating. The time required depends on the hardness of the steel and the thickness of the electro-deposit. Because zinc acts as a barrier to the escape and high strength steels are particularly prone to embrittlement, for items like springs the baking times may be 24 h or more. Table 5.3 gives the minimum baking times recommended in BS1076. The small company that made these hooks and keepers had never heard of hydrogen embrittlement and sent them out to a specialist electroplater to be zinc coated. The plating firm was fully aware of the heat treatment requirements but was not told the items were spring steel, and had assumed they TABLE 5.3 Baking Times for Steels after Zinc Plating Maximum Tensile Strength (MN m –2 ) Heat Treatment Up to 1050 None required Above 1050 up to 1450 8 h minimum between 190˚C and 220˚C Above 1450 up to 1800 18 h minimum between 190˚C and 220˚C Above 1800 24 h minimum between 190˚C and 220˚C
158 Forensic Materials Engineering: Case Studies were made from low carbon steel wire. They did not inquire and dispatched them as plated, without any baking treatment. However, the onus was on the plating firm to inquire before carrying out the process and this was taken into account when the respective insurers negotiated settlement of the substantial claims. 5.8 Rivet Failure in Multipurpose Tool This case is a reflection of poor design specification that led to manufacture of an intrinsically faulty and unsafe product. Although quite a number of similar tools were discovered to have failed in the same way, this one came to light when a young man nearly severed an index finger when the knife blade suddenly folded as he was pressing hard. The tools were essentially large pliers with hollow handles, into which a variety of implements such as knife blades, screwdrivers, spikes, hooks and even small socket spanners could be folded away. They represented a compact portable toolbox and were particularly popular with people following outdoor pursuits such as angling. For use, the chosen implement would have to be opened fully until it locked in place in line with the handle. It could be released only by partially opening any of the other implements in the same handle. This action lifted a spring locking tab that engaged in a slot behind the pivot in the handle of the tool fully unfolded. The security of any of the five tools mounted inside the handle was thus entirely dependent on the locking tab being fully engaged in its slot and the pivot reacting all the externally applied force. The accident occurred when the young man had opened out a large pointed knife blade and was attempting to push it through a plastic cap on the top of a container. It was the first time he had used the tool, which had been given to him as a present. While he was pressing hard and waggling the blade from side to side to force the point through the plastic it suddenly folded, cutting his index finger to the bone. The head of the rivet, which served as the pivot, had separated and allowed the pivot to escape from its bearing in the handle and consequently disengaged the locking tab. The head is a tapered plug that fit into a hole at one end of the rivet. The body of the rivet had been machined from bar stock and the hole extended about half way down. The manufacturer of these tools chose to assemble the five implements inside the handle and then press in the tapered plug, rather than use a solid rivet. Tapered joints are only suitable in applications where the external loads are compressive or place the joint in shear. They are easily broken if applied forces are, or occasionally become, tensile.
Page 5 and 6:
Library of Congress Cataloging-in-P
Page 8 and 9:
Preface Case studies of product fai
Page 10 and 11:
could not be simpler in shape, they
Page 12 and 13:
Acknowledgments We thank The Open U
Page 14 and 15:
The Authors Peter R. Lewis, Ph.D.,
Page 16:
Laboratories of Imperial College of
Page 19 and 20:
3 Establishing the Load Transfer Pa
Page 21 and 22:
6.5.2 A Problem in Eire 197 6.5.3 M
Page 23 and 24:
9.4.2 Failure in Femoral Stem of To
Page 25 and 26:
13.3.7 Design Development Sequence
Page 27 and 28:
2 Forensic Materials Engineering: C
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
10 Forensic Materials Engineering:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Page 50 and 51:
Materials in Distress 2.1 Introduct
Page 52 and 53:
Materials in Distress 27 It is usef
Page 54 and 55:
Materials in Distress 29 (A) Unload
Page 56 and 57:
Materials in Distress 31 1. Flowing
Page 58 and 59:
Materials in Distress 33 to compens
Page 60 and 61:
Materials in Distress 35 Fracture o
Page 62 and 63:
Materials in Distress 37 Force A Fr
Page 64 and 65:
Materials in Distress 39 Such fract
Page 66 and 67:
Materials in Distress 41 somewhat b
Page 68 and 69:
Materials in Distress 43 Figure 2.8
Page 70 and 71:
Page 72 and 73:
Page 74 and 75:
Materials in Distress 49 Stress Amp
Page 76 and 77:
Page 78 and 79:
Materials in Distress 53 solutions.
Page 80 and 81:
Page 82 and 83:
Page 84:
Materials in Distress 59 short time
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132: 106 Forensic Materials Engineering:
Page 181: 156 Forensic Materials Engineering:
Page 233 and 234:
Page 235 and 236:
Page 237 and 238:
Page 240 and 241:
Failure of Storage Vessels 215 7 Th
Page 242 and 243:
Failure of Storage Vessels 217 cont
Page 244 and 245:
Failure of Storage Vessels 219 Figu
Page 246 and 247:
Page 248 and 249:
Page 250 and 251:
Page 252 and 253:
Failure of Storage Vessels 227 been
Page 254 and 255:
Page 256 and 257:
Failure of Storage Vessels 231 Mean
Page 258 and 259:
Page 260 and 261:
Page 262 and 263:
Page 264 and 265:
Failure of Storage Vessels 239 Stre
Page 266 and 267:
Page 268 and 269:
Page 270 and 271:
Failure of Storage Vessels 245 (Sur
Page 272 and 273:
Failure of Storage Vessels 247 Were
Page 274 and 275:
Failure of Storage Vessels 249 Dam
Page 276 and 277:
Failure of Storage Vessels 251 Bund
Page 278 and 279:
Failure of Storage Vessels 253 Hull
Page 280 and 281:
Accidents in the Workplace 255 8 De
Page 282 and 283:
Accidents in the Workplace 257 ensu
Page 284 and 285:
Accidents in the Workplace 259 4. F
Page 286 and 287:
Accidents in the Workplace 261 is a
Page 288 and 289:
Accidents in the Workplace 263 Figu
Page 290 and 291:
Accidents in the Workplace 265 be b
Page 292 and 293:
Page 294 and 295:
Page 296 and 297:
Page 298 and 299:
Accidents in the Workplace 273 8.4
Page 300 and 301:
Accidents in the Workplace 275 The
Page 302 and 303:
Accidents in the Workplace 277 (Fig
Page 304 and 305:
Page 306 and 307:
Page 308 and 309:
Page 310 and 311:
Page 312 and 313:
Failure of Medical Implements 9.1 I
Page 314 and 315:
Failure of Medical Implements 289 b
Page 316 and 317:
Failure of Medical Implements 291 F
Page 318 and 319:
Failure of Medical Implements 293 A
Page 320 and 321:
Page 322 and 323:
Failure of Medical Implements 297 9
Page 324 and 325:
Failure of Medical Implements 299 L
Page 326 and 327:
Failure of Medical Implements 301 T
Page 328 and 329:
Failure of Medical Implements 303 N
Page 330 and 331:
Failure of Medical Implements 305 t
Page 332 and 333:
Page 334 and 335:
Page 336 and 337:
Page 338 and 339:
Failure of Medical Implements 313 S
Page 340 and 341:
Failure of Medical Implements 315 T
Page 342:
Failure of Medical Implements 317 R
Page 345 and 346:
Page 347 and 348:
Page 349 and 350:
Page 351 and 352:
Page 353 and 354:
Page 355 and 356:
Page 357 and 358:
Page 359 and 360:
Page 361 and 362:
Page 363 and 364:
Page 365 and 366:
Page 367 and 368:
Page 369 and 370:
Page 371 and 372:
Page 374 and 375:
Fraudulent Insurance Claims 349 11
Page 376 and 377:
Fraudulent Insurance Claims 351 som
Page 378 and 379:
Fraudulent Insurance Claims 353 Fig
Page 380 and 381:
Fraudulent Insurance Claims 355 go
Page 382 and 383:
Page 384 and 385:
Page 386 and 387:
Page 388:
Fraudulent Insurance Claims 363 roa
Page 391 and 392:
Page 393 and 394:
Page 395 and 396:
Page 397 and 398:
Page 399 and 400:
Page 401 and 402:
Page 404 and 405:
Intellectual Property Cases 13.1 In
Page 406 and 407:
Intellectual Property Cases 381 man
Page 408 and 409:
Intellectual Property Cases 383 1 2
Page 410 and 411:
Intellectual Property Cases 385 Fig
Page 412 and 413:
Intellectual Property Cases 387 21
Page 414 and 415:
Intellectual Property Cases 389 lar
Page 416 and 417:
Intellectual Property Cases 391 Sec
Page 418 and 419:
Intellectual Property Cases 393 Fro
Page 420 and 421:
Intellectual Property Cases 395 a h
Page 422 and 423:
Intellectual Property Cases 397 13.
Page 424 and 425:
Intellectual Property Cases 399 and
Page 426 and 427:
Intellectual Property Cases 401 2 I
Page 428 and 429:
Intellectual Property Cases 403 so
Page 430 and 431:
Intellectual Property Cases 405 Bon
Page 432 and 433:
Intellectual Property Cases 407 doc
Page 434 and 435:
Intellectual Property Cases 409 des
Page 436 and 437:
Intellectual Property Cases 411 Ano
Page 438 and 439:
Intellectual Property Cases 413 not
Page 440 and 441:
Intellectual Property Cases 415 Jun
Page 442 and 443:
Intellectual Property Cases 417 Fig
Page 444 and 445:
Intellectual Property Cases 419 S 1
Page 446 and 447:
Intellectual Property Cases 421 Lev
Page 448 and 449:
Page 450 and 451:
Intellectual Property Cases 425 to
Page 452:
Page 455 and 456:
Page 457 and 458:
Page 459 and 460:
Page 461 and 462:
Page 463:
show all

A “Toolbox” for Forensic Engineers

Create successful ePaper yourself

Delete template?

Save as template?